Citation
Effect of Growing Season, Storage Temperature and Ethylene Exposure on the Quality of Greenhouse-Grown Beit Alpha Cucumber (Cucumis sativus L.) in North Florida

Material Information

Title:
Effect of Growing Season, Storage Temperature and Ethylene Exposure on the Quality of Greenhouse-Grown Beit Alpha Cucumber (Cucumis sativus L.) in North Florida
Creator:
OLIVA, ALFREDO MAURICIO VILLALTA
Copyright Date:
2008

Subjects

Subjects / Keywords:
Agricultural seasons ( jstor )
Colors ( jstor )
Cucumbers ( jstor )
Electrolytes ( jstor )
Fruits ( jstor )
Harvesting seasons ( jstor )
Mesocarp ( jstor )
Respiration ( jstor )
Standard error ( jstor )
Weight loss ( jstor )
City of Gainesville ( local )

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright Alfredo Mauricio Villalta Oliva. Permission granted to University of Florida to digitize and display this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Embargo Date:
5/1/2005
Resource Identifier:
436098651 ( OCLC )

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Full Text












EFFECT OF GROWING SEASON, STORAGE TEMPERATURE AND ETHYLENE
EXPOSURE ON THE QUALITY OF GREENHOUSE-GROWN BEIT ALPHA
CUCUMBER (Cucumis sativus L.) IN NORTH FLORIDA

















By
ALFREDO MAURICIO VILLALTA OLIVA














A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2005



























Copyright 2005

by

Alfredo Mauricio Villalta Oliva



























Dedicated to my mother Florentina Oliva Izaguirre.















ACKNOWLEDGMENTS

I owe my deepest thanks to my mother, Florentina Oliva Izaguirre, my father, Jose

Carlos Villalta, my sister, Daysi Valdez and her family, my brothers and their families

and my friends for giving me the support, the freedom, the encouragement and the

inspiration to pursue my goals.

I must also thank Mr. Zaid Flores, Mrs. Elizabeth Zabaneh and the Banana

Growers Association of Belize for paving the way for my career; where I am today would

not be possible without them.

I owe my most sincere thanks to Dr. Steven A. Sargent for his mentoring over the

last two years; his support, encouragement and understanding made it possible to

successfully complete this project.

I would also like to thank Mr. Emil Belibasis and family of Beli Farms for their

continued support of this project and for providing all the fruit used in these experiments.

Their kindness and willingness made a huge contribution to this project.

I must also thank all the other people that contributed to the completion of this

project; Mrs. Patricia Hill, Mrs. Adrian D. Berry, Mrs. Kim Cordasco, Dr. Jeff Brecht,

Dr. Gamal Riad, Dr. Allen Wysocki, Dr. Mark Ritenour, Dr. Donald Huber and Dr.

Daniel Cantliffe.

Also, I need to thank Dr. James A. Sterns for his contribution to my academic

formation and for being an excellent professor.
















TABLE OF CONTENTS
page

A C K N O W L E D G M E N T S ................................................................................................. iv

LIST OF TABLES ............................... .............. ....... ....... ix

LIST OF FIGURES ......... ......................... ...... ........ ............ xi

ABSTRACT ............. .................................................................. xvii

CHAPTER

1 IN TR OD U CTION ............................................... .. ......................... ..

F ruit and V vegetable T rade ............................................................ ......... ...........
Fruit and V vegetable Consum ption ........................................ ....................... 7
U .S. Cucum ber C onsum ption ............................................ ........... ............... 9
U .S C u cum b er Indu stry ........................................... ....................................... 12
Florida Cucum ber Industry ............................................................... ...............16

2 LITERATURE REVIEW ........................................................................... 19

B o ta n y .......................................................................................................1 9
C ucum ber Production ................................................................. ............... 20
M maturity Indices ................................................. ....... .. ........ .... 21
Postharvest Considerations ............................................................................22
S to ra g e .......................................................................... 2 2
Physiological Stresses .................. ............................ .... .. .. .. ........ .... 24
C hilling Injury ................................................................... 24
E thy len e Inju ry ................................................ ................ 2 5
R research O bjectives........... ........................................................ .... .... ..... .. 27

3 EFFECT OF STORAGE TEMPERATURE ON THE MARKETABLE LIFE OF
BEIT ALPH A CU CU M BER ........................................................... ............... 28

Introduction ......................... ......................... 28
M materials and M ethods................................................. .............................. 29
Plant Material ............. ........ ......... ......................29
Visual Quality ............... .......................... .......... ........ 31
Color Evaluation ........... .............................. ........ 31
W eight Loss .................................... ........ ...........................3 1


v









R expiration .............. ................................................ 32
E thylene P reduction ................................................. ............. ............... 32
M esocarp Firm ness ...................... ...................... .. .. ....... ............ .... 33
Electrolyte Leakage ................... .... .......... ............. .... ........33
M oisture C ontent ......................... ...................... .. .. ...... ........... 35
C om positional A naly sis ............................................................... ............... 35
Data Analysis ................................ ................................ .......... 35
R e su lts .............................................................................................................. 3 6
A p p earan ce ...............................................................3 6
External Color...........................................37
Internal Color ..................................... ........ ............ ....... 38
W e ig h t L o ss ............................................................................................... 3 8
R expiration .............................................................................................. ....... 38
E thy len e P ro du action ................................................................................... 4 3
Firmness.......................................... 43
E lectroly te L eak ag e ................................................................................... 4 4
M o istu re C o n ten t ....................................................................................... 4 7
Compositional Analysis..................... ...............48
D iscu ssio n .......... ....................................................................................... 4 9
A p p earan ce ...............................................................4 9
C o lo r ................................................................5 0
W e ig h t L o ss ............................................................................................... 5 0
R esp iration ........................... ................................. .................................5 1
E thylene Production ................................... ......... ..............................51
Firm ness.......................................... 52
E lectroly te L eak ag e ................................................................................... 53
Com positional Analysis..............................................................53
C onclu sion s ............................................ ........................ 55

4 RESPONSE OF BEIT ALPHA CUCUMBERS TO EXOGENOUS ETHYLENE
D U R IN G ST O R A G E ........................................................................................... 56

Introduction ................. ........ ...... ....... ...............56
M materials and M ethods ....................................................... 58
E x p e rim e n t I............................................................................................... 5 8
P la n t m ate ria l .......................................................................................... 5 8
Appearance ........................ ....... .... ........59
Color evaluation .............. .... ................ ........ 59
Weight loss ...... ...................... .......... ........60
R e sp iratio n ............................................................................................. 6 0
M eso carp firm n ess ................................................................................. 6 0
E lectroly te leak ag e ................................................................................. 6 0
D ata an aly sis ............................................................6 1
E x p e rim e n t II ............................................................................................. 6 1
Plant m aterial................................................... 61
A p p earan ce ........................................................................... 62
Color evaluation ....................... ............ .............. 62









Weight loss ................ ....... .......... ......... 62
M esocarp firm ness ....................................... .......................62
Electrolyte leakage ..................................... ............................ 62
D ata an aly sis ............................................................62
E xperim ent III .............. ........................................................... .................. ....... 62
P la n t m ate ria l .......................................................................................... 6 2
A p p earan ce .......................................................................... 62
Color evaluation ........................... .......... ................................63
W eight loss ................................ ....................... .. ................63
M esocarp firm ness ....................................... .......................63
Electrolyte leakage ..................................... ............................ 63
D ata an aly sis ............................................................6 3
R e su lts .....................................................................................................6 3
E x p e rim e n t I............................................................................................... 6 3
A p p earan ce .......................................................................... 6 3
C o lo r ....................................................................................................... 6 9
W e ig h t lo ss ........................................... .. .............................................. 7 1
R e sp iratio n ............................................................................................. 7 2
M eso carp firm n ess ................................................................................. 7 3
E lectroly te leak ag e ................................................................................. 74
Experiment II .................................................... 77
Appearance of Beit Alpha cucumbers ...................... ............................. 77
Appearance of European cucumbers ..................................80
External color of Beit Alpha cucumbers ........................84
External color of European cucumbers .................................................... 86
Internal color ................................. ........................ ...90
W eight loss ................................... ............................. .. ... ...... .... 94
Mesocarp firmness of Beit Alpha cucumbers ...........................................96
Mesocarp firmness of European cucumbers .............................................97
Electrolyte leakage of Beit Alpha cucumbers ................... .... ........... 102
Electrolyte leakage of European cucumbers ............................................. 104
E xperim ent III ..................................................... ............... 108
A appearance ... ................................................. .................. 108
E x tern al color ..................1 11..............................................
Internal color .............................................................. ........ 117
W eig h t lo ss .............................................................................. 12 2
M esocarp firm ness ............................................... ......... 123
Electrolyte leakage ................................... ................. ............... 127
D iscu ssion ......................................... .. .. ................................. 13 1
A p p earan c e .......................................... ............... ...... ............... 13 1
External C olor ........................ .................. .. .. .... .......... ....... 132
Internal Color........................................... 132
W e ig h t L o ss ................................................................................................. 1 3 2
Respiration ....................... ..................... 133
F irm n e ss ........................................ ........ ........................ .... ......... .. 1 3 3
Electrolyte Leakage ... .......... .................................. ...... ......... 134









C on clu sion s ...................................... ............................................ 13 5

5 EFFECT OF HARVEST DATE AND GROWING SEASON ON THE
MARKETABLE LIFE OF BEIT ALPHA CUCUMBERS ............... ................137

Introduction ......... ..... ........................ ...... .. ......... 137
M materials and M ethods.............................. ................ ............... 138
Plant Material ..... .......... ......... ......... .........138
A p p e a ra n c e ............................................................................................... 1 3 9
Color Evaluation ...................................................... .............. 139
Weight Loss ..... .......... ........ ......... ...............140
Fruit Firmness ........... ......... ............. ..... .......... 140
Data Analysis ...... .................. .......... ......... 140
R esu lts an d D iscu ssion ............................................ ....................................... 14 0
A p p earan ce .................................................................. 14 0
E xtern al C olor .............................................................. 14 9
Internal Color ...... .................. .......... .........156
Weight Loss ................ ........ ........ ...........158
F irm n e s s .................................................................................................... 1 6 0
Conclusions ............. ..... ......... ...................167

6 C O N C L U SIO N S ................................................................................................. 16 8

APPENDIX

A APPEARANCE RATING SCALE FOR STORED CUCUMBERS .....................170

B ISOTONIC MANNITOL CONCENTRATION ...............................................171

L IST O F R E F E R E N C E S ............................................................................................ 172

B IO G R A PH IC A L SK E T C H ...................................................................................... 183
















LIST OF TABLES


Table page

1-1. Ranking of selected commodities the U.S., based on the total value of production
(fresh and processed) between 1999 and 2003 (in $1, 000). Economic Research
Service, U SD A (2004). ................................ ......................13

1-2. Value of the U.S. cucumber production between 1998 and 2002 (in $ millions).
National Agricultural Statistical Service (2004). ..................................... 13

1-3. Total U. S. cucumber production between 1998 and 2002 (in thousands MT).
National Agricultural Statistical Service (2004). ..................................... 15

1-4. U. S. cucumber cultivation between 1998 and 2002 (hectares). National Agricultural
Statistical Service (2004). ............................................................. 15

1-5. Value of cucumber production in Florida between 1998 and 2002 ($ million).
National Agricultural Statistical Service (2004). ..................................... 17

1-6. Total production of cucumbers in Florida between 1998 and 2002 (1, 000 MT).
National Agricultural Statistical Service (2004). ..................................... 17

1-7. Florida cucumber cultivation between 1998 and 2002 (in hectares). National
A agricultural Statistical Service (2004). .............................................. .....18

3-1. Internal hue angle of Beit Alpha cucumbers stored at four different temperatures; 5,
7.5, 10 or 12.5 'C for 21 days.................................... ................... 39

3-2. Weight loss of Beit Alpha cucumbers stored at four different temperatures; 5, 7.5, 10
and 12.5 'C for 21 days. ...............................................................40

3-3. Compositional analysis of Beit Alpha cucumbers stored at four temperatures (5, 7.5,
10 or 12.5 1 'C) for 21 days. ...................... ....... ...............48

4-1. Weight loss of Beit Alpha cucumbers exposed to four concentrations of exogenous
ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC (1 oC) for 12 days.................71

4-2. Weight loss of Beit Alpha cucumbers exposed to four concentrations of exogenous
ethylene (0, 1, 5 and 10 ppm) after transfer to 20 oC for 1 day..........................72

4-3. Respiration rates of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC (1 oC)...................73


our concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC (1 oC)..................73









4-4. Internal hue angle of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d.......91

4-5. Internal hue angle of unwrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC (1
C ) for 12 d. ...........................................................................92

4-6. Internal hue angle of wrapped European cucumbers exposed to four concentrations
of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC (+1 C) for 12 d...93

4-7. Weight loss of Beit Alpha cucumbers exposed to four concentrations of exogenous
ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d.......................95

4-8. Weight loss of unwrapped European cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d.......95

4-9. Weight loss of wrapped European cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d.......96

4-10. Internal hue angle of unwrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC (1
C) for 12 d ...................................................................... ....... ...... 118

4-11. Internal hue angle of wrapped European cucumbers exposed to four concentrations
of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC (+1 C) for 12 d. 119

4-12. Weight loss of unwrapped European cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d.....122

4-13. Weight loss of wrapped European cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d.....123

5-1. Internal hue angle of Beit Alpha cucumbers harvested during three different growing
seasons (October-2003, January-2004 and July-2004) and stored at 10 C for 18 d.
Each season consists of an early and late harvest. ............ ................................ 157

5-2. Weight loss (%) of Beit Alpha cucumbers harvested during three different growing
seasons (October-2003, January-2004 and July-2004) and stored at 10 C for 18 d.
Each season consists of an early and late harvest. ............ ................................ 159















LIST OF FIGURES


Figure pge

1-1. The US agricultural trade: exports, imports and trade balance ($ billions). 2005 is a
forecast. Economic Research Service, USDA (2004)..............................................2

1-2. The US horticultural trade: exports, imports and trade balance ($ billions).
Horticultural trade includes vegetables, fruits, nuts, essential oils, nursery products,
cut flowers, wine and beer. Foreign Agricultural Service, USDA (2004). .............3

1-3. The US-NAFTA horticultural trade: combined exports, imports and trade balance
with Canada and Mexico ($ billions). Foreign Agricultural Service, USDA (2004).4

1-4. The US cucumber trade between 1970 and 2004: domestic production, imports and
exports (1, 000 MT). Economic Research Service, USDA (2004). .......................6

1-5. Total annual consumption (kg/capita) of fruit and vegetables in the U.S. Each
category (fruit or vegetables) includes fresh and processed. Food Consumption
Data System, Economic Research Service, USDA (2004) ......................................8

1-6. Total annual consumption (kg/capita) of fruit and vegetables in the U.S. in the form
that they are consumed. Food Consumption Data System, Economic Research
Service, U SD A (2004). ........................... .......... ......... .............. 10

1-7. Annual cucumber consumption (kg/capita) in the U.S. in the form that they are
consumed. Food Consumption Data System, Economic Research Service, USDA
(2004). ....................................................... ......... ........ ........... 11

3-1. Respiration rate (ml CO2 kg- hr-) of Beit Alpha cucumbers stored for 21 d at six
different temperatures; 5, 7.5, 10, 12.5, 15 and 20 C. Vertical bars represent the +
standard error from the m ean. ............................................................................41

3-2 Mesocarp firmness, expressed in Newtons, of Beit Alpha cucumbers stored for 21 d
at 5, 7.5, 10 or 12.5 C. Vertical bars represent the standard error from the mean.45

3-3. Electrolyte leakage, as a percent of total electrolyte leakage, of Beit Alpha
cucumbers stored for 21 d at four different temperatures; 5, 7.5, 10 or 12.5 C.
Vertical bars represent the standard error from the mean .................................46









4-1. Appearance rating of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 or 10 ppm) and stored at 10 C for 12 d. Fruit exposed
to 5 and 10 ppm of ethylene had identical results. Vertical bars represent the +
standard error from the mean, were not shown standard error falls within the
m arker size. .......................................... ............................ 64

4-2. Appearance of Beit Alpha cucumbers exposed to four concentrations of exogenous
ethylene for 12 d at 10 C. A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10 ppm. Arrows
indicate fungal growth (B and C) and reddish-brown spots on the peel (D). ..........66

4-3. Ethylene injury symptoms as reddish-brown spots (arrows) on Beit Alpha cucumbers
exposed to 10 ppm of exogenous ethylene for 12 d..........................................68

4-4. Changes in the external color, as measured by the hue angle, of Beit Alpha
cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10
ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from
the m ean ............................................................................70

4-5. Mesocarp firmness (Newtons) ofBeit Alpha cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for
12 d. Vertical bars represent the standard error from the mean..........................75

4-6. Rate of electrolyte leakage (%) of Beit Alpha cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for
12 d. Vertical bars represent the standard error from the mean, were not shown
standard error falls within the marker size. .................................... ...............76

4-7. Appearance rating of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars
represent the standard error from the mean, were not shown standard error falls
w within the m arker size. ....................................... ........................ 79

4-8. Appearance rating of unwrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for
12 d. 1, 5 and 10 ppm had identical results. Vertical bars represent the standard
error from the mean, were not shown standard error falls within the marker size... 82

4-9. Appearance rating of wrapped European cucumbers exposed to four concentrations
of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. 1, 5 and 10
ppm had identical results. Vertical bars represent the standard error from the
mean, were not shown standard error falls within the marker size........................83

4-10. Changes in the external color, as measured by the hue angle (o), of Beit Alpha-type
cucumbers exposed to four different concentrations of exogenous ethylene and
stored at 10 C for 12 d ................................. ... ................. .. ... ............... 85









4-11. Changes in the external color, as measured by the hue angle (o), of unwrapped
European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5
and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard
error from the m ean....... .............................. ... ............ .. .. ............ 87

4-12. Changes in the external color, as measured by the hue angle (o), of wrapped
European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5
and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard
error from the m ean............ ... ... ......... .... ...... ........ .. .... ........ .............. 89

4-13. Mesocarp firmness of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. +1 indicates
that the fruit was transferred to 20 C for 1 day (ethylene-free) after being in
storage at 10 C. Vertical bars represent the standard error from the mean..........98

4-14. Mesocarp firmness of unwrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for
12 d. +1 indicates that the fruit was transferred to 20 C for 1 day (ethylene-free)
after being in storage at 10 C. Vertical bars represent the standard error from the
m e a n ............................................................................. 9 9

4-15. Mesocarp firmness of wrapped European cucumbers exposed to four concentrations
of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. +1
indicates that the fruit was transferred to 20 C for 1 day (ethylene-free) after being
in storage at 10 C. Vertical bars represent the standard error from the mean.... 101

4-16. Electrolyte leakage (%) of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars
represent the standard error from the mean, were not shown standard error falls
w within the m arker size. ................................................ .............. ............. 103

4-17. Electrolyte leakage (%) of unwrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for
12 d. Vertical bars represent the standard error from the mean, were not shown
standard error falls within the marker size. .....................................................105

4-18. Electrolyte leakage (%) of wrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for
12 d. Vertical bars represent the standard error from the mean, were not shown
standard error falls within the marker size. .....................................................107

4-19. Appearance rating of unwrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for
12 d. 1, 5 and 10 ppm had identical results. Vertical bars represent the standard
error from the mean, were not shown standard error falls within the marker size. 109









4-20. Appearance rating of wrapped European cucumbers exposed to four concentrations
of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. 1 and 5
ppm had identical results. Vertical bars represent the standard error from the
mean, were not shown standard error falls within the marker size.....................110

4-21. Appearance of unwrapped European cucumbers exposed to four concentrations of
exogenous ethylene for 12 d at 10 C. A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10
p p m ...................................... .................................................... 1 1 2

4-22. Appearance of wrapped European cucumbers exposed to four concentrations of
exogenous ethylene for 12 d at 10 C. A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10
p p m ...................................... .................................................... 1 1 3

4-23. Changes in the external color, as measured by the hue angle, of unwrapped
European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5
and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard
error from th e m ean .............. ........ ........................................................ 14

4-24. Changes in the external color, as measured by the hue angle, of wrapped European
cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10
ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from
th e m ean ...................... .. .. ......... .. .. .......... .................................... 1 16

4-25. Internal appearance of unwrapped European cucumbers exposed to four
concentrations of exogenous ethylene for 12 d at 10 oC (+1 oC). A) 0 ppm, B) 1
ppm C) 5 ppm and D ) 10 ppm ........................................ ........................... 120

4-26. Internal appearance of wrapped European cucumbers exposed to four
concentrations of exogenous ethylene for 12 d at 10 oC (+1 oC). A) 0 ppm, B) 1
ppm C) 5 ppm and D ) 10 ppm ........................................ ........................... 121

4-27. Mesocarp firmness of unwrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for
12 d. Vertical bars represent the standard error from the mean........................124

4-28. Mesocarp firmness of wrapped European cucumbers exposed to four concentrations
of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical
bars represent the standard error from the mean............................ .............126

4-29. Electrolyte leakage (%) of unwrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for
12 d. Vertical bars represent the standard error from the mean, were not shown
standard error falls within the marker size. .....................................................128

4-30. Electrolyte leakage (%) of wrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for
12 d. Vertical bars represent the standard error from the mean, were not shown
standard error falls within the marker size. .....................................................130









5-1. Appearance rating of Beit Alpha cucumbers harvested during three different seasons
and stored at 10 oC for 18 d. Each season is an average of the early and late
harvests. Vertical lines represent standard error from the mean. .........................142

5-2. Appearance rating of Beit Alpha cucumbers harvested early and late in the October
2003 season and stored at 10 oC for 18 d. Vertical lines represent standard error
from the mean................... ... ..... .... ..............143

5-3. Appearance rating of Beit Alpha cucumbers harvested early and late in the January
2004 season and stored at 10 oC for 18 d. Vertical lines represent standard error
from the mean.................... ..... .................. 144

5-4. Appearance rating of Beit Alpha cucumbers harvested early and late in the July 2004
season and stored at 10 oC for 18 d. Vertical lines represent the standard error from
the mean, were not shown they fall within the marker size. ................................145

5-5. Overall appearance rating of Beit Alpha cucumbers harvested early or late in the
harvest season and stored at 10 oC for 18 d. Ratings represent an average of the
three seasons. Vertical lines represent standard error from the mean, were not
shown they fall within the marker size................................... 146

5-6. External color (hue angle 0) of Beit Alpha-type cucumbers harvested during three
different seasons and stored at 10 oC for 18 d. Each season is an average of two
harvests. Vertical lines represent the standard error from the mean, were not shown
they fall within the marker size. ....................................................... 151

5-7. External color (hue angle 0) of Beit Alpha cucumbers harvested early and late in the
October 2003 season and stored at 10 oC for 18 d. Vertical lines represent the
standard error from the mean, were not shown they fall within the marker size...152

5-8. External color (hue angle 0) of Beit Alpha cucumbers harvested early and late in the
January 2004 season and stored at 10 oC for 18 d. Vertical lines represent standard
error from the mean, were not shown they fall within the marker size..................153

5-9. External color (hue angle 0) of Beit Alpha cucumbers harvested early and late in the
July 2004 season and stored at 10 oC for 18 d. Vertical lines represent standard
error from the mean, were not shown they fall within the marker size..................154

5-10. Overall external color (hue angle 0) of Beit Alpha cucumbers harvested early and
late in harvest season and stored at 10 oC for 18 d. Each harvest time is an average
of all three seasons. Vertical lines represent standard error from the mean, were not
shown they fall within the marker size................................................................ 155

5-11. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested during three
different seasons and stored at 10 oC for 18 d. Each season is an average of two
harvests. Vertical lines represent standard error from the mean. .........................162


from the mean ..........................162









5-12. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and late in
the October 2003 season and stored at 10 C for 18 d. Vertical lines represent
standard error from the m ean. ...........................................................................163

5-13. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and late in
the January 2004 season and stored at 10 C for 18 d. Vertical lines represent
standard error from the m ean. ...........................................................................164

5-14. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and late in
the July 2004 season and stored at 10 C for 18 d. Vertical lines represent standard
error from the m ean .................. ..................................... .. ........ .... 165

5-15. Overall mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and
late in harvest season and stored at 10 C for 18 d. Each harvest time is an average
of all three seasons. Vertical lines represent standard error from the mean...........166















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

EFFECT OF GROWING SEASON, STORAGE TEMPERATURE AND ETHYLENE
EXPOSURE ON THE QUALITY OF GREENHOUSE-GROWN BEIT ALPHA
CUCUMBER (Cucumis sativus L.) IN NORTH FLORIDA

By

Alfredo Mauricio Villalta Oliva
May, 2005

Chair: Steven A. Sargent
Major Department: Horticultural Sciences

Cucumber is a very important horticultural crop in the United States with an annual

production valued at approximately $376 million in 2002. Imports of fresh cucumbers

play an important role in meeting the national demand, but imports negatively affect

domestic growers.

Beit Alpha cucumber (Cucumis sativus L.), also referred to as Bet Alfa, mini,

Lebanese or Middle Eastern cucumber, are a type of fresh cucumber widely grown in the

Middle East and Europe. It is a much shorter version of the European-type cucumber and

remains relatively unknown in the U.S. This type of cucumber produces well under

greenhouse conditions in Florida, has excellent flavor and taste attributes, and represents

a potential crop for growers seeking to diversify their product line and take advantage of

an increasing demand for fresh vegetables.

Beit Alpha cucumbers had a maximum shelf life of 15 to 18 days when stored in

rigid, vented clamshells at 10 oC and -90% RH. Storage of cucumbers at 5 or 7.5 'C









reduced the quality due to chilling injury while quality at 12.5 'C was reduced due to the

development of firm protrusions that negatively affected appearance but not the edibility.

Although internal production of ethylene by Beit Alpha cucumbers was

undetectable the fruit is sensitive to concentrations as low as 1 ppm. The marketable life

of Beit Alpha cucumbers was reduced by 20% when exposed to 1 ppm exogenous

ethylene and 60% when exposed to 10 ppm external ethylene. In contrast, the marketable

life of European (English or Dutch-type) cucumber was limited to approximately 9 days

when exposed to ethylene. Shrink-wrapping is a standard practice for European

cucumbers to protect against moisture loss but is not necessary for Beit Alpha cucumbers.

Unwrapped, unwaxed Beit Alpha cucumbers had similar weight loss as wrapped

European cucumbers after 12 days in storage.

The effect of the growing season and time of harvest on the quality of greenhouse-

grown Beit Alpha cucumbers was also studied. The growing season did not affect the

marketable life of cucumbers and fruit from three different seasons had an average

marketable life of 15 to 18 days in storage at 10 oC. The time of harvest, early and late in

the harvest period, also had no effect on the marketable life of Beit Alpha cucumbers.

Beit Alpha cucumbers store well at similar conditions as traditional varieties of

cucumbers and do not require plastic shrink-wrapping to protect from moisture loss. Beit

Alpha cucumbers, as well as European cucumbers, should be stored in ethylene-free

environment to prevent quality losses.


xviii















CHAPTER 1
INTRODUCTION

Fruit and Vegetable Trade

The United States remains a net agricultural exporter but despite an increase in

agricultural exports, agricultural imports have increased at a faster pace thus reducing the

trade balance year after year. The U.S. agricultural trade balance peaked at $27.4 billion

in 1996 but decreased to $9.5 billion in 2004 and is predicted to further decrease in 2005

to $2.5 billion (Figure 1-1); the lowest levels since 1972 (Whitton and Carter, 2004).

Despite the fact that the U.S. has a positive overall agricultural trade balance it is

a net importer of horticultural products, which includes vegetables, fruits, nuts, essential

oils, cut flowers, wine and beer (United States Department of Agriculture, 2004). The

negative trade balance of horticultural products has increased 61.6% in the last 5 years

alone; from $5.87 billion in 1999 to $9.49 billion in 2003 (Figure 1-2). Although the U.S.

has a large number of trading partners, Canada and Mexico are the two largest import

sources of horticultural products and two of the top three largest destinations of U.S.

horticultural exports. Canada and Mexico combined account for more than a third of the

total U.S. exports; in 1999 37% of total horticultural exports worth $3.8 billion were to

these two trading partners and it increased to 41% or $5.06 billion in 2003 (Foreign

Agricultural Service, 2004). Imports from these two countries also increased over the

same period; from $5.19 billion in 1999 to $7.35 billion in 2003 (Figure 1-3).









70.0



60.0



50.0



S40.0



Q q30.0




20.0



10.0



0.0
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 F
2005


Exports Imports -- Bdance
Figure 1-1. The US agricultural trade: exports, imports and trade balance ($ billions).
2005 is a forecast. Economic Research Service, USDA (2004).










25.0

21.9

20.0 18.7

16.1 16.6 172

15.0
12.

10.10. 11. 11.
10.0



5.0





0 199) 200 2000 200 200
0.0



-5.0

-5.9 -5.8 -6.2
-7.4
-10.0 -9.5



-15.0


I Export I Irport [ Balance

Figure 1-2. The US horticultural trade: exports, imports and trade balance ($ billions).
Horticultural trade includes vegetables, fruits, nuts, essential oils, nursery
products, cut flowers, wine and beer. Foreign Agricultural Service, USDA
(2004).









































-1.8 -1.8


I NFTA Exports


I NFTA Imports


[ NAFTA Balance


Figure 1-3. The US-NAFTA horticultural trade: combined exports, imports and trade
balance with Canada and Mexico ($ billions). Foreign Agricultural Service,
USDA (2004).


0.0 E


-2.0





-4.0-


I









The U.S. has a positive trade balance with Canada but a larger negative trade

balance with Mexico, in terms of horticultural products. As for cucumbers, the U.S. is a

net importer of fresh cucumbers; while imports of cucumbers have more than tripled

since 1970 exports have only increased 60%. In 1970-79 the U.S. imported a total of 93,

227 MT of fresh cucumbers and exported 13, 454 MT during the same period (Figure 1-

4). Since then, according to the Economic Research Service (2004) imports have

increased remarkably, reaching 393, 636 thousand MT in 2003 while exports were only

21, 636 thousand MT. According to statistics compiled from the U.S. Commerce

Department and other government sources by the private agribusiness consulting firm

FINTRAC Inc. Agribusiness Online (2004), imports of cucumbers into the U.S. come

mainly from Mexico with smaller quantities sourced to Canada, Honduras, Costa Rica,

Spain, the Dominican Republic, Guatemala and the Netherlands among other countries.

According to FINTRAC Inc., Agribusiness Online, the U.S. imported a total of 334, 735

MT ($171.2 million) of fresh cucumbers from Mexico, 33, 577 MT ($34.5 million) from

Canada and 18, 768 MT ($3.02 million) from Honduras; respectively, each country

accounted for 85, 8.5 and 4.7% of the total U.S. cucumber import.

Horticultural trade is important and necessary to eliminate seasonal fluctuations in

supply, therefore assuring a year-round supply to U.S. consumers. Trade, however, has

tremendous implications for U.S. growers. The statistics indicate that market forces are

favoring the importation of cucumbers, as well as other horticultural products, not only

from regional North American Free Trade Agreement trading partners but also from other

countries that are becoming competitive enough to penetrate the lucrative U.S. market.















500 501.8490
452.8 459.7



900 3.6 02.3
.8

334.4


0 300
0
57.3
227.1

200 79.1




100 3.2


3.5 7.6 3.0 .4 1.6 5.9
0
19 -79 1980-89 1990-99 2000-02 2003 2004


I Production I Import Export

Figure 1-4. The US cucumber trade between 1970 and 2004: domestic production,
imports and exports (1, 000 MT). Economic Research Service, USDA (2004).


and exports (1, 000 MT). Economic Research Service, USDA (2004).









Fruit and Vegetable Consumption

The United States Department of Agriculture recommends a daily intake of at least

three servings of vegetables and two servings of fruit and an optimum daily intake of 7 to

9 servings combined (Center for Nutrition Policy and Promotion, 2000). Despite the

guidelines, daily consumption of fruit and vegetables in the U.S. falls below federal

recommendations. Ironically, part of the problem was a shortage of fruits and vegetables.

Putnam et al. (2002) reported that the fruit and vegetable supply in 2002 was 5.2

servings, slightly more than the minimum five daily servings suggested but below the

optimum 7 to 9 daily servings recommended. Despite the lower than recommended

consumption, annual consumption of fruits and vegetables has increased 25% since 1970

from 262 kg/capita in 1970 to 310.7 kg/capita in 2002. Although the consumption of

vegetables is higher than that of fruits the consumption of both has increased since the

1970's (Figure 1-5). In 1970, annual per capital consumption of fruit in both forms was

109.7 kg while the consumption of vegetables was 153.1 kg. Since then, consumption of

both fruits and vegetables has increased by 12.5 and 22.3%, respectively. In both cases,

there has been a higher increase in the consumption of the fresh form instead of the

processed form. Annual consumption of fresh fruit between 1970 and 2002 has increased

by 11.1 kg/capita or 24.2%; from 46 to 57.1 kg/capita while consumption of processed

fruit increased only 2.7 kg/capita or 4.2%.

Notwithstanding the ample variety of fruit and vegetables available in the US, six

fruits and five vegetables (including French fries) accounted for roughly half of the total

fruit and vegetable consumption. The same authors also report that fruit and vegetable

intake increased with income and education; an indication that produce companies need

to become more aggressive marketers as well as educators.










































1986 1990


1994


1998 2002


- Totd front -n- Totd vegetables


-- Totd front and vegetables


Figure 1-5. Total annual consumption (kg/capita) of fruit and vegetables in the U.S. Each
category (fruit or vegetables) includes fresh and processed. Food
Consumption Data System, Economic Research Service, USDA (2004).


350.0



300.0



250.0


200.0



150.0


100.0



50.0



0.0


1970


1974


1978


1982


10 11111. jjq iio ` 1111 11,11 10 0 11 1!111,









Although consumption of vegetables remains higher in the processed form, growth

in the consumption of fresh vegetables has increased at a faster rate than the consumption

of processed vegetables. Consumption of fresh vegetables increased 25.4% between 1970

and 2002; from 70.1 to 87.9 kg/capita while the consumption of processed vegetables

increased 19.8% or 16.4 kg/capita; a higher increase than that seen in processed fruits

(Figure 1-6).

Marketing specialists are optimistic that consumption of fruits and vegetables will

continue to increase and cite as evidence the increasing variety of fruits and vegetables

available to the U.S. consumer increases, the aggressive education and marketing

campaigns undertaken by the government and food purveyors as well as the move

towards more wholesome and healthier lifestyles.


U.S. Cucumber Consumption

According to the Food Consumption Data System (2004), the annual consumption

of both fresh and processed cucumbers in the U.S. has followed a similar trend to the

overall trend in fruit and vegetable consumption. Cucumber consumption has increased

by 36.2% since the 1970's; from 3.85 kg/per capital in 1970 to 5.25 kg/per capital in 2002

(Figure 1-7). Initially, consumption of processed cucumbers was higher than the

consumption of fresh cucumbers but that trend was reversed in the early 1990's when the

consumption of fresh cucumbers reached 2.3 kg/capita, surpassing that of processing

cucumbers. Since then the annual per capital consumption of fresh cucumbers has

increased while the processed cucumbers has decreased.




































1974


1978


1982


1986


+ Processed Fruit
- Fresh Fruit


1990


1994


-1- Processed \Mgetables
Fresh Vegetables


Figure 1-6. Total annual consumption (kg/capita) of fruit and vegetables in the U.S. in the
form that they are consumed. Food Consumption Data System, Economic
Research Service, USDA (2004).


1970


1998


2002


4-j-
ct
U

S.-
2 t


~J ~rr-"i



rt~-L"--~r~_~









6.0 -





5.0





4.0




0 3.0





-<--
19a




2.0





1.0





0.0 r-
1970


-w- Processed


Figure 1-7. Annual cucumber consumption (kg/capita) in the U.S. in the form that they
are consumed. Food Consumption Data System, Economic Research Service,
USDA (2004).


1975


1980


1985


1990


- Fresh


1995


2000


-&- Total









U.S. Cucumber Industry

Tomato is the largest crop in the U.S. based on the value of total domestic

production (fresh and processed) and is followed by lettuce, onions and sweet corn (Table

1-1) while cucumbers rank 11th (Economic Research Service, 2004). The cucumber

industry in the U.S. consists mainly of two types; fresh-market cucumbers and processing

cucumbers. Fresh-market cucumbers are called slicers and can and are grown either in

open-fields or greenhouses with specific varieties adapted for each cultivation system,

while processing cucumbers are grown in open-fields. Another type of cucumbers is the

specialty cucumbers, or varieties that are not commercially grown in large scale such as

the Middle Eastern types or Beit Alpha cucumbers. Beit Alpha cucumbers have been

shown to produce well in Florida well year-round under protected culture in Florida,

representing an opportunity for Florida growers (Lamb et al., 2001).

The total value of the domestic cucumber production in 2002 was $376 million

(Table 1-2). In 2002, fresh-market cucumbers accounted for 55.6% of the total value of

the domestic production; slightly lower than in 1998, when it accounted for 61.6%. Since

then, the total value of the fresh-market production has declined. In 1998, the value of the

U.S. production of fresh-market production was $226 million and it decreased to $214

million in 2002. During the same period the value of the U.S. production of processing

cucumbers increased from $141 to $171 million. Although both types of cucumbers can

be grown in all 50 states, the production is highly concentrated in a handful of states.

Florida, California and Georgia dominate the production of fresh-market cucumbers and

account for 62% of the total value of the domestic production. The production of

processing or pickling cucumbers is similarly concentrated; Florida, Michigan and North

Carolina account for 50% of the total value of the domestic production.










Table 1-1. Ranking of selected commodities the U.S., based on the total value of
production (fresh and processed) between 1999 and 2003 (in $1, 000).
Economic Research Service, USDA (2004).

1999 2000 2001 2002 2003



Value of Production ( $ 1 000)


Tomatoes

Head Lettuce

Onions

Romaine Lettuce

Sweet Corn

Broccoli

Carrots

Bell Pepper

Snap Beans

Cantaloupe

Cucumber


1,878,574

972,917

641,278

492, 149

670,512

493,087

484,654

483, 807

394,057

377,360

364,774


1, 843, 776

1, 208, 140

735,939

654,936

713,037

620,606

390,002

531,018

392,763

371,984

381,660


1,678,894

1,234,981

680,350

604, 555

753,245

484,467

510,816

473, 557

389,625

429,281

374,647


1,932,624

1,435,296

764,994

919, 170

718, 124

567,767

521,362

464,401

404,003

398,302

376,790


1, 865,328

1, 187,984

918,774

911,051

789,522

643,791

553, 889

505, 159

384,819

371,721

367, 645


Table 1-2. Value of the U.S. cucumber production between 1998 and 2002 (in $
millions). National Agricultural Statistical Service (2004).

1998 1999 2000 2001 20

Value of Production ( $ millions)

Fresh 226 217 218 211 21

Processing 141 150 165 169 17

Total 366 367 383 380 38


02


4

1

5









Total production of cucumbers in the U.S. (both fresh and processing) has

remained relatively unchanged in the past five years. In 1998, total domestic production

was 1.051 million MT and increased slightly to 1.078 million MT in 2002. Between 1998

and 2002, total production has remained almost evenly split between fresh-market and

processing cucumbers; production of fresh-market cucumbers accounts for 48% of the

total domestic production and in 2002 it was 517 MT while the production of processing

cucumbers was 561 MT (Table 1-3). Since 1998, the price per MT of fresh-market

cucumbers has decreased slightly while it has tended to increase for processing

cucumbers. In 1998, the average price for a MT of fresh-market cucumbers was $440 and

decreased to $413.6 in 2002. On the other hand, the price of a MT of processing

cucumbers increased from $260.7 in 1998 to $304.7 in 2002 (National Agricultural

Statistical Services, 2003).

In 2002 approximately 73, 450 hectares were dedicated to the production of

cucumbers in the U.S., with 33% of this acreage dedicated to the production of fresh-

market cucumbers. Although the total area under cultivation increased by more than six

thousand hectares between 1998 and 2002, all the additional area has been devoted to the

production of processing or pickling cucumbers. The area dedicated to the production of

fresh-market cucumbers remained relatively unchanged during the same period, in 1998

it was 24, 475 hectares and decreased to 24, 160 hectares in 2002 (Table 1-4). Although

the area dedicated to the production of fresh-market cucumbers is smaller than that of

processing cucumbers; higher yields, multiple harvests per crop and longer harvest

seasons due to climatic conditions result in higher tonnage of fresh-market cucumbers per

area planted. Annual national yields for fresh-market cucumbers are approximately 9.13









MT per hectare (average of national yield between 1998 and 2002) compared to 5.12 MT

per hectare for processing cucumbers (National Agricultural Statistical Services, USDA,

2003). A large portion of the production of processing cucumbers is in Northern states

which have shorter production season than Southern states such as Florida, Georgia and

California which together account for more than 60% of the total domestic production of

fresh-market cucumbers (National Agricultural Statistical Service, 2004).


Table 1-3. Total U. S. cucumber production between 1998 and 2002 (in thousands MT).
National Agricultural Statistical Service (2004).

1998 1999 2000 2001 2002

Domestic Production (1 000 MT)

Fresh 512 542 498 489 517.23

Processing 540 571 557 529 561.18

Total 1051.7 1113.1 1055.1 1017.6 1078.4

Table 1-4. U. S. cucumber cultivation between 1998 and 2002 (hectares). National
Agricultural Statistical Service (2004).
1998 1999 2000 2001 2002

Production Area (hectares)

Fresh 24, 475 25, 940 22, 905 23,553 24, 160

Processing 42, 885 44, 366 43,791 45, 369 49, 291

Total 67, 360 70, 306 66, 696 68, 922 73,450









Florida Cucumber Industry

Cucumber production is very important in the state of Florida. The value of

cucumber production ranks 5th in order of the most valuable vegetable crop to the state,

after tomatoes, bell peppers, snap beans and sweet corn (Florida Agricultural Statistical

Service, 2004). Florida accounts for roughly 20% of the total U.S. cucumber production.

In 2002, the most recent year for which data is available, Florida had a 27.7% market

share of the fresh-market cucumbers (based on the value of production) and a 14%

market share in the processing cucumber segment; the largest combined market share of

any state. The value of total cucumber production in Florida increased from more than

$75 million in 1998 to more than $106 million in 2000, before decreasing to slightly

more than $83 million in 2002. Since 1998 Florida has been the leading supplier of fresh-

market cucumbers and is also one of the major players in the processing cucumber

market; it was the leading supplier in 2001 and 2002 of processing cucumbers (based on

the value of production). Although both types of cucumbers are grown in substantial

amounts in Florida, Florida is by far a fresh-market producer. Production of fresh-market

cucumbers account for roughly 70% of the value of the state's total cucumber production

(Table 1-5).

Florida's total cucumber output in 2002 was 194 thousand MT, higher than the 172

thousand MT harvested in 1998 but not as high as in 2000 when total state output was

230 thousand MT (Table 1-6). Although total production of both types is currently at

higher levels than in 1998, it has decreased in the fresh-market segment in the last three

years and has remained stagnant in the processing segment over the same period.

Although the total area under cucumber cultivation in the U.S. increased 9%

between 1998 and 2002, it decreased 14% in the state of Florida. In 1998, Florida had 6,









677 hectares under cucumber cultivation, 58% of which was dedicated to the production

of fresh-market cucumbers, and it decreased to 5, 787 hectares in 2002 (Table 1-7). More

cultivation area has been lost in the fresh-market segment than in the processing segment.

The area under cultivation of fresh-market cucumbers has decreased 18% since 1998,

from 3, 804 hectares to 3, 157 hectares in 2002. Over the same period, the area under

cultivation of processing cucumbers decreased 8.5%, from 2, 873 hectares in 1998 to 2,

630 hectares in 2002.


Table 1-5. Value of cucumber production in Florida between 1998 and 2002 ($ million).
National Agricultural Statistical Service (2004).
1998 1999 2000 2001 2002


Production Value ($millions)

Fresh 51.88 61.69 73.73 60.23 59.28

Processing 23.20 19.60 32.95 19.03 23.98

Total 75.08 81.29 106.68 79.26 83.26

Table 1-6. Total production of cucumbers in Florida between 1998 and 2002 (1, 000
MT). National Agricultural Statistical Service (2004).
1998 1999 2000 2001 2002


Production (1 000 MT)

Fresh 118 153 166 121 130

Processing 54 46 64 64 64

Total 172 200 230 186 194






18


Table 1-7. Florida cucumber cultivation between 1998 and 2002 (in hectares). National
Agricultural Statistical Service (2004).

1998 1999 2000 2001 2002


Production Area

4, 371 4,087

2, 752 2, 630

7, 122 6, 718


(hectares)

3, 157

2, 630

5, 787


Fresh

Processing

Total


3,804

2, 873

6, 677


3, 116

2, 630

5, 747














CHAPTER 2
LITERATURE REVIEW

Botany

The cultivated cucumber varieties belong to the Cucurbitaceae family and are

classified in the Cucumis genus which contains 34 species; including cucumbers, melon

and gherkins as well as the synthetic specie hytivus (Andres, 2004) which is a cucumber-

melon hybrid (Zhuang et al., 2003). The garden cucumber (Cucumis sativus L.) is

thought to have originated in India (Staub et al., 1998; Dhillon, 2004). Cucumber plants

exhibit different patterns of sex expression with monoecious (female and male flowers on

the same plant) being the most common form of sex expression in cucumbers (Yamasaki

et al., 2001). Other forms of sex expression include gynoecious plants (produce

predominantly female flowers), hermaphrodite and andromonoecious cultivars (Byers et

al., 1972).

Beit Alpha (Bet Alfa) cucumbers (Cucumis sativus L.), also referred to as mini,

Lebanese or Middle Eastern cucumbers are a type of fresh cucumbers widely grown in

the Middle East, Europe and parts of the Mediterranean region (Mendlinger, undated) as

well as Australia. They are thought to have originated in the Middle East region with

some cultivar improvement done in Israel and other countries (Pers. Comm. Daniel

Cantliffe, Horticultural Sciences Department, University of Florida and Harry Paris,

Department of Vegetable Crops & Plant Genetics, Agricultural Research Organization,

Israel).









Beit Alpha cucumbers are a much shorter version of the European cucumber (Pers.

Comm. John Meeuwsen, Breeder/Product Manager, De Ruiter Seeds) which is also

known as English or Dutch-type cucumber. Beit Alpha cucumbers remain relatively

unknown in the U.S. fresh market, which is dominated by slicer and European cucumber

varieties. This could eventually change since Beit Alpha varieties have appeared in

commercial markets, both as imports and locally grown, in localized markets such as

California, Florida and some areas in the North East. Specific varieties of Beit Alpha

cucumbers have been developed for open field production (e.g. 'Beit Alpha Hybrid

EM75', Emerald Seed Company, El Centro, CA) as well as for production under

protected culture (e.g. 'Manar', DeRuiter Seeds, Columbus, OH). Commercial varieties

of Beit Alpha cucumbers have been reported to be gynoecious; however monoecious

varieties are also available (e.g. 'Beit Alpha', Atlas Seeds Inc., Suisun City, CA).

Unlike European cucumbers, Beit Alpha cucumbers ('Manar') are significantly

smaller, generally from 125 to 175 mm in length, weigh less than 100 g, and are

outstanding in flavor. Another characteristic of Beit Alpha cucumbers is that they can be

consumed unpeeled since they have a smooth and edible thin skin and are seedless. This

new crop represents an opportunity for Florida growers since it has been proven to grow

well year-round under protected culture in Florida (Lamb et al., 2001). Successful

introduction and marketing of Beit Alpha cucumbers will be highly dependent upon

adequate postharvest handling and marketing, which underscores the need for reliable

data on the storage characteristics of this commodity.

Cucumber Production

Cucumber harvest season in the U.S. varies by geographic location and production

system used. The production system can be open-field production (fresh market and









pickling cucumbers) or protected cultivation systems (fresh market only). Production in

open fields will limit the harvest season as well as quality of the commodity. Production

in protected culture systems, however, can extend the harvest season throughout the year

and generate fruit of higher quality. Florida has a long harvest season for field-grown

cucumbers and it extends from Mid-September through June depending on the growing

region (Florida Facts 2004). The harvest season of both open-field and greenhouse

production systems is limited in other states by the cold weather, creating price

fluctuations. In Florida, it is possible to obtain year-round harvests in protected

cultivation systems, as is currently the case with the production of Beit Alpha cucumbers

in North Florida.

Maturity Indices

Cucumbers destined for fresh consumption are manually harvested, unlike

processing cucumbers which are also harvested mechanically; approximately two-thirds

of the national production is machine-harvested (Estes and Cates, 2001). Cucumbers

grown for the fresh market are harvested as they reach commercial maturity, allowing for

multiple harvests per season. The maturity at harvest is the most important factor that

determines postharvest quality (Kader, 1996; Schouten et al., 2004). Cucumbers reach

commercial maturity or the optimum eating quality at a physiologically immature stage

(Kays, 1999) and delaying harvest will tend to lower the quality at harvest and hasten the

postharvest deterioration rate (Kader, 1996). Maturity on cucumbers is assessed

subjectively based on color, shape, size and appearance (freedom of malformations,

injury and decay) (Kader, 1996; U.S. Standards for Grades of Greenhouse Cucumbers,

1997).









Postharvest Considerations

Cucumbers that meet USDA standards are harvested and go through a short

packaging process. Fresh-market cucumbers such as the greenhouse-grown, European

types are hand harvested and transported in plastic bins to the packing house. Depending

on the size and layout of the farm, the packing house may be a few meters away from the

growing area, which would reduce both the transportation time and manipulation of the

product. After sorting and grading, cucumbers are mechanically shrink-wrapped, without

being sanitized or surfaced washed, using heat and then manually packed in corrugated

cartons.

Beit Alpha cucumbers are also manually harvested and graded according to the

grower's experience based on size, color, shape and freedom of injury or any other

defect, since there are no federal standards for grades of Beit Alpha cucumbers in the

U.S. A typical crop of Beit Alpha cucumbers grown in North Florida is harvested 4 to 6

times a week for 7 to 9 weeks and are packed unwashed, unwaxed and unwrapped in 7-

kg unwaxed, corrugated cartons.

Storage

After harvest, the quality of a commodity starts to decline, making the shelf-life

dependent on the postharvest treatments the commodity receives. Temperature

management is generally the most effective and the most used tool to extend the

postharvest life of many horticultural commodities, including cucumbers (Kader, 2002).

Due to their chilling-sensitive nature, it is recommended that cucumbers be stored at 7 to

10 C and 85 to 95% relative humidity (RH) in air (DeEll et al., 2000; Thompson, 2002),

8 to 12 C in 1 to 4% 02 and 0% CO2 (Cantwell and Kasmire, 2002), or 10 to 12.5 C

(Paull, 1999; Kader, 2002; Suslow, 2002). Storing the commodity at temperatures below









the recommended storage temperature will not only limit the quality and shelf life of a

product but is also a redundant cost.

Appropriate temperature management is also essential from a food safety and

marketing standpoint. In part driven by consumer pressure as well as other competitive

market forces, food purveyors need suppliers that will provide product that is safe and of

consistent quality year round. Therefore, growers and food handlers must ensure that

every step taken is in accordance with recommended guidelines for that particular

commodity.

Another important aspect of cucumber storage is the use of protective shrink-wrap

films, such as polyethylene films, to protect greenhouse-grown from excessive water loss

(Cazier, 2000) and consequent shriveling. Film wrapping has been reported to extend the

shelf-life of some fruits due to the modified-atmosphere effect it creates (Wang and Qi,

1997). Depending on the permeability of the film, the gas composition of the atmosphere

between the fruit and the protective film can be modified through the respiration and

transpiration of the product (Thompson, 2003). The consumption of 02 through

respiration causes the level of 02 to be diminished while the levels of CO2 increase.

Transpiration on the other hand causes water vapor to accumulate inside sealed films,

increasing the relative humidity of the atmosphere and leading to condensation when the

RH reaches 100%. These three variables along with ethylene, storage temperature and the

duration of storage form the six environmental variables that are regulated in modified

atmosphere packaging (Saltveit, 2002).

Modified atmosphere packaging has also been reported to reduce both the onset

and severity of chilling injury in wrapped cucumbers as a result of increased levels of









polyamines in wrapped fruit (Wang and Qi, 1997). Reduction in the expression of

chilling injury symptoms as a result of modified atmosphere have also been reported in

mango (Pesis et al., 2000), carambola (Ali et al., 2004) and citrus (Porat et al., 2004). In

the case of cucumbers the main benefit obtained from shrink-wrap film for individual

cucumbers is the reduction of moisture loss, since the permeable film wrap offers

protection from moisture exchange but does not restrict gas movement (Wang and Qi,

1997).

Physiological Stresses

Chilling Injury

Chilling injury is a physiological disorder that occurs when chilling-sensitive fruits

or vegetables are exposed to low but non-freezing temperatures (Hakim et al., 1999;

Kang et al., 2002; Saltveit, 2002). It is believed that cell membranes are the primary sites

of storage disorders such as chilling injury expression (Shewfelt and del Rosario, 2000)

but a biochemical pathway to elucidate the chilling injury mechanism has not been

established yet (Balandran-Quintana et al., 2003). Chilling injury is a cumulative process

and the level of damage will depend on the temperature and the length of exposure

(Cantwell and Kasmire, 2002; Saltveit, 2002). For chilling injury damage, to be evident

in cucumbers the fruit must be exposed to chilling temperatures for several days (Hakim

et al., 1999; Saltveit, 2002) and visual symptoms may not be expressed until after the

fruit is transferred to higher storage temperatures (DeEll et al., 2000). Although chilling

injury in cucumbers can vary depending on the cultivar (Hakim et al., 1999; Thompson,

2002) and preharvest factors, it is generally accepted that cucumber storage below 10 C

will cause chilling injury thus limiting the shelf life of the product. Chilling injury in

cucumbers results in the sinking of spines, water soaking, pit formation (Hakim et al.,









1999), increased susceptibility to decay and the development of brown or black lesions

that follow pitting (Cantwell and Kasmire, 2002), reduced storage life, increased rates of

ion leakage due to membrane damage (Kang et al., 2002; Saltveit, 2002), as well as the

appearance of dark watery patches (DeEll et al., 2000).

As mentioned above, many symptoms are related to the expression of chilling

injury damage. However, changes in membrane integrity is the primary effect that results

when plant tissue such as fruits is exposed to stressful environments such as chilling

temperatures or ethylene (DeEll et al., 2000; Balandran-Quintana et al., 2003). Membrane

deterioration reduces its ability to act as a diffusion barrier causing cell contents to leak

(Stanley, 1991), which translates into higher rates of electrolyte leakage (Hakim et al.,

1999; Kang et al., 2001; Saltveit, 2002). This makes electrolyte leakage assessments

useful in quantifying cell damage in chilled cucumber fruit (Whitlow et al., 1991;

Knowles et al., 2001). Although the precise biochemical pathway linked to chilling injury

is not clear, it has been suggested that the level of membrane lipid unsaturation is

inversely correlated with chilling sensitivity (Nishida and Murata, 1996) since it has been

observed that higher amounts of unsaturated fatty acids are synthesized by organisms

exposed to chilling temperatures (Stanley, 1996).

Ethylene Injury

The drive to remain competitive in a global horticultural market place has forced

some growers to rethink their vision. One of the changes that handlers of horticultural

commodities have been forced to adopt is the diversification of the product line thus

bringing different commodities into contact with each other. Temperature management

abuses are not the only potential cause of damage that horticultural commodities may

encounter as they make their way to the consumer. One very important physiological









aspect of horticultural commodities is their response to ethylene. Given the variability

that exists in cucumber germplasm it is important to determine the postharvest behavior

of cultivars grown under protected culture with the aim of reducing losses due to

postharvest mismanagement

Horticultural commodities are classified as climacteric or non-climacteric

depending on their respiration and ethylene production patterns (Giovannoni, 2001;

White, 2002). Ethylene is required to complete the ripening process in climacteric fruit

but not in non-climacteric fruit (Lelievre et al., 1997; Phillips et al., 2004). Cucumbers

produce little or no ethylene after harvest and there is no concomitant rise in respiration

rate allowing for the classification of cucumbers as non-climacteric (Saltveit and

McFeeters, 1980; Wehner et al., 2000). It is important to note that cucumbers become

horticulturally or commercially mature at a physiologically immature stage, which makes

ripening unnecessary from a marketing standpoint. Cucumbers respond negatively to

ethylene and the changes associated with ethylene exposure are deemed as detrimental.

The role of ethylene, a gaseous plant hormone (Huang et al., 2003), is widely

documented in regulating many physiological and developmental plant processes

(Deikman, 1997; Johnson and Ecker, 1998; Kader, 2002; Huang et al., 2003; Hongwei

and Ecker, 2004). In cucumber plants, ethylene plays a role in determining sex

expression, however its effects on fruit tissue are deemed detrimental because they

reduce consumer acceptance of the product by negatively affecting appearance, firmness

and other attributes, such as color, that define the quality of cucumbers. Cucumbers are

highly sensitive to external ethylene (Kader, 2002) and its exposure results in accelerated

color loss, higher susceptibility to decay and unwanted tissue softening (Saltveit, 1998).









Ethylene is synthesized in plant tissue from methionine via a series of enzymatic

reactions (Saltveit, 1999). Production of ethylene prior to ripening is very low but

increases at the onset of ripening (Yang and Oetiker, 1998) which controls the initiation

of changes in biochemical and physiological attributes such as texture, color, aroma

volatiles and flavor (Lelievre et al., 1997) associated with fruit ripening in climacteric

fruits, but which result in unacceptable quality in non-climacteric fruit such as

cucumbers. Ethylene molecules bind to membrane-bound receptors or binding sites -such

as ETR1/ETR2, ERS 1/ERS2 and EIN4 in Arabidopsis (Guo and Ecker, 2004)- on plant

cells which result in the formation of messenger RNA, which is thought to then be

translated into enzymes that cause the ethylene response (changes in color, tissue

softening among others) (Reid, 2002).

Research Objectives

This research project had three objectives:
1. study the storage behavior of locally grown cultivars of Beit Alpha cucumbers and
determine the optimum storage temperature;

2. evaluate the response of Beit Alpha cucumbers to exogenous ethylene compared to
that of the traditional long, European cucumber and

3. evaluate the effect of the growing season and time of harvest on the postharvest
quality of Beit Alpha cucumbers.















CHAPTER 3
EFFECT OF STORAGE TEMPERATURE ON THE MARKETABLE LIFE OF BEIT
ALPHA CUCUMBER

Introduction

An understanding of the postharvest parameters is essential for the successful

market introduction of Beit Alpha cucumbers (Sargent et al., 2001). One of these

postharvest parameters is the optimum storage temperature, the temperature at which a

commodity will have the longest marketable life with minimal loss in quality. Low

temperature storage is one of the most widely used postharvest treatments and it is relied

upon as the most effective tool for prolonging the marketable life of horticultural

commodities (Kader, 2002). Low temperatures, however, can induce physiological

disorders such as chilling injury that may render the commodity unfit for marketing

(Paull, 1999). Chilling injury in cucumbers results in the sinking of spines, water soaking,

pit formation (Hakim et al., 1999), increased susceptibility to decay and the development

of brown or black lesions that follow pitting (Cantwell and Kasmire, 2002). Development

of chilling injury is dependent on the temperature and length of exposure (DeEll et al.,

2000) and the expression of symptoms varies depending on the cultivar as well as the

environmental conditions prior to exposure to chilling temperatures (Hakim et al., 1999;

Kang et al., 2002; Kader, 2002). It is therefore essential to determine the proper storage

temperature of locally grown cultivars is essential for growers to reduce the losses that

could result from chilling injury.









Cucumbers suffer chilling injury above freezing temperatures and generally should

not be stored long term below 7 to 10 oC (DeEll et al., 2000); optimum storage

temperature for cucumbers is 10 to 12.5 'C at -95% relative humidity (Paull, 1999;

Kader, 2002; Suslow, 2002). Chilling injury in cucumbers is characterized by accelerated

water loss, surface pitting, and increased susceptibility to decay (Kang et al., 2001).

Chilling injury is just one of many disorders that could develop during storage; other

postharvest disorders include shriveling as a result of water loss (G6mez et al., 2004),

yellowing of the peel (Lin, 1989), decay and general deterioration of appearance. In

cucumbers quality is based on appearance, shape, firmness, color as well as freedom from

growth or handling defects and freedom from decay (Agricultural Marketing Services,

1985); parameters that jointly determine the quality rating of the commodity. Research

related to the chilling sensitivity and other storage characteristics of Beit Alpha

cucumbers, specifically to the cultivars being grown under protected culture in Florida is

scarce, underscoring the need and value of this type of research.

The objectives of these experiments were to determine the optimum storage

temperature for Beit Alpha cucumbers based on the determination of key quality

characteristics under simulated commercial storage conditions.


Materials and Methods

Plant Material

Seedless, Beit Alpha cucumbers (Cucumis sativus L., 'Manar', DeRuiter Seeds,

Columbus, OH) were grown under commercial greenhouse conditions (double-poly,

passively ventilated greenhouses) in soilless media (composted pine bark), using nursery

pots, at Beli Farms in Wellborn, Florida. Two experiments were carried out and for both









experiments, cucumbers were harvested in the morning (March 15, 2003 and June 30,

2003) and packed unwashed in 7-kg unwaxed, corrugated cartons and transported the

same day to the Postharvest Horticulture Laboratory at the University of Florida in

Gainesville, Florida. Cucumbers were then sorted and graded by size and appearance.

Since no quality standards are available for Beit Alpha cucumbers in the U.S., cucumbers

were manually graded according to shipper's recommendations (dark green color and

free of any visible defects or injuries) and size (diameter of no less than 2.5 cm and no

more than 4.0 cm).

Beit Alpha cucumbers used in this test had an average weight of 80.4 g, an average

length of 136 mm and an average equatorial diameter of 29.4 mm. After sorting, the

cucumbers were dipped in a 100-ppm free chlorine solution for 2 minutes, after which

they were air-dried, randomized and placed in rigid, vented, 2-L, polystyrene clamshells.

Beit Alpha cucumbers are currently marketed in film over-wrapped trays; however, an

alternative package is the rigid, vented clamshell that protects from injury during

transportation, handling and/or displaying while still allowing a clear view of the product.

Cucumbers (10 cucumbers/clamshell) were stored for 21 d at 5, 7.5, 10, or 12.5 C and

assessed for quality every 3 d. Relative humidity (RH) inside the clamshells reached

-95% (Hobo Data Logger, Onset Computer Corporation, Bourne, MA) after 2 d and

remained at this level throughout the duration of the experiment. The quality parameters

assessed were the following.











Visual Quality

Fruit were visually assessed for yellowing, pitting, pathogen infection or any other

disorder that could render the commodity unmarketable. Visual quality assessments were

made every 3 d for 21 d.


Color Evaluation

Both external and internal color was assessed using a CR-200 Chroma Meter

(Konica-Minolta USA, Inc., Ramsey, NJ). External color readings were taken on an

equatorial spot predetermined and marked before placing the fruit in storage. Two

measurements were taken on opposite sides of the fruit (n=10) and averaged to obtain a

final value for each fruit. Internal color was also measured on the mesocarp tissue of

equatorial slices. Two measurements were taken per slice (n=5) and averaged to obtain a

final value. Each slice was obtained from a different cucumber. Chroma meter was white

calibrated using a white calibration plate (Konica Minolta Photo Imaging USA Inc.,

Mahwah, NJ) using the following parameters; Illuminant C, L = 97.08, C = 1.84 and h =

90.76 (Y=92.6, X = 0.3135 and y = 0.3196).


Weight Loss

Weight loss was determined by weighing 10 individual cucumbers 3 d and after

being transferred to 20 oC (68 F) for 24 hours. Weight loss is expressed as a percent of

the initial weight (fresh weight basis).











Respiration

The respiration rate was measured on fruit stored in sealable 1-L Tupperware

containers equipped with a septum for headspace sample retrieval. Three cucumbers were

weighed and placed in each container (4 containers/treatment) and stored at six different

temperatures; 5, 7.5, 10, 12.5, 15 and 20 C. Cucumbers were weighed continuously

during storage to reflect the weight loss in the respiration rate calculation. Containers

were sealed for 2 hours (avoiding accumulation of CO2 greater than 5%) before retrieving

headspace samples and unsealed after the headspace samples had been analyzed for CO2.

Headspace samples (n=8) were withdrawn every 2 d for 14 d, with the initial

measurement taken 2 d after harvest.

Headspace samples were withdrawn using a 1-ml disposable hypodermic syringe

and analyzed using a Gow Mac, Series 580 gas chromatograph (Gow Mac Instruments

Co., Bridgewater, NJ) equipped with a thermal conductivity detector. Respiration rates

were expressed as ml C02/kg-1 hr-1.


Ethylene Production

The production of internal ethylene was measured on stored cucumbers. Ethylene

production was measured on the same cucumbers at the same time that respiration rate

was measured. Ethylene was quantified on headspace samples (n=8) withdrawn every 2 d

for 14 d and analyzed using a Tracor 540 gas chromatograph (Tremetrics Analytical

Division, Austin, TX), equipped with a photoionization detector, an Alumina Fl column

with a mesh size of 80/100.









Mesocarp Firmness

Fruit firmness was assessed as the bioyield point on equatorial slices using an

Instron Universal Testing Instrument Model 4411 (Instron Corporation, Canton, MA)

equipped with a 3.0-mm diameter probe, a crosshead speed of 50.0 mm/min, a 5-kg load

cell and a 7-mm displacement. Firmness was evaluated on the mesocarp area (between

the epidermis and locular tissue, approximately 2 mm from the epidermis) of similarly

sized, transverse, equatorial slices (n=5) of fruit. Fruit slices were obtained using a

double-bladed cutting instrument with an 11-mm separation between blades, which

produced slices identical in thickness. Two firmness measurements were taken per slice,

and averaged to obtain a final value. Each slice was obtained from a different cucumber.


Electrolyte Leakage

Various aqueous solutions have been used as the bathing solution to assess

electrolyte leakage (EL) in cucumber fruit tissue. Kang et al. (2001) and Mattson (1996)

reported the use of 0.3 M mannitol as the isotonic concentration while Hakim et al.

(1999) used 0.4 M mannitol for EL assessments while others have used distilled

deionized water as the bathing solution (Knowles et al., 2001). Determining the isotonic

solution is important to accurately assess membrane permeability since the use of hypo or

hypertonic solutions could obscure real changes in permeability because they can cause

osmotic shock to the cells that would influence the rate of ion leakage (Saltveit, 2002).

Since recommendations for the isotonic solutions for Beit Alpha cucumbers could not be

found it was necessary to determine it. Isotonic mannitol concentration was determined

by weight difference after the mesocarp cores had been immersed in mannitol solution

for 4 hours. Five mesocarp cores (9 mm long by 7 mm thick) excised from equatorial









cucumber slices using a No. 5 cork borer were placed in 50-ml conical bottom plastic

centrifuge tubes containing 35 ml of 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 M

mannitol solution. The mesocarp cores were weighed and gently rinsed with deionized

water before being placed in the bathing solution. A final weight measurement was taken

after the samples had been on a slow shaker for 4 hours. The weight difference was then

used to determine the isotonic mannitol concentration, which was determined at 0.25 M

mannitol. Mesocarp cores did not gain or lose weight after being immersed for four hours

in 0.25 M mannitol solution (Appendix B). Higher concentrations hypertonicc solution)

caused a weight loss in mesocarp tissue while concentrations below 0.25 N hypotonicc)

caused a weight gain after the four-hour immersion.

Samples for electrolyte leakage assessments of stored fruit were prepared as

follows. Four cores (9 mm long by 7 mm thick), per treatment, of mesocarp tissue were

excised from transverse slices using a No. 5 brass cork borer. Each sample was excised

from a different cucumber. The mesocarp cores were cleaned of torn tissue by gently

rinsing them with deionized water before placing them in 50-ml conical-bottom

centrifuge plastic vials containing 35 ml of 0.25 M isotonic mannitol solution (obtained

as described above). The samples (n=4) were then placed on a slow shaker for 4 hours

before measuring the electro conductivity (EC) of the bathing solution using a digital,

temperature-compensated YSI 3100 conductance bridge (YSI Inc., Yellow Springs, OH).

The samples were then frozen at -20 oC, subsequently boiled for 30 minutes and allowed

to cool to room temperature before obtaining a final EC measurement of the bathing

solution. Electrolyte leakage was expressed as a percent of the total electrolyte leakage.









Moisture Content

Moisture content of the fruit was determined by placing 25 g of unpeeled fruit

slices in tared, aluminum weighing boats (n=6). The boats were placed on a tray wrapped

with aluminum foil and placed in an oven for two weeks. Weight difference was used to

calculate moisture content throughout the storage period (fresh-weight basis).


Compositional Analysis

After each evaluation period three cucumbers per treatment were immediately

frozen at -20 C for later analysis. The frozen samples were then thawed and blended at

high speed for 45 sec using a laboratory blender. A portion of each homogenate was

centrifuged at 15,000 RPM for 20 minutes. The resulting supernatant was filtered using

cheesecloth and stored in scintillation vials at -20 oC for later analysis. Total titratable

acidity, expressed as a percent of malic acid, was determined by diluting 6 g of

supernatant in distilled water and titrating to pH 8.2 with 0.1 N NaOH solution using an

automatic titrimeter (Fisher Titrimeter II, Fisher Scientific, Pittsburg, PA). Soluble solids

content, expressed as Brix, was determined by placing a drop of cucumber supernatant

on a tabletop, digital refractometer (Abbe Mark II, Reichart-Jung, Buffalo, NY). The pH

measurements were done on the remaining supernatant in the scintillation vials using a

digital pH meter (Model 140, Coming Scientific Instruments, Medfield, MA).


Data Analysis

Both experiments were designed as completely randomized experiments using four

temperature treatments. Data collected were analyzed using the GLM procedure (SAS

Institute Inc., Cary, NC). All data presented were subject to a Duncan's Multiple Range









Test using a P-value of <0.05. Results of both experiments were not significantly

different and were combined for analysis.

Results

Appearance

The storage temperature had a significant effect on the postharvest quality and

marketable life of cucumbers with different disorders observed on fruit stored at different

storage temperatures. All fruit retained acceptable appearance for the first 6 d in storage

with deterioration in fruit quality becoming evident by 9 d on fruit stored at 5 or 12.5 C.

Quality started to deteriorate on fruit stored at the two extreme temperatures, 5.0

and 12.5 C, between 6 to 9 d in storage. At this point, fruit stored at 5.0 oC lost quality

due to pitting and water soaking that was present on 70% of the fruit while fruit stored at

12.5 C lost quality due to the presence of solid protrusions or bumps that developed on

the surface of the fruit. The presence of these bumps affected 45% of the fruit and

negatively affected the smooth, waxy appearance of Beit Alpha cucumbers. Although

fruit stored at 5 C was no longer marketable after this period, it was kept in storage for

observation purposes. Fruit stored at the two intermediate temperatures, 7.5 and 10 C,

did not show signs of pitting, bumps or other disorders at this point in the storage period.

The appearance of fruit stored at 7.5 C showed signs of deterioration and became

unmarketable after 12 d in storage. Yellowing on 50% of fruit, slight pitting and water

soaking were the predominant factors that negatively affected the appearance of this fruit

while fruit stored at 10 oC retained good appearance after the same storage period.

The presence of bumps and yellowing continued to reduce the quality of fruit

stored at 12.5 C and it was no longer unmarketable after 12 to 15 d in storage. Fruit

stored at 10 oC retained good appearance until 15 to 18 d in storage at which point









yellowing and stem-end shriveling negatively affected appearance, making the fruit

unmarketable.

Marketability of stored fruit, independent of storage temperature, was lost between

18 and 21 d in storage. In the first experiment, fruit stored at 10 oC or below showed

symptoms of bacterial (Pseudomonas sp.) and fungal (Botrytis sp. decay by 21 d storage.

Decay, however, was not observed in the second experiment.


External Color

Varying the storage temperature had no significant impact on the external color, as

measured by the hue angle, of stored Beit Alpha cucumbers. The external color was

however, influenced by the length of the storage period and it exhibited a downwards

trend, reflecting a departure from dark green towards yellow, as the storage period

progressed (data not shown).

External color for all treatments averaged 128.50 ( 1.1) initially (12 hours after

harvest) and it declined to between 123.1 ( 1.5) and 124.70 ( 1.5) after 21 d in storage;

a decline of 2.7 to 3.4% from the initial values observed at harvest but with no significant

differences among temperature treatments.

In these experiments it was not possible to accurately correlate external hue angle

measurements with the yellowing detected upon visual inspection, perhaps due to the fact

that hue angle measurements were taken on equatorial spots of the fruit, which remained

green even after incipient yellowing had set on the blossom (distal) end of the fruit.

During the storage period it was observed that yellowing advanced from the blossom end

(distal) to the stem end proximall) of the fruit. Also, the storage treatment had no effect

on the L* (lightness) or chroma values. Lightness (L*) averaged 39.9 ( 1.1) at harvest









and was 41.5 ( 1.5) after 21 d storage while the initial chroma value of all four

treatments averaged 23.2 ( 0.9) and was 26.2 ( 2.9) after 21-d in storage.


Internal Color

The internal color decreased in fruit stored at the two intermediate temperatures

(7.5 and 10 C) but not in fruit stored at either 5 or 12.5 C (Table 3-1). Internal L* and

chroma values were not affected by the storage treatments Lightness (L*) averaged 68.8

( 1.5) at harvest and was 68.3 ( 1.5) after 21 d storage while the initial internal chroma

value of all four treatments averaged 25.4 ( 1.6) and was 21.8 ( 1.1) after 21-d in

storage.


Weight Loss

Weight loss increased almost linearly (R2 = 0.99) over time, reaching 4.4% after 21

d on fruit stored at 12.5 C (Table 3-2). Weight loss of fruit stored at 12.5 C was

significantly higher, throughout the storage period, than the weight loss of fruit stored

below 12.5 C. Weight loss in fruit stored between 5.0 and 10 C was less pronounced

and ranged between 1.6 and 2.6% after 21 d, with no significant differences.


Respiration

The storage temperature significantly affected the respiration rate of Beit Alpha

cucumber fruit during the first 6 d in storage. After this period, only the lowest

temperature (5.0 C) effectively suppressed the respiration rate (Figure 3-1).













Table 3-1. Internal hue angle of Beit Alpha cucumbers stored at four different temperatures; 5, 7.5, 10 or 12.5 'C for 21 days.
Storage Length (d)
0 3 6 9 12 15 18 21


Internal Hue Angle (0)
Temperature Mean s Mean s Mean s Mean s Mean s Mean s Mean s Mean s
Tre
atm
ent

5 oC 113.5z 0.23Y 113.1 0.28 113.4 0.30 110.9 0.37 111.1 0.31 114.6 0.35 113.3 0.37 114.4 0.33
a a a a a a a a


7.5 oC 113.5 0.23 114.2 0.32 113.4 0.34 107.8 0.25 108.1 0.46 110.6 0.40 108.3 0.27 105.8 0.43
a a a a b b b b


10 C 113.5 0.23 114.0 0.20 113.7 0.17 107.3 0.31 108.5 0.15 109.5 0.53 107.9 0.46 108.1 0.17
a a a a b c c c


12.5 oC 113.5 0.23 114.6 0.20 113.4 0.32 111.9 0.37 111.4 0.29 111.2 0.18 109.9 0.36 112.5 0.32
a a a a a b b d


ZMean values within the same column are not significantly different from each other. Mean separation based on Duncan's Multiple
Range Test using a P value < 0.05.
Y Standard error from the mean (n=5).













Table 3-2. Weight loss of Beit Alpha cucumbers stored at four different temperatures; 5, 7.5, 10 and 12.5 C for 21 days.

Days in Storage
3 6 9 12 15 18 21

Weight Loss (%)
Temperature Treatment Mean s Mean s Mean s Mean s Mean s Mean s Mean s



5 oC 0.6z 0.04y 0.7 0.06 1.1 0.09 2.0 0.16 2.3 0.19 2.5 0.18 2.7 0.19

7.5 oC 0.3 0.02 0.4 0.03 0.7 0.05 1.1 0.07 1.3 0.07 1.7 0.09 2.5 0.11

10 C 0.3 0.05 0.5 0.06 0.9 0.08 1.5 0.11 1.8 0.13 2.1 0.15 2.3 0.19

12.5 oC 0.4 0.06 1.3 0.13 2.1 0.20 3.2 0.22 3.7 0.27 3.9 0.30 4.4 0.34

zMean values in the same column with different letters are significantly different at a P-value <0.05 based on Duncan's Multiple
Range Test.
Y+ Standard error from the mean (n=10).









12.0




10.0-


8.0


I-
hi-
'4
(N
0
u


4.0




2.0




0.0


2 4 6 8 10 12


Days in Storage (d)


-- 5.0 C -- 7.5 C -- 10.0 C


12.5 C -15.0 C -- 20.0 C


Figure 3-1. Respiration rate (ml CO2 kg-1 hr-) of Beit Alpha cucumbers stored for 21 d at
six different temperatures; 5, 7.5, 10, 12.5, 15 and 20 C. Vertical bars
represent the + standard error from the mean.


;ry









Initially, respiration rates were significantly higher in fruit stored at higher

temperatures (10 and 12.5 C) but these differences became indistinguishable as the

storage period progressed. The only exception was fruit stored at 5 oC in which the

respiration rate remained suppressed throughout the 21-d storage period. After 2 d in

storage (initial measurement), the respiration rate was lowest in fruit stored at 5 C,

averaging 2.6 ml C02/kg-1 hr-1. Fruit stored at 7.5 or 10 C had average respiration rates

of 4.0 and 4.4 ml CO2/kg-1 hr-1, respectively, and were significantly different from all the

fruit stored at other temperatures but not between each other. The next highest respiration

rates were for fruit stored at 12.5 and 15 C, both having a respiration rate of 6.0 ml

CO2/kg-' hr-1; these were significantly higher than those of fruit stored at lower

temperatures but significantly lower than that of fruit stored at 20 oC.

The highest respiration rate after 2 d in storage was observed on fruit stored at 20

C and averaged 9.5 ml CO2/kg-1 hr1. Over time the respiration rate of this fruit (20 oC)

declined while that of fruit stored between 7.5 and 15 C tended to increase until there

were no significant differences in respiration rate of fruit stored between 7.5 and 20 C.

The respiration rate of fruit stored between 5.0 and 15 C reached its peak after 7 d

in storage, increasing between 30 and 130% while that of fruit stored at 20 oC decreased

slightly (3%). The highest increase in respiration rate over this 7-day period was observed

in fruit stored at 10 oC which increased 130%, from 3.9 to 8.9 ml CO2 kg-' hr-1.

Significant differences in respiration rate were less obvious after 7 d in storage. At

this point there were no significant differences in the respiration rate of fruit stored

between 7.5 and 20 C. Although the respiration rate of fruit stored at 5.0 oC increased









30% over the same period it was still significantly lower than the respiration rate of fruit

stored at higher temperatures.

The respiration rate of fruit stored between 5 and 15 C remained at similar levels

after 14 d in storage when compared to the 7-day peak but it was still higher than the

initial respiration rate. On the other hand the respiration rate of fruit stored at 20 C

decreased from 9.2 ml to 7.8 ml CO2 kg-1 hr- over the same period. At this stage there

were no significant differences in the respiration rate of fruit stored between 7.5 and 20

C; which on average had a respiration rate of 7.7 ml CO2 kg- hr- and ranged between

7.1 and 7.9 ml CO2 kg- hr-. Fruit stored at 5.0 oC had an average respiration rate of 4.6

ml CO2 kg- hr-, significantly lower than all the other storage temperatures after the same

storage period. Respiration rate was not measured beyond 14 d in storage due to the

presence of decay and other storage disorders.


Ethylene Production

Ethylene synthesis was assessed for the first 2 weeks in storage but ethylene levels

were not detectable during this evaluation period. This is in agreement with results

obtained by Lima and Huber (unpublished).


Firmness

The storage temperature had no remarkable effect on the mesocarp firmness of

stored cucumbers. Measurements of mesocarp firmness decreased between 22 and 28%

after the first 3 d in storage with no significant difference among the four storage

temperatures. Initial mesocarp firmness was very different in both experiments and it

behaved differently during storage. In Exp. I, the initial firmness was 9.1 N while in Exp.

II the initial firmness was 18.8 N. Mesocarp firmness did not change significantly when









the initial firmness was relatively low, as in Exp. I, but decreased independent of storage

temperature when it was high at harvest, as in Exp. II. Since moisture content was only

measured in the second experiment it is not possible to say if the high water content

during storage influenced the loss of firmness seen in the second experiment.

In Exp. II, initial firmness (12 hrs after harvest) was 18.8 N and after 3 d in storage,

fruit softened to 13.6 to 14.7 N (with no significant difference among the four storage

temperatures) (Figure 3-2). After this period, the general trend was for mesocarp firmness

values to remain stable. At the end of the 21-day storage period, fruit stored at 5, 7.5, 10

and 12.5 had similar firmness of 13.2, 13.8 and 14.1 N, respectively, with the exception

of fruit stored at 7.5 C which had softened to 9.4 N.


Electrolyte Leakage

The rate of electrolyte leakage of Beit Alpha cucumbers was dependent on the

storage temperature. Lower storage temperatures severely increased the rate of electrolyte

leakage with the effect becoming evident after the fruit had been in storage for 6 to 9 d.

The electrolyte leakage (EL), expressed as a percent of total electrolyte leakage,

was 15% at harvest and remained at similar levels for the first 6 d in storage, independent

of the storage temperature (Figure 3-3). Electrolyte leakage rates increased after 9 d in

storage to an average of 32.5% in fruit stored at 5 or 7.5 C, more than twice the rate seen

at harvest. There was no significant difference between these two temperatures but both

were significantly higher than the EL rate of fruit stored at either 10 or 12.5 C, which

had EL rates of 19.1 and 11.6%, respectively.










25.0





20.0






15.0

C/



10.0






5.0





0.0


0 3 6 9 12 15 18 21
Days in Storage


* 5.0 oC


* 7.5 oC


O 10.0 oC


E 12.5 oC


Figure 3-2 Mesocarp firmness, expressed in Newtons, ofBeit Alpha cucumbers stored for
21 d at 5, 7.5, 10 or 12.5 TC. Vertical bars represent the standard error from
the mean.










90.00


80.00


70.00


60.00


50.00


40.00


30.00


20.00


10.00


0.00


0 3 6 9 12 15 18 21


Days in Storage (d)


15.0 C


07.5 C


0 10.0 C


E 12.5 C


Figure 3-3. Electrolyte leakage, as a percent of total electrolyte leakage, of Beit Alpha
cucumbers stored for 21 d at four different temperatures; 5, 7.5, 10 or 12.5 C.
Vertical bars represent the + standard error from the mean.









For the remaining storage period the same pattern persisted in that the EL rates of

fruit stored at the two lower temperatures (5 and 7.5 C) increased almost linearly and

were significantly higher than those of fruit stored at the two higher temperatures (10 and

12.5 C).

Electrolyte leakage increased almost linearly (R2 = 0.93) throughout the 21-day

storage period on fruit stored at 5 oC and at the end of the 21-day storage period it had

increased to 79.5%, more than five times the initial rate. Fruit stored at 7.5 C also

showed an increased EL rate as the storage period progressed and peaked after 15 d at

67.2%.

Unlike the other two groups (5 and 7.5 C); the EL rates of fruit stored at either 10

or 12.5 C remained below 25% throughout the storage period with no significant

difference between these two temperatures.


Moisture Content

The storage temperature did not affect the moisture content of stored Beit Alpha

cucumbers. The moisture content of whole fruit at harvest was 95.5%. Moisture content

measurements remained within a narrow range (96 98%) during the 21 d in storage

with no significant differences among storage treatments (data not shown). Furthermore,

moisture content obtained at different intervals throughout the 21-day storage period was

not significantly different from the values obtained at harvest. Similar moisture content

levels were reported at harvest in commercial-size, fresh cucumbers of unspecified

cultivars (Mattson, 1996; Sajnin, 2003).









Compositional Analysis

Total soluble solids content, although variable during the storage period, tended to

remain between 2 to 3 Brix (Table 3-3). A clear effect of the storage temperature on total

titratable acidity could not be strictly defined. Total titratable acidity (TTA), expressed as

percent of malic acid, tended to decrease slightly over time. Initial TTA was 0.15 % 12 hr

after harvest and declined between 15 and 42 %, depending on the storage temperature, at

the end of the 21-day storage period (Table 3-3).

As with TTA, a clear effect of the storage temperature on the pH of stored Beit

Alpha cucumbers could not be well defined. The pH values of stored fruit tended to

increase over time independent of the storage temperature.

The sugar acid ratio, although highly variable during storage, ended the 21-day

storage period with relatively similar values to those observed at harvest. Initial sugar

acid ratio, 12 hours after harvest, was 20.2 and increased to between 20 and 25 after 21 d

in storage. Differences among storage temperatures, although observed at different

intervals during the storage period were not systematic to accurately conclude that

storage temperature had a significant effect on the sugar-acid ratio of stored cucumbers.


Table 3-3. Compositional analysis of Beit Alpha cucumbers stored at four temperatures
(5, 7.5, 10 or 12.5 +1 C) for 21 days.
TTA Sugar/Acid
Treatment SSC(Brix) pH (% Malic Acid) Ratio
Mean s Mean s Mean s Mean s
Initial 2.59 0.33 0.15 0.01 20.2 0.71
After 21 d
5 oC 2.24 0.26 6.26 0.05 0.1 0.01 21.5 0.55
7.5 C 2.53 0.12 5.75 0.06 0.13 0.01 20 1.18
10 C 2.33 0.34 5.91 0.05 0.11 0.01 20.4 0.82
12.5 oC 2.23 0.3 6.66 0.03 0.09 0.01 25 1.4









Discussion

Appearance

Short-term storage of harvested commodities, mainly used to preserve quality until

it gets to the final consumer, is a marketing strategy that is relied upon to satisfy

consumer demand on a daily basis. One of the principles of storage, as an efficient

marketing strategy, is to maximize the length of storage or marketable life while

minimizing quality losses. The concept of quality is interpreted differently by the

different handlers in the food distribution network (Shewfelt, 1998). Although the

definition of quality for the end consumer can be a complex of attributes, such as sensory

characteristics, safety, nutrition and lately functional properties, the two parameters that

are most influential in the initial purchase are appearance and freshness (Kays, 1998;

Bruhn, 2002). With new crops such as Beit Alpha cucumbers, inducing the initial

purchase is one of the first steps in accomplishing the overall goal of inducing repeat

purchases and establishing a market presence.

In these experiments the maximum marketable life was obtained when the fruit was

stored at 10 oC. At the two lowest temperatures (5 and 7.5 C), chilling injury became the

deciding factor in limiting fruit quality while on fruit stored at 12.5 C it was the presence

of firm protrusions. Sargent et al., (2002) reported the development of these bumps on

Beit Alpha cucumbers after 14 d in storage at 10 and 12.5 C and speculated that they

may have been caused by the high internal turgor pressure exerted on the senescing

epidermal tissue. A similar storage disorder was reported by Kannelis et al., (1986) on

greenhouse-grown fresh-market cucumbers ('Deliva'). Although the bumps were

noticeable they did not affect the edible quality of the stored fruit.









Color

Changes in peel color are a natural development in horticultural commodities and

are part of the ripening and the natural senescing process (Funamoto et al., 2002); during

this process carotenoids (and other pigments such as anthocyanins) replace chlorophylls

(Hobson, 1994) causing a degreening of the fruit. Changes in pigmentation can be

accelerated by stress, such as ethylene exposure, but can occur naturally during storage.

Unlike other fruits, such as tomato and bananas that need to undergo ripening to reach

commercial maturity, this process is detrimental to fruit quality in cucumber since it

reach commercial maturity at a physiologically immature stage. The rate of chlorophyll

metabolism, or days to incipient color, has been associated with the keeping quality of

cucumbers (Schouten et al., 2002) and other commodities such as broccoli (Yamasaki et

al., 1997; Funamoto et al., 2002; Costa et al., In press).

Weight Loss

Loss of turgidity or shriveling, as a result of water loss, decreases the freshness of a

horticultural commodity making it less acceptable to consumers (Burdon and Clark,

2001; G6mez et al., In press). Reducing weight loss is critical in maintaining consumer

acceptability of fruits and vegetables since even minimal losses of 1 to 2% are considered

sufficient to start decreasing the appeal of a commodity (Hobson, 1994). Stem-end

shriveling, as a result of water loss, became evident between 15 to 18 d of Beit Alpha

cucumbers stored at 10 oC, negatively affecting the appearance. At this stage the weight

loss was less than 3%, well below the marketability threshold of 7% (Kang et al., 2001)

set for traditional cucumber varieties; an indication perhaps that Beit Alpha cucumbers

have a lower weight loss threshold than that recommended for traditional cucumber.









Respiration

The respiration rate is inversely related to the marketable life of fruits (Knowles,

2001; Kader, 2002) and it can vary depending on the storage temperature (Suslow et al.,

2002), the maturity stage of the fruit and plant at harvest, the days in storage, as well as

the nutrient regime (Knowles et al., 2001). Cucumber respiration has been reported to be

between 10 to 20 mg CO2 kg-1 hr-1 (Kader, 2002); between 3 to 11 Imol CO2 kg-1 min-

for the cultivar 'Carmen' and between 12 to 30 .imol CO2 kg-1 min- for the cultivar

'Corona' depending on the length of storage at 23 C (Knowles et al., 2002); between 5

and 28 mg CO2 kg-1 hr-1 for the cultivar 'Deliva' when stored in modified atmosphere at

12.5 C (Kanellis et al., 1988); between 10.5 to 35.6 mg CO2 kg-1 hr-1, at harvest, and

between 2.7 and 15 mg CO2 kg-1 hr-1 (Watada et al., 1996).

These results show that respiration rates are significantly higher when the fruit is

stored at higher temperatures but these differences become indistinguishable after 2 to 3

weeks in storage, since respiration rate tended to increase in fruit stored at lower

temperatures. The only exception was fruit stored at 5 oC, which tended to have relatively

suppressed respiration rates throughout the 21-day storage period. This temperature,

however, is not recommended for cucumber storage due to the chilling and marketable

life limiting effect it has on cucumber fruit.


Ethylene Production

Ethylene production by fresh-market cucumbers has been previously reported

(Cantwell, 2002). Kanellis et al. (1977) reported that greenhouse-grown cucumbers

('Deliva') produced between 5 to 15 nl kg-1 hr-1 when stored at 12.5 C.









Pickling cultivars also produce ethylene; 'Explorer', a pickling cultivar, was

reported to produce ethylene when stored at 30 oC (Poenicke et al., 1977) and Saltveit and

McFeeters (1980) also reported that, at harvest, the pickling cultivar 'Chipper' produced

ethylene at a rate between 32 to 279 nl kg-1 hr-1. Based on the method previously

described, production of ethylene by Beit Alpha cucumbers was not detectable. These

results are comparable to those of Lima and Huber (unpublished).


Firmness

Initial mesocarp firmness was very different in both experiments and it behaved

differently during storage. In Exp. I, the initial firmness was 9.02 N while in Exp. II the

initial firmness was 18.77 N. Mesocarp firmness did not change significantly when the

initial firmness was relatively low, as in Exp. I, but decreased independent of storage

temperature when it was high at harvest, as in Exp. II. Since moisture content was only

measured in the second experiment it is not possible to say if the high water content

during storage influenced the loss of firmness seen in the second experiment.

Firmness is one of the components of texture which is a complex sensory attribute

that also includes crispiness and juiciness (Konopacka and Plocharski, 2003) and is

critical in determining the acceptability of horticultural commodities (Abbott and Harker,

2004). Untrained panelists determined that cucumbers in one experiment stored at 10 C

for 15 days had acceptable texture, although the peel was described as slightly tough or

leathery while the mesocarp tasted slightly watery. These observations were empirical

and are not in any way conclusive in determining the effect of storage temperature on the

texture of fresh cucumbers.









Electrolyte Leakage

Electrolyte leakage can be used to determine changes in membrane permeability

caused by environmental stress (Whitlow et al., 1991; Knowles et al., 2001). In

cucumbers, higher rates of ion leakage are associated with cell damage due to chilling

injury (Hakim et al., 1999; Kang et al., 2001; Saltveit, 2002) as well as other types of

stress. Although fruit exposed to chilling temperatures exhibit symptoms such as pitting,

membrane alteration is the primary effect (DeEll et al., 2000; Balandran-Quintana et al.,

2003). Changes in membrane permeability, such as damage from the exposure to chilling

temperatures, accumulate over time and do not occur immediately after exposure to

chilling temperatures (Saltveit, 2002). DeEll (2000) reports that irreversible membrane

injury due to chilling injury requires at least 7 d at 4.0 oC (chilling temperature) in

cucumber. The results presented here are in agreement with those of DeEll (2000) since

significant changes in membrane permeability were not evident until between 6 and 9 d

exposure to chilling temperatures of 7.5 C or lower. Changes in electrolyte leakage rates

was the first parameter to reflect significant differences, based on the storage

temperature, an indication that changes in quality of the fruit are first reflected in changes

in membrane permeability.


Compositional Analysis

Malic acid is the most abundant acid in commercial-sized pickling cucumbers

(McFeeters et al., 1982) as well as in slicing cucumbers (Mattsson, 1996). The TTA of

stored cucumbers has been shown to vary in storage in response to different nutrition

regimes (Altunlu and Gill, 1999) while malic acid has also been reported to remain stable

or decline slightly in kiwi fruit, depending on the growing region (Marsh et al., 2004). A









decrease in malic acid could be explained by its utilization in respiration. Malate appears

to be the major organic acid used as respiratory substrate (Tucker, 1993). Mattsson

(1996) also reports a decline in malic acid of cucumber fruit during storage; from 4 mg/g

of fresh weight at harvest to 3.2 mg/g of fresh weight after 21 d storage at 13.5 oC.

Statistical differences were observed at different intervals in the storage period but they

were not systematic and no clear conclusions could be made in relation to the storage

temperature.

The pH of cucumbers has been reported to behave differently during storage. The

pH of fresh-market cucumbers has been reported to increase during storage (Srilaong,

2003). However, Altunlu and Gul (1999) also reported a decrease in the pH of fresh

cucumbers ('Alara') stored for 21 d at 13 oC and 85 to 90% RH; from 6.35 to 5.77.

Increases in the pH of other commodities during storage have also been reported;

Perkins-Veazie (2003) reports a slight increase in the pH of fresh-cut watermelon as well

as in celery (Gomez and Artez, In press). The pH of cucumber fruit is important because

it influences enzyme activity responsible for cucumber flavor and aroma; lower pH

causes the enzyme system responsible for cucumber flavor and aroma to become unstable

(Palma-Harris et al., 2002).

Although some differences in soluble solids were observed at different intervals in

the storage period, these differences were not systematic therefore a clear effect of the

storage temperature on the soluble solid content of the stored fruit could not be

established.

The values presented here are similar to those reported at harvest by Sajnin et al.

(2003), who reported total soluble solids content of 2.3 Brix on fresh cucumbers of









unspecified cultivar. These values, however, are slightly lower than those reported earlier

by Altunlu and Gul (1999) who report total soluble solids between 3.32 and 4.04 for the

greenhouse-grown cultivar 'Alara'.


Conclusions

It can be concluded that the optimum storage temperature for Beit Alpha

cucumbers is 10 C at 90% RH. Storage under these conditions yielded the maximum

marketable life of 15 to 18 d based on the parameters assessed. It is noteworthy to

indicate that quality should be assessed as a complex of all the different parameters

(appearance, color, weight loss and firmness) that affect quality and should reflect the

nature of the commodity as well as the intended market use














CHAPTER 4
RESPONSE OF BEIT ALPHA CUCUMBERS TO EXOGENOUS ETHYLENE
DURING STORAGE

Introduction

Appearance is perhaps one of the most important factors in making an initial

purchasing decision for many commodities (Bruhn, 2002) and is a combination of

parameters such as color, size, shape and the freedom of defects or foreign matter on the

surface of the commodity. Greenhouse-grown cucumbers are grouped into four different

grades based largely on general appearance (color, shape, size, freshness, and freedom of

decay, diseases and injuries). These grade standards apply only to greenhouse-grown

European-type cucumbers (English or Dutch-type), which are the traditional types grown

in greenhouses in the U. S (United States Standards for Grades of Greenhouse

Cucumbers, 1997). Since Beit Alpha cucumbers are not widely commercialized

commodity there are no federal grade standards yet.

However, injury can be present in the internal tissue before it appears on the

external appearance of a commodity (DeEll et al., 2000; Balandran-Quintana et al., 2003)

but given the destructive nature of the techniques available to assess the condition of

internal tissue, quality assessments usually rely on the evaluation of external appearance.

Given the substantial role that appearance plays in purchasing decision as well as in

determining the grade standards, it is therefore important to evaluate the factors that

could negatively affect the appearance of a commodity and render it unmarketable,

especially since the desired characteristic will vary depending on the commodity.









Depending on the commodity ethylene can either have beneficial or deleterious

effects (Saltveit, 1998). Ethylene promotes the breakdown of chlorophyll and tissue

softening and is therefore essential for ripening of climacteric fruit such as bananas and

tomatoes but unnecessary and detrimental in commodities such as cucumbers. The

acceleration of senescence, the enhancing of fruit softening and the promotion of

chlorophyll loss (yellowing) are among the deleterious effects of ethylene on cucumbers

(Poenicke et al., 1977; Saltveit, 1998; Saltveit and McFeeters, 1980; Lelievre, 1997). The

undesirable impact of ethylene on pulp firmness is well-established in many commodities

including apples (Johnston et al., 2002), strawberries and pears (Bower et al., 2003), and

watermelons (Karakurt et al., 2002). The extent of the effect that ethylene has on

parameters such as appearance, color, texture and decay impacts consumer acceptability

of a commodity.

Cucumbers are a non-climacteric fruit (Mattsson, 1996; Wehner et al., 2000) and

are harvested at a physiologically immature stage. Several types are reported to produce

very little ethylene and are highly sensitive to the exposure of exogenous ethylene

(Kader, 2002). Cucumbers (Cucumis sativus L.), of an unspecified cultivar, have been

reported to produce between 0.1 1.0 [l kg1 hr-1 of ethylene at 20 OC (Kader, 2002)

while the parthenocarpic cultivar 'Deliva' is reported to produce between 5 and 15 nl kg-1

hr- at 12.5 C (Kanellis et al., 1988). Other cultivars such as 'Explorer', a pickling

cultivar, have also been reported to produce ethylene when stored at 30 oC (Poenicke et

al., 1977). Saltveit and McFeeters (1980) also report the production of ethylene by the

pickling cultivar 'Chipper', which produced between 32 -280 nl kg-1 hr-1 when stored

overnight at room temperature. The amount of endogenous ethylene produced by









cucumbers varies and is affected by the fruit size, cultivar, storage temperature (Poenicke

et al., 1977), fruit age (Kanellis et al., 1986) and in many plant tissues can be induced as a

response to environmental stresses (Yang and Oetiker, 1998). In previous storage trials, it

was not possible to detect the production of ethylene in Beit Alpha-cucumbers stored for

9 d at 10 C, the recommended storage temperature.

The objectives of these studies were to determine threshold levels of exogenously

applied ethylene to Beit Alpha cucumbers and European cucumbers based on the quality

and shelf life parameters.

Materials and Methods

Experiment I


Plant material

Cucumbers were obtained as described in Chapter 3. Cucumbers were then surface

sanitized by immersion for 90 sec in a 150-ppm free-chlorine solution and air-dried.

Sanitized cucumbers were placed in rigid, vented, hinged 2-L polystyrene containers,

with 10 cucumbers per clamshell. Beit Alpha cucumbers are currently marketed in film

over-wrapped trays; however, rigid clamshells provide a layer of protection from injury

due to transportation, handling and/or displaying while still allowing a clear view of the

product. Clamshells were subsequently placed in sealed 200-L metal gassing chambers at

10 C + 1.0 for storage under constant flow. Gassing chambers were connected to a

mixing board using 0.6-cm polyethylene tube. The gas mixture (ethylene and compressed

air) was humidified (85 to 90% RH) by bubbling it through a 2-L glass jar with water

then introduced into the gassing chambers. Cucumbers were continuously exposed to

ethylene at four different concentrations; 0 (control), 1, 5 and 10 ppm (+ 5%). Total gas









flow through the gassing chamber was monitored using a digital ADM 1000 flow meter

(J & W Scientific, Folsom, CA) and adjusted to ensure the internal atmosphere remained

less than 2% CO2. To ensure consistency of ethylene concentrations in the gassing

chambers headspace samples were collected three times a day and analyzed using a

Tracor 540 gas chromatograph (Tremetrics Analytical Division, Austin, TX), equipped

with a photoionization detector, an Alumina Fl column with a mesh size of 80/100. The

following quality parameters were measured every 3 d for 12 d to assess the quality of the

stored fruit.


Appearance

Appearance of stored cucumbers was rated using a subjective scale (Appendix A)

from 1 to 9, with 9 representing field-fresh fruit, 3 representing the marketability

threshold and 1 representing inedible fruit. Fruit with dark green external color and free

of defects and decay received higher ratings while fruit that exhibited yellowing

shriveling and/or decay received lower ratings.


Color evaluation

Both external and internal color was assessed using a CR-400 Chroma Meter

(Konica Minolta Sensing Co., Japan). External color readings were taken on an equatorial

spot predetermined and marked before placing the fruit in storage. Color measurements

were taken every three days using the CIE XYZ color space and converted to L* C H

values (Lightness intensity, Chroma and Hue) using the CR-400 Utility software (Konica

Minolta Sensing Co., Japan). Two measurements (on opposite sides of the fruit) were

taken and averaged to obtain a final value for each fruit. Internal color was measured on

the sliced mesocarp tissue, as with external color, two measurements were taken per slice









(n=10) and averaged to obtain a final value. Each slice was obtained from a different

cucumber. Chroma meter was white calibrated using a CR-A43 white calibration plate

(Konica Minolta Photo Imaging USA Inc., Mahwah, NJ) using the following parameters;

Illuminant C, L = 97.08, C = 1.84 and h = 90.76 (Y=92.6, X = 0.3135 and y = 0.3196).


Weight loss

As described in Chapter 3.


Respiration

The rate of respiration of the stored fruit was measured on fruit stored in 1-L

sealable containers (Tupperware, Orlando). Three cucumbers were weighed and placed in

each of four respiration chambers per treatment. The respiration chambers were

subsequently placed in the gassing chambers alongside the other fruit. Respiration

chambers were retrieved and sealed for two hours prior to every measurement.

Headspace samples (2/container) were withdrawn every 3 d using a 1-ml disposable

hypodermic syringe and analyzed for carbon dioxide content using a Gow Mac, series

580 gas chromatograph (Gow Mac Instruments Co., Bridgewater, NJ) equipped with a

thermal conductivity detector. Respiration rates were expressed as ml CO2 kg1 hr-1.


Mesocarp firmness

As described in Chapter 3.


Electrolyte leakage

As described in Exp. II, Chapter 3.









Data analysis

The experiment was designed as a completely randomized experiment and the data

collected were analyzed using the GLM procedure (SAS Institute Inc., Cary, NC). All

data presented were subject to a Duncan's Multiple Range Test using a P-value of <0.05.


Experiment II


Plant material

Beit Alpha cucumbers were obtained as described above in Exp. I.

European cucumbers ('Logica') were also grown under commercial greenhouse

conditions in soilless media (perlite), using lay-flat bag culture, in Ft. Pierce, Florida (K

& M of the Treasure Coast Inc.). European cucumbers were manually harvested in the

morning (May 14, 2004), wrapped unwashed and packed in two layers in unwaxed

cartons (12, US No. 1 cucumbers per carton). Cucumbers were wrapped mechanically

with low density, micro perforated, 17-micron thick polyethylene film (Global

Horticulture, Inc., Ontario, Canada) using a conveyor shrink-wrap machine equipped

with a heat tunnel. Each carton contained. The cucumbers were transported the same day

to the Postharvest Laboratory at the Horticultural Sciences Department at the University

of Florida in Gainesville and stored for 2 d at 10 OC in their original plastic packaging

before setting up the experiment (May 15, 2004) to coordinate with the delivery of the

Beit Alpha cucumbers. Both European and Beit Alpha cucumbers were harvested on the

same day at their respective commercial maturity. For this experiment, half of the

European cucumbers were removed from their plastic wrap while the other half was left

wrapped as would normally be done under commercial conditions. Unlike Beit Alpha









cucumbers, European cucumbers were not surfaced-sanitized with chlorinated water prior

to storage. The cucumbers (both types) were ethylene-treated as in Exp. I.


Appearance

Appearance of cucumber types was rated as in Exp. I.


Color evaluation

As described above in Exp. I.


Weight loss

As described above in Exp. I.


Mesocarp firmness

As described above in Exp. I.


Electrolyte leakage

Electrolyte leakage on both cucumber types was measured as described in Exp. I.


Data analysis

Experimental design and data analysis was done as described in Exp. I.


Experiment III


Plant material

As described above in Exp. II.


Appearance

As described above in Exp. II.









Color evaluation

Both external and internal color was assessed as described in Exp. II.


Weight loss

Weight loss was determined as described in Exp. II.


Mesocarp firmness

Fruit firmness was assessed as described in Exp. II.


Electrolyte leakage

Electrolyte leakage was assessed as described in Exp. II.


Data analysis

Experimental design and data analysis was done as described in Exp. I and II.


Results

Experiment I


Appearance

The exposure to external ethylene had a negative effect on the external appearance

of stored cucumbers. Appearance remained practically unchanged for the first 6 d of

ethylene exposure (Figure 4-1). At this stage all four treatments had very good, dark

green color with no visible defects such as shriveling, water soaking or microbial rot and

all four treatments scored 8 on a scale from 1 to 9. However, the external appearance of

fruit exposed to ethylene deteriorated after transfer to ethylene-free storage at 20 OC for

24 hours. After the transfer period, ethylene-treated fruit (1, 5 and 10 ppm) had an

average external appearance rating of 5 while the control fruit rated 8.






64



10.0


9.0 -- ,


8.0


7.0


6.0


5.0-


4.0


3.0


2.0


1.0


0.0
0 3 6 9 12


Duration of Ethylene Exposure (d)


-- 0 ppm 1 ppm -- 5 ppm 10 ppm Threshold


Figure 4-1. Appearance rating of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 or 10 ppm) and stored at 10 C for 12 d. Fruit
exposed to 5 and 10 ppm of ethylene had identical results. Vertical bars
represent the + standard error from the mean, were not shown standard error
falls within the marker size.









Ethylene-treated fruit showed yellowing and stem-end shriveling in varying

degrees while the control fruit retained its pre-transfer appearance. External appearance

ratings continued to decline as the storage period progressed with higher decreases

observed in fruit exposed to higher concentrations of ethylene. Significant differences in

external appearance were observed after 9 d of ethylene exposure. At this stage the

ethylene treated fruit had significantly lower appearance rating than the control fruit.

Fruit continuously exposed to either 5 or 10 ppm of ethylene reached the marketability

threshold, an appearance rating of 3, after 9 d in storage with no difference between these

two treatments. The appearance rating of fruit exposed to 5 or 10 ppm was negatively

affected by yellowing of the peel and stem-end shriveling. The appearance rating

declined further when the fruit was transferred to an ethylene-free storage environment

for 24 hours at 20 oC.

After the 24-hr transfer period fruit exposed to 0, 1, 5 or 10 ppm ethylene had an

average appearance rating of 6, 3, 3, and 2.5, respectively. The ethylene-treated fruit

exhibited yellowing, stem-end shriveling and overall softness when touched. The control

fruit had a lower post transfer rating because it showed slight yellowing, which was

absent before it was transferred, but was not as severe as the yellowing observed in

ethylene-treated fruit.

Fruit exposed to 1 ppm reached the appearance threshold rating of 3 after 12 d of

continuous ethylene exposure. The loss of appearance was due to yellowing of the peel

and the presence of stem-end shriveling (Figure 4-2). This fruit, however, became

unmarketable prior to 12 d of ethylene exposure due to excessive pulp softening, which

was reflected in the low firmness values and high rates of electrolyte leakage.





















































Figure 4-2. Appearance of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene for 12 d at 10 C. A) 0 ppm, B) 1 ppm, C) 5 ppm and D)
10 ppm. Arrows indicate fungal growth (B and C) and reddish-brown spots on
the peel (D).









Fruit that had not been exposed to ethylene (control) scored an appearance rating of

7 after the same exposure period, significantly higher than the ethylene-treated fruit.

All the treatments were kept for observation for the entire duration of the

experiment, even if they had already become unmarketable prior to the end of the 12-day

storage period. Microbial rot was first observed on fruit that had been exposed to 10 ppm

of ethylene for 9 d and then transferred to 20 OC for 24 hours in an ethylene-free

environment, while the control group (0 ppm) and fruit exposed to 1 or 5 ppm did not

show any development of microbial rot after the same transfer period.

Microbial infection was observed in all the ethylene-treated fruit, but not on the

control fruit, after 12 d of ethylene exposure and at this point all three ethylene-treated

groups (1, 5 and 10 ppm) experienced a 90% infection rate, while the control group

remained unaffected. The severity of the infection was not assessed; therefore it is not

possible to assert if fruit exposed to higher concentrations of ethylene developed more

severe rates of infection as indicated by the surface area affected. Any level of pathogen

infection would have made the fruit unmarketable so the severity of the infection in

relation to the ethylene concentration in the environment is an aspect that may be

important from a physiological standpoint.

Besides the storage disorders such as tissue softening and decay, fruit exposed to 5

or 10 ppm ethylene also developed reddish-brown spots on the peel after 12 d in storage

(Figure 4-3). The spots were limited to the surface of the fruit, did not extend to the

mesocarp nor were there any visible exudates. The development of these spots did not

affect the marketable life of the product since they developed after the fruit had become

unmarketable due to the effect of ethylene on other parameters such as firmness or color.























































Figure 4-3. Ethylene injury symptoms as reddish-brown spots (arrows) on Beit Alpha
cucumbers exposed to 10 ppm of exogenous ethylene for 12 d.









Color

Exposure of cucumbers to external ethylene caused yellowing of the peel at an

accelerated rate but varying the ethylene concentration in the storage atmosphere had no

effect on the rate of color loss. Hue angle values decreased during storage on fruit

continuously exposed to ethylene but not in the control group (Figure 4-4). At harvest,

external hue angle values averaged 124 and decreased to 1210 in the ethylene-treated

fruit after 12 d ethylene exposure, while the control group had an average hue angle of

123.70 at the end of the 12-day exposure period. L* values (lightness intensity) remained

relatively unchanged during the storage period (data not shown) while chroma values

increased slightly from 23.2 at harvest to between 26 and 29.6, depending on the

temperature, but with no significant differences among storage treatments (data not

shown).

Exposure to exogenous ethylene had no significant impact on the mesocarp color as

measured by the hue angle. Although there was a 2 to 3% decrease in internal hue angle

values after 12 d ethylene exposure there were no significant differences among

treatments. Although statistical differences in internal hue angle measurements were not

evident, slight yellowing of internal tissue was detectable upon visual inspection in fruit

exposed to 10 ppm ethylene for 12 d. Unlike the external L*, internal L* values

decreased during storage from 71.2 at harvest to between 60.1 and 64.8 but was not

significantly affected by the ethylene treatment. Chroma values decreased slightly from

33.2 at harvest to between 26.9 and 31.8 but with no significant differences among

ethylene treatments.









125.0


124.0 T


123.0


122.0


S 121.0


120.0


119.0


118.0


117.0
0 3 6 9 12

Duration of Ethylene Exposure (d)


0 PPM 1 PPM -A- 5 PPM 10PPM

Figure 4-4. Changes in the external color, as measured by the hue angle, of Beit Alpha
cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and
10 ppm) and stored at 10 C for 12 d. Vertical bars represent the + standard
error from the mean.


an.









Weight loss

Exposure to continuous ethylene had no effect on the weight loss of cucumber fruit

(Table 4-1). Weight loss increased from an average of 0.86% at 3 d in storage to an

average of 1.02% after 12 d in storage at 10 OC without any differences among

treatments.

However, differences in weight loss were observed when the fruit was transferred

to an ethylene-free environment at 20 OC and 90% RH for 24 hours (Table 4-2). Weight

loss increased when fruit held for 9 d at 10 OC in ethylene was transferred to 20 OC for 1

d. After this transfer period, the weight loss ranged from 3.2 to 4.7%, with no differences

among treatments. This increment in weight loss was due to the high-temperature effect

(20 C) and not to the ethylene exposure since there were no significant differences

among the four treatments.


Table 4-1. Weight loss of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC (1 oC) for 12
days.

Duration of Ethylene Exposure (d)
3 6 9 12
Weight Loss (%)
Ethylene
Etlene Mean s Mean s Mean s Mean s
Treatment
0 ppm 0.5 a 0.05 0.8 a 0.03 0.9 a 0.06 0.9 a 0.06

1 ppm 0.7 a 0.03 0.7 a 0.09 0.9 a 0.04 1.2 a 0.08

5 ppm 0.7 a 0.12 0.9 a 0.03 0.8 a 0.09 1.1 a 0.07

10 ppm 0.6 a 0.03 0.7 a 0.10 0.9 a 0.06 1.0 a 0.13

zMean values in the same column with different letters are significantly different at a P-
value < 0.05. Mean separation based on Duncan's Multiple Range Test.
Y Standard error from the mean (n= 10).









Table 4-2. Weight loss of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) after transfer to 20 oC for 1 day.

Duration of Ethylene Exposure (d)
6 days at 10 C 9 days at 10 C
+ 1 day at 20 C + 1 day at 20 C

Weight Loss (%)
Ethylene Treatment Mean s Mean s


0 ppm 1.1 a 0.3 3.7 a 0.06

1 ppm 1.5 a 1.6 4.7 a 0.08

5 ppm 1.4 a 0.7 3.9 a 0.07

10 ppm 3.2b 1.1 3.2 a 0.13

zMean values in the same column with different letters are significantly different at a P-
value < 0.05. Mean separation based on Duncan's Multiple Range Test.
Y Standard error from the mean (n= 10).


Respiration

Fruit exposed to higher concentrations of ethylene had higher respiration rates than

the control fruit for the first 6 d in storage (Table 4-3). At 3 d in storage, fruit exposed to

either 5 or 10 ppm had an average respiration rate of 10.9 ml kg-1 hrf1, with no difference

between these two treatments but significantly higher than the control group. Fruit

exposed to 1 ppm had an intermediate respiration rate (9.3 ml kg-1 hr1); significantly

lower than either 5 or 10 ppm but significantly higher than the control group (5.8 ml kg-1

hr-1).

The respiration rate of stored fruit increased between 25 and 60% between the third

and sixth day of ethylene exposure, with the highest increase observed in the control

group and fruit exposed to 1 ppm. At 6 d in storage the ethylene-treated fruit (1, 5 and 10









ppm) respired at an average rate of 13.9 ml kg-1 hr-1, with no difference among these

three groups. The ethylene-treated fruit had a higher respiration rate than the control

group which had a respiration rate of 8.3 ml kg'1 hr1 after the same storage period.

Respiration rate continued to increase in the control group as the exposure period

progressed but not in the ethylene-treated fruit; at 9 d in storage the control group had an

average respiration rate of 14.4 ml kg-' hri, significantly higher or equal to some of the

ethylene-treated fruit. Signs of decay were not visible at 9 d on any of the four treatments.

Respiration was not measured beyond 9 d in storage due to the onset of bacterial and

fungal infections on the ethylene-treated fruit.


Table 4-3. Respiration rates of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC (1 oC).

Duration of Ethylene Exposure (d)
3 6 9

Respiration (ml CO2 kg-1 hr1)
Ethylene Treatment Mean s Mean s Mean s

0 ppm 5.8 az 0.04y 8.3 a 0.20 14.3 a 0.44

1 ppm 9.3 b 0.52 14.0 b 0.51 11.8 b 0.74

5 ppm 11.2 c 0.37 14.3 b 0.89 14.3 a 0.60

10 ppm 10.7 c 0.56 13.5 b 0.74 10.2 c 0.41

z Mean values in the same column with different letters are significantly different at a P-
value < 0.05. Mean separation based on Duncan's Multiple Range Test.
Y Standard error from the mean (n=8).

Mesocarp firmness

Beit Alpha cucumbers showed pronounced softening of the mesocarp tissue during

storage as a consequence of ethylene exposure. After 6 d of storage, severe softening of









the mesocarp (55% reduction of the initial firmness) was evident in fruit continuously

exposed to 10 ppm ethylene, (Figure 4-5). Even though visual appearance and external

color remained acceptable in these fruit, they were unmarketable due to excessive

softening. After 6 d fruit exposed to either 0, 1 or 5 ppm ethylene remained marketable

and had acceptable firmness, color, and visual appearance.

Mesocarp firmness continued to decline after this period with more pronounced

softening observed in ethylene-treated fruit. After 9 d ethylene exposure (5 ppm), fruit

lost 81% of the initial firmness and was no longer marketable even though external

appearance and color remained acceptable. Cucumbers exposed to 1 ppm ethylene and

the control group still remained marketable after the same exposure period, with no

significant differences in firmness between these two treatments.

Mesocarp firmness declined further as the duration of the ethylene exposure

increased. After 12 d of ethylene exposure, fruit exposed to 1 ppm of ethylene had lost

63% of the initial firmness and was no longer marketable due to excessive pulp softening

and microbial decay. On the other hand, the control fruit remained marketable after this

period and was free of microbial rot, had very good external appearance, acceptable

firmness (65% of initial firmness) and acceptable external color.


Electrolyte leakage

Exposure to external ethylene caused electrolyte leakage (EL) rates of stored

cucumber fruit to increase Electrolyte leakage rates remained relatively unchanged the

first 3 d but increased after 6 d of continuous ethylene exposure, with higher increases

observed in fruit exposed to higher concentrations of ethylene (Figure 4-6).









20.0


18.0


16.0


14.0


12.0


10.0


8.0


6.0


4.0


2.0


0.0


Duration of Ethylene Bxposure (d)


--0 ppm


-- 1 ppm


-A-5 ppm


Figure 4-5. Mesocarp firmness (Newtons) ofBeit Alpha cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C
for 12 d. Vertical bars represent the + standard error from the mean.


10 ppm


~---I






76


90.0


80.0


70.0


60.0


( 50.0


d 40.0


o 30.0


20.0


10.0


0.0
0 3 6 9 12


Duration of Ethylene Exposure (d)


SOPPM 1 PPM -A- 5 PPM 10 PPM

Figure 4-6. Rate of electrolyte leakage (%) of Beit Alpha cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC
for 12 d. Vertical bars represent the standard error from the mean, were not
shown standard error falls within the marker size.









Initial EL rates (12 hr after harvest) were 9.5% and increased to 15.4, 21.5, 22.6

and 26.1% on fruit exposed to 0, 1, 5 or 10 ppm ethylene, respectively, for 6 d. These

rates were significantly higher in ethylene-treated fruit than in the control group. Fruit

exposed to 5 or 10 ppm had significantly higher EL rates than the control group but not

significantly different between each other. Fruit exposed to 1 ppm had an EL rate of

21.5%, significantly different than either the control group or fruit exposed to 10 ppm

ethylene.

Although the EL rate of the control group also increased over time, it was not as

remarkable as the increase observed in ethylene-treated fruit. After 9 d ethylene exposure,

fruit exposed to 5 or 10 ppm had an EL rate of 44.8 and 46.l1%, respectively, and was

significantly higher than the EL rate of 0 and 1 ppm. Fruit exposed to 1 ppm had an EL

rate of 26.4%, significantly different from the other three treatments. The control group

had, significantly, the lowest EL rate of all four treatments; 12.4%.

At the end of the 12-day storage period, the EL rates of the control fruit reached

16%, almost twice the rate at harvest yet significantly lower than the ethylene-treated

fruit. EL in fruit exposed to 1 ppm increased five-fold after 12 d in storage to 48% while

fruit exposed to 5 or 10 ppm increased seven-fold to 67% after the same period, with no

difference between these two treatments.



Experiment II


Appearance of Beit Alpha cucumbers

As in Exp. I, the external appearance of Beit Alpha cucumbers was negatively

affected by the continuous exposure to exogenous ethylene. Beit Alpha cucumbers









retained similar appearance up to the 6th day of continuous ethylene gassing, independent

of the ethylene concentration in the environment (Figure 4-7). At this stage all groups had

very good, dark green color with no visible defects such as shriveling, water soaking or

microbial rot; fruit exposed to 1, 5 or 10 ppm scored a respectable 7 on a scale from 1 to

9 (9 representing field-fresh fruit and 1 representing inedible fruit) while the control

group scored an average of 7.8. As in previous studies, the external appearance of fruit

exposed to ethylene deteriorated after being transferred to ethylene-free storage at 20 C

for 24 hours while the control fruit retained its pre-transfer visual appearance (data not

shown). After the transfer period, fruit exposed to 1, 5 or 10 ppm showed moderate stem-

end shriveling and irregular yellowing that gave the fruit a blotchy appearance thus

negatively affecting the external appearance in ethylene-treated fruit. Ethylene-treated

fruit rated 5.1, 4.8 and 3.6 (1, 5 and 10 ppm, respectively) while the control group rated

an average of 7.0 after the transfer period.

Differences in external appearances were evident on fruit continuously exposed to

ethylene for 9 d, at which point 90% of the fruit exposed to 10 ppm of exogenous

ethylene rated below the appearance marketability threshold. The major defects of this

group were yellowing, decay and stem-end shriveling.

Fruit exposed to 5 or 1 ppm remained above the marketability threshold at this

point, scoring 6.7 and 5.0 respectively while the control rated an average of 7.2. As in

previous experiments, the external appearance declined rapidly after the fruit was

transferred to ethylene-free storage at 20 oC for 24 hours. After this transfer period, the

ethylene-treated fruit (all three groups) had an external appearance that rated at 1.0 (data

not shown).









10.0

9.0

8.0

7.0

6.0


5.0

4.0

3.0


2.0


1.0

0.0
0 3 6 9 12


Duration of Ethylene ExposLre (d)


-- 0 ppm -a- 1 ppm -- 5 ppm


10 ppm Threshold


Figure 4-7. Appearance rating of Beit Alpha cucumbers exposed to four concentrations of
exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC for 12 d. Vertical
bars represent the standard error from the mean, were not shown standard
error falls wethin the marker size.









All the fruit exposed to 10 ppm of ethylene showed signs of decay while only 60%

and 40% of the fruit exposed to 5 and 1 ppm, respectively, showed signs of decay. The

control fruit had good appearance after the transfer period, showing no signs of decay or

yellowing. Quality of control fruit was only affected by a hardening of the fruit (the fruit

did not yield when flexed) and a slight leathery appearance of the peel. Quality continued

to deteriorate as the exposure period increased.

Fruit exposed to 1 or 5 ppm reached below the marketability threshold after 12 d in

storage and rated an average of 1.0 (inedible) while the control group had an average

external appearance rating of 5.6. At this point, appearance on ethylene-treated fruit was

negatively affected mainly by decay; 60% of the fruit exposed to 1 ppm showed some

level of decay while on the 5 ppm group the decay reached 90%. The decay was only

rated as present or absent and the severity of the decay was not rated since the fruit was

rendered unmarketable once decay was noticeable. Yellowing was also a major factor of

quality loss, with 90% of fruit exposed to 1 or 5 ppm showing yellowing of the peel.



Appearance of European cucumbers

Similar to Beit Alpha cucumbers, the appearance of European cucumbers was also

negatively affected by the exposure to continuous ethylene but it followed a slightly

different pattern than Beit Alpha cucumbers. The appearance rating of the ethylene-

treated fruit (1, 5 and 10 ppm) reached the marketability threshold between 6 and 9 d of

continuous ethylene gassing and unlike Beit Alpha cucumbers varying the ethylene

concentration in the storage atmosphere had no effect on the rate at which appearance

deteriorated.









Shrink-wrapping of European cucumbers was not beneficial in mitigating the

effects of ethylene on cucumber quality since there were no differences in appearance

rating between wrapped and unwrapped cucumbers throughout the gassing period.

After 6 d of continuous ethylene gassing there was no difference among the four

ethylene treatments in the appearance rating of unwrapped or wrapped European

cucumbers. At this point all four treatments of both unwrapped (Figure 4-8) and wrapped

(Figure 4-9) cucumbers had very good external appearance, dark green color and no

stem-end shriveling or other visible defect. Wrapped cucumbers exposed to 0, 1, 5 or 10

ppm ethylene had an average external appearance rating of 8, 7, 7 and 7, respectively

while unwrapped cucumbers exposed to 0, 1, 5 or 10 ppm ethylene had an average

external appearance rating of 8, 7, 7 and 7, respectively.

Deterioration in appearance of European cucumbers became evident after the fruit

had been in the gassing chambers for 9 d. All the four treatments, both the ethylene-

treated fruit and the control group, of unwrapped cucumbers reached the limit of their

marketable life at 9 d of continuous ethylene exposure. The ethylene-treated fruit was

affected by yellowing, stem-end shriveling, the development of reddish-brown spots and

water soaking while the control group exhibited only shriveling of the stem-end. The

control group (unwrapped) became unmarketable as a result of excessive water loss and

not as a direct effect of ethylene. Wrapped European cucumbers also reached the limit of

their marketable life at 9 d of continuous ethylene gassing due to the same disorders

described above for unwrapped cucumbers; however the control group remained

marketable beyond this point due to the protective shrink-wrap that reduced the amount

of water loss.










10.0-


9.0 -1


7.0


5.0


4.0 -


ao-
3.0 -


2.0


1.0


0.0


3 6 9 12


Duration of Ethylene Exposure (d)


-*- 0 ppm


-M- 1 ppm


-- 5 ppm


10 ppm Threshold


Figure 4-8. Appearance rating of unwrapped European cucumbers exposed to four
concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 oC
for 12 d. 1, 5 and 10 ppm had identical results. Vertical bars represent the
standard error from the mean, were not shown standard error falls within the
marker size.


u^




Full Text

PAGE 1

EFFECT OF GROWING SEASON, ST ORAGE TEMPERATURE AND ETHYLENE EXPOSURE ON THE QUALITY OF GR EENHOUSE-GROWN BEIT ALPHA CUCUMBER ( Cucumis sativus L.) IN NORTH FLORIDA By ALFREDO MAURICIO VILLALTA OLIVA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2005

PAGE 2

Copyright 2005 by Alfredo Mauricio Villalta Oliva

PAGE 3

Dedicated to my mother Florentina Oliva Izagurre.

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iv ACKNOWLEDGMENTS I owe my deepest thanks to my mother, Fl orentina Oliva Izaguirre my father, Jose Carlos Villalta, my sister, Daysi Valdez and her family, my brothers and their families and my friends for giving me the support, the freedom, the encouragement and the inspiration to pursue my goals. I must also thank Mr. Zaid Flores, Mr s. Elizabeth Zabaneh and the Banana Growers Association of Belize for paving the way for my career; where I am today would not be possible without them. I owe my most sincere thanks to Dr. Stev en A. Sargent for his mentoring over the last two years; his support, encouragemen t and understanding made it possible to successfully complete this project. I would also like to thank Mr. Emil Belibasis and family of Beli Farms for their continued support of this projec t and for providing all the frui t used in these experiments. Their kindness and willingness made a huge contribution to this project. I must also thank all the other people th at contributed to the completion of this project; Mrs. Patricia Hill, Mrs. Adrian D. Berry, Mrs. Kim Cordasco, Dr. Jeff Brecht, Dr. Gamal Riad, Dr. Allen Wysocki, Dr. Mark Ritenour, Dr. Donald Huber and Dr. Daniel Cantliffe. Also, I need to thank Dr. James A. St erns for his contribution to my academic formation and for being an excellent professor.

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v TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES.............................................................................................................ix LIST OF FIGURES...........................................................................................................xi ABSTRACT....................................................................................................................xvi i CHAPTER 1 INTRODUCTION........................................................................................................1 Fruit and Vegetable Trade.......................................................................................1 Fruit and Vegetable Consumption...........................................................................7 U.S. Cucumber Consumption..................................................................................9 U.S. Cucumber Industry........................................................................................12 Florida Cucumber Industry....................................................................................16 2 LITERATURE REVIEW...........................................................................................19 Botany....................................................................................................................19 Cucumber Production............................................................................................20 Maturity Indices.....................................................................................................21 Postharvest Considerations....................................................................................22 Storage...................................................................................................................22 Physiological Stresses............................................................................................24 Chilling Injury................................................................................................24 Ethylene Injury...............................................................................................25 Research Objectives...............................................................................................27 3 EFFECT OF STORAGE TEMPERATURE ON THE MARKETABLE LIFE OF BEIT ALPHA CUCUMBER......................................................................................28 Introduction............................................................................................................28 Materials and Methods...........................................................................................29 Plant Material...................................................................................................29 Visual Quality..................................................................................................31 Color Evaluation..............................................................................................31 Weight Loss.....................................................................................................31

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vi Respiration.......................................................................................................32 Ethylene Production.........................................................................................32 Mesocarp Firmness..........................................................................................33 Electrolyte Leakage.........................................................................................33 Moisture Content.............................................................................................35 Compositional Analysis...................................................................................35 Data Analysis...................................................................................................35 Results....................................................................................................................36 Appearance......................................................................................................36 External Color..................................................................................................37 Internal Color...................................................................................................38 Weight Loss.....................................................................................................38 Respiration.......................................................................................................38 Ethylene Production.........................................................................................43 Firmness...........................................................................................................43 Electrolyte Leakage.........................................................................................44 Moisture Content.............................................................................................47 Compositional Analysis...................................................................................48 Discussion..............................................................................................................49 Appearance......................................................................................................49 Color................................................................................................................50 Weight Loss.....................................................................................................50 Respiration.......................................................................................................51 Ethylene Production.........................................................................................51 Firmness...........................................................................................................52 Electrolyte Leakage.........................................................................................53 Compositional Analysis...................................................................................53 Conclusions............................................................................................................55 4 RESPONSE OF BEIT ALPHA CUCU MBERS TO EXOGENOUS ETHYLENE DURING STORAGE.................................................................................................56 Introduction............................................................................................................56 Materials and Methods...........................................................................................58 Experiment I.....................................................................................................58 Plant material................................................................................................58 Appearance...................................................................................................59 Color evaluation...........................................................................................59 Weight loss...................................................................................................60 Respiration...................................................................................................60 Mesocarp firmness.......................................................................................60 Electrolyte leakage.......................................................................................60 Data analysis................................................................................................61 Experiment II...................................................................................................61 Plant material................................................................................................61 Appearance...................................................................................................62 Color evaluation...........................................................................................62

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vii Weight loss...................................................................................................62 Mesocarp firmness.......................................................................................62 Electrolyte leakage.......................................................................................62 Data analysis................................................................................................62 Experiment III..................................................................................................62 Plant material................................................................................................62 Appearance...................................................................................................62 Color evaluation...........................................................................................63 Weight loss...................................................................................................63 Mesocarp firmness.......................................................................................63 Electrolyte leakage.......................................................................................63 Data analysis................................................................................................63 Results....................................................................................................................63 Experiment I.....................................................................................................63 Appearance...................................................................................................63 Color.............................................................................................................69 Weight loss...................................................................................................71 Respiration...................................................................................................72 Mesocarp firmness.......................................................................................73 Electrolyte leakage.......................................................................................74 Experiment II...................................................................................................77 Appearance of Beit Alpha cucumbers..........................................................77 Appearance of European cucumbers............................................................80 External color of Beit Alpha cucumbers......................................................84 External color of European cucumbers........................................................86 Internal color................................................................................................90 Weight loss...................................................................................................94 Mesocarp firmness of Beit Alpha cucumbers..............................................96 Mesocarp firmness of European cucumbers................................................97 Electrolyte leakage of Beit Alpha cucumbers............................................102 Electrolyte leakage of European cucumbers..............................................104 Experiment III................................................................................................108 Appearance.................................................................................................108 External color.............................................................................................111 Internal color..............................................................................................117 Weight loss.................................................................................................122 Mesocarp firmness.....................................................................................123 Electrolyte leakage.....................................................................................127 Discussion............................................................................................................131 Appearance........................................................................................................131 External Color...................................................................................................132 Internal Color.....................................................................................................132 Weight Loss.......................................................................................................132 Respiration.........................................................................................................133 Firmness............................................................................................................133 Electrolyte Leakage...........................................................................................134

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viii Conclusions..........................................................................................................135 5 EFFECT OF HARVEST DATE AND GROWING SEASON ON THE MARKETABLE LIFE OF BE IT ALPHA CUCUMBERS......................................137 Introduction..........................................................................................................137 Materials and Methods.........................................................................................138 Plant Material.................................................................................................138 Appearance....................................................................................................139 Color Evaluation............................................................................................139 Weight Loss...................................................................................................140 Fruit Firmness................................................................................................140 Data Analysis.................................................................................................140 Results and Discussion........................................................................................140 Appearance....................................................................................................140 External Color................................................................................................149 Internal Color.................................................................................................156 Weight Loss...................................................................................................158 Firmness.........................................................................................................160 Conclusions..........................................................................................................167 6 CONCLUSIONS......................................................................................................168 APPENDIX A APPEARANCE RATING SCALE FOR STORED CUCUMBERS.......................170 B ISOTONIC MANNITOL CONCENTRATION......................................................171 LIST OF REFERENCES.................................................................................................172 BIOGRAPHICAL SKETCH...........................................................................................183

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ix LIST OF TABLES Table page 1-1. Ranking of selected commodities the U. S., based on the total value of production (fresh and processed) between 1999 and 2003 (in $1, 000). Economic Research Service, USDA (2004).............................................................................................13 1-2. Value of the U.S. cucumber production between 1998 and 2002 (in $ millions). National Agricultural Sta tistical Service (2004)......................................................13 1-3. Total U. S. cucumber production be tween 1998 and 2002 (in thousands MT). National Agricultural Sta tistical Service (2004)......................................................15 1-4. U. S. cucumber cultivation between 1998 and 2002 (hectares). Na tional Agricultural Statistical Service (2004).........................................................................................15 1-5. Value of cucumber production in Florida between 1998 and 2002 ($ million). National Agricultural Sta tistical Service (2004)......................................................17 1-6. Total production of cucumbers in Florida between 1998 and 2002 (1, 000 MT). National Agricultural Sta tistical Service (2004)......................................................17 1-7. Florida cucumber cultivation between 1998 and 2002 (in hectares). National Agricultural Statistical Service (2004).....................................................................18 3-1. Internal hue angle of Beit Alpha cucumber s stored at four diffe rent temperatures; 5, 7.5, 10 or 12.5 C for 21 days...................................................................................39 3-2. Weight loss of Beit Alpha cucumbers stored at four different temperatures; 5, 7.5, 10 and 12.5 C for 21 days............................................................................................40 3-3. Compositional analysis of Beit Alpha cucu mbers stored at four temperatures (5, 7.5, 10 or 12.5 1 C) for 21 days...................................................................................48 4-1. Weight loss of Beit Alpha cucumbers e xposed to four concen trations of exogenous ethylene (0, 1, 5 and 10 ppm) and stor ed at 10 C (1 C) for 12 days....................71 4-2. Weight loss of Beit Alpha cucumbers e xposed to four concen trations of exogenous ethylene (0, 1, 5 and 10 ppm) after transfer to 20 C for 1 day................................72 4-3. Respiration rates of Beit Alpha cucumb ers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C).....................73

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x 4-4. Internal hue angle of Beit Alpha cucu mbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) a nd stored at 10 C (1 C) for 12 d.......91 4-5. Internal hue angle of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d...............................................................................................................92 4-6. Internal hue angle of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d...93 4-7. Weight loss of Beit Alpha cucumbers e xposed to four concen trations of exogenous ethylene (0, 1, 5 and 10 ppm) and st ored at 10 C (1 C) for 12 d.........................95 4-8. Weight loss of unwrapped European cucu mbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) a nd stored at 10 C (1 C) for 12 d.......95 4-9. Weight loss of wrapped European cucu mbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) a nd stored at 10 C (1 C) for 12 d.......96 4-10. Internal hue angle of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d.............................................................................................................118 4-11. Internal hue angle of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d.119 4-12. Weight loss of unwrapped European cucu mbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) a nd stored at 10 C (1 C) for 12 d.....122 4-13. Weight loss of wrapped European cucu mbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) a nd stored at 10 C (1 C) for 12 d.....123 5-1. Internal hue angle of Beit Alpha cucumb ers harvested during three different growing seasons (October-2003, January-2004 and July -2004) and stored at 10 C for 18 d. Each season consists of an early and late harvest..................................................157 5-2. Weight loss (%) of Beit Alpha cucumber s harvested during three different growing seasons (October-2003, January-2004 and July -2004) and stored at 10 C for 18 d. Each season consists of an early and late harvest..................................................159

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xi LIST OF FIGURES Figure page 1-1. The US agricultural trade: exports, imports and trade balance ($ billions). 2005 is a forecast. Economic Research Service, USDA (2004)................................................2 1-2. The US horticultural trad e: exports, imports and tr ade balance ($ billions). Horticultural trade includes vegetables, fr uits, nuts, essential oils, nursery products, cut flowers, wine and beer. Foreign Agricultural Service, USDA (2004).................3 1-3. The US-NAFTA horticultural trade: co mbined exports, imports and trade balance with Canada and Mexico ($ billions). Foreign Agricu ltural Service, USDA (2004).4 1-4. The US cucumber trade between 1970 and 2004: domestic production, imports and exports (1, 000 MT). Economic Re search Service, USDA (2004)............................6 1-5. Total annual consumption ( kg/capita) of fruit and vege tables in the U.S. Each category (fruit or vegetables) includes fresh and processed. Food Consumption Data System, Economic Research Service, USDA (2004)........................................8 1-6. Total annual consumption (kg/ capita) of fruit and vegetables in the U.S. in the form that they are consumed. Food Consump tion Data System, Economic Research Service, USDA (2004).............................................................................................10 1-7. Annual cucumber consumption (kg/capita) in the U.S. in the form that they are consumed. Food Consumption Data System Economic Research Service, USDA (2004).......................................................................................................................11 3-1. Respiration rate (ml CO2 kg-1 hr-1) of Beit Alpha cucumbers stored for 21 d at six different temperatures; 5, 7.5, 10, 12.5, 15 and 20 C. Vertical bars represent the standard error from the mean...................................................................................41 3-2 Mesocarp firmness, expressed in Newtons of Beit Alpha cucumbers stored for 21 d at 5, 7.5, 10 or 12.5 C. Vertical bars represent the standard error from the mean.45 3-3. Electrolyte leakage, as a percent of total electrol yte leakage, of Beit Alpha cucumbers stored for 21 d at four diffe rent temperatures; 5, 7.5, 10 or 12.5 C. Vertical bars represent the standard error from the mean.....................................46

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xii 4-1. Appearance rating of Beit Alpha cucumber s exposed to four concentrations of exogenous ethylene (0, 1, 5 or 10 ppm) and stored at 10 C for 12 d. Fruit exposed to 5 and 10 ppm of ethylene had identical results. Vertical bars represent the standard error from the mean, were not shown standard error falls within the marker size...............................................................................................................64 4-2. Appearance of Beit Alpha cucumbers expos ed to four concentrations of exogenous ethylene for 12 d at 10 C. A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10 ppm. Arrows indicate fungal growth (B and C) and reddish-brown spots on the peel (D)...........66 4-3. Ethylene injury symptoms as reddish-b rown spots (arrows) on Beit Alpha cucumbers exposed to 10 ppm of ex ogenous ethylene for 12 d.................................................68 4-4. Changes in the external color, as m easured by the hue angle, of Beit Alpha cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean...................................................................................................................70 4-5. Mesocarp firmness (Newtons) of Be it Alpha cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean............................75 4-6. Rate of electrolyte l eakage (%) of Beit Alpha cu cumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standa rd error from the mean, were not shown standard error falls within the marker size...............................................................76 4-7. Appearance rating of Beit Alpha cucumber s exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the m ean, were not shown standard error falls within the marker size..............................................................................................79 4-8. Appearance rating of unwrapped Eur opean cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. 1, 5 and 10 ppm had identical results. Ve rtical bars represent the standard error from the mean, were not shown standa rd error falls within the marker size...82 4-9. Appearance rating of wrapped European cu cumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) a nd stored at 10 C for 12 d. 1, 5 and 10 ppm had identical results. Vertical bars represent the standard error from the mean, were not shown standard erro r falls within the marker size..........................83 4-10. Changes in the external color, as meas ured by the hue angle (), of Beit Alpha-type cucumbers exposed to four different c oncentrations of exogenous ethylene and stored at 10 C for 12 d.............................................................................................85

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xiii 4-11. Changes in the external color, as m easured by the hue angle (), of unwrapped European cucumbers exposed to four con centrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean..................................................................................................87 4-12. Changes in the external color, as m easured by the hue angle (), of wrapped European cucumbers exposed to four con centrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean..................................................................................................89 4-13. Mesocarp firmness of Beit Alpha cucumb ers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. +1 indicates that the fruit was transferred to 20 C for 1 day (ethylene-free) after being in storage at 10 C. Vertical bars repres ent the standard error from the mean..........98 4-14. Mesocarp firmness of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. +1 indicates that the fruit was transf erred to 20 C for 1 day (ethylene-free) after being in storage at 10 C Vertical bars represent the standard error from the mean.........................................................................................................................99 4-15. Mesocarp firmness of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. +1 indicates that the fruit was transferred to 20 C for 1 day (ethylene-free) after being in storage at 10 C. Vertical bars repres ent the standard error from the mean....101 4-16. Electrolyte leakage (%) of Beit Alpha cucu mbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the m ean, were not shown standard error falls within the marker size............................................................................................103 4-17. Electrolyte leakage (%) of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standa rd error from the mean, were not shown standard error falls within the marker size.............................................................105 4-18. Electrolyte leakage (%) of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standa rd error from the mean, were not shown standard error falls within the marker size.............................................................107 4-19. Appearance rating of unwrapped Eur opean cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. 1, 5 and 10 ppm had identical results. Ve rtical bars represent the standard error from the mean, were not shown standa rd error falls within the marker size.109

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xiv 4-20. Appearance rating of wrapped European cu cumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. 1 and 5 ppm had identical results. Vertical bars represent the standard error from the mean, were not shown standard erro r falls within the marker size........................110 4-21. Appearance of unwrapped European cucumb ers exposed to four concentrations of exogenous ethylene for 12 d at 10 C. A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10 ppm.........................................................................................................................112 4-22. Appearance of wrapped European cucumb ers exposed to four concentrations of exogenous ethylene for 12 d at 10 C. A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10 ppm.........................................................................................................................113 4-23. Changes in the external color, as measured by the hue angle, of unwrapped European cucumbers exposed to four con centrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean................................................................................................114 4-24. Changes in the external color, as meas ured by the hue angle, of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean.................................................................................................................116 4-25. Internal appearance of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene for 12 d at 10 C (1 C). A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10 ppm...............................................................................120 4-26. Internal appearance of wrapped European cucumbers exposed to four concentrations of exogenous ethylene for 12 d at 10 C (1 C). A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10 ppm...............................................................................121 4-27. Mesocarp firmness of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean..........................124 4-28. Mesocarp firmness of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean.................................................126 4-29. Electrolyte leakage (%) of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standa rd error from the mean, were not shown standard error falls within the marker size.............................................................128 4-30. Electrolyte leakage (%) of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standa rd error from the mean, were not shown standard error falls within the marker size.............................................................130

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xv 5-1. Appearance rating of Beit Alpha cucumber s harvested during three different seasons and stored at 10 C for 18 d. Each season is an average of the early and late harvests. Vertical lines represent standard error from the mean............................142 5-2. Appearance rating of Beit Alpha cucumbers harvested early and late in the October 2003 season and stored at 10 C for 18 d. Vertical lines repres ent standard error from the mean.........................................................................................................143 5-3. Appearance rating of Beit Alpha cucumbers harvested early and late in the January 2004 season and stored at 10 C for 18 d. Vertical lines repres ent standard error from the mean.........................................................................................................144 5-4. Appearance rating of Beit Alpha cucumbers harvested early and late in the July 2004 season and stored at 10 C for 18 d. Vertical lines represent the standard error from the mean, were not shown they fall within the marker size...................................145 5-5. Overall appearance rating of Beit Alpha cucumbers harvested early or late in the harvest season and stored at 10 C for 18 d. Ratings represent an average of the three seasons. Vertical lines represent standard error from the mean, were not shown they fall within the marker size...................................................................146 5-6. External color (hue angl e ) of Beit Alpha-type cucu mbers harvested during three different seasons and stored at 10 C for 18 d. Each s eason is an average of two harvests. Vertical lines represent the sta ndard error from the mean, were not shown they fall within the marker size..............................................................................151 5-7. External color (hue angle ) of Beit Alpha cucumbers harv ested early and late in the October 2003 season and stored at 10 C for 18 d. Vertical lines represent the standard error from the mean, were not shown they fall within the marker size...152 5-8. External color (hue angle ) of Beit Alpha cucumbers harv ested early and late in the January 2004 season and stored at 10 C fo r 18 d. Vertical lines represent standard error from the mean, were not shown they fall within the marker size..................153 5-9. External color (hue angle ) of Beit Alpha cucumbers harv ested early and late in the July 2004 season and stored at 10 C for 18 d. Vertical lines represent standard error from the mean, were not shown they fall within the marker size..................154 5-10. Overall external color ( hue angle ) of Beit Alpha cu cumbers harvested early and late in harvest season and stored at 10 C for 18 d. Each harvest time is an average of all three seasons. Vertical lines represen t standard error from the mean, were not shown they fall within the marker size...................................................................155 5-11. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested during three different seasons and stored at 10 C for 18 d. Each s eason is an average of two harvests. Vertical lines represent standard error from the mean............................162

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xvi 5-12. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and late in the October 2003 season and stored at 10 C for 18 d. Vertic al lines represent standard error from the mean.................................................................................163 5-13. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and late in the January 2004 season and stored at 10 C for 18 d. Vertic al lines represent standard error from the mean.................................................................................164 5-14. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and late in the July 2004 season and stored at 10 C for 18 d. Vertical lines represent standard error from the mean................................................................................................165 5-15. Overall mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and late in harvest season and stored at 10 C for 18 d. Each harvest time is an average of all three seasons. Vertical lines repr esent standard error from the mean...........166

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xvii Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EFFECT OF GROWING SEASON, ST ORAGE TEMPERATURE AND ETHYLENE EXPOSURE ON THE QUALITY OF GR EENHOUSE-GROWN BEIT ALPHA CUCUMBER ( Cucumis sativus L.) IN NORTH FLORIDA By Alfredo Mauricio Villalta Oliva May, 2005 Chair: Steven A. Sargent Major Department: Horticultural Sciences Cucumber is a very important horticultural crop in the United States with an annual production valued at approximately $376 million in 2002. Imports of fresh cucumbers play an important role in meeting the na tional demand, but imports negatively affect domestic growers. Beit Alpha cucumber ( Cucumis sativus L.), also referred to as Bet Alfa, mini, Lebanese or Middle Eastern cucumber, are a ty pe of fresh cucumber widely grown in the Middle East and Europe. It is a much shorter version of th e European-type cucumber and remains relatively unknown in the U.S. Th is type of cucumber produces well under greenhouse conditions in Florida, has excellent flavor and taste attributes, and represents a potential crop for growers seek ing to diversify their product line and take advantage of an increasing demand for fresh vegetables. Beit Alpha cucumbers had a maximum shelf life of 15 to 18 days when stored in rigid, vented clamshells at 10 C and ~90% RH. Storage of cucumbers at 5 or 7.5 C

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xviii reduced the quality due to chilling injury wh ile quality at 12.5 C wa s reduced due to the development of firm protrusions that negativ ely affected appearance but not the edibility. Although internal production of ethyl ene by Beit Alpha cucumbers was undetectable the fruit is sensit ive to concentrations as low as 1 ppm. The marketable life of Beit Alpha cucumbers was reduced by 20% when exposed to 1 ppm exogenous ethylene and 60% when exposed to 10 ppm exte rnal ethylene. In contrast, the marketable life of European (English or Dutch-type) cucu mber was limited to approximately 9 days when exposed to ethylene. Shrink-wrappi ng is a standard practice for European cucumbers to protect against moisture loss but is not necessary for Beit Alpha cucumbers. Unwrapped, unwaxed Beit Alpha cucumbers had similar weight loss as wrapped European cucumbers after 12 days in storage. The effect of the growing season and tim e of harvest on the quality of greenhousegrown Beit Alpha cucumbers was also studie d. The growing season did not affect the marketable life of cucumbers and fruit fr om three different seasons had an average marketable life of 15 to 18 days in storage at 10 C. The time of harvest, early and late in the harvest period, also had no effect on the marketable life of Beit Alpha cucumbers. Beit Alpha cucumbers store well at similar conditions as traditional varieties of cucumbers and do not require plastic shrink-wr apping to protect from moisture loss. Beit Alpha cucumbers, as well as European cucu mbers, should be stor ed in ethylene-free environment to prevent quality losses.

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1 CHAPTER 1 INTRODUCTION Fruit and Vegetable Trade The United States remains a net agricultura l exporter but despite an increase in agricultural exports, agri cultural imports have increased at a faster pace thus reducing the trade balance year after year The U.S. agricultural trade balance peaked at $27.4 billion in 1996 but decreased to $9.5 bill ion in 2004 and is predicted to further decrease in 2005 to $2.5 billion (Figure 1-1); the lowest levels since 1972 (Whitton and Carter, 2004). Despite the fact that the U.S. has a positive overall agricultural trade balance it is a net importer of horticultural products, which includes vegetables, fruits, nuts, essential oils, cut flowers, wine and beer (United St ates Department of Agriculture, 2004). The negative trade balance of hortic ultural products has increased 61.6% in the last 5 years alone; from $5.87 billion in 1999 to $9.49 bill ion in 2003 (Figure 1-2). Although the U.S. has a large number of trading partners, Ca nada and Mexico are the two largest import sources of horticultural products and two of the top three la rgest destinations of U.S. horticultural exports. Canada and Mexico comb ined account for more than a third of the total U.S. exports; in 1999 37% of total hor ticultural exports wort h $3.8 billion were to these two trading partners and it increased to 41% or $5.06 billion in 2003 (Foreign Agricultural Service, 2004). Imports from these two countries also increased over the same period; from $5.19 billion in 1999 to $7.35 billion in 2003 (Figure 1-3).

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2 $ Billions 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 19911992199319941995199619971998199920002001200220032004F 2005 Exports Imports Balance Figure 1-1. The US agricultural trade: exports, imports and tr ade balance ($ billions). 2005 is a forecast. Economic Research Service, USDA (2004).

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3 10.3 10.8 11.0 11.3 12.4 16.1 16.6 17.2 18.7 21.9 -5.9 -5.8 -6.2 -7.4 -9.5 -15.0 -10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0 19992000200120022003 Export Import Balance Figure 1-2. The US horticultural trade: exports, imports and trade balance ($ billions). Horticultural trade includes vegetables fruits, nuts, essential oils, nursery products, cut flowers, wine and beer. Foreign Agricultural Service, USDA (2004). $ Billions

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4 3.8 4.2 4.3 4.7 5.1 5.2 5.5 6.1 6.5 7.4 -1.4 -1.4 -1.8 -1.8 -2.3 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 19992000200120022003 NAFTA Exports NAFTA Imports NAFTA Balance Figure 1-3. The US-NAFTA horticultural trad e: combined exports, imports and trade balance with Canada and Mexico ($ b illions). Foreign Agricultural Service, USDA (2004). $ Billions

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5 The U.S. has a positive trade balance with Canada but a larger negative trade balance with Mexico, in terms of horticultural products. As for cucumbers, the U.S. is a net importer of fresh cucumbers; while imports of cucumbers have more than tripled since 1970 exports have only increased 60%. In 1970-79 the U.S. imported a total of 93, 227 MT of fresh cucumbers and exported 13, 454 MT during the same period (Figure 14). Since then, according to the Economic Research Service (2004) imports have increased remarkably, reaching 393, 636 thousand MT in 2003 while exports were only 21, 636 thousand MT. According to statisti cs compiled from the U.S. Commerce Department and other government sources by the private agribusiness consulting firm FINTRAC Inc. Agribusiness Online (2004), impor ts of cucumbers into the U.S. come mainly from Mexico with smaller quantitie s sourced to Canada, Honduras, Costa Rica, Spain, the Dominican Republic, Guatemala and the Netherlands among other countries. According to FINTRAC Inc., Agribusiness On line, the U.S. imported a total of 334, 735 MT ($171.2 million) of fresh cucumbers from Mexico, 33, 577 MT ($34.5 million) from Canada and 18, 768 MT ($3.02 million) from Honduras; respectively, each country accounted for 85, 8.5 and 4.7% of the total U.S. cucumber import. Horticultural trade is important and necessa ry to eliminate seasonal fluctuations in supply, therefore assuring a year-round supply to U.S. consumers. Trade, however, has tremendous implications for U.S. growers. The statistics indicate that market forces are favoring the importation of cucumbers, as we ll as other horticultural products, not only from regional North American Free Trade Agreem ent trading partners but also from other countries that are becoming competitive enough to penetrate the lucr ative U.S. market.

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6 227.1 334.4 452.8 501.8 459.7 490.9 93.2 179.1 257.3 366.8 393.6 402.3 13.5 27.6 33.0 26.4 21.6 25.9 0 100 200 300 400 500 600 1970-791980-891990-992000-0220032004 Production Import Export Figure 1-4. The US cucumber trade be tween 1970 and 2004: domestic production, imports and exports (1, 000 MT). Ec onomic Research Service, USDA (2004). 1, 000 MT

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7 Fruit and Vegetable Consumption The United States Department of Agriculture recommends a daily intake of at least three servings of vegetables a nd two servings of fruit and an optimum daily intake of 7 to 9 servings combined (Center for Nutriti on Policy and Promo tion, 2000). Despite the guidelines, daily consumption of fruit and ve getables in the U.S. falls below federal recommendations. Ironically, part of the proble m was a shortage of fr uits and vegetables. Putnam et al. (2002) reported that the fruit and vegetable supply in 2002 was 5.2 servings, slightly more than the minimum fi ve daily servings suggested but below the optimum 7 to 9 daily servings recommended. Despite the lower than recommended consumption, annual consumption of fruits a nd vegetables has increased 25% since 1970 from 262 kg/capita in 1970 to 310.7 kg/cap ita in 2002. Although the consumption of vegetables is higher than that of fruits th e consumption of both ha s increased since the 1970Â’s (Figure 1-5). In 1970, annua l per capita consumption of fruit in both forms was 109.7 kg while the consumption of vegetables was 153.1 kg. Since then, consumption of both fruits and vegetables has increased by 12.5 and 22.3%, respectively. In both cases, there has been a higher increase in the cons umption of the fresh form instead of the processed form. Annual consumption of fr esh fruit between 1970 and 2002 has increased by 11.1 kg/capita or 24.2%; from 46 to 57.1 kg/ capita while consumption of processed fruit increased only 2.7 kg/capita or 4.2%. Notwithstanding the ample variety of fruit and vegetables available in the US, six fruits and five vegetables (i ncluding French fries) accounted for roughly half of the total fruit and vegetable consumption. The same au thors also report that fruit and vegetable intake increased with income and education; an indication that produce companies need to become more aggressive marketers as well as educators.

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8 0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 197019741978198219861990199419982002 Total fruit Total vegetables Total fruit and vegetables Figure 1-5. Total annual consumption (kg/capita) of fruit and vegetables in the U.S. Each category (fruit or vegetables) in cludes fresh and processed. Food Consumption Data System, Economi c Research Service, USDA (2004). Annual Consumption (kg/capita)

PAGE 27

9 Although consumption of vegetables remain s higher in the processed form, growth in the consumption of fresh vegetables has incr eased at a faster rate than the consumption of processed vegetables. Consumption of fr esh vegetables increased 25.4% between 1970 and 2002; from 70.1 to 87.9 kg/capita while the consumption of processed vegetables increased 19.8% or 16.4 kg/capita; a higher increase than that seen in processed fruits (Figure 1-6). Marketing specialists are optimistic that co nsumption of fruits and vegetables will continue to increase and cite as evidence the increasing variety of fruits and vegetables available to the U.S. consumer increases, the aggressive education and marketing campaigns undertaken by the government and food purveyors as well as the move towards more wholesome and healthier lifestyles. U.S. Cucumber Consumption According to the Food Consumption Data System (2004), the annual consumption of both fresh and processed cucumbers in th e U.S. has followed a similar trend to the overall trend in fruit and vegetable consum ption. Cucumber consumption has increased by 36.2% since the 1970Â’s; from 3.85 kg/per ca pita in 1970 to 5.25 kg/per capita in 2002 (Figure 1-7). Initially, consumption of processed cucumbers was higher than the consumption of fresh cucumbers but that tre nd was reversed in the early 1990Â’s when the consumption of fresh cucumbers reached 2.3 kg/capita, surpassing that of processing cucumbers. Since then the annual per cap ita consumption of fresh cucumbers has increased while the processed cucumbers has decreased.

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10 Annual Consumption ( k g /ca p ita ) 10 30 50 70 90 110 130 197019741978198219861990199419982002 Processed Fruit Processed Vegetables Fresh Fruit Fresh Vegetables Figure 1-6. Total annual consumption (kg/capita) of fruit and vegetables in the U.S. in the form that they are consumed. Food Consumption Data System, Economic Research Service, USDA (2004).

PAGE 29

11 Annual Consumption (kg/capita) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 1970197519801985199019952000 Fresh Processed Total Figure 1-7. Annual cucumber consumption (kg/capit a) in the U.S. in the form that they are consumed. Food Consumption Data System, Economic Research Service, USDA (2004).

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12 U.S. Cucumber Industry Tomato is the largest crop in the U.S. based on the value of total domestic production (fresh and processed) and is followe d by lettuce, onions and sweet corn (Table 1-1) while cucumbers rank 11th (Economic Research Service, 2004). The cucumber industry in the U.S. consists mainly of two types; fresh-market cucumbers and processing cucumbers. Fresh-market cucumbers are calle d slicers and can and are grown either in open-fields or greenhouses with specific va rieties adapted for each cultivation system, while processing cucumbers are grown in openfields. Another type of cucumbers is the specialty cucumbers, or varieties that are no t commercially grown in large scale such as the Middle Eastern types or Beit Alpha cucumbers. Beit Alpha cucumbers have been shown to produce well in Florida well year-r ound under protected cu lture in Florida, representing an opportunity for Fl orida growers (Lamb et al., 2001). The total value of the domestic cucumber production in 2002 was $376 million (Table 1-2). In 2002, fresh-market cucumber s accounted for 55.6% of the total value of the domestic production; slightly lower than in 1998, when it accounted for 61.6%. Since then, the total value of the fresh-market pr oduction has declined. In 1998, the value of the U.S. production of fresh-market producti on was $226 million and it decreased to $214 million in 2002. During the same period the value of the U.S. production of processing cucumbers increased from $141 to $171 million. Although both types of cucumbers can be grown in all 50 states, the production is hi ghly concentrated in a handful of states. Florida, California and Georgia dominate th e production of fresh-market cucumbers and account for 62% of the total value of the domestic production. The production of processing or pickling cucumbers is similarly concentrated; Florida, Michigan and North Carolina account for 50% of the tota l value of the domestic production.

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13 Table 1-1. Ranking of selected commodities the U.S., based on the total value of production (fresh and processed) between 1999 and 2003 (in $1, 000). Economic Research Service, USDA (2004). 1999 2000 2001 2002 2003 Value of Production ( $ 1 000) Tomatoes 1, 878, 574 1, 843, 776 1, 678, 894 1, 932, 624 1, 865, 328 Head Lettuce 972, 917 1, 208, 140 1, 234, 981 1, 435, 296 1, 187, 984 Onions 641, 278 735, 939 680, 350 764, 994 918, 774 Romaine Lettuce 492, 149 654, 936 604, 555 919, 170 911, 051 Sweet Corn 670, 512 713, 037 753, 245 718, 124 789, 522 Broccoli 493, 087 620, 606 484, 467 567, 767 643, 791 Carrots 484, 654 390, 002 510, 816 521, 362 553, 889 Bell Pepper 483, 807 531, 018 473, 557 464, 401 505, 159 Snap Beans 394, 057 392, 763 389, 625 404, 003 384, 819 Cantaloupe 377, 360 371, 984 429, 281 398, 302 371, 721 Cucumber 364, 774 381, 660 374, 647 376, 790 367, 645 Table 1-2. Value of the U.S. cucumb er production between 1998 and 2002 (in $ millions). National Agricultura l Statistical Service (2004). 1998 1999 2000 2001 2002 Value of Production ( $ millions) Fresh 226 217 218 211 214 Processing 141 150 165 169 171 Total 366 367 383 380 385

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14 Total production of cucumbers in the U.S. (both fresh and processing) has remained relatively unchanged in the past fi ve years. In 1998, total domestic production was 1.051 million MT and increased slight ly to 1.078 million MT in 2002. Between 1998 and 2002, total production has remained almost evenly split between fresh-market and processing cucumbers; production of freshmarket cucumbers accounts for 48% of the total domestic production and in 2002 it was 517 MT while the production of processing cucumbers was 561 MT (Table 1-3). Since 1998, the price per MT of fresh-market cucumbers has decreased slightly while it has tended to increase for processing cucumbers. In 1998, the average price for a MT of fresh-market cucumbers was $440 and decreased to $413.6 in 2002. On the other ha nd, the price of a MT of processing cucumbers increased from $260.7 in 1998 to $304.7 in 2002 (National Agricultural Statistical Services, 2003). In 2002 approximately 73, 450 hectares we re dedicated to the production of cucumbers in the U.S., with 33% of this acreage dedicated to the production of freshmarket cucumbers. Although the total area under cultiv ation increased by more than six thousand hectares between 1998 and 2002, all the additional area has been devoted to the production of processing or pickling cucumber s. The area dedicated to the production of fresh-market cucumbers remained relativel y unchanged during the same period, in 1998 it was 24, 475 hectares and decreased to 24, 160 hectares in 2002 (Table 1-4). Although the area dedicated to the production of fresh-ma rket cucumbers is smaller than that of processing cucumbers; higher yields, multiple harvests per crop and longer harvest seasons due to climatic conditions result in higher tonnage of fresh-market cucumbers per area planted. Annual national yields for fr esh-market cucumbers are approximately 9.13

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15 MT per hectare (average of national yiel d between 1998 and 2002) compared to 5.12 MT per hectare for processing cucumbers (Nati onal Agricultural Statistical Services, USDA, 2003). A large portion of the production of proc essing cucumbers is in Northern states which have shorter production season than Sout hern states such as Florida, Georgia and California which together account for more th an 60% of the total domestic production of fresh-market cucumbers (National Ag ricultural Statistical Service, 2004). Table 1-3. Total U. S. cucumber producti on between 1998 and 2002 (in thousands MT). National Agricultural Sta tistical Service (2004). 1998 1999 2000 2001 2002 Domestic Production (1 000 MT) Fresh 512 542 498 489 517.23 Processing 540 571 557 529 561.18 Total 1051.7 1113.1 1055.1 1017.6 1078.4 Table 1-4. U. S. cucumber cultivation between 1998 and 2002 (h ectares). National Agricultural Statisti cal Service (2004). 1998 1999 2000 2001 2002 Production Area (hectares) Fresh 24, 475 25, 940 22, 905 23, 553 24, 160 Processing 42, 885 44, 366 43, 791 45, 369 49, 291 Total 67, 360 70, 306 66, 696 68, 922 73, 450

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16 Florida Cucumber Industry Cucumber production is very important in the state of Florida. The value of cucumber production ranks 5th in order of the most valuable vegetable crop to the state, after tomatoes, bell peppers, snap beans and sweet corn (Florida Ag ricultural Statistical Service, 2004). Florida accounts for roughly 20% of the total U.S. cucumber production. In 2002, the most recent year for which data is available, Florida had a 27.7% market share of the fresh-market cucumbers (bas ed on the value of production) and a 14% market share in the processing cucumber segm ent; the largest combined market share of any state. The value of total cucumber pr oduction in Florida increased from more than $75 million in 1998 to more than $106 million in 2000, before decreasing to slightly more than $83 million in 2002. Since 1998 Florid a has been the leading supplier of freshmarket cucumbers and is also one of the major players in the processing cucumber market; it was the leading s upplier in 2001 and 2002 of processing cucumbers (based on the value of production). Although both types of cucumbers are grown in substantial amounts in Florida, Florida is by far a fres h-market producer. Production of fresh-market cucumbers account for roughly 70% of the valu e of the state’s tota l cucumber production (Table 1–5). Florida’s total cucumber output in 20 02 was 194 thousand MT, higher than the 172 thousand MT harvested in 1998 but not as hi gh as in 2000 when total state output was 230 thousand MT (Table 1–6). A lthough total production of bo th types is currently at higher levels than in 1998, it has decreased in the fresh-market segment in the last three years and has remained stagnant in the processing segment over the same period. Although the total area under cucumber cultivation in the U.S. increased 9% between 1998 and 2002, it decreased 14% in the state of Flor ida. In 1998, Florida had 6,

PAGE 35

17 677 hectares under cucumber cultivation, 58% of which was dedicated to the production of fresh-market cucumbers, and it decreased to 5, 787 hectares in 2002 (Table 1–7). More cultivation area has been lost in the fresh-mar ket segment than in the processing segment. The area under cultivation of fresh-market cucumbers has decr eased 18% since 1998, from 3, 804 hectares to 3, 157 hectares in 2002. Over the same period, the area under cultivation of processing cucumbers decrease d 8.5%, from 2, 873 hectares in 1998 to 2, 630 hectares in 2002. Table 1-5. Value of cucumber production in Florida between 1998 and 2002 ($ million). National Agricultural Sta tistical Service (2004). 1998 1999 2000 2001 2002 Production Value ($millions) Fresh 51.88 61.69 73.73 60.23 59.28 Processing 23.20 19.60 32.95 19.03 23.98 Total 75.08 81.29 106.68 79.26 83.26 Table 1-6. Total production of cucumber s in Florida between 1998 and 2002 (1, 000 MT). National Agricultural Statistical Service (2004). 1998 1999 2000 2001 2002 Production (1 000 MT) Fresh 118 153 166 121 130 Processing 54 46 64 64 64 Total 172 200 230 186 194

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18 Table 1-7. Florida cucumber cultivation be tween 1998 and 2002 (in hectares). National Agricultural Statisti cal Service (2004). 1998 1999 2000 2001 2002 Production Area (hectares) Fresh 3, 804 4, 371 4, 087 3, 157 3, 116 Processing 2, 873 2, 752 2, 630 2, 630 2, 630 Total 6, 677 7, 122 6, 718 5, 787 5, 747

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19 CHAPTER 2 LITERATURE REVIEW Botany The cultivated cucumber varieties bel ong to the Cucurbitaceae family and are classified in the Cucumis genus which contains 34 speci es; including cucumbers, melon and gherkins as well as the synthetic specie hytivus (Andres, 2004) which is a cucumbermelon hybrid (Zhuang et al., 2003). The garden cucumber ( Cucumis sativus L.) is thought to have originated in India (Staub et al., 1998; Dhillon, 2004). Cucumber plants exhibit different patterns of sex expression with monoecious (female and male flowers on the same plant) being the most common form of sex expression in cucumbers (Yamasaki et al., 2001). Other forms of sex expr ession include gynoecious plants (produce predominantly female flowers), hermaphrodite and andromonoecious cultivars (Byers et al., 1972). Beit Alpha (Bet Alfa) cucumbers ( Cucumis sativus L.), also referred to as mini, Lebanese or Middle Eastern cucumbers are a type of fresh cucumbers widely grown in the Middle East, Europe and parts of the Me diterranean region (Me ndlinger, undated) as well as Australia. They are thought to have originated in the Mi ddle East region with some cultivar improvement done in Israel and other countries (Pers. Comm. Daniel Cantliffe, Horticultural Sciences Department University of Florida and Harry Paris, Department of Vegetable Crops & Plant Gene tics, Agricultural Research Organization, Israel).

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20 Beit Alpha cucumbers are a much shorter version of the European cucumber (Pers. Comm. John Meeuwsen, Breeder/Product Manage r, De Ruiter Seeds) which is also known as English or Dutch-type cucumber Beit Alpha cucumbers remain relatively unknown in the U.S. fresh market, which is dom inated by slicer and European cucumber varieties. This could eventual ly change since Beit Alpha varieties have appeared in commercial markets, both as imports and loca lly grown, in localized markets such as California, Florida and some areas in the No rth East. Specific va rieties of Beit Alpha cucumbers have been developed for open field production (e.g. ‘Beit Alpha Hybrid EM75’, Emerald Seed Company, El Centr o, CA) as well as for production under protected culture (e.g. ‘Manar’, DeRuiter S eeds, Columbus, OH). Co mmercial varieties of Beit Alpha cucumbers have been repor ted to be gynoecious; however monoecious varieties are also available (e.g. ‘Beit Alpha’, Atlas Seed s Inc., Suisun City, CA). Unlike European cucumbers, Beit Alpha cucumbers (‘Manar’) are significantly smaller, generally from 125 to 175 mm in length, weigh less than 100 g, and are outstanding in flavor. Another ch aracteristic of Beit Alpha cucumbers is that they can be consumed unpeeled since they have a smooth a nd edible thin skin and are seedless. This new crop represents an opportuni ty for Florida growers since it has been proven to grow well year-round under protected culture in Florida (Lamb et al., 2001). Successful introduction and marketing of Beit Alpha cucumbers will be highly dependent upon adequate postharvest handling and marketi ng, which underscores the need for reliable data on the storage characteri stics of this commodity. Cucumber Production Cucumber harvest season in the U.S. varies by geographic location and production system used. The production system can be open-field production (fresh market and

PAGE 39

21 pickling cucumbers) or protected cultivation systems (fresh market only). Production in open fields will limit the harvest season as well as quality of the commodity. Production in protected culture systems, however, can extend the harvest seas on throughout the year and generate fruit of higher quality. Flor ida has a long harvest season for field-grown cucumbers and it extends from Mid-Septem ber through June depending on the growing region (Florida Facts 2004). The harves t season of both open-field and greenhouse production systems is limited in other stat es by the cold weather, creating price fluctuations. In Florida, it is possible to obtain year-round harvests in protected cultivation systems, as is cu rrently the case with the produc tion of Beit Alpha cucumbers in North Florida. Maturity Indices Cucumbers destined for fresh consum ption are manually harvested, unlike processing cucumbers which are also harveste d mechanically; approximately two-thirds of the national production is machine-harv ested (Estes and Cates, 2001). Cucumbers grown for the fresh market are harvested as they reach commercial maturity, allowing for multiple harvests per season. The maturity at harvest is the most important factor that determines postharvest quali ty (Kader, 1996; Schouten et al., 2004). Cucumbers reach commercial maturity or the optimum eating qu ality at a physiologically immature stage (Kays, 1999) and delaying harvest will tend to lo wer the quality at harvest and hasten the postharvest deterioration rate (Kader, 1996). Maturity on cucumbers is assessed subjectively based on color, shape, size a nd appearance (freedom of malformations, injury and decay) (Kader, 1996; U.S. Standa rds for Grades of Greenhouse Cucumbers, 1997).

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22 Postharvest Considerations Cucumbers that meet USDA standards are harvested and go through a short packaging process. Fresh-market cucumber s such as the greenhouse-grown, European types are hand harvested and transported in plastic bins to the packing house. Depending on the size and layout of the farm, the packing house may be a few meters away from the growing area, which would reduce both the transportation time and manipulation of the product. After sorting and grading, cucumber s are mechanically shrink-wrapped, without being sanitized or surfaced washed, using he at and then manually packed in corrugated cartons. Beit Alpha cucumbers are also manually ha rvested and graded according to the growerÂ’s experience based on size, color, sh ape and freedom of injury or any other defect, since there are no federal standards for grades of Beit Alpha cucumbers in the U.S. A typical crop of Beit Alpha cucumbers gr own in North Florida is harvested 4 to 6 times a week for 7 to 9 weeks and are p acked unwashed, unwaxed and unwrapped in 7kg unwaxed, corrugated cartons. Storage After harvest, the quality of a commodity starts to decline, making the shelf-life dependent on the postharvest treatments the commodity receives. Temperature management is generally the most effectiv e and the most used tool to extend the postharvest life of many horticultural comm odities, including cucumbers (Kader, 2002). Due to their chilling-sensitive na ture, it is recommended that cucumbers be stored at 7 to 10 C and 85 to 95% relative humidity (RH) in air (DeEll et al., 2000; Thompson, 2002), 8 to 12 C in 1 to 4% 02 and 0% CO2 (Cantwell and Kasmire, 2002), or 10 to 12.5 C (Paull, 1999; Kader, 2002; Suslow, 2002). Stor ing the commodity at temperatures below

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23 the recommended storage temperature will not only limit the quality and shelf life of a product but is also a redundant cost. Appropriate temperature management is also essential from a food safety and marketing standpoint. In part driven by cons umer pressure as well as other competitive market forces, food purveyors need suppliers th at will provide product that is safe and of consistent quality year round. Therefore, growers and food handlers must ensure that every step taken is in accordance with r ecommended guidelines for that particular commodity. Another important aspect of cucumber stor age is the use of protective shrink-wrap films, such as polyethylene films, to prot ect greenhouse-grown from excessive water loss (Cazier, 2000) and consequent shriveling. Film wrapping has been reported to extend the shelf-life of some fruits due to the modifi ed-atmosphere effect it creates (Wang and Qi, 1997). Depending on the permeability of the film the gas composition of the atmosphere between the fruit and the prot ective film can be modified through the respiration and transpiration of the product (Thompson, 2003). The consumption of O2 through respiration causes the level of O2 to be diminished while the levels of CO2 increase. Transpiration on the other hand causes water va por to accumulate inside sealed films, increasing the relative humidity of the atmos phere and leading to condensation when the RH reaches 100%. These three variables along w ith ethylene, storage temperature and the duration of storage form the six environmenta l variables that are re gulated in modified atmosphere packaging (Saltveit, 2002). Modified atmosphere packaging has also been reported to reduce both the onset and severity of chilling injury in wrapped cucumbers as a result of increased levels of

PAGE 42

24 polyamines in wrapped fruit (Wang and Qi, 1997). Reduction in the expression of chilling injury symptoms as a result of modifi ed atmosphere have also been reported in mango (Pesis et al., 2000), carambola (Ali et al ., 2004) and citrus (P orat et al., 2004). In the case of cucumbers the main benefit obtai ned from shrink-wrap film for individual cucumbers is the reduction of moisture lo ss, since the permeable film wrap offers protection from moisture exchange but does not restrict gas move ment (Wang and Qi, 1997). Physiological Stresses Chilling Injury Chilling injury is a physiological disorder th at occurs when chilling-sensitive fruits or vegetables are exposed to low but nonfreezing temperatures (Hakim et al., 1999; Kang et al., 2002; Saltveit, 2002). It is believed that cell me mbranes are the primary sites of storage disorders such as chilling injury expression (S hewfelt and del Rosario, 2000) but a biochemical pathway to elucidate th e chilling injury mechanism has not been established yet (Balandrn-Quintana et al., 2003 ). Chilling injury is a cumulative process and the level of damage will depend on th e temperature and the length of exposure (Cantwell and Kasmire, 2002; Sa ltveit, 2002). For chilling injury damage, to be evident in cucumbers the fruit must be exposed to ch illing temperatures for several days (Hakim et al., 1999; Saltveit, 2002) and visual symp toms may not be expressed until after the fruit is transferred to high er storage temperatures (DeE ll et al., 2000). Although chilling injury in cucumbers can vary depending on the cultivar (Hakim et al., 1999; Thompson, 2002) and preharvest factors, it is generally accepted that cucumber storage below 10 C will cause chilling injury thus limiting the sh elf life of the product. Chilling injury in cucumbers results in the sinking of spines, water soaking, pit formation (Hakim et al.,

PAGE 43

25 1999), increased susceptibility to decay and the development of brown or black lesions that follow pitting (Cantwell and Kasmire, 2002) reduced storage life increased rates of ion leakage due to membrane damage (Kang et al., 2002; Saltveit, 2002), as well as the appearance of dark watery patches (DeEll et al., 2000). As mentioned above, many symptoms are related to the expr ession of chilling injury damage. However, changes in membrane integrity is the primary effect that results when plant tissue such as fruits is exposed to stressful environmen ts such as chilling temperatures or ethylene (DeEll et al., 2000; Balandrn-Quintana et al., 2003). Membrane deterioration reduces its ability to act as a diffusion barrier causing cell contents to leak (Stanley, 1991), which translates into higher rates of electrolyte leakage (Hakim et al., 1999; Kang et al., 2001; Saltveit, 2002). This makes electrolyte leakage assessments useful in quantifying cell damage in ch illed cucumber fruit (Whitlow et al., 1991; Knowles et al., 2001). Although the precise bioc hemical pathway linked to chilling injury is not clear, it has been s uggested that the level of me mbrane lipid unsaturation is inversely correlated with chilling sensitivity (Nishida and Murata, 1996) since it has been observed that higher amounts of unsaturated fatty acids are synthesized by organisms exposed to chilling temp eratures (Stanley, 1996). Ethylene Injury The drive to remain competitive in a globa l horticultural market place has forced some growers to rethink their vision. One of the changes that handlers of horticultural commodities have been forced to adopt is th e diversification of the product line thus bringing different commodities into contact with each other. Temperature management abuses are not the only potential cause of damage that horticultural commodities may encounter as they make their way to the consumer. One very important physiological

PAGE 44

26 aspect of horticultural commodities is their response to ethylene. Given the variability that exists in cucumber germplasm it is impor tant to determine the postharvest behavior of cultivars grown under protected culture w ith the aim of reducing losses due to postharvest mismanagement Horticultural commodities are classified as climacteric or non-climacteric depending on their respiration and ethyl ene production pattern s (Giovannoni, 2001; White, 2002). Ethylene is required to complete the ripening process in climacteric fruit but not in non-climacteric fruit (Lelivre et al., 1997; Phillips et al., 2004). Cucumbers produce little or no ethylene after harvest and there is no concomitant rise in respiration rate allowing for the classification of cucumbers as non-climacteric (Saltveit and McFeeters, 1980; Wehner et al ., 2000). It is important to note that cucumbers become horticulturally or commercially mature at a physiologically immature stage, which makes ripening unnecessary from a marketing st andpoint. Cucumbers respond negatively to ethylene and the changes associated with ethy lene exposure are deemed as detrimental. The role of ethylene, a gaseous plant hormone (Huang et al., 2003), is widely documented in regulating many physiologi cal and developmental plant processes (Deikman, 1997; Johnson and Ecker, 1998; Kader, 2002; Huang et al., 2003; Hongwei and Ecker, 2004). In cucumber plants, et hylene plays a role in determining sex expression, however its effects on fruit tissu e are deemed detrimental because they reduce consumer acceptance of the product by negatively affecting appearance, firmness and other attributes, such as color, that de fine the quality of cucumbers. Cucumbers are highly sensitive to external ethylene (Kader 2002) and its exposure results in accelerated color loss, higher susceptibilit y to decay and unwanted tissue softening (Saltveit, 1998).

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27 Ethylene is synthesized in pl ant tissue from methionine via a series of enzymatic reactions (Saltveit, 1999). Pr oduction of ethylene prior to ripening is very low but increases at the onset of ri pening (Yang and Oetiker, 1998) which controls the initiation of changes in biochemical and physiological at tributes such as texture, color, aroma volatiles and flavor (Lelivre et al., 1997) associated with fruit ripening in climacteric fruits, but which result in unacceptable qua lity in non-climacteric fruit such as cucumbers. Ethylene molecules bind to memb rane-bound receptors or binding sites –such as ETR1/ETR2, ERS1/ERS2 and EIN4 in Arabidopsis (Guo and Ecker, 2004)– on plant cells which result in the formation of me ssenger RNA, which is thought to then be translated into enzymes that cause the ethylene response (change s in color, tissue softening among others) (Reid, 2002). Research Objectives This research project had three objectives: 1. study the storage behavior of locally grow n cultivars of Beit Alpha cucumbers and determine the optimum storage temperature; 2. evaluate the response of Beit Alpha cucu mbers to exogenous ethylene compared to that of the traditional lo ng, European cucumber and 3. evaluate the effect of the growing seas on and time of harvest on the postharvest quality of Beit Alpha cucumbers.

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28 CHAPTER 3 EFFECT OF STORAGE TEMPERATURE ON THE MARKETABLE LIFE OF BEIT ALPHA CUCUMBER Introduction An understanding of the postharvest parame ters is essential for the successful market introduction of Beit Alpha cucumb ers (Sargent et al., 2001). One of these postharvest parameters is the optimum storag e temperature, the temperature at which a commodity will have the longest marketable life with minimal loss in quality. Low temperature storage is one of the most widely used postharvest treat ments and it is relied upon as the most effective tool for prolongi ng the marketable life of horticultural commodities (Kader, 2002). Low temperatur es, however, can induce physiological disorders such as chilling injury that may render the commodity unfit for marketing (Paull, 1999). Chilling injury in cucumbers resu lts in the sinking of spines, water soaking, pit formation (Hakim et al., 1999), increased susceptibility to decay and the development of brown or black lesions that follow pitt ing (Cantwell and Kasmire, 2002). Development of chilling injury is dependent on the temperat ure and length of exposure (DeEll et al., 2000) and the expression of sy mptoms varies depending on th e cultivar as well as the environmental conditions prior to exposure to chilling temperatures (Hakim et al., 1999; Kang et al., 2002; Kader, 2002). It is therefore essential to determine the proper storage temperature of locally grown cultivars is esse ntial for growers to reduce the losses that could result from chilling injury.

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29 Cucumbers suffer chilling injury above fr eezing temperatures and generally should not be stored long term below 7 to 10 oC (DeEll et al., 2000); optimum storage temperature for cucumbers is 10 to 12.5 C at ~95% relative humidity (Paull, 1999; Kader, 2002; Suslow, 2002). Chilling injury in cucumbers is characterized by accelerated water loss, surface pitting, and increased su sceptibility to decay (Kang et al., 2001). Chilling injury is just one of many disorder s that could develop during storage; other postharvest disorders include shriveling as a result of wate r loss (Gmez et al., 2004), yellowing of the peel (Lin, 1989), decay and general deterioration of appearance. In cucumbers quality is based on appearance, shape, firmness, color as well as freedom from growth or handling defects and freedom from decay (Agricultural Marketing Services, 1985); parameters that jointly determine the quality rating of the commodity. Research related to the chilling sensitivity and othe r storage characteristics of Beit Alpha cucumbers, specifically to the cultivars being grown under prot ected culture in Florida is scarce, underscoring the need and va lue of this type of research. The objectives of these experiments were to determine the optimum storage temperature for Beit Alpha cucumbers base d on the determination of key quality characteristics under simulated commercial storage conditions. Materials and Methods Plant Material Seedless, Beit Alpha cucumbers ( Cucumis sativus L., ‘Manar’, DeRuiter Seeds, Columbus, OH) were grown under commer cial greenhouse conditions (double-poly, passively ventilated greenhouses ) in soilless media (composted pine bark), using nursery pots, at Beli Farms in Wellborn, Florida. Tw o experiments were carried out and for both

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30 experiments, cucumbers were harvested in the morning (March 15, 2003 and June 30, 2003) and packed unwashed in 7-kg unwaxe d, corrugated cartons and transported the same day to the Postharvest Horticulture La boratory at the University of Florida in Gainesville, Florida. Cucumbers were then sorted and graded by size and appearance. Since no quality standards are available for Beit Alpha cucumbers in the U.S., cucumbers were manually graded according to shippe rÂ’s recommendations (dark green color and free of any visible defects or injuries) and size (diameter of no less than 2.5 cm and no more than 4.0 cm). Beit Alpha cucumbers used in this test ha d an average weight of 80.4 g, an average length of 136 mm and an average equatorial diam eter of 29.4 mm After sorting, the cucumbers were dipped in a 100-ppm free chlo rine solution for 2 minutes, after which they were air-dried, randomized and placed in rigid, vented, 2-L, polystyrene clamshells. Beit Alpha cucumbers are currently marketed in film over-wrapped trays; however, an alternative package is the rigid, vented cl amshell that protects from injury during transportation, handling and/or di splaying while still allowing a clear view of the product. Cucumbers (10 cucumbers/clamshell) we re stored for 21 d at 5, 7.5, 10, or 12.5 oC and assessed for quality every 3 d. Relative humid ity (RH) inside the clamshells reached ~95% (Hobo Data Logger, Onset Computer Corporation, Bourne, MA) after 2 d and remained at this level throughout the durati on of the experiment. The quality parameters assessed were the following.

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31 Visual Quality Fruit were visually assessed for yellowing, pitting, pathogen infection or any other disorder that could render the commodity unm arketable. Visual quality assessments were made every 3 d for 21 d. Color Evaluation Both external and intern al color was assessed using a CR-200 Chroma Meter (Konica-Minolta USA, Inc., Ramsey, NJ). Ex ternal color readings were taken on an equatorial spot predetermined and marked before placing the fr uit in storage. Two measurements were taken on opposite sides of the fruit (n=10) and averaged to obtain a final value for each fruit. Internal color was also measured on the mesocarp tissue of equatorial slices. Two measurements were ta ken per slice (n=5) and averaged to obtain a final value. Each slice was obtained from a different cucumber. Chroma meter was white calibrated using a white calibration plate (Konica Minolta Photo Imaging USA Inc., Mahwah, NJ) using the following parameters ; Illuminant C, L = 97.08, C = 1.84 and h = 90.76 (Y=92.6, X = 0.3135 and y = 0.3196). Weight Loss Weight loss was determined by weighing 10 individual cucumbers 3 d and after being transferred to 20 C (68 F) for 24 hours. Weight loss is expre ssed as a percent of the initial weight (f resh weight basis)

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32 Respiration The respiration rate was measured on fru it stored in sealable 1-L Tupperware containers equipped with a septum for headsp ace sample retrieval. Three cucumbers were weighed and placed in each container (4 cont ainers/treatment) and stor ed at six different temperatures; 5, 7.5, 10, 12.5, 15 and 20 C. Cucumbers were weighed continuously during storage to reflect the we ight loss in the respiration rate calculation. Containers were sealed for 2 hours (a voiding accumulation of CO2 greater than 5%) before retrieving headspace samples and unsealed after the h eadspace samples had been analyzed for CO2. Headspace samples (n=8) were withdrawn every 2 d for 14 d, with the initial measurement taken 2 d after harvest. Headspace samples were withdrawn using a 1-ml disposable hypodermic syringe and analyzed using a Gow Mac, Series 580 gas chromatograph (Gow Mac Instruments Co., Bridgewater, NJ) equipped with a thermal conductivity detector Respiration rates were expressed as ml CO2/kg-1 hr-1. Ethylene Production The production of internal ethylene was measured on stored cucumbers. Ethylene production was measured on the same cucumbers at the same time that respiration rate was measured. Ethylene was quantified on headspace samples (n=8) withdrawn every 2 d for 14 d and analyzed using a Tracor 540 ga s chromatograph (Tremetrics Analytical Division, Austin, TX), equipped with a photoion ization detector, an Alumina F1 column with a mesh size of 80/100.

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33 Mesocarp Firmness Fruit firmness was assessed as the bioyiel d point on equatorial slices using an Instron Universal Testing Instrument M odel 4411 (Instron Corporation, Canton, MA) equipped with a 3.0-mm diameter probe, a crosshead speed of 50.0 mm/min, a 5-kg load cell and a 7-mm displacement. Firmness was ev aluated on the mesocarp area (between the epidermis and locular tissue, approximately 2 mm from the epidermis) of similarly sized, transverse, equatorial slices (n=5) of fruit. Fruit slices were obtained using a double-bladed cutting instrument with an 11-mm separation between blades, which produced slices identical in thickness. Two fi rmness measurements were taken per slice, and averaged to obtain a final value. Each slice was obtained from a different cucumber. Electrolyte Leakage Various aqueous solutions have been us ed as the bathing solution to assess electrolyte leakage (EL) in cucumber fruit tissue. Kang et al. ( 2001) and Mattson (1996) reported the use of 0.3 M mannitol as the is otonic concentration while Hakim et al. (1999) used 0.4 M mannitol for EL assessments while others have used distilled deionized water as the bathing solution (Know les et al., 2001). Determining the isotonic solution is important to accura tely assess membrane permeability since the use of hypo or hypertonic solutions could obscure real chan ges in permeability because they can cause osmotic shock to the cells that would influen ce the rate of ion leakage (Saltveit, 2002). Since recommendations for the isotonic solu tions for Beit Alpha cucumbers could not be found it was necessary to determine it. Isot onic mannitol concentration was determined by weight difference after the mesocarp cores had been immersed in mannitol solution for 4 hours. Five mesocarp cores (9 mm long by 7 mm thick) excised from equatorial

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34 cucumber slices using a No. 5 cork borer were placed in 50-ml conical bottom plastic centrifuge tubes containing 35 ml of 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 M mannitol solution. The mesocarp cores were we ighed and gently rinsed with deionized water before being placed in the bathing so lution. A final weight measurement was taken after the samples had been on a slow shaker for 4 hours. The weight difference was then used to determine the isotonic mannitol c oncentration, which was determined at 0.25 M mannitol. Mesocarp cores did not gain or lose weight after being immersed for four hours in 0.25 M mannitol solution (Appendix B). Highe r concentrations (hypertonic solution) caused a weight loss in mesocarp tissue wh ile concentrations below 0.25 N (hypotonic) caused a weight gain after the four-hour immersion. Samples for electrolyte leakage assessment s of stored fruit were prepared as follows. Four cores (9 mm long by 7 mm thick) per treatment, of mesocarp tissue were excised from transverse slices using a No. 5 brass cork borer. Each sample was excised from a different cucumber. The mesocarp core s were cleaned of torn tissue by gently rinsing them with deionized water befo re placing them in 50-ml conical-bottom centrifuge plastic vials contai ning 35 ml of 0.25 M isotonic mannitol solution (obtained as described above). The samples (n=4) were then placed on a slow shaker for 4 hours before measuring the electro conductivity (EC) of the bathing solution using a digital, temperature-compensated YSI 3100 conductance bridge (YSI Inc., Yellow Springs, OH). The samples were then frozen at -20 C, s ubsequently boiled for 30 minutes and allowed to cool to room temperature before obtain ing a final EC measurement of the bathing solution. Electrolyte leakage was expressed as a percent of the total electrolyte leakage.

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35 Moisture Content Moisture content of the fruit was dete rmined by placing 25 g of unpeeled fruit slices in tared, aluminum weighing boats (n=6 ). The boats were placed on a tray wrapped with aluminum foil and placed in an oven for two weeks. Weight difference was used to calculate moisture content throughout th e storage period (fresh-weight basis). Compositional Analysis After each evaluation period three cucumbers per treatment were immediately frozen at -20 C for later analysis. The fro zen samples were then thawed and blended at high speed for 45 sec using a laboratory bl ender. A portion of each homogenate was centrifuged at 15,000 RPM for 20 minutes. The re sulting supernatant was filtered using cheesecloth and stored in scintillation vials at -20 C for later analysis. Total titratable acidity, expressed as a percent of malic acid, was determined by diluting 6 g of supernatant in distilled wate r and titrating to pH 8.2 with 0.1 N NaOH solution using an automatic titrimeter (Fisher Titrimeter II, Fi sher Scientific, Pittsburg, PA). Soluble solids content, expressed as Brix, was determined by placing a drop of cucumber supernatant on a tabletop, digital refractometer (Abbe Mark II, Reichart-Jung, Buffalo, NY). The pH measurements were done on the remaining supe rnatant in the scint illation vials using a digital pH meter (Model 140, Corning Scie ntific Instruments, Medfield, MA). Data Analysis Both experiments were designed as comple tely randomized experiments using four temperature treatments. Data collected were analyzed using the GLM procedure (SAS Institute Inc., Cary, NC). All data presente d were subject to a DuncanÂ’s Multiple Range

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36 Test using a P-value of <0.05. Results of both experiments were not significantly different and were combined for analysis. Results Appearance The storage temperature had a significant effect on the postharvest quality and marketable life of cucumbers with different disorders observed on fru it stored at different storage temperatures. All fruit retained accepta ble appearance for the first 6 d in storage with deterioration in fruit quality becoming evident by 9 d on fruit stored at 5 or 12.5 C. Quality started to deteriorate on fruit st ored at the two extreme temperatures, 5.0 and 12.5 C, between 6 to 9 d in storage. At th is point, fruit stored at 5.0 C lost quality due to pitting and water soaking that was presen t on 70% of the fruit while fruit stored at 12.5 C lost quality due to the presence of solid protrusions or bumps that developed on the surface of the fruit. The presence of th ese bumps affected 45% of the fruit and negatively affected the smooth, waxy appear ance of Beit Alpha cucumbers. Although fruit stored at 5 C was no longer marketable after this period, it was kept in storage for observation purposes. Fruit stored at the two intermediate temperatures, 7.5 and 10 C, did not show signs of pitting, bumps or other di sorders at this point in the storage period. The appearance of fruit stored at 7.5 C showed signs of deterioration and became unmarketable after 12 d in storage. Yellowing on 50% of fruit, slight pitting and water soaking were the predominant factors that negati vely affected the appearance of this fruit while fruit stored at 10 C retained g ood appearance after the same storage period. The presence of bumps and yellowing con tinued to reduce the quality of fruit stored at 12.5 C and it was no longer unmarke table after 12 to 15 d in storage. Fruit stored at 10 C retained good appearance until 15 to 18 d in storage at which point

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37 yellowing and stem-end shriveling negatively affected appearance, making the fruit unmarketable. Marketability of stored fruit, independent of storage temperature, was lost between 18 and 21 d in storage. In the first experime nt, fruit stored at 10 C or below showed symptoms of bacterial ( Pseudomonas sp. ) and fungal ( Botrytis sp. decay by 21 d storage. Decay, however, was not observed in the second experiment. External Color Varying the storage temperatur e had no significant impact on the external color, as measured by the hue angle, of stored Beit Alpha cucumbers. The external color was however, influenced by the length of the st orage period and it exhibited a downwards trend, reflecting a departure from dark gr een towards yellow, as the storage period progressed (data not shown). External color for all treatments averag ed 128.5 ( 1.1) initia lly (12 hours after harvest) and it declined to between 123.1 ( 1.5) and 124.7 ( 1.5) af ter 21 d in storage; a decline of 2.7 to 3.4% from th e initial values observed at harvest but with no significant differences among temperature treatments. In these experiments it was not possible to accurately correlate external hue angle measurements with the yellowing detected upon visual inspection, perhaps due to the fact that hue angle measurements were taken on equa torial spots of the fruit, which remained green even after incipient yellowing had set on the blossom (distal) end of the fruit. During the storage period it was observed that yellowing advanced from the blossom end (distal) to the stem end (proximal) of the fr uit. Also, the storage treatment had no effect on the L* (lightness) or chroma values. Light ness (L*) averaged 39.9 ( 1.1) at harvest

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38 and was 41.5 ( 1.5) after 21 d storage while the initial chroma value of all four treatments averaged 23.2 ( 0.9) and was 26.2 ( 2.9) after 21-d in storage. Internal Color The internal color decreased in fruit stored at the two intermediate temperatures (7.5 and 10 C) but not in fruit stored at either 5 or 12.5 C (Table 3-1). Internal L* and chroma values were not affected by the st orage treatments Lightness (L*) averaged 68.8 ( 1.5) at harvest and was 68.3 ( 1.5) after 21 d storage while the initial internal chroma value of all four treatments averaged 25.4 ( 1.6) and was 21.8 ( 1.1) after 21-d in storage. Weight Loss Weight loss increased almost linearly (R2 = 0.99) over time, reaching 4.4% after 21 d on fruit stored at 12.5 C (T able 3-2). Weight loss of fruit stored at 12.5 C was significantly higher, throughout th e storage period, than the we ight loss of fruit stored below 12.5 oC. Weight loss in fruit stored be tween 5.0 and 10 C was less pronounced and ranged between 1.6 and 2.6% after 21 d, with no significant differences. Respiration The storage temperature significantly affect ed the respiration rate of Beit Alpha cucumber fruit during the first 6 d in stor age. After this period, only the lowest temperature (5.0 C) effectively suppresse d the respiration rate (Figure 3-1).

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39Table 3-1. Internal hue angle of Beit Alpha cucumbers stored at four differe nt temperatures; 5, 7.5, 10 or 12.5 C for 21 days. Storage Length (d) 0 3 6 9 12 15 18 21 Internal Hue Angle () Temperature Tre atm ent Mean s Mean s Mean s Mean s Mean s Mean s Mean s Mean s 5 C 113.5z 0.23y 113.1 0.28 113.4 0.30 110.9 0.37 111.1 0.31 114.6 0.35 113.3 0.37 114.4 0.33 a a a a a a a a 7.5 C 113.5 0.23 114.2 0.32 113.4 0.34 107.8 0.25 108.1 0.46 110.6 0.40 108.3 0.27 105.8 0.43 a a a a b b b b 10 C 113.5 0.23 114.0 0.20 113.7 0.17 107.3 0.31 108.5 0.15 109.5 0.53 107.9 0.46 108.1 0.17 a a a a b c c c 12.5 C 113.5 0.23 114.6 0.20 113.4 0.32 111.9 0.37 111.4 0.29 111.2 0.18 109.9 0.36 112.5 0.32 a a a a a b b d ZMean values within the same column are not significantly differe nt from each other. Mean separation based on DuncanÂ’s Multiple Range Test using a P value < 0.05. y Standard error from the mean (n=5).

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40 Table 3-2. Weight loss of Beit Alpha cucu mbers stored at four different temp eratures; 5, 7.5, 10 and 12.5 C for 21 days. Days in Storage 3 6 9 12 15 18 21 Weight Loss (%) Temperature Treatment Mean s Means Means Means Means Means Means 5 C 0.6z 0.04y0.7 0.061.1 0.092.0 0.16 2.3 0.192.5 0.182.7 0.19 7.5 C 0.3 0.02 0.4 0.030.7 0.051.1 0.07 1.3 0.071.7 0.092.5 0.11 10 C 0.3 0.05 0.5 0.060.9 0.081.5 0.11 1.8 0.132.1 0.152.3 0.19 12.5 C 0.4 0.06 1.3 0.132.1 0.203.2 0.22 3.7 0.273.9 0.304.4 0.34 zMean values in the same column with different letters are si gnificantly different at a P-value <0.05 based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=10).

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41 ml CO2 kg-1 hr-1 0.0 2.0 4.0 6.0 8.0 10.0 12.0 2468101214 Days in Storage (d) 5.0 C 7.5 C 10.0 C 12.5 C 15.0 C 20.0 C Figure 3-1. Respiration rate (ml CO2 kg-1 hr-1) of Beit Alpha cucumbers stored for 21 d at six different temperatures; 5, 7.5, 10, 12.5, 15 and 20 C. Vertical bars represent the standard error from the mean.

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42 Initially, respiration rates were significan tly higher in fruit stored at higher temperatures (10 and 12.5 oC) but these differences became indistinguishable as the storage period progressed. The only exception wa s fruit stored at 5 C in which the respiration rate remained suppressed throughou t the 21-d storage pe riod. After 2 d in storage (initial measurement), the respiration rate was lowest in fr uit stored at 5 C, averaging 2.6 ml CO2/kg-1 hr-1. Fruit stored at 7.5 or 10 C had average respiration rates of 4.0 and 4.4 ml CO2/kg-1 hr-1, respectively, and were signifi cantly different from all the fruit stored at other temperatures but not be tween each other. The ne xt highest respiration rates were for fruit stored at 12.5 and 15 C both having a respiration rate of 6.0 ml CO2/kg-1 hr-1; these were significantly higher than those of fruit stored at lower temperatures but significantly lower th an that of fruit stored at 20 C. The highest respiration rate after 2 d in storage was observed on fruit stored at 20 C and averaged 9.5 ml CO2/kg-1 hr-1. Over time the respiration rate of this fruit (20 C) declined while that of fruit stored between 7.5 and 15 C te nded to increase until there were no significant differences in respiration rate of fruit stored between 7.5 and 20 C. The respiration rate of fruit stored between 5.0 and 15 C reached its peak after 7 d in storage, increasing between 30 and 130% while that of fruit stored at 20 C decreased slightly (3%). The highest increase in respirat ion rate over this 7-day period was observed in fruit stored at 10 C which increased 130%, from 3.9 to 8.9 ml CO2 kg-1 hr-1. Significant differences in respiration rate were less obvious after 7 d in storage. At this point there were no signi ficant differences in the respiration rate of fruit stored between 7.5 and 20 C. Although the respiration rate of fruit st ored at 5.0 C increased

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43 30% over the same period it was st ill significantly lower than the respiration rate of fruit stored at higher temperatures. The respiration rate of fruit stored between 5 and 15 C remained at similar levels after 14 d in storage when compared to the 7day peak but it was still higher than the initial respiration rate. On the other hand the respiration rate of fr uit stored at 20 C decreased from 9.2 ml to 7.8 ml CO2 kg-1 hr-1 over the same period. At this stage there were no significant differences in the respir ation rate of fruit stored between 7.5 and 20 C; which on average had a re spiration rate of 7.7 ml CO2 kg-1 hr-1 and ranged between 7.1 and 7.9 ml CO2 kg-1 hr-1. Fruit stored at 5.0 C had an average respiration rate of 4.6 ml CO2 kg-1 hr-1, significantly lower than all the othe r storage temperatures after the same storage period. Respiration rate was not m easured beyond 14 d in storage due to the presence of decay and other storage disorders. Ethylene Production Ethylene synthesis was assessed for the first 2 weeks in storage but ethylene levels were not detectable during th is evaluation period. This is in agreement with results obtained by Lima and Huber (unpublished). Firmness The storage temperature had no remarkab le effect on the mesocarp firmness of stored cucumbers. Measurements of meso carp firmness decreased between 22 and 28% after the first 3 d in storage with no si gnificant difference among the four storage temperatures. Initial mesocarp firmness was very different in both experiments and it behaved differently during storage. In Exp. I, the initial firmness was 9.1 N while in Exp. II the initial firmness was 18.8 N. Mesocarp fi rmness did not change significantly when

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44 the initial firmness was relative ly low, as in Exp. I, but de creased independent of storage temperature when it was high at harvest, as in Exp. II. Since moistu re content was only measured in the second experiment it is not possible to say if the high water content during storage influenced the loss of fi rmness seen in the second experiment. In Exp. II, initial firmness (12 hrs after ha rvest) was 18.8 N and after 3 d in storage, fruit softened to 13.6 to 14.7 N (with no signi ficant difference among the four storage temperatures) (Figure 3-2). After this peri od, the general trend wa s for mesocarp firmness values to remain stable. At the end of th e 21-day storage period, fr uit stored at 5, 7.5, 10 and 12.5 had similar firmness of 13.2, 13.8 a nd 14.1 N, respectively, with the exception of fruit stored at 7.5 C which had softened to 9.4 N. Electrolyte Leakage The rate of electrolyte leakage of Be it Alpha cucumbers was dependent on the storage temperature. Lower storage temperatures severely increased th e rate of electrolyte leakage with the effect becoming evident after the fruit had been in storage for 6 to 9 d. The electrolyte leakage (EL), expressed as a percent of total el ectrolyte leakage, was 15% at harvest and remained at similar leve ls for the first 6 d in storage, independent of the storage temperature (Figure 3-3). Elec trolyte leakage rates in creased after 9 d in storage to an average of 32.5% in fruit stored at 5 or 7.5 C, mo re than twice the rate seen at harvest. There was no significant differen ce between these two temperatures but both were significantly higher than the EL rate of fruit stored at either 10 or 12.5 C, which had EL rates of 19.1 and 11.6%, respectively.

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45 0.0 5.0 10.0 15.0 20.0 25.0 036912151821 Days in Storage 5.0 C 7.5 C 10.0 C 12.5 C Figure 3-2 Mesocarp firmness, expressed in Ne wtons, of Beit Alpha cucumbers stored for 21 d at 5, 7.5, 10 or 12.5 C. Vertical bars represent the standard error from the mean. Firmness (N)

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46 Electrolyte Leakage (%) 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 036912151821 Days in Storage (d) 5.0 C 7.5 C 10.0 C 12.5 C Figure 3-3. Electrolyte leakage, as a percent of total electrolyte leakage, of Beit Alpha cucumbers stored for 21 d at four diffe rent temperatures; 5, 7.5, 10 or 12.5 C. Vertical bars represent the standard error from the mean.

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47 For the remaining storage period the same pa ttern persisted in that the EL rates of fruit stored at the two lower temperatures (5 and 7.5 C) increased almost linearly and were significantly higher than those of fruit st ored at the two higher temperatures (10 and 12.5 C). Electrolyte leakage increased almost linearly (R2 = 0.93) throughout the 21-day storage period on fruit stored at 5 C and at the end of the 21-da y storage period it had increased to 79.5%, more than five times the initial rate. Fruit stored at 7.5 C also showed an increased EL rate as the storage period progressed and peaked after 15 d at 67.2%. Unlike the other two groups (5 and 7.5 C); the EL rates of fruit stored at either 10 or 12.5 C remained below 25% throughout th e storage period with no significant difference between these two temperatures. Moisture Content The storage temperature did not affect th e moisture content of stored Beit Alpha cucumbers. The moisture content of whole fruit at harvest was 95.5%. Moisture content measurements remained within a narrow range (96 – 98%) during the 21 d in storage with no significant differences among storage treatments (data not shown). Furthermore, moisture content obtained at different inte rvals throughout the 21-day storage period was not significantly different from the values ob tained at harvest. Similar moisture content levels were reported at harvest in commerc ial-size, fresh cucumbers of unspecified cultivars (Mattson, 1996 ; Sajnn, 2003).

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48 Compositional Analysis Total soluble solids content, although variable during th e storage period, tended to remain between 2 to 3 Brix (Table 3-3). A cl ear effect of the storage temperature on total titratable acidity could not be strictly defined. Total titratabl e acidity (TTA), expressed as percent of malic acid, tended to decrease slightly over time. Initial TTA was 0.15 % 12 hr after harvest and declined between 15 and 42 %, depending on the stor age temperature, at the end of the 21-day storage period (Table 3-3). As with TTA, a clear effect of the stor age temperature on the pH of stored Beit Alpha cucumbers could not be well defined. The pH values of stored fruit tended to increase over time independent of the storage temperature. The sugar acid ratio, alth ough highly variable during st orage, ended the 21-day storage period with relatively similar values to those observed at ha rvest. Initial sugar acid ratio, 12 hours after harvest, was 20.2 and increased to between 20 and 25 after 21 d in storage. Differences among storage temp eratures, although observed at different intervals during the storage period were not systematic to accurately conclude that storage temperature had a significant effect on the sugar-acid ratio of stored cucumbers. Table 3-3. Compositional analysis of Beit Alpha cucumbers stored at four temperatures (5, 7.5, 10 or 12.5 1 C) for 21 days. Treatment SSC(Brix) pH TTA (% Malic Acid) Sugar/Acid Ratio Mean s Mean s Mean s Mean s Initial 2.59 0.33 0.150.01 20.20.71 After 21 d 5 C 2.24 0.266.260.050.10.01 21.50.55 7.5 C 2.53 0.125.750.060.130.01 201.18 10 C 2.33 0.345.910.050.110.01 20.40.82 12.5 C 2.23 0.36.660.030.090.01 251.4

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49 Discussion Appearance Short-term storage of harvested commodities, mainly used to preserve quality until it gets to the final consumer, is a market ing strategy that is relied upon to satisfy consumer demand on a daily basis. One of the principles of storage, as an efficient marketing strategy, is to maximize the lengt h of storage or marketable life while minimizing quality losses. The concept of quality is interpreted differently by the different handlers in the food distribution network (S hewfelt, 1998). Although the definition of quality for the end consumer can be a complex of attributes, such as sensory characteristics, safety, nutrition and lately functional properties, th e two parameters that are most influential in the initial purchase are appearan ce and freshness (Kays, 1998; Bruhn, 2002). With new crops such as Beit Alpha cucumbers, inducing the initial purchase is one of the first steps in acco mplishing the overall goal of inducing repeat purchases and establishing a market presence. In these experiments the maximum marketab le life was obtained when the fruit was stored at 10 C. At the two lo west temperatures (5 and 7.5 C), chilling injury became the deciding factor in limiting fruit quality while on fruit stored at 12.5 C it was the presence of firm protrusions. Sargent et al., (2002) reported the developmen t of these bumps on Beit Alpha cucumbers after 14 d in storage at 10 and 12.5 oC and speculated that they may have been caused by the high internal turgor pressure exer ted on the senescing epidermal tissue. A similar storage disorder was reported by Kannelis et al., (1986) on greenhouse-grown fresh-market cucumbers (‘Deliva’). Altho ugh the bumps were noticeable they did not affect the ed ible quality of the stored fruit.

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50 Color Changes in peel color are a natural development in horticultural commodities and are part of the ripening and the natural senescing process (Funamoto et al., 2002); during this process carotenoids (and other pigments such as ant hocyanins) replace chlorophylls (Hobson, 1994) causing a degreenin g of the fruit. Changes in pigmentation can be accelerated by stress, such as ethylene exposur e, but can occur naturally during storage. Unlike other fruits, such as tomato and bana nas that need to undergo ripening to reach commercial maturity, this process is detrimen tal to fruit quality in cucumber since it reach commercial maturity at a physiologically immature stage. The rate of chlorophyll metabolism, or days to incipient color, has been associated with the keeping quality of cucumbers (Schouten et al., 2002) and other commodities such as broccoli (Yamasaki et al., 1997; Funamoto et al., 2002; Costa et al., In press). Weight Loss Loss of turgidity or shriveling, as a result of water loss, decreases the freshness of a horticultural commodity making it less accep table to consumers (Burdon and Clark, 2001; Gmez et al., In press). Reducing weight loss is critical in maintaining consumer acceptability of fruits and vegetables since ev en minimal losses of 1 to 2% are considered sufficient to start decreasing the appe al of a commodity (Hobson, 1994). Stem-end shriveling, as a result of water loss, became evident between 15 to 18 d of Beit Alpha cucumbers stored at 10 C, negatively affecti ng the appearance. At this stage the weight loss was less than 3%, well below the marketab ility threshold of 7% (Kang et al., 2001) set for traditional cucumber varieties; an indication perhaps that Beit Alpha cucumbers have a lower weight loss threshold than that recommended for traditional cucumber.

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51 Respiration The respiration rate is inversely related to the marketable life of fruits (Knowles, 2001; Kader, 2002) and it can vary depending on the storage temperature (Suslow et al., 2002), the maturity stage of the fruit and plant at harvest, the days in storage, as well as the nutrient regime (Knowles et al., 2001). Cucumber respira tion has been reported to be between 10 to 20 mg CO2 kg-1 hr-1 (Kader, 2002); between 3 to 11 mol CO2 kg-1 min-1 for the cultivar ‘Carmen’ and between 12 to 30 mol CO2 kg-1 min-1 for the cultivar ‘Corona’ depending on the length of storage at 23 C (Knowles et al., 2002); between 5 and 28 mg CO2 kg-1 hr-1 for the cultivar ‘Deliva’ when stored in modified atmosphere at 12.5 C (Kanellis et al., 1988) ; between 10.5 to 35.6 mg CO2 kg-1 hr-1, at harvest, and between 2.7 and 15 mg CO2 kg-1 hr-1 (Watada et al., 1996). These results show that respiration rates ar e significantly higher when the fruit is stored at higher temperatures but these differences become indistinguishabl e after 2 to 3 weeks in storage, since respiration rate tend ed to increase in fruit stored at lower temperatures. The only exception was fruit stored at 5 C, which tended to have relatively suppressed respiration rates throughout the 21-day storag e period. This temperature, however, is not recommended for cucumber st orage due to the chilling and marketable life limiting effect it has on cucumber fruit. Ethylene Production Ethylene production by fresh-market cucumb ers has been previously reported (Cantwell, 2002). Kanellis et al. (1977) reported that greenhouse-grown cucumbers (‘Deliva’) produced be tween 5 to 15 nl kg-1 hr-1 when stored at 12.5 C.

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52 Pickling cultivars also pr oduce ethylene; ‘Explorer’, a pickling cultivar, was reported to produce ethylene when stored at 30 C (Poenicke et al., 1977) and Saltveit and McFeeters (1980) also reported that, at harvest, the pickli ng cultivar ‘Chipper’ produced ethylene at a rate between 32 to 279 nl kg-1 hr-1. Based on the method previously described, production of ethylene by Beit Al pha cucumbers was not detectable. These results are comparable to those of Lima and Huber (unpublished). Firmness Initial mesocarp firmness was very differe nt in both experiments and it behaved differently during storage. In Exp. I, the initial firmness was 9.02 N while in Exp. II the initial firmness was 18.77 N. Mesocarp firmne ss did not change significantly when the initial firmness was relatively low, as in Exp. I, but decreased independent of storage temperature when it was high at harvest, as in Exp. II. Since moistu re content was only measured in the second experiment it is not possible to say if the high water content during storage influenced the loss of fi rmness seen in the second experiment. Firmness is one of the components of text ure which is a complex sensory attribute that also includes crispiness and juicine ss (Konopacka and Plocharski, 2003) and is critical in determining the acceptability of horticultural commodities (Abbott and Harker, 2004). Untrained panelists determined that cucu mbers in one experiment stored at 10 C for 15 days had acceptable texture, although the peel was described as slightly tough or leathery while the mesocarp tasted slightly watery. These observations were empirical and are not in any way conclusive in determin ing the effect of storage temperature on the texture of fresh cucumbers.

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53 Electrolyte Leakage Electrolyte leakage can be used to determine changes in membrane permeability caused by environmental stress (Whitlow et al., 1991; Knowles et al., 2001). In cucumbers, higher rates of ion leakage are a ssociated with cell damage due to chilling injury (Hakim et al., 1999; Kang et al., 2001; Saltveit, 2002) as well as other types of stress. Although fruit exposed to chilling temperatures exhibit symptoms such as pitting, membrane alteration is the primary effect (DeEll et al., 2000; Bala ndrn-Quintana et al., 2003). Changes in membrane permeability, such as damage from the exposure to chilling temperatures, accumulate over time and do not occur immediately after exposure to chilling temperatures (Saltveit, 2002). DeEll (2000) reports that irreversible membrane injury due to chilling injury requires at least 7 d at 4.0 C (chilling temperature) in cucumber. The results presented here are in agreement with those of DeEll (2000) since significant changes in membrane permeability were not evident until between 6 and 9 d exposure to chilling temperatures of 7.5 C or lower. Changes in electrolyte leakage rates was the first parameter to reflect significant differences, based on the storage temperature, an indication that changes in quality of the fruit are first reflected in changes in membrane permeability. Compositional Analysis Malic acid is the most abundant acid in commercial-sized pickling cucumbers (McFeeters et al., 1982) as we ll as in slicing cucumbers (Mattsson, 1996). The TTA of stored cucumbers has been shown to vary in storage in response to different nutrition regimes (Altunlu and Gl, 1999) while malic acid has also been reported to remain stable or decline slightly in kiwi fruit, dependi ng on the growing region (M arsh et al., 2004). A

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54 decrease in malic acid could be explained by it s utilization in respir ation. Malate appears to be the major organic acid used as re spiratory substrate (Tucker, 1993). Mattsson (1996) also reports a decline in malic acid of cucumber fruit during storage; from 4 mg/g of fresh weight at harvest to 3.2 mg/g of fresh weight after 21 d storage at 13.5 C. Statistical differences were obs erved at different intervals in the storage period but they were not systematic and no clear conclusions could be made in relation to the storage temperature. The pH of cucumbers has been reported to behave differently during storage. The pH of fresh-market cucumbers has been re ported to increase dur ing storage (Srilaong, 2003). However, Altunlu and Gl (1999) also reported a decrease in the pH of fresh cucumbers (‘Alara’) stored for 21 d at 13 C and 85 to 90% RH; from 6.35 to 5.77. Increases in the pH of other commodities during storage have al so been reported; Perkins-Veazie (2003) reports a slight increas e in the pH of freshcut watermelon as well as in celery (Gomez and Artez, In press). Th e pH of cucumber fruit is important because it influences enzyme activity responsible fo r cucumber flavor and aroma; lower pH causes the enzyme system responsible for cucu mber flavor and aroma to become unstable (Palma-Harris et al., 2002). Although some differences in soluble solids were observed at diffe rent intervals in the storage period, these differen ces were not systematic ther efore a clear effect of the storage temperature on the soluble solid co ntent of the stored fruit could not be established. The values presented here are similar to t hose reported at harvest by Sajnn et al. (2003), who reported total soluble solids cont ent of 2.3 Brix on fresh cucumbers of

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55 unspecified cultivar. These values, however, ar e slightly lower than those reported earlier by Altunlu and Gl (1999) who report total soluble solids between 3.32 and 4.04 for the greenhouse-grown cultivar ‘Alara’. Conclusions It can be concluded that the optimum storage temperature for Beit Alpha cucumbers is 10 C at ~ 90% RH. Storage under these conditions yielded the maximum marketable life of 15 to 18 d based on the parameters assessed. It is noteworthy to indicate that quality should be assessed as a complex of all the different parameters (appearance, color, weight loss and firmness) that affect quality and should reflect the nature of the commodity as well as the intended market use

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56 CHAPTER 4 RESPONSE OF BEIT ALPHA CUCU MBERS TO EXOGENOUS ETHYLENE DURING STORAGE Introduction Appearance is perhaps one of the most important factors in making an initial purchasing decision for many commodities (Bruhn, 2002) and is a combination of parameters such as color, size, shape and th e freedom of defects or foreign matter on the surface of the commodity. Greenhouse-grown cucumbers are grouped into four different grades based largely on general appearance (col or, shape, size, freshness, and freedom of decay, diseases and injuries). These grad e standards apply only to greenhouse-grown European-type cucumbers (English or Dutch-ty pe), which are the traditional types grown in greenhouses in the U.S (United Stat es Standards for Grades of Greenhouse Cucumbers, 1997). Since Beit Alpha cucu mbers are not widely commercialized commodity there are no federal grade standards yet. However, injury can be present in the internal tissue before it appears on the external appearance of a commodity (DeEll et al., 2000; Balandrn-Quintana et al., 2003) but given the destructive natu re of the techniques availabl e to assess the condition of internal tissue, quality assessments usually re ly on the evaluation of external appearance. Given the substantial role that appearance plays in purchasing decision as well as in determining the grade standards, it is theref ore important to evalua te the factors that could negatively affect the appearance of a commodity and render it unmarketable, especially since the desired characteristic will vary depending on the commodity.

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57 Depending on the commodity ethylene can eith er have beneficial or deleterious effects (Saltveit, 1998). Ethylene promot es the breakdown of chlorophyll and tissue softening and is therefore essential for ripeni ng of climacteric fruit such as bananas and tomatoes but unnecessary and detrimental in commodities such as cucumbers. The acceleration of senescence, the enhancing of fruit softening and the promotion of chlorophyll loss (yellowing) ar e among the deleterious effects of ethylene on cucumbers (Poenicke et al., 1977; Saltve it, 1998; Saltveit an d McFeeters, 1980; Lelivre, 1997). The undesirable impact of ethylene on pulp firmne ss is well-established in many commodities including apples (Johnston et al., 2002), strawberries and pe ars (Bower et al., 2003), and watermelons (Karakurt et al., 2002). The exte nt of the effect that ethylene has on parameters such as appearance, color, texture and decay impacts consumer acceptability of a commodity. Cucumbers are a non-climacteric fruit (Mat tsson, 1996; Wehner et al., 2000) and are harvested at a physiologica lly immature stage. Several types are reported to produce very little ethylene and are highly sens itive to the exposure of exogenous ethylene (Kader, 2002). Cucumbers (Cucumis sativus L.), of an unspecified cultivar, have been reported to produce between 0.1 – 1.0 l kg-1 hr-1 of ethylene at 20 C (Kader, 2002) while the parthenocarpic cultivar ‘Deliva’ is reported to produce between 5 and 15 nl kg-1 hr-1 at 12.5 C (Kanellis et al ., 1988). Other cultivars such as ‘Explorer’, a pickling cultivar, have also been reported to produce et hylene when stored at 30 C (Poenicke et al., 1977). Saltveit and McFeeters (1980) also report the producti on of ethylene by the pickling cultivar ‘Chipper’, which produced between 32 –280 nl kg-1 hr-1 when stored overnight at room temperature. The amount of endogenous ethylene produced by

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58 cucumbers varies and is affected by the fruit size, cultivar, storage temperature (Poenicke et al., 1977), fruit age (Kanelli s et al., 1986) and in many plant tissues can be induced as a response to environmental stresses (Yang and Oetiker, 1998). In previous storage trials, it was not possible to detect th e production of ethylene in Beit Alpha-cucumbers stored for 9 d at 10 C, the recommende d storage temperature. The objectives of these studies were to determine threshold levels of exogenously applied ethylene to Beit Alpha cucumbers and European cucumbers based on the quality and shelf life parameters. Materials and Methods Experiment I Plant material Cucumbers were obtained as described in Chapter 3. Cucumbers were then surface sanitized by immersion for 90 sec in a 150ppm free-chlorine solution and air-dried. Sanitized cucumbers were placed in rigid, vented, hinged 2-L polystyrene containers, with 10 cucumbers per clamshell. Beit Alpha cucumbers are currently marketed in film over-wrapped trays; however, rigid clamshells provide a layer of protection from injury due to transportation, handling and/or displayi ng while still allowing a clear view of the product. Clamshells were subsequently placed in sealed 200-L metal gassing chambers at 10 C 1.0 for storage under constant flow. Gassing chambers were connected to a mixing board using 0.6-cm polyethylene tube. The gas mixture (ethylene and compressed air) was humidified (85 to 90% RH) by bubb ling it through a 2-L glass jar with water then introduced into the ga ssing chambers. Cucumbers were continuously exposed to ethylene at four different concentra tions; 0 (control), 1, 5 and 10 ppm ( 5%). Total gas

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59 flow through the gassing chamber was mon itored using a digital ADM 1000 flow meter (J & W Scientific, Folsom, CA) and adjusted to ensure the internal atmosphere remained less than 2% CO2. To ensure consistency of ethyle ne concentrations in the gassing chambers headspace samples were collected three times a day and analyzed using a Tracor 540 gas chromatograph (Tremetrics An alytical Division, Au stin, TX), equipped with a photoionization detector, an Alumina F1 column with a mesh size of 80/100. The following quality parameters were measured ever y 3 d for 12 d to assess the quality of the stored fruit. Appearance Appearance of stored cucumbers was rate d using a subjective scale (Appendix A) from 1 to 9, with 9 representing field-fres h fruit, 3 representing the marketability threshold and 1 representing ined ible fruit. Fruit with dark green external color and free of defects and decay received higher rati ngs while fruit that exhibited yellowing shriveling and/or decay received lower ratings. Color evaluation Both external and intern al color was assessed using a CR-400 Chroma Meter (Konica Minolta Sensing Co., Japa n). External color readings were taken on an equatorial spot predetermined and marked before placi ng the fruit in storage. Color measurements were taken every three days using the CIE XYZ color space and converted to L* C H values (Lightness intensity, Chroma and Hue) using the CR-400 Utility software (Konica Minolta Sensing Co., Japan). Two measuremen ts (on opposite sides of the fruit) were taken and averaged to obtain a final value fo r each fruit. Internal color was measured on the sliced mesocarp tissue, as with external color, two measurements were taken per slice

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60 (n=10) and averaged to obtain a final valu e. Each slice was obtained from a different cucumber. Chroma meter was white calibrate d using a CR-A43 white calibration plate (Konica Minolta Photo Imaging USA Inc., Ma hwah, NJ) using the following parameters; Illuminant C, L = 97.08, C = 1.84 and h = 90.76 (Y=92.6, X = 0.3135 and y = 0.3196). Weight loss As described in Chapter 3. Respiration The rate of respiration of the stored fruit was measured on fruit stored in 1-L sealable containers (Tupperware, Orlando). Th ree cucumbers were weighed and placed in each of four respiration chambers per tr eatment. The respiration chambers were subsequently placed in the gassing chambers alongside the other fruit. Respiration chambers were retrieved and sealed for two hours prior to every measurement. Headspace samples (2/container) were withdr awn every 3 d using a 1-ml disposable hypodermic syringe and analyzed for carbon di oxide content using a Gow Mac, series 580 gas chromatograph (Gow Mac Instrument s Co., Bridgewater, NJ) equipped with a thermal conductivity detect or. Respiration rates we re expressed as ml CO2 kg-1 hr-1. Mesocarp firmness As described in Chapter 3. Electrolyte leakage As described in Exp. II, Chapter 3.

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61 Data analysis The experiment was designed as a complete ly randomized experiment and the data collected were analyzed using the GLM pro cedure (SAS Institute Inc., Cary, NC). All data presented were subject to a Duncan’s Mu ltiple Range Test usi ng a P-value of <0.05. Experiment II Plant material Beit Alpha cucumbers were obtained as described above in Exp. I. European cucumbers (‘Logica’) were also grown under commercial greenhouse conditions in soilless media (perlite), using la y-flat bag culture, in Ft. Pierce, Florida (K & M of the Treasure Coast Inc.). European cucumbers were manually harvested in the morning (May 14, 2004), wrapped unwashed a nd packed in two layers in unwaxed cartons (12, US No. 1 cucumb ers per carton). Cucumbers were wrapped mechanically with low density, micro perforated, 17-m icron thick polyethylene film (Global Horticulture, Inc., Ontario, Canada) usi ng a conveyor shrink-wrap machine equipped with a heat tunnel. Each car ton contained. The cucumbers we re transported the same day to the Postharvest Laboratory at the Horticultural Sciences Department at the University of Florida in Gainesville and stored for 2 d at 10 C in their original plastic packaging before setting up the experiment (May 15, 2004) to coordinate with the delivery of the Beit Alpha cucumbers. Both European and Beit Alpha cucumbers were harvested on the same day at their respective commercial ma turity. For this expe riment, half of the European cucumbers were removed from their pl astic wrap while the other half was left wrapped as would normally be done under co mmercial conditions. Unlike Beit Alpha

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62 cucumbers, European cucumbers were not surf aced-sanitized with chlorinated water prior to storage. The cucumbers (both types) were ethylene-treated as in Exp. I. Appearance Appearance of cucumber types was rated as in Exp. I. Color evaluation As described above in Exp. I. Weight loss As described above in Exp. I. Mesocarp firmness As described above in Exp. I. Electrolyte leakage Electrolyte leakage on both cucumber type s was measured as described in Exp. I. Data analysis Experimental design and data analys is was done as described in Exp. I. Experiment III Plant material As described above in Exp. II. Appearance As described above in Exp. II.

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63 Color evaluation Both external and intern al color was assessed as described in Exp. II. Weight loss Weight loss was determined as described in Exp. II. Mesocarp firmness Fruit firmness was assessed as described in Exp. II. Electrolyte leakage Electrolyte leakage was assesse d as described in Exp. II. Data analysis Experimental design and data analysis was done as described in Exp. I and II. Results Experiment I Appearance The exposure to external ethylene had a nega tive effect on the ex ternal appearance of stored cucumbers. Appearance remained practically unchanged for the first 6 d of ethylene exposure (Figure 4-1). At this st age all four treatments had very good, dark green color with no visible def ects such as shriveling, water soaking or microbial rot and all four treatments scored 8 on a scale from 1 to 9. However, the external appearance of fruit exposed to ethylene deteriorated af ter transfer to ethylene-free storage at 20 C for 24 hours. After the transfer period, ethylen e-treated fruit (1, 5 and 10 ppm) had an average external appearance rating of 5 while the control fruit rated 8.

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64 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Threshold Figure 4-1. Appearance rating of Beit Alpha cucu mbers exposed to four concentrations of exogenous ethylene (0, 1, 5 or 10 ppm) and stored at 10 C for 12 d. Fruit exposed to 5 and 10 ppm of ethylene ha d identical results Vertical bars represent the standard error from th e mean, were not shown standard error falls within the marker size. Appearance Rating

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65 Ethylene-treated fruit showed yellowi ng and stem-end shriveling in varying degrees while the control fruit retained its pr e-transfer appearance. External appearance ratings continued to decline as the storag e period progressed w ith higher decreases observed in fruit exposed to higher concentratio ns of ethylene. Signifi cant differences in external appearance were observed after 9 d of ethylene exposure At this stage the ethylene treated fruit had signi ficantly lower appearance rating than the control fruit. Fruit continuously exposed to either 5 or 10 ppm of ethylene reached the marketability threshold, an appearance rating of 3, after 9 d in storage with no di fference between these two treatments. The appearance rating of fruit exposed to 5 or 10 ppm was negatively affected by yellowing of the peel and st em-end shriveling. The appearance rating declined further when the fruit was transfe rred to an ethylene-free storage environment for 24 hours at 20 C. After the 24-hr transfer pe riod fruit exposed to 0, 1, 5 or 10 ppm ethylene had an average appearance rating of 6, 3, 3, and 2.5, respectively. The ethylene-treated fruit exhibited yellowing, stem-end shriveling and ov erall softness when touched. The control fruit had a lower post transfer rating becau se it showed slight yellowing, which was absent before it was transferred, but was not as severe as the yellowing observed in ethylene-treated fruit. Fruit exposed to 1 ppm reached the appearan ce threshold rating of 3 after 12 d of continuous ethylene exposure. The loss of app earance was due to yellowing of the peel and the presence of stem-end shriveling (F igure 4-2). This fruit, however, became unmarketable prior to 12 d of ethylene exposure due to ex cessive pulp softening, which was reflected in the low firmness values a nd high rates of electrolyte leakage.

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66 Figure 4-2. Appearance of Beit Alpha cucumber s exposed to four concentrations of exogenous ethylene for 12 d at 10 C. A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10 ppm. Arrows indicate fungal growth (B and C) and reddish-brown spots on the peel (D).

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67 Fruit that had not been exposed to ethylene (control) scored an appearance rating of 7 after the same exposure period, significantl y higher than the ethyl ene-treated fruit. All the treatments were kept for obser vation for the entire duration of the experiment, even if they had already become unmarketable prior to the end of the 12-day storage period. Microbial rot was first observe d on fruit that had been exposed to 10 ppm of ethylene for 9 d and then transferred to 20 C for 24 hours in an ethylene-free environment, while the control group (0 ppm ) and fruit exposed to 1 or 5 ppm did not show any development of microbial ro t after the same transfer period. Microbial infection was observed in all th e ethylene-treated fruit, but not on the control fruit, after 12 d of et hylene exposure and at this point all three ethylene-treated groups (1, 5 and 10 ppm) experienced a 90% infection rate, while the control group remained unaffected. The severity of the inf ection was not assessed; therefore it is not possible to assert if fruit exposed to highe r concentrations of et hylene developed more severe rates of infection as indicated by the surface area affected. Any level of pathogen infection would have made the fruit unmarket able so the severity of the infection in relation to the ethylene concentration in th e environment is an aspect that may be important from a physiological standpoint. Besides the storage disorders such as tissu e softening and decay, fruit exposed to 5 or 10 ppm ethylene also devel oped reddish-brown spots on the peel after 12 d in storage (Figure 4-3). The spots were limited to the surface of the fruit, did not extend to the mesocarp nor were there any visible exudates. The development of these spots did not affect the marketable life of the product since they develope d after the fruit had become unmarketable due to the effect of ethylene on ot her parameters such as firmness or color.

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68 Figure 4-3. Ethylene injury symptoms as re ddish-brown spots (arrows) on Beit Alpha cucumbers exposed to 10 ppm of exogenous ethylene for 12 d.

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69 Color Exposure of cucumbers to external ethylen e caused yellowing of the peel at an accelerated rate but varying the ethylene con centration in the storage atmosphere had no effect on the rate of color loss. Hue angl e values decreased during storage on fruit continuously exposed to ethylen e but not in the control group (Figure 4-4). At harvest, external hue angle values av eraged 124 and decreased to 121 in the ethylene-treated fruit after 12 d ethylene expos ure, while the control group ha d an average hue angle of 123.7 at the end of the 12-day exposure period. L* values (lightness intensity) remained relatively unchanged during the storage peri od (data not shown) wh ile chroma values increased slightly from 23.2 at harv est to between 26 a nd 29.6, depending on the temperature, but with no significant differe nces among storage treatments (data not shown). Exposure to exogenous ethylene had no significant impact on the mesocarp color as measured by the hue angle. Although there was a 2 to 3% decrease in internal hue angle values after 12 d ethylene exposure there were no si gnificant differences among treatments. Although statistical differences in internal hue angle measurements were not evident, slight yellowing of internal tissue was detectable upon visu al inspection in fruit exposed to 10 ppm ethylene for 12 d. Unlike the external L*, internal L* values decreased during storage from 71.2 at harv est to between 60.1 and 64.8 but was not significantly affected by the ethylene treatmen t. Chroma values decreased slightly from 33.2 at harvest to between 26.9 and 31.8 but with no significant differences among ethylene treatments.

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70 117.0 118.0 119.0 120.0 121.0 122.0 123.0 124.0 125.0 036912 Duration of Ethylene Exposure (d) 0 PPM 1 PPM 5 PPM 10 PPM Figure 4-4. Changes in the external color, as measured by the hue angle, of Beit Alpha cucumbers exposed to four concentrati ons of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Ve rtical bars represent the standard error from the mean. Hue Angle ()

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71 Weight loss Exposure to continuous ethylen e had no effect on the weight loss of cucumber fruit (Table 4-1). Weight loss incr eased from an average of 0.86% at 3 d in storage to an average of 1.02% after 12 d in storage at 10 C without any differences among treatments. However, differences in weight loss were observed when the fruit was transferred to an ethylene-free environment at 20 C and 90% RH for 24 hours (Table 4-2). Weight loss increased when fruit held for 9 d at 10 C in ethylene was transferred to 20 C for 1 d. After this transfer period, the weight loss ranged from 3.2 to 4.7%, with no differences among treatments. This increment in weight loss was due to the high-temperature effect (20 C) and not to the ethyl ene exposure since there were no significant differences among the four treatments. Table 4-1. Weight loss of Beit Alpha cucumb ers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 days. Duration of Ethylene Exposure (d) 3 6 9 12 Weight Loss (%) Ethylene Treatment Mean s Mean s Mean s Mean s 0 ppm 0.5 a 0.05 0.8 a 0.03 0.9 a 0.06 0.9 a 0.06 1 ppm 0.7 a 0.03 0.7 a 0.09 0.9 a 0.04 1.2 a 0.08 5 ppm 0.7 a 0.12 0.9 a 0.03 0.8 a 0.09 1.1 a 0.07 10 ppm 0.6 a 0.03 0.7 a 0.10 0.9 a 0.06 1.0 a 0.13 z Mean values in the same column with differe nt letters are significantly different at a Pvalue < 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=10).

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72 Table 4-2. Weight loss of Beit Alpha cucumb ers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) after transfer to 20 C for 1 day. Duration of Ethylene Exposure (d) 6 days at 10 C 9 days at 10 C + 1 day at 20 C + 1 day at 20 C Weight Loss (%) Ethylene Treatment Mean s Mean s 0 ppm 1.1 a 0.3 3.7 a 0.06 1 ppm 1.5 a 1.6 4.7 a 0.08 5 ppm 1.4 a 0.7 3.9 a 0.07 10 ppm 3.2 b 1.1 3.2 a 0.13 z Mean values in the same column with differe nt letters are significantly different at a Pvalue < 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=10). Respiration Fruit exposed to higher concentrations of ethylene had higher resp iration rates than the control fruit for the first 6 d in storage (Table 4-3). At 3 d in storage, fruit exposed to either 5 or 10 ppm had an aver age respiration rate of 10.9 ml kg-1 hr-1, with no difference between these two treatments but significan tly higher than the control group. Fruit exposed to 1 ppm had an intermediate respiration rate (9.3 ml kg-1 hr-1); significantly lower than either 5 or 10 ppm but signifi cantly higher than the c ontrol group (5.8 ml kg-1 hr-1). The respiration rate of stor ed fruit increased between 25 and 60% between the third and sixth day of ethylene exposure, with th e highest increase observed in the control group and fruit exposed to 1 ppm. At 6 d in st orage the ethylene-treated fruit (1, 5 and 10

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73 ppm) respired at an average rate of 13.9 ml kg-1 hr-1, with no difference among these three groups. The ethylene-treated fruit had a higher respiration ra te than the control group which had a respiration rate of 8.3 ml kg-1 hr-1 after the same storage period. Respiration rate continued to increase in the control group as the exposure period progressed but not in the ethylen e-treated fruit; at 9 d in storage the control group had an average respiration rate of 14.4 ml kg-1 hr-1, significantly higher or equal to some of the ethylene-treated fruit. Signs of decay were not visible at 9 d on any of the four treatments. Respiration was not measured beyond 9 d in storage due to the onset of bacterial and fungal infections on the ethylene-treated fruit. Table 4-3. Respiration rates of Beit Alpha cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C). Duration of Ethylene Exposure (d) 3 6 9 Respiration (ml CO2 kg-1 hr-1) Ethylene Treatment Mean s Mean s Mean s 0 ppm 5.8 az 0.04y 8.3 a 0.20 14.3 a 0.44 1 ppm 9.3 b 0.52 14.0 b 0.51 11.8 b 0.74 5 ppm 11.2 c 0.37 14.3 b 0.89 14.3 a 0.60 10 ppm 10.7 c 0.56 13.5 b 0.74 10.2 c 0.41 z Mean values in the same column with differe nt letters are significantly different at a Pvalue < 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=8). Mesocarp firmness Beit Alpha cucumbers showed pronounced so ftening of the mesocarp tissue during storage as a consequence of ethylene exposure. After 6 d of storage, severe softening of

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74 the mesocarp (55% reduction of the initial firmness) was evident in fruit continuously exposed to 10 ppm ethylene, (Figure 4-5). Even though visual appearance and external color remained acceptable in these fruit, they were unmarketable due to excessive softening. After 6 d fruit exposed to either 0, 1 or 5 ppm ethylene remained marketable and had acceptable firmness, co lor, and visual appearance. Mesocarp firmness continued to decline after this period with more pronounced softening observed in ethylene -treated fruit. After 9 d et hylene exposure (5 ppm), fruit lost 81% of the initial firmness and was no longer marketable even though external appearance and color remained acceptable. Cucumbers exposed to 1 ppm ethylene and the control group still remained marketable after the same exposure period, with no significant differences in firmness between these two treatments. Mesocarp firmness declined further as the duration of the ethylene exposure increased. After 12 d of ethylene exposure, fr uit exposed to 1 ppm of ethylene had lost 63% of the initial firmness and was no longer marketable due to excessive pulp softening and microbial decay. On the other hand, the cont rol fruit remained marketable after this period and was free of microbial rot, had ve ry good external app earance, acceptable firmness (65% of initial firmness) and acceptable external color. Electrolyte leakage Exposure to external ethylene caused elec trolyte leakage (EL) rates of stored cucumber fruit to increase Electrolyte le akage rates remained relatively unchanged the first 3 d but increased after 6 d of continuous ethylene exposure, with higher increases observed in fruit exposed to higher con centrations of ethylene (Figure 4-6).

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75 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-5. Mesocarp firmness (Newtons) of Beit Alpha cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent th e standard error from the mean. Mesocarp Firmness (N)

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76 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 036912 Duration of Ethylene Exposure (d) 0 PPM 1 PPM 5 PPM 10 PPM Figure 4-6. Rate of electrolyte leakage (%) of Beit Alpha cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars repr esent the standard error from the mean, were not shown standard error falls within the marker size. Electrolyte Leakage (%)

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77 Initial EL rates (12 hr after harvest) were 9.5% and increased to 15.4, 21.5, 22.6 and 26.1% on fruit exposed to 0, 1, 5 or 10 ppm ethylene, respectively, for 6 d. These rates were significantly higher in ethylene-treated fruit th an in the control group. Fruit exposed to 5 or 10 ppm had significantly high er EL rates than the control group but not significantly different between each other. Fr uit exposed to 1 ppm had an EL rate of 21.5%, significantly different than either th e control group or fruit exposed to 10 ppm ethylene. Although the EL rate of the control group al so increased over time, it was not as remarkable as the increase observed in ethylene -treated fruit. After 9 d ethylene exposure, fruit exposed to 5 or 10 ppm had an EL ra te of 44.8 and 46.1%, respectively, and was significantly higher than the EL rate of 0 and 1 ppm. Fruit exposed to 1 ppm had an EL rate of 26.4%, significantly different from the other three treatments. The control group had, significantly, the lowest EL rate of all four treatments; 12.4%. At the end of the 12-day storage period, th e EL rates of the control fruit reached 16%, almost twice the rate at harvest yet significantly lower than the ethylene-treated fruit. EL in fruit exposed to 1 ppm increased five-fold after 12 d in storage to 48% while fruit exposed to 5 or 10 ppm increased sevenfold to 67% after the same period, with no difference between these two treatments. Experiment II Appearance of Beit Alpha cucumbers As in Exp. I, the external appearance of Beit Alpha cucumbers was negatively affected by the continuous exposure to exogenous ethylene. Beit Alpha cucumbers

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78 retained similar appearance up to the 6th day of continuous ethyl ene gassing, independent of the ethylene concentration in the environmen t (Figure 4-7). At this stage all groups had very good, dark green color with no visible de fects such as shriveling, water soaking or microbial rot; fruit exposed to 1, 5 or 10 ppm scored a respectable 7 on a scale from 1 to 9 (9 representing field-fresh fruit and 1 repr esenting inedible fruit) while the control group scored an average of 7.8. As in previous studies, the external appearance of fruit exposed to ethylene deteriorated after being transferred to ethylene-free storage at 20 C for 24 hours while the control fr uit retained its pre-transfer visual appearance (data not shown). After the transfer pe riod, fruit exposed to 1, 5 or 10 ppm showed moderate stemend shriveling and irregular yellowing that gave the fruit a blotchy appearance thus negatively affecting the external appearance in ethylene-treated fruit. Ethylene-treated fruit rated 5.1, 4.8 and 3.6 (1, 5 and 10 ppm, respectively) while th e control group rated an average of 7.0 after the transfer period. Differences in external appearances were evident on fruit continuously exposed to ethylene for 9 d, at which point 90% of th e fruit exposed to 10 ppm of exogenous ethylene rated below the appearance marketabil ity threshold. The major defects of this group were yellowing, decay and stem-end shriveling. Fruit exposed to 5 or 1 ppm remained a bove the marketability threshold at this point, scoring 6.7 and 5.0 respectively while th e control rated an av erage of 7.2. As in previous experiments, the external appear ance declined rapidly after the fruit was transferred to ethylene-free storage at 20 C for 24 hours. After this transfer period, the ethylene-treated fruit (all thr ee groups) had an external app earance that rated at 1.0 (data not shown).

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79 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Threshold Figure 4-7. Appearance rating of Beit Alpha cucu mbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) a nd stored at 10 C for 12 d. Vertical bars represent the standard error fro m the mean, were not shown standard error falls within the marker size. Appearance Rating

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80 All the fruit exposed to 10 ppm of ethylen e showed signs of decay while only 60% and 40% of the fruit exposed to 5 and 1 pp m, respectively, showed signs of decay. The control fruit had good appearance after the tr ansfer period, showing no signs of decay or yellowing. Quality of control fru it was only affected by a hardening of the fruit (the fruit did not yield when flexed) and a slight leathe ry appearance of the peel. Quality continued to deteriorate as the exposure period increased. Fruit exposed to 1 or 5 ppm reached below the marketability threshold after 12 d in storage and rated an average of 1.0 (inedible) while the control group had an average external appearance rating of 5.6. At this poi nt, appearance on ethylene-treated fruit was negatively affected mainly by decay; 60% of the fruit exposed to 1 ppm showed some level of decay while on the 5 ppm group the decay reached 90%. The decay was only rated as present or absent and the severity of the decay was not rated since the fruit was rendered unmarketable once decay was noticeab le. Yellowing was also a major factor of quality loss, with 90% of fruit exposed to 1 or 5 ppm showing yellowing of the peel. Appearance of European cucumbers Similar to Beit Alpha cucumbers, the app earance of European cucumbers was also negatively affected by the exposure to con tinuous ethylene but it followed a slightly different pattern than Beit Alpha cucumbers. The appear ance rating of the ethylenetreated fruit (1, 5 and 10 ppm) reached the ma rketability threshold between 6 and 9 d of continuous ethylene gassing and unlike Be it Alpha cucumbers va rying the ethylene concentration in the storage atmosphere had no effect on the rate at which appearance deteriorated.

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81 Shrink-wrapping of European cucumbers was not beneficial in mitigating the effects of ethylene on cucumber quality since there were no differences in appearance rating between wrapped and unwrapped cu cumbers throughout the gassing period. After 6 d of continuous ethylene gassi ng there was no difference among the four ethylene treatments in the appearance ra ting of unwrapped or wrapped European cucumbers. At this point all four treatments of both unwrapped (Figure 4-8) and wrapped (Figure 4-9) cucumbers had very good exte rnal appearance, dark green color and no stem-end shriveling or other vi sible defect. Wrapped cucumbers exposed to 0, 1, 5 or 10 ppm ethylene had an average external appe arance rating of 8, 7, 7 and 7, respectively while unwrapped cucumbers exposed to 0, 1, 5 or 10 ppm ethylene had an average external appearance rating of 8, 7, 7 and 7, respectively. Deterioration in appearance of European cucumbers became evident after the fruit had been in the gassing chambers for 9 d. All the four treatmen ts, both the ethylenetreated fruit and the control group, of unwra pped cucumbers reached the limit of their marketable life at 9 d of continuous ethyl ene exposure. The ethylene-treated fruit was affected by yellowing, stem-end shriveling, the development of reddish-brown spots and water soaking while the cont rol group exhibited only shri veling of the stem-end. The control group (unwrapped) became unmarketable as a result of excessive water loss and not as a direct effect of ethylene. Wrapped European cucumbers also reached the limit of their marketable life at 9 d of continuous ethylene gassing due to the same disorders described above for unwrapped cucumbers; however the control group remained marketable beyond this point due to the protective shrink-w rap that reduced the amount of water loss.

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82 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Threshold Figure 4-8. Appearance rating of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. 1, 5 and 10 ppm had identical resu lts. Vertical bars represent the standard error from the mean, were not shown standard error falls within the marker size. Appearance Rating

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83 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Threshold Figure 4-9. Appearance rating of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. 1, 5 and 10 ppm had identical resu lts. Vertical bars represent the standard error from the mean, were not shown standard error falls within the marker size. Appearance Rating

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84 In regards to the developm ent of the reddish-brown s pots, it is worth noting two observations. First, unwrapped fruit seemed to have higher incidence of these reddishbrown spots. Second, the severity of these re ddish-brown spots appeared to be higher in fruit exposed to higher concentrations of ethylene. These however, are empirical observations since the actual severity was not scientifically quantified and their development was only noted as either present or absent since even a slight presence of these spots was enough to render the produc t unmarketable. Development of these reddish-brown spots was also observed in E xp. I on Beit Alpha cucumbers that had been exposed to 5 or 10 ppm ethylene for 12 d (Figure 4-3). External color of Beit Alpha cucumbers Exposure to external ethylene caused an accelerated rate of yellowing in stored cucumbers but varying the ethyl ene concentration had no effect on the rate of yellowing. A decrease in external color, as measured by the hue angle, was observed on Beit Alpha cucumbers exposed to ethylene while the cont rol group retained very similar hue angle values throughout the 12-day storage period (Figure 4-10). The decrease in hue angle measurements on ethylene-treated fruit was ev ident after 9 d of continuous exposure, at which point ethylene-treated (1, 5 and 10 ppm) fruit had significantly lower hue angle values than the control fruit (0 ppm). Fruit exposed to 5 or 10 ppm had the lowest hue angle value, 123.1, significantly lower than both the control fruit and fruit exposed to 1 ppm ethylene. Fruit exposed to 1 ppm ethylene had an intermediate hue angle at this point, 123.7; significantly higher than either 5 or 10 ppm but signifi cantly lower than the control group, which had the highest hue angle value of all four groups, 124.2.

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85 114.0 116.0 118.0 120.0 122.0 124.0 126.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-10. Changes in the external color, as measured by the hue angle (), of Beit Alpha-type cucumbers exposed to four different concentrations of exogenous ethylene and stored at 10 C for 12 d. Hue Angle ()

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86 Hue angle values continued to decrease on ethylene-treated fruit and at 12 d of continuous exposure had decreased to 120.2, 120.5, and 119.8 on fruit exposed to 1, 5 or 10 ppm ethylene, respectively, with no si gnificant difference among these three ethylene treatments. However, as a group these three et hylene treatments ha d significantly lower hue angle values than the control fruit ( 123.5). Although a significant decrease in hue angle values was detected, it was not possible to use this parameter as a unique indicator to segregate the fruit based on the severity of ethylene. As in Exp. I., L* values (lightness inte nsity) of Beit Alpha cucumbers remained relatively unchanged during the storage peri od (data not shown) wh ile chroma values increased slightly from an average of 21.5 at harvest to between 26.8 and 28.3, depending on the temperature, but with no significant differences among storage treatments (data not shown). External color of European cucumbers Similar to Beit Alpha cucumbers, ethylen e caused an accelerated yellowing of the peel of European cucumbers with no di fference between wrapped and unwrapped fruit but unlike Beit Alpha cucumbers, significantl y lower hue angle values became evident on both wrapped and unwrapped cucumbers after 6 d of continuous exposure to ethylene (Figure 4-11). After 6 d of continuous ethyl ene exposure, the ethylene-treated fruit had lower hue angle values than the control group. At 9 d in storage the ethylene-treated fr uit also had significantly lower hue angle values than the control group but there was no difference among fruit exposed to 1, 5 or 10 ppm ethylene. However, as a group the ethylene-treated fru it (1, 5, 10 ppm) had significantly lower hue angle valu es than the control fruit.

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87 114.0 116.0 118.0 120.0 122.0 124.0 126.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-11. Changes in the external color, as measured by the hue angle (), of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean. Hue Angle ()

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88 At the end of the 12-day storage period th ere was a clearer segr egation based on the ethylene concentrati on in the storage environment. Fruit exposed to 10 ppm had, significantly, the lowest hue angle value (116.8 ) followed by fruit exposed to 1 or 5 ppm which had an intermediate hue angle va lue of 118.3 and 118.5, respectively, with no significant difference between these two concentrations. The control group had, significantly, the highest hue a ngle value at the end of the 12-day gassing period (124.3). As with Beit Alpha cucumbers, the L* values (lightness in tensity) of unwrapped European cucumbers remained relatively unchanged during the storage period (data not shown) while chroma values increased slig htly from an average of 21.4 at harvest to between 24.4 and 30.2, depending on the temperat ure, but with no significant differences among storage treatments (data not shown). As with unwrapped cucumbers, exposure to external ethylene caused yellowing of the peel; an indication that shrink wrapping did not prot ect the fruit from ethylene damage. External hue angle measurements of wrapped European cucumbers decreased over time on fruit exposed to ethylene (1 to 10 ppm) but remained stable on the control group (0 ppm) throughout the 12-day storag e period (Figure 4-12). As in unwrapped fruit, significantly lower hue angle values be came evident in ethylene-treated fruit after 6 d in storage and although the differences we re not systematic according to the ethylene concentration; ethylene-treated fruit (1, 5 and 10 ppm) as a group had significantly lower hue angle values than the control group. Hue angle values continued to decline and after 12 d in storage it had declined from 124.9 to 114.3 on fruit exposed to 10 ppm, significantly lower than the other three treatments.

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89 112.0 114.0 116.0 118.0 120.0 122.0 124.0 126.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-12. Changes in the external color, as measured by the hue angle (), of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean. Hue Angle ()

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90 External hue angle values of fruit exposed to 1 or 5 ppm decreased from an initial hue angle of 124.4 to 117.9 after 12 d in storage while that of the control group remained stable throughout the storage pe riod and ended at 124.3. The L* values (lightness intensity) of wrapped European cucu mbers behaved similarly to those of either Beit Alpha or unwrapped European cucumber s and were not affected by the storage treatment remaining relatively unchanged dur ing the storage period (data not shown) while chroma values increased slightly from an average of 22.1 at harvest to between 23.6 and 32.5, depending on the temperature, but with no significant differences among storage treatments (data not shown). Internal color Exposure to exogenous ethylene did not affect the intern al color of either Beit Alpha or European cucumbers. Internal hue angle of Beit Alpha (Table 4-4), unwrapped (Table 4-5) and wrapped (Table 4-6) European cucumbers declined as a function of the storage period, with no significant differences among the four groups. Internal L* values of Beit Alpha cucumbers decreased slightly duri ng storage, as in Exp. I, from an average of 71.3 at harvest to between 65.5 and 71.0, depending on the storage temperature but was not significantly affected by the storage treatment (data not shown). Chroma values decreased slightly from 35.3 at harvest to between 28.8 and 33.7, depending on the temperature, but with no significant differe nces among storage treatments (data not shown).

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91Table 4-4. Internal hue angle of Beit Alpha cucumbers exposed to four concen trations of exogenous ethylene (0, 1, 5 and 10 ppm ) and stored at 10 C (1 C) for 12 d. Storage Length (d) 0 3 6 9 12 Internal Hue Angle () Temperature Treatment Mean s Mean s Mean s Mean s Mean s 0 ppm 111.0 0.2 112.6 0.2 111.5 0.3 110.1 0.4 109.9 0.2 1 ppm 111.0 0.2 112.8 0.4 110.7 0.5 110.4 0.3 108.5 0.4 5 ppm 111.0 0.2 112.5 0.3 112.3 0.3 110.2 0.5 108.4 0.6 10 ppm 111.0 0.2 112.7 0.4 111.5 0.2 109.8 0.4 109.0 0.3 z Mean values in the same colu mn with different letters are significantly different at a P-va lue < 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=5).

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92Table 4-5. Internal hue angle of unwrapped European cucumbers exposed to four concentrations of e xogenous ethylene (0, 1, 5 an d 10 ppm) and stored at 10 C (1 C) for 12 d. Storage Length (d) 0 3 6 9 12 Internal Hue Angle () Temperature Treatment Mean s Mean s Mean s Mean s Mean s 0 ppm 111.3 0.3 111.2 0.4 108.6 0.5 108.0 0.4 102.5 0.7 1 ppm 111.3 0.3 110.7 0.4 107.4 0.5 105.6 0.6 106.7 0.3 5 ppm 111.3 0.3 111.7 0.4 110.2 039 109.9 0.3 104.8 0.5 10 ppm 111.3 0.3 111.7 0.3 109.4 0.5 109.6 0.6 105.3 0.4 z Mean values in the same colu mn with different letters are significantly different at a P-va lue < 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=3).

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93Table 4-6. Internal hue angle of wrapped European cucumbers exposed to four c oncentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d. Storage Length (d) 0 3 6 9 12 Internal Hue Angle () Temperature Treatment Mean s Mean s Mean s Mean s Mean s 0 ppm 111.3 0.3 111.2 0.6 109.3 0.5 108.9 0.4 107.1 0.5 1 ppm 111.3 0.3 110.3 0.1 108.6 0.5 108.2 0.5 105.9 0.4 5 ppm 111.3 0.3 109.8 0.3 109.0 0.8 108.6 0.8 108.1 0.7 10 ppm 111.3 0.3 111.6 0.3 109.2 0.3 108.8 0.3 105.9 0.5 z Mean values in the same colu mn with different letters are significantly different at a P-va lue < 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=3).

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94 Internal L* (data not shown) and chroma values (data not shown) of unwrapped European cucumbers also decreased slightly as a function of the length of storage but were not affected by the storage temperature. Internal L* (data not shown) and chroma values (data not shown) of wrapped European cucumbers behaved in a similar manner to the unwrapped ones. Weight loss The exposure of cucumbers, Beit Alpha or European, to external ethylene had no effect on the rate of weight lost. Howeve r, unwrapped European cucumbers lost more weight than either wrapped European or Be it Alpha cucumbers (Table 4-7). After 12 d in storage, Beit Alpha and wrapped European cucumbers lost approximately 1% fresh weight, with no significant differences am ong the four treatments. On the other hand, unwrapped European (Table 4-8) cucumbers lo st significantly more weight than either Beit-Alpha or wrapped European cucumber s (Table 4-9) but with no significant differences among the four treatments; an indica tion that the shrinkage was in fact due to the lack of wrapping and not as a direct eff ect of external ethylene exposure. Unwrapped European cucumbers lost approximately 4% af ter 12 d in storage, which was significantly higher than the weight loss of either wr apped European or Beit Alpha cucumbers.

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95 Table 4-7. Weight loss of Beit Alpha cucumb ers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) a nd stored at 10 C (1 C) for 12 d. Storage Length (d) 3 6 9 12 Weight loss (%) Ethylene Treatment Mean s Mean s Mean s Mean s 0 ppm 0.76 a 0.05 0.77 a 0.03 0.80 a 0.05 1.02 a 0.10 1 ppm 0.58 bc 0.05 0.68 a 0.05 0.83 a 0.15 1.04 a 0.16 5 ppm 0.68 ab 0.06 0.91 b 0.08 0.91 a 0.07 0.90 a 0.13 10 ppm 0.50 c 0.05 0.57 a 0.07 0.79 a 0.10 1.02 a 0.08 z NS: values within the same column are not significantly different at P-value of 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=10). Table 4-8. Weight loss of unwrapped Eu ropean cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d. Storage Length (d) 3 6 9 12 Weight loss (%) Ethylene Treatment Mean s Mean s Mean s Mean s 0 ppm 1.45 a 0.03 1.56 a 0.10 2.86 a 0.11 4.21 a 0.18 1 ppm 1.45 a 0.03 2.09 a 0.12 3.06 a 0.10 4.04 a 0.14 5 ppm 1.96 a 0.26 2.08 a 0.06 4.20 a 0.16 5.10 a 0.03 10 ppm 2.15 a 0.20 1.92 a 0.04 3.02 a 0.17 3.77 a 0.17 z Mean values in the same column with differe nt letters are significantly different at a Pvalue < 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=3)

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96 Table 4-9. Weight loss of wr apped European cucumbers expos ed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d. Storage Length (d) 3 6 9 12 Weight loss (%) Ethylene Treatment Mean s Mean s Mean s Mean s 0 ppm 0.10 a 0.02 0.28 a 0.03 0.30 a 0.02 0.30 a 0.00 1 ppm 0.08 a 0.01 0.20 a 0.03 0.49 a 0.03 0.50 a 0.00 5 ppm 0.19 a 0.02 0.23 a 0.02 0.49 a 0.02 0.50 a 0.02 10 ppm 0.21 a 0.18 0.30 a 0.01 0.45 a 0.04 0.93 b 0.13 z Mean values in the same column with differe nt letters are significantly different at a Pvalue < 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=3). Mesocarp firmness of Beit Alpha cucumbers Unlike Exp. I, it was not possible to dete ct difference in mesocarp firmness until the 12th day of ethylene exposure. Measuremen ts of mesocarp firmness were highly variable during the first days in storage and increased dur ing the first 6 d of ethylene exposure (Figure 4-13). Fruit exposed to 0, 1 or 5 ppm ethylene increased 77%, after 6 d in storage while fruit exposed to 10 ppm e xperienced a 50% increase in pulp firmness measurement after the same storage period and was significantly lower than the other three groups. Pulp firmness values have been observed to increase after 3 d in previous ethylene-free storage experiments but this wa s the first time that pulp firmness values increased in this magnitude and relativ ely this late in the storage period. After this period, pulp firmness decrease d in ethylene-treated fruit while it remained stable in the control fruit. At the end of the 12-day storage period fruit that had

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97 been exposed to higher concentrations of ethylene had significantly lower mesocarp firmness values than the control group. Fr uit continuously exposed to 5 or 10 ppm ethylene for 12 d experienced a 20% decrea se from the initial mesocarp firmness measurement (48 hours after harvest) and e nded the 12-day storage period with average mesocarp firmness of 6.2 and 8.6 N, respectiv ely; significantly lowe r than the control group. Mesocarp firmness of European cucumbers Mesocarp firmness of unwrapped Europ ean cucumbers responded similarly to exogenous ethylene as did wrapped cucumber s. Like Beit Alpha cucumbers, mesocarp firmness of both wrapped and unwrapped cucu mbers remained relatively unchanged for the first 3 d in storage before increasing a nd peaking at 6 d. In unwrapped cucumbers the highest increase in pulp firmness was obser ved in the control group, which increased 67%, from 10.4 N (48 hours after harvest) to 17.4 N after 6 d in storage (Figure 4-14). The ethylene-treated fruit also increased dur ing the same period but the increment was less pronounced. Mesocarp firmness values in ethylene-treated fruit (1, 5 and 10 ppm) increased 40% from 10.4 to 14.6 N; signi ficantly lower than the control group. Pulp firmness of ethylene-treated unwrapped fruit started to decline after peaking at 6 d in storage while those of the control gr oup remained stable for the remaining portion of the gassing period. At 9 d in storage unw rapped fruit exposed to either 5 or 10 ppm had an average pulp firmness value of 11.5 N; significantly lower than either the control group or fruit exposed to 1 ppm of ethylene.

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98 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 0366+199+112 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-13. Mesocarp firmness of Beit Alpha cu cumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. +1 indicates that the fruit was transferred to 20 C for 1 day (ethylene-free) after being in storage at 10 C. Vertical bars represent the standard error from the mean. Mesocarp Firmness (N)

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99 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 0366+1912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-14. Mesocarp firmness of unwrappe d European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. +1 indicates that the fruit was transferred to 20 C for 1 day (ethylene-free) after being in storage at 10 C. Vertical bars represent the standard error from the mean Mesocarp Firmness (N)

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100 Pulp firmness of fruit exposed to 1 ppm of ethylene was 13.8 after the same period; significantly lower than the control group which had a pulp firmness value of 17.7 N. Pulp firmness of ethylene-treated unwrappe d cucumbers declined further and at the end of the 12-day gassing period, unwrappe d fruit continuously exposed to 10 ppm ethylene experienced a 33% decrease in pulp firmness and had the lowest pulp firmness (7.0 N) of all the four groups. Fruit expos ed to either 1 or 5 ppm ethylene had intermediate pulp firmness values after th e same storage period and ended the 12-day storage period with an average pulp firmne ss of 11.8 N; significantly lower than the control group which had an av erage pulp firmness of 17.3 N. Similar to Beit Alpha and unwrapped Europ ean cucumbers, mesocarp firmness of wrapped European cucumbers remained stable for the first 3 d in storage but increased between 3 and 6 d. As with Beit Alpha cucu mbers, the highest increase was observed in fruit exposed to lower concentrations of et hylene (Figure 4-15). Fr uit exposed to 10 ppm also increased at 6 d in storage but the in crease was less pronounced than the other three groups. Fruit exposed to either 1 or 5 ppm, along w ith the control group, increased from an average of 10.4 N 48 hours after harvest to an average of 16.3 N afte r 6 d in storage; a 60% increase. Although fruit exposed to 10 ppm also experienced an increment in mesocarp firmness during the same period, it wa s significantly lower than that observed in the other three treatments. During this period, pulp firmness values increased 30% from 10.4 N to 13.5 N on fruit exposed to 10 ppm. Mesocarp firmness of wrapped European cucumbers was highly variable maki ng it impossible to draw clear conclusions from its behavior under ethylene gassing.

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101 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 0366+1912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-15. Mesocarp firmness of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. +1 indicates that the fruit was transferred to 20 C for 1 day (ethylene-free) after being in storage at 10 C. Vertical bars represent the standard error from the mean. Mesocarp Firmness (N)

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102 Poenicke et al., (1977) also reported an increase in firmness of processing cucumbers exposed to ethylene. The author s report that fruit exposed to ethylene concentrations between 0.1 and 1.0 resulted in si gnificantly harder fruit that in the control but firmness declined if the fruit was exposed to ethylene concentrations between 5 and 10 ppm. Electrolyte leakage of Beit Alpha cucumbers The rate of electrolyte leakage (EL) in creased as the gassing period progressed and was significantly affected by the ethylene concentration in the storage atmosphere. Electrolyte leakage of Beit Alpha cucumber s averaged 6.9% 48 hours after harvest and increased to 19.4% on fruit exposed to 10 ppm of exogenous ethylene for 6 d; significantly higher than the cont rol fruit or fruit exposed to 1 ppm (Figure 4-16). At this point the EL rates of fruit exposed to 0, 1 or 5 ppm ethylene had average EL rate of 11.5, 13.1 and 14.8%, respectively and were not signi ficantly different from each other. The same pattern was observed after 9 d in storage; fruit e xposed to 10 ppm of ethylene had significantly higher rates of EL ( 30.1%) than fruit exposed to concentrations lower than 10 ppm. Fruit exposed to 0, 1, or 5 ppm ethylene for 9 d had an average EL rate of 13, 19.7 and 15.4, respectively, with no difference among thes e three treatments. Higher rates of EL were also observed afte r 12 d of continuous e xposure to external ethylene. Fruit continuously exposed to 10 ppm of ethylene had an EL rate of 58.2%, significantly higher than the ot her three groups. Fru it exposed to either 1 or 5 ppm had average EL rates of 39.9 and 37.5%, with no significant differen ce between these two treatments. On the other hand, the EL rate of the control fruit decrea sed slightly to 10.3% and was significantly lower than the EL ra tes observed in the other three groups.

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103 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-16. Electrolyte l eakage (%) of Beit Alpha cu cumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars repr esent the standard error from the mean, were not shown standard error falls within the marker size.

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104 Electrolyte leakage of European cucumbers Similar to Beit Alpha cucumbers, expos ure to exogenous ethylene caused an increase in the rate of electrolyte leak age in both unwrapped and wrapped European cucumbers. Electrolyte leakage in unwrappe d cucumber fruit expos ed to 0 ppm ethylene (control) increased from 8.7% 48 hours after ha rvest to 13% after 3 d. Fruit exposed to 1, 5 or 10 ppm had average EL rate of 27, 25.7 and 22.9%, respectively, after the same period and with no significant difference am ong these three treatments but significantly higher than the control group (Figure 4-17). Electrolyte leakage rates increased, as th e exposure period progressed, in all four treatments with higher increments observed in the ethylene-treated fruit. After 6 d of continuous gassing, EL rates increased to 34.5, 32.3 and 36.2% on fruit exposed to 1, 5 or 10 pp, respectively, with no significant differe nce among these treatments. However, as a group these three treatments had significan tly higher EL rates than the control group which had an average EL rate of 22.9% after the same period. Although EL rates increased after 9 d of continuous ethylene e xposure, the same pattern was observed; fruit exposed to 1, 5 or 10 ppm had statistically similar EL rates to each other but as a group were significantly higher than the ra te observed on the control fruit. Electrolyte leakage rates continued to increase in unwrapped fruit exposed to ethylene. After 12 d of continuous ethylene expo sure fruit exposed to either 5 or 10 ppm had statistically higher EL rates than either th e control fruit or fru it exposed to 1 ppm. After this period, fruit exposed to 5 or 10 ppm had an average EL rate of 50.5 and 55.1, respectively, with no significant diff erence between these two treatments.

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105 0.0 10.0 20.0 30.0 40.0 50.0 60.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-17. Electrolyte leakag e (%) of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars repr esent the standard error from the mean, were not shown standard error falls within the marker size. Electrolyte Leakage ()

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106 Fruit exposed to 1 ppm had an average EL rate of 42.1, significantly different than the other three treatments. The control group had the lowest EL rate (consistent throughout the storage period) at this stage; 31.8%. Continuous exposure to exogenous also cau sed an increase in the EL rates of wrapped cucumber. Unlike unwrapped European cucumbers, all four treatments of wrapped European cucumbers had statistica lly similar EL rates for the first 3 d of ethylene exposure. Average EL rates increas ed from 8.7% 48 hours after harvest to between 23.3 to 31.2% after 3 d with no signifi cant difference among the four treatments (Figure. 4-18). Electrolyte leakage rate of th e control fruit (0 ppm) peaked at 23.3% after 3 d of continuous exposure and remained at si milar levels for the rest of the storage period while the EL rate of ethylene-treat ed fruit increased as the gassing period progressed. Differences in EL rates became evident at 6 d of continuous ethylene exposure. Fruit exposed to 10 ppm had higher EL rates than the other three treatments. After 6 d, fruit exposed to 10 ppm had an average EL rate of 32.4%, significantly higher than the other three treatments. Electroly te leakage rates continued to increase in ethylene-treated fruit, inverting this pattern. After 12 d in of continuous exposure there was no significant difference in the EL rates of fruit exposed to 1, 5 or 10 ppm. However, as a group these three treatments had significantly higher EL ra tes than the control group. Fruit exposed to 0, 1, 5 or 10 ppm had average EL rate s of 20.3, 43.4, 43.9, and 47.7%, respectively.

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107 0.0 10.0 20.0 30.0 40.0 50.0 60.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-18. Electrolyte leakag e (%) of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars repr esent the standard error from the mean, were not shown standard error falls within the marker size.

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108 Experiment III Appearance As in Exp. II, exposure to external ethylen e negatively affected the appearance of European cucumbers between 6 and 9 d of continuous ethylene ga ssing but varying the level of ethylene in the atmosphere had no impact on the severity of the damage. Wrapped cucumbers not exposed to ethyl ene (control group) retained very good appearance throughout the 12-day storage period while the unwrapped control group (0 ppm) exhibited moderate to severe shriveli ng of the stem-end due to the absence of a protective wrap and reached the limit of its marketable life at the same time as the ethylene-treated fruit. Besi des shriveling of the stem-e nd, no other visible sign of deterioration was observed in the unwrapped control group. Both unwrapped (Figure. 4-19) and wrappe d (Figure. 4-20) cucumbers exposed to ethylene reached the limit of their marketab le life after 9 d in storage. Unwrapped cucumbers loss of quality was due mainly to bacterial decay, yellowing, stem-end shriveling, browning of the peel (reddish-br own spots) and general water-soaking. The bacterial decay gave the fruit a slimy appearan ce and the infected areas coalesced to form water-soaked spots. Yellowing was the sec ond factor that caused the loss of quality during storage of unwrapped cucumbers. Yellowi ng of the peel occurred in an irregular pattern; asymmetrical yellow areas appeared scattered on the fruit which gave the fruit a blotchy appearance. Irregular reddish-brown sp ots, as described in Exp. I and II, also appeared on the peel of ethylene-treated fr uit after 9 d of continuous ethylene gassing.

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109 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Threshold Figure 4-19. Appearance rating of unwrappe d European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. 1, 5 and 10 ppm had identical resu lts. Vertical bars represent the standard error from the mean, were not shown standard error falls within the marker size. Appearance Rating

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110 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Threshold Figure 4-20. Appearance rating of wrappe d European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. 1 and 5 ppm had identical resu lts. Vertical bars represent the standard error from the mean, were not shown standard error falls within the marker size. Appearance Rating

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111 As noted in Exp. II, unwrapped fruit (Fi gure. 4-21) appeared to have a higher incidence of these reddish-brown spots and th e incidence seemed to be more severe on fruit exposed to higher concentrations of ethylene in both unwrapped and wrapped fruit. However, even very low incidences as in the case of wrapped fruit exposed to 1 ppm, were sufficient to render the commodity unm arketable. In both wrapped and unwrapped cucumbers the development of reddish-brown spots occurred only on the peel and did not extend to the mesocarp. On the other hand, the deterioration of wrapped cucumbers was due mainly to yellowing of the peel, followed by the incide nce of reddish-brown spots and bacterial decay (Figure. 4-22). Fruit exposed to 10 pp m of ethylene had the highest incidence of both bacterial decay and the develo pment of reddish-brown spots. External color Continuous exposure to ethylene in the stor age atmosphere had a yellowing effect on both wrapped and unwrapped European cucumbers. However, varying the concentration in the storage atmosphere from 1 to 10 ppm had no effect on the rate of color loss. External color of unwrapped Eu ropean cucumbers remained statistically similar on all four groups for the first 3 d of ethylene gassing and st arted to decline in ethylene-treated fruit after 6 d of continuous et hylene gassing but not in the control group (Figure. 4-23). The decline in hue angle va lues, a departure from green towards yellow, continued in ethylene-treated fruit th roughout the 12-day storage period with no significant difference among the three ethylene treatments (1, 5 and 10 ppm). The control group did not experience any yellowing and as a result the hue angle values did not decline.

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112 Figure 4-21. Appearance of unwrapped Eu ropean cucumbers exposed to four concentrations of exogenous ethylene fo r 12 d at 10 C. A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10 ppm.

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113 Figure 4-22. Appearance of wrapped European cucumbers exposed to four concentrations of exogenous ethylene for 12 d at 10 C. A) 0 ppm, B) 1 pp m, C) 5 ppm and D) 10 ppm.

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114 116.0 117.0 118.0 119.0 120.0 121.0 122.0 123.0 124.0 125.0 126.0 127.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-23. Changes in the external color, as measured by the hue angle, of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean. Hue An g le ( )

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115 Overall, external hue angle values decrea sed 2.5% in ethylene-tr eated fruit after 12 d of ethylene gassing but with no significant differences among these three groups (1, 5 and 10 ppm) while hue angle of the control group did not vary significantly throughout the 12-day storage period. As in Exp. II, the L* values (lightness intensity) of unwrapped European cucumbers remained relatively unchanged during the storage period (data not shown) while chroma values increased slig htly from an average of 15.6 at harvest to between 22.6 but with no significant differe nces among storage treatments (data not shown). External color of wrapped European cu cumbers behaved similar to that of unwrapped European cucumbers, remaining st able for the first 3 d in storage and decreasing in ethylene-treated fruit after 6 d of continuous exposure to ethylene; at this stage ethylene treated fruit ( 1, 5 and 10 ppm) had significan tly lower hue angle values than the control group (Figure. 4-24). As in unwrapped cucumbers there were no significant differences in hue angle values am ong the ethylene-treated fruit (1, 5 and 10 ppm) throughout the 12-day st orage period; this group howev er, had consistently lower hue angle values than the control group and at the end of the 12-day storage period had decreased 2.3%, similar to th e decrease observed in unwrappe d fruit. The control group retained statistically simila r hue angle values throughout th e storage period, only varying 0.5% during the 12-day storage period. The L* values (lightness intensity) of wrapped European cucumbers not affected by the et hylene treatment and remaining relatively unchanged during the storage period (data not shown) while chroma values increased slightly from an average of 15.6 at ha rvest to between 21.2 and 24.5, but with no significant differences among storag e treatments (data not shown).

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116 116.0 117.0 118.0 119.0 120.0 121.0 122.0 123.0 124.0 125.0 126.0 127.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-24. Changes in the external color, as measured by the hue angle, of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent the standard error from the mean. Hue An g le ( )

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117 In all three experiments, a decline in external color wa s first observed after 6 d of continuous exposure, with no difference be tween unwrapped and wrapped fruit and like Beit Alpha cucumbers, varying the concentr ation of ethylene from 1 to 10 ppm had no effect in the rate of color loss. Internal color Exposure to exogenous ethylene did not a ffect the internal color of either unwrapped or wrapped European cucumbers. Internal hue angle of unwrapped (Table 411) and wrapped (Table 4-12) European cucumb ers declined as a function of the storage period, with no significant diffe rences among the four groups (Figure. 4-26 and Figure. 427). Although internal color de clined in all three experime nts, it was a result of the storage period and not a result of exposure to ethylene. The results we re consistent in all three experiments. Internal L* values (data not shown) unwrapped European cucumbers decreased slightly, consistent with the previous experiments, as a function of storage length and were not affected by the storage temperature. Chroma values also decreased slightly but only on fruit stored at 5 and 10 C (data not shown). Internal L* (data not shown) and chroma values (data not shown) of wrappe d European cucumbers behaved in a similar manner to the unwrapped ones.

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118Table 4-10. Internal hue angle of unwrapped European cucumbers exposed to four concentrations of e xogenous ethylene (0, 1, 5 a nd 10 ppm) and stored at 10 C (1 C) for 12 d. Storage Length (d) 0 3 6 9 12 Internal Hue Angle () Temperature Treatment Mean s Mean s Mean s Mean s Mean s 0 ppm 113.2 a 0.53 113.8 a 0.49 112.3 a 0.41 111.3 ab 0.36 106.9 a 0.31 1 ppm 113.2 a 0.53 113.4 a 0.25 112.2 a 0.28 110.9 bc 0.16 108.8 bc 0.49 5 ppm 113.2 a 0.53 113.9 a 0.18 112.3 a 0.33 111.9 a 0.16 109.6 c 0.58 10 ppm 113.2 a 0.53 113.4 a 0.24 112.9 a 0.22 110.3 c 0.37 108.4 ab 0.61 z Mean values in the same colu mn with different letters are significantly different at a P-va lue < 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=3).

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119Table 4-11. Internal hue angle of wrapped European cucumbers exposed to four c oncentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d. Storage Length (d) 0 3 6 9 12 Internal Hue Angle () Temperature Treatment Mean s Mean s Mean s Mean s Mean s 0 ppm 113.2 a 0.53 113.1 a 0.53 112.9 a 0.30 110.9 a 0.44 107.8 a 0.34 1 ppm 113.2 a 0.53 114.1 a 0.11 112.5 ab 0.10 110.2 a 0.21 110.1 bc 0.37 5 ppm 113.2 a 0.53 113.3 a 0.42 111.7 bc 0.42 110.9 a 0.26 109.3 ab 0.45 10 ppm 113.2 a 0.53 113.1 a 0.25 111.3 c 0.33 110.3 a 0.41 111.4 c 0.68 z Mean values in the same colu mn with different letters are significantly different at a P-va lue < 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=3).

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120 Figure 4-25. Internal appear ance of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene for 12 d at 10 C (1 C). A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10 ppm.

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121 Figure 4-26. Internal appearance of wra pped European cucumbers exposed to four concentrations of exogenous ethylene for 12 d at 10 C (1 C). A) 0 ppm, B) 1 ppm, C) 5 ppm and D) 10 ppm.

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122 Weight loss As described in Exp. II, the concentration of ethylene in the storage atmosphere had no effect on the rate of weight loss of eith er wrapped or unwrapped European cucumbers. Total weight loss after 12 d of continuous exposure to ethylene ranged between 3.38 and 3.69% in unwrapped fruit (Table 4-13) with no difference among treatments. Unwrapped cucumbers, however, did lose more weight th an wrapped cucumbers due to the lack of the protective shrink-wrap. Wrapped cucumbers lost between 0.19 and 0.37% after the same length of exposure (Table 4-14) with no significant differences among treatments. These results are comparable to those obtained Exp. I and Exp. II; Beit Alpha and wrapped cucumbers exhibited a weight loss of less than 1% while unwrapped European cucumbers lost approximately 4%. Table 4-12. Weight loss of unwrapped Eu ropean cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d. Storage Length (d) 3 6 9 12 Weight loss (%) Ethylene Treatment Mean s Mean s Mean s Mean s 0 ppm 1.78 a 0.10 2.43 a 0.36 2.92 a 0.20 3.69 a 0.26 1 ppm 1.75 a 0.15 2.02 a 0.16 3.48 a 0.52 3.38 a 0.16 5 ppm 1.59 a 0.13 2.22 a 0.11 3.07 a 0.18 3.51 a 0.31 10 ppm 2.13 a 0.21 2.77 a 0.35 3.13 a 0.32 3.54 a 0.30 z Mean values within the same column are not significantly different at P-value of 0.05. Mean separation based on DuncanÂ’s Multiple Range Test. y Standard error from the mean (n=3).

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123 Table 4-13. Weight loss of wr apped European cucumbers expos ed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C (1 C) for 12 d. Storage Length (d) 3 6 9 12 Weight loss (%) Ethylene Treatment Mean s Mean s Mean s Mean s 0 ppm 0.07 a 0.02 0.13 a 0.03 0.17 a 0.00 0.19 a 0.03 1 ppm 0.01 b 0.01 0.13 a 0.04 0.21 a 0.01 0.15 a 0.01 5 ppm 0.03 ab 0.02 0.13 a 0.01 0.21 a 0.01 0.17 a 0.04 10 ppm 0.04 ab 0.01 0.09 a 0.02 0.25 a 0.04 0.37 b 0.06 z Mean values in the same column with differe nt letters are significantly different at a Pvalue < 0.05. Mean separation based on Duncan’s Multiple Range Test. y Standard error from the mean (n=3). Mesocarp firmness Continuous exposure to external ethylene caused softening of the mesocarp of both unwrapped and wrapped European cucumbers. Mesocarp firmness remained unchanged for the first 3 d in ethylene-tr eated fruit but increased slightly in the control fruit (Figure. 4-27). Similar increases in firmness or ‘toughe ning’ have been observed during the first 3 d in ethylene-free storage experiments. However, pulp softening became evident after 6 d of continuous ethylene gassing; although a decrease in pulp firmness was also observed on the cont rol fruit, the fruit exposed to higher concentrations of ethylene had significantly softer mesocarp. After this period, fruit exposed to 5 or 10 ppm had an average mesocarp firmness of 8.02 and 7.95 N, respectively with no signifi cant difference between these two treatments but both were significantly lower than e ither the control group or fruit exposed to 1 ppm.

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124 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-27. Mesocarp firmness of unwrappe d European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent th e standard error from the mean. Mesocarp Firmness (N)

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125 Overall, fruit exposed to 1, 5 or 10 ppm experienced a 30.4, 55.9, and 52.1% decrease in pulp firmness, re spectively, after 12 d of conti nuous exposure to ethylene with the largest decrease obser ved during the first 6 d of e xposure. At the end of the 12day exposure period, the control group had statistically simila r mesocarp firmness to that obtained at harvest. Firmness of wrapped European cucumbers behaved similar to that of unwrapped European cucumbers. A slight increase in pulp firmness was observed in all four treatments after 3 d of continuous ethylen e exposure, and with the exception of the control group, the values were not significantly different to those obtained at harvest. Pulp firmness of the control group increas ed from an average of 13.6 N (24 hours after harvest) to an average of 16 N after 3 d in storage; a 17% in crease in pulp firmness (Figure. 4-28). A significantly smaller increas e in pulp firmness was also observed in the ethylene-treated fruit (1, 5 and 10 ppm); whic h rose from an average of 13.6 N (24 hours after harvest) to between 14.5 to 14.8 N af ter 3 d of continuous exposure, with no difference among these three ethylene treatmen ts (1, 5 and 10 ppm). However, at this stage the ethylene-treated fruit had significan tly lower mesocarp firmness than the control group. This same pattern was observed in the subsequent measurements; the control fruit retained significantly higher pulp firmness valu es than the ethylene-treated fruit and with the only exception at 6 d, there were no si gnificant differences among the three ethylene treatments (1 5 and 10 ppm). As in unwrapped cucumbers, a dramatic d ecrease in pulp firmness of wrapped fruit was observed on all four treatments afte r 6 d of continuous ethylene gassing.

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126 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-28. Mesocarp firmness of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars represent th e standard error from the mean. Mesocarp Firmness (N)

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127 Pulp firmness of the control group declined 30.5% to 9.5 N from its initial firmness of 13.6 N but remained significan tly higher than the other th ree groups (1, 5 and 10 ppm). Fruit exposed to either 1 or 5 ppm experi enced a decrease in pulp firmness of 35.7 and 34.9%, respectively, with no significant differe nce between these tw o treatments. Fruit exposed to 10 ppm, the highest ethylene con centration used in this experiment, was the softest of all four treatmen ts after the same exposure period. Pulp firmness on this fruit declined from an initial firm ness of 13.6 N to 8.2 N; a 40% in pulp firmness. This pattern, however, did not become established th roughout the storage period and significant differences in pulp firmness among the ethylenetreated fruit (1, 5 a nd 10 ppm) were not observed after this point in the storage period. At the end of the 12-day storage period, fr uit exposed to ethylene was significantly softer than the control group but there wa s no significant difference among the three ethylene concentrations (1, 5 and 10 ppm). Th e control group ended the 12-day gassing period with an average pulp firmness of 14.01 N while fruit exposed to 1, 5 or 10 ppm had an average pulp firmness of 11.5, 11.1 and 10.7, respectively. Electrolyte leakage Exposure to external ethylene caused an in crease in the electrol yte leakage of but the minimum exposure required for a significant effect to be seen was between 6 and 9 d. The EL rate of unwrapped cucumbers remained stable for the first 3 d of ethylene exposure before increasing to between 32 and 36% after 6 d of continuous ethylene gassing, without any significant difference amon g all four treatments. While the EL rate of ethylene-treated fruit continued to increas e as the duration of exposure increased, the EL rate peaked at 6 d and decrea sed thereafter (Figure. 4-29).

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128 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-29. Electrolyte leakag e (%) of unwrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars repr esent the standard error from the mean, were not shown standard error falls within the marker size. Electrolyte Leakage (%)

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129 After 9 d of continuous ethylene gassing, the EL rate increased to between 50 and 53% on ethylene-treated fruit (1, 5 or 10 ppm) without significant differences among these three treatments, which as a group had significantly higher EL rate than the control group (23%). EL rate continued to increase in fruit exposed to ethylene and after 12 d of continuous exposure the EL rate of ethylenetreated fruit (1, 5 and 10 ppm) was between 53 and 61% with no significant difference am ong these three treatments; however as a group the ethylene-treated fruit had significan tly higher EL rates than the control group (19%). Similar to unwrapped cucumbers, the EL rate remained stable for the first 3 d of ethylene exposure, averaging 10.4% with no significant differences among the four treatments (Figure. 4-30). EL rates increased on all four treatments between 3 and 6 d of ethylene exposure but without any significant differences among the four treatments and ranged between 24.8 and 30.7%. EL rates continue d to increase in fruit exposed to ethylene, however on the cont rol group it peaked at 29.5% after 9 d and decreased to 19.5% at 12 d. Fruit exposed to 5 or 10 ppm ethylene for 9 d had statistically similar EL rates (40.5 and 40.2%, respectively) but as a gr oup these two treatments had significantly higher EL rates than either the control group or fruit exposed to 1 ppm. At 12 d there was a clear mean separation based on the concentration of ethylene in the storage atmosphere; EL rates were signifi cantly different among all four groups. Fruit exposed to 10 ppm had an EL rate of 57% af ter 12 d exposure, significantly the highest EL rate of all the four treatments while fr uit exposed to 5 ppm, 1 ppm and 0 ppm had average EL rates of 47, 38, and 19.5% respecti vely; all treatments were significantly different at a P-value < 0.05.

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130 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 036912 Duration of Ethylene Exposure (d) 0 ppm 1 ppm 5 ppm 10 ppm Figure 4-30. Electrolyte leakag e (%) of wrapped European cucumbers exposed to four concentrations of exogenous ethylene (0, 1, 5 and 10 ppm) and stored at 10 C for 12 d. Vertical bars repr esent the standard error from the mean, were not shown standard error falls within the marker size. Electrolyte Leakage (%)

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131 Discussion Appearance Acceptable appearance of Beit Alpha cucu mbers was maintained for 15 to 18 d when stored at 10 C, ~90% relative humidity and in an ethylene-free environment. However, appearance is negatively affected when Beit Alpha cucumbers are exposed to ethylene in the storage atmosphere. In both e xperiments, all four treatments maintained acceptable appearance for the first 6 d of et hylene exposure but masked changes in other attributes such as mesocarp firmness and elec trolyte leakage. Ethylene-treated fruit that had acceptable appearance suffered severe changes in appearance when this fruit was transferred to 20 C (ethylenefree), an aspect that coul d be troublesome for marketers that are unable to maintain a consistent co ld chain throughout the marketing process. Deterioration of the appearance of Beit Alpha cucumbers exposed to ethylene was gradual and occurred first on the fruit that was exposed to the highe r concentrations of ethylene. Like Beit Alpha cucumbers, European cucumbers retained acceptable appearance for the first 6 d of ethylene e xposure and experienced deterioration in appearance thereafter. However, unlike Beit Al pha cucumbers, changes in appearance of European cucumbers did not increase in sever ity when the concentration of ethylene in the storage environment was increased from 1 to 10 ppm, an indication that perhaps European are more sensitive to ethylene than Beit Alpha cucumbers. Shrink-wrapping of European cucumbers was not beneficial in reducing the effect of ethylene on the external appearance, due to the permeability of the film, but was effective in reducing the moisture loss and consequent shriveling of the fruit. Although Beit Alpha cucumbers were not wrapped, they we re more tolerant to moisture loss than unwrapped European cucumbers.

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132 External Color External color is an important quality i ndicator and days to incipient yellowing is sometimes used to define marketable life in cucumbers (Lin and Ehret, 1991). Yellowing, as a result of chlorophyll loss, is a natural phenomenon in senescent plant tissue (Matile, 1999). It can be accelerated by external factor s such as ethylene (Funamoto, 2002) which is thought to promote the breakdown of chlor ophyll (Lelivre, 1997) due to an increased de novo synthesis of chlorophyllase (Jacob-Wilk et al., 1999). Chlor ophyllase is regarded as the enzyme mediating the initial step in chlo rophyll breakdown (Matile, 1999). Yellowing as a result of ethylene exposure wa s evident in both Beit Alpha and European cucumbers but increasing the concentration in the storage atmosphere (from t1 to 10 ppm) had no significant effect of the rate of yellowing. As w ith the effect of ethylene on appearance, the film wrap did not mitigat e the effect of ethylene on color loss. Internal Color Internal color of either Beit Alpha or European (wrapped and unwrapped) cucumbers was not affected by the ethylen e in the storage a tmosphere. Although the internal color is not a grade st andard used in the marketing of cucumbers in the U.S. it can play an important role if the product were to be destined for fresh-cut. Weight Loss Weight loss and internal color are the only two parameters that were not affected by ethylene. Beit Alpha cucumbers had weight lo ss similar to that of wrapped European cucumbers, approximately 1%. Shrink-wrapping was effective in reducing the rate of weight loss in European cucumbers and the re sulting stem-end shrive ling. Given that Beit Alpha cucumbers do not suffer from excessive weight loss, shrink-wr ap is not necessary

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133 for these cucumbers and represents an adva ntage of Beit Alpha cucumbers over European cucumbers since the wrapping, and accompanying co sts, of individual frui ts is a step that is eliminated. The film wrap, although permeab le was effective in creating a moisture barrier that protected the fr uit from dehydration that w ould have eroded the market acceptance of the product. Respiration In Beit Alpha cucumbers, higher respirati on was only observed in the first 6 d of continuous ethylene exposure. Initial respirati on rates of the control group (0 ppm) were comparable to those obtained in previous e xperiments at 10 C (Chapters 2 and 3), while those of the ethylene treated fruit were higher. However, these differences became indistinguishable later in the exposure period, since the respiration rate of the control group increased to similar rates of those of ethylene-treated fruit. Firmness Fruit softening is one of the ripening processes that is most sensitive to ethylene (Lelivre, 1997) and is promoted as part of the ripening process (S altveit, 1998) in some fruits. However softening is an undesirable e ffect in the case of cucumbers, which are consumed at a physiologically immature stage and do not need to undergo ripening to become edible as other fruits, such as banana s. Ethylene has been shown to be partially responsible for pulp softening in climacteric fr uits, such as Charantais cantaloupe melons (Flores et al., 2001). Softening of watermelon placental tissue as a response to exogenous ethylene has also been reporte d (Karakurt and Huber, 2002). Beit Alpha cucumbers showed severe so ftening by 6 d of exposure to 10 ppm ethylene when the fruit had relatively high initial pulp fi rmness (Exp. I), however, when

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134 the fruit had relatively low mesocarp firmness at harvest, significant differences in mesocarp firmness were not observed until 9 to 12 d of ethylene exposure (Exp. II). Similar observations can be made for European cucumbers. In Exp. I, the fruit had lower mesocarp firmness at harvest than fruit in E xp. II. Mesocarp firmness va lues of this fruit were variable during the 12-day exposure pe riod, and systematic pulp softening was not observed until between 9 to 12 day of ethylen e exposure. On the other hand, fruit from Exp. II had relatively higher initial mesocarp firmness values, which started to decrease after 6 d of continuous ethylene exposure. As with appearance ratings, shrink-wrapping of European cucumbers had no effect on the rate of fruit softening. Electrolyte Leakage Ion leakage was measured to determine the relative health of cell membranes, since increased rates in electrolyte leakage are co rrelated to changes in membrane permeability (Knowles et al., 2000). Increased rates of electrolyte leakag e have been observed in watermelon fruit (Elkashif and Huber, 1988) a nd Charantais cantaloup e melons (Flores et al., 2001) exposed to external ethylene. Ion leakage was the first parameter in these experiments indicative of quality loss in cucumber fruit exposed to continuous ethylene gassing. In both Exp. I and Exp. II comparable rates of electrolyte leakage were observed at harvest in Beit Alpha cucumbers; less than 10%. This rate remained virtually unchanged in all four treatments for th e first 3 d of ethylene exposur e but increased by 6 d, with higher rates observed in fruit exposed to highe r concentrations of ethylene. Changes in membrane permeability accumulate over time (S altveit, 2002) and irreversible membrane damage takes at least 7 d to be translated into higher EL rates (DeEll et al., 2000).

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135 Exposure to ethylene causes changes in appe arance, firmness and other parameters. As mentioned earlier, changes in firmness were variable depending on the initial mesocarp firmness at harvest. However, changes in EL rates were consistent in both experiments and present a more reliable method in determinin g the effect of stresse s, such as ethylene exposure, on commodities such as Beit Alpha cucumbers. DeEll et al. (2000) and Balandrn-Quintana et al. (2003) observed that changes in membrane permeability are the primary result of stress, while other physic al changes such as changes in appearance are secondary. European cucumbers also had comparable initial EL rates in both Exp. II and Exp. III and these rates were also similar to those seen in Beit Alpha cucumbers. However, unlike Beit Alpha cucumbers, varying the conc entration of ethylene from 1 to 10 ppm in the storage atmosphere did not increase the EL rate in unwrapped European cucumbers. In wrapped European cucumbers, mean disc rimination was only possible in one of the experiments and only after 12 d of continuous exposure at 10 pp m, indicating that European cucumbers respond differently to et hylene than Beit Alpha cucumbers. Shrinkwrapping was not effective in moderating the deteriorating effects of ethylene. Conclusions Based on the data obtained from this experiment it can be concluded that environmental concentrations of ethylene as low as 1 ppm adversely affect the marketable life of Beit Alpha cucumbers. Duri ng storage at 10 C, adverse effects were observed in fruit exposed to 1 ppm ethylene be tween 9 and 12 d storage, in fruit exposed to 5 ppm between 6 and 9 d storage, and in fruit exposed to 10 ppm ethylene between 3 and 6 d storage. The quality of stored cucumb ers could deteriorate further if the fruit is

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136 also subjected to additio nal stress such as ambient temperatures above 10 oC. The primary effects of exogenous ethylene were in creased electrolyte leakage rates and fruit softening, while changes in appearance and ye llowing of the epidermis were secondary. It can also be concluded that external appearance is misl eading as the sole means of assessing greenhouse cucumber quality (marketable life) following exposure to exogenous ethylene. The deleterious effects of ethylene are expressed faster in other attributes such as cell permeability. Even t hough loss of chlorophyll, as determined by external hue angle measurements, was observe d in all four treatme nts during storage, it was less in the control fruit than those from the ethylene treatments. Exposure to ethylene also promoted the fruit decay but decay was only apparent after the fruit became unmarketable due to softening a nd deterioration of cell integrity. Even though the deteriorating effects of 1 ppm took between 9 to 12 d to show, Beit Alpha cucumbers should be handled and stored in an ethylene-free environment because an added stress, such as a break in the cold chain, in conjunction to exposure to 1 ppm ethylene could accele rate quality loss in Beit Alpha cucumbers. European cucumbers were also negatively affected by exposure to ethylene in the storage atmosphere, but unlike Beit Alpha cu cumbers, they did not respond differently when the ethylene concentration in the stor age atmosphere was increased from 1 to 10 ppm. Similar losses of quality, due to et hylene damage, occurred when the fruit was exposed to 1, 5 or 10 ppm. Shrink-wrapping protected European cucumbers from weight loss but not from the adverse effects of ethylene. Shrinkwrapping is not recommended for Beit Alpha cucumbers, since weight lo ss of unwrapped Beit Alpha cucumbers was comparable to that of wrapped European cucumbers.

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137 CHAPTER 5 EFFECT OF HARVEST DATE AND GROWING SEASON ON THE MARKETABLE LIFE OF BEIT ALPHA CUCUMBERS Introduction One of the problems encountered in the ma rketing of produce is the variation in quality from season to season as well as w ithin season (Cook, 2002). Variations in quality and storing ability are more pronounced in frui ts and vegetables grown in the open fields than those grown under protecte d culture. In protected culture systems, the grower has the ability to moderate the effect of the weather and produce a higher quality product (Bailey and Day, 1999). The higher producti on cost associated with greenhouse production is compensated by the higher price that greenhouse-grown commodities command (Jovicich et al., 2004) due to their better and consistent quality (Polat et al., In press) and the benefit of having year -round supplier or buyer. Greenhouse production, depending on the climate, is possible year round and the grower can profit from having product available during off seasons when pr ices are generally higher, which coupled with higher productivity (Cantl iffe and Vansickle, 2003) contribute to offset the higher production costs. The objectives of this research project were to evaluate the effect of the growing season and time of harvest on the marketable life of greenhouse-grown Beit Alpha cucumbers.

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138 Materials and Methods Plant Material Beit Alpha cucumbers (‘Manar’, DeRuiter Seeds, Columbus, OH) were grown under commercial conditions in soilless media (composted pi ne bark) in double-poly, passively ventilated greenhouses in Wellborn, Florida (Beli Farms Inc.). Cucumbers were harvested during three different season s (October-November 2003, January-February 2004 and July-August 2004) spanning 10 mont hs. For each season, two harvests were made from the same crop; one early in the harvest period and one late in the harvest period. For the early harvest, cucumbers we re collected between the first and second week of harvest and for the la te harvest between the sixth and seventh week of harvest; generally the grower harvests the same crop for seven to nine weeks. Cucumbers from both harvest dates (all three seasons) were of the same commercial maturity as determined by the grower based on the si ze and color of the fruit at picking. The cucumbers were always harvested in the afternoon and transported the same day to the Postharvest Horticulture Laborator y at the Horticultural Sciences Department, University of Florida in Gainesvi lle and stored overnight at 10 C in their original packaging (unwaxed, corrugated cartons). The cucumbers were then sorted and graded by size and appearance. Since no quality standard s are available for Beit Alpha cucumbers in the U.S., cucumbers were manually graded according to ship per’s recommendations (dark green color and free of any visible def ects or injuries) and size (diameter of no less than 2.5 cm to 4 cm). Cucumbers were th en surface sanitized by immersion for 90 seconds in a 150-ppm free-chlorine so lution, randomized and air-dried. Sanitized cucumbers were then placed in vented, rigid, hinged, 2-L, polystyrene containers (10 cucumbers/clamshell) and stor ed at 10 C. Beit Alpha cucumbers used in

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139 these experiments had an average length of 137.1 mm (120 to 150 mm), average weight of 83.5 g (69 to 120 g) and an average equato rial diameter of 29.5 mm (26.4 mm to 35.6 mm). Appearance Appearance of stored cucumbers was rate d using a subjective scale (Appendix A) from 1 to 9; 9 representing field-fresh fr uit, 3 the marketability threshold and 1 representing inedible fruit. Fruit with da rk green external color and free of defects received higher ratings while fruit that exhibited yellowing, sh riveling and/or decay received lower ratings. Appearance assessments were made on 30 cucumbers per harvest. Color Evaluation Both external and inte rnal color was assessed by reflectance using a CR-400 Chroma Meter (Konica Minolta Photo Imagi ng USA Inc., Mahwah, NJ). External color readings were taken on 30 cucumbers on equa torial spots predetermined and marked before placing the fruit in storage. Two m easurements (on opposite sides of the fruit) were taken and averaged to obtain a final value for each fruit. Internal color was measured on the sliced mesocarp tissue, as w ith external color, two measurements were taken per slice (n=5) and averaged to obtain a final value. Each slice was obtained from a different cucumber. Chroma meter was white calibrated us ing a CR-A43 white calibration plate (Konica Minolta Photo Imaging USA Inc., Ma hwah, NJ) using the following parameters; Illuminant C, L = 97.08, C = 1.84 and h = 90.76 (Y=92.6, X = 0.3135 and y = 0.3196).

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140 Weight Loss Weight loss was determined by weighi ng 30 individual cucumbers every 3 d. Weight loss is expressed as a per cent of the initial fresh weight. Fruit Firmness Fruit firmness was assessed as the bioyiel d point on equatorial slices using an Instron Universal Testing Instrument M odel 4411 (Instron Corporation, Canton, MA) equipped with a 3.0-mm diameter probe, a crosshead speed of 50.0 mm/min, a 5-kg load cell and a 7-mm displacement. Firmness was ev aluated on the mesocarp area (between the epidermis and locular tissue, approximately 2 mm from the epidermis) of similarly sized, transverse, equatorial s lices of fruit. Fruit slices were obtained using a doublebladed cutting instrument with an 11-mm separation between blades, which produced slices identical in thickness. Two firmne ss measurements (bioyield force reported in Newtons) were taken per slice, and averaged to obtain a final value. Each slice was obtained from a different cucumber (n=5). Data Analysis Color, firmness and weight loss data were subjected to an F test using SAS (SAS Institute Inc., Cary, NC), while the appearance data was s ubjected to a non-parametric one-way test (Kruskall-Wallis Test). All si gnificant differences have a P-value < 0.05. Results and Discussion Appearance The growing season had a significant effect on the appearance rating of Beit Alpha cucumbers (each season is an average of the early and late harvest) with significant differences becoming evident after the fruit ha d been in storage for 9 d. Fruit from the

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141 January season had an appearance rating of 7.7 on a scale from 1 to 9, significantly higher than fruit from the other two seasons (Figure. 5-1). Although the appearance rating continued to decline after th is period on fruit from all th e three seasons, the January season fruit had a consistently higher appear ance rating than the ot her two seasons. The growing season, however, did not affect the ma rketable life and all stored fruit reached the end of marketable life between 15 and 18 d in storage, independent of the growing season. A season-by-season analysis showed that there were no signi ficant differences in the appearance rating between the early a nd late harvest fruit in the October 2003 (Figure. 5-2) and January 2004 seasons (Figur e. 5-3). The July 2004 season was the only season where there were significant differences in the appearance rating of early and late harvest fruit (Figure. 5-4) and it was the only season in which the late harvest fruit had a 3-day shorter marketable life than the early harvest fruit. The time of harvest, early versus late, also had an effect on the appearance rating of stored Beit Alpha cucumbers (Figure. 5-5). Cucumbers harvested late in the harvest season (6-7th week of harvest) had significantl y lower appearance ratings than fruit harvested early in the harvest season (first 2 weeks of harvest). However, this difference in appearance rating did not affect the marketable life of the fruit; marketable life was between 15-18 d, independent of the time of harvest.

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142 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0369121518 Days in Storage (d) October January July Threshold Figure 5-1. Appearance rating of Beit Alpha cu cumbers harvested during three different seasons and stored at 10 C for 18 d. Each season is an average of the early and late harvests. Vertical lines repr esent standard error from the mean. Appearance Rating

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143 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0369121518 Days in Storage (d) Early October Late October Threshold Figure 5-2. Appearance rating of Beit Alpha cu cumbers harvested early and late in the October 2003 season and stored at 10 C for 18 d. Vertical lines represent standard error from the mean. Appearance Rating

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144 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0369121518 Days in Storage (d) Early January Late January Threshold Figure 5-3. Appearance rating of Beit Alpha cu cumbers harvested early and late in the January 2004 season and stored at 10 C for 18 d. Vertical lines represent standard error from the mean. Appearance Rating

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145 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0369121518 Days in Storage (d) Early July Late July Threshold Figure 5-4. Appearance rating of Beit Alpha cu cumbers harvested early and late in the July 2004 season and stored at 10 C fo r 18 d. Vertical lines represent the standard error from the mean, were not shown they fall within the marker size. Appearance Rating

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146 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0369121518 Time in Storage (d) Early Harvest Late Harvest Threshold Figure 5-5. Overall appearance rating of Beit Alpha cucumbers harvested early or late in the harvest season and stor ed at 10 C for 18 d. Ratings represent an average of the three seasons. Vertical lines re present standard error from the mean, were not shown they fall within the marker size. Appearance Rating

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147 Various seasonal and harvest effects on the postharvest quality and storability has been reported on such diverse commodities as grapefruit (Pailley et al ., 2004; Patil et al., 2004), lemons (Aung et al., 2004), apples (L au, 1998; Echeverra et al., 2003), guavas– Psidium guajava L.– (Mercado-Silva et al., 1998) cher ries (Chrisosto et al., 2001), red ginger inflorescence (Chantrach it and Paull, 1998), kiwifrui t (Burdon et al., In press), asparagus (Bhowmik et al., 2002), sapote mamey – Pouteria sapote Jacq.– (BautistaBaos et al, 2002) and avocado (Hofman et al., 2002) among others. The seasonal variations observed include differences in phy totoxicity in lemons fumigated with methyl iodide (Aung et al., 2004), differences in susc eptibility to Braeburn browning disorder in apples (Lau, 1998) as well as differences in aroma volatiles (Echeverra et al., 2003), differences in the growth rate and chemical profile of guavas (Mercado-Silva et al., 1998) and cherries (Chrisosto et al ., 2001), changes in vase life and the effectiveness of hot water treatments on red ginger inflorescence (Chantrachit and Paull, 1998), difference in dry matter content of kiwifruit (Burdon et al., In press), differe nces in textural quality of asparagus (Bhowmik et al., 2002), differences in susceptibility to pathogenic infection in sapote mamey (Bautista-Baos et al, 2002) as well as differences in the response to hot water treatments by avocado (Hofman et al., 2002). In many instances the commodity was grown in the open fields, which could e xplain some of the variations in storage quality of the product. In othe r cases there is no mention of the growing practices since the produce is acquired at retail outlets and not directly from the grower. Arguably, the produce could have come from different grow ers, production regions, growing systems or inclusively from different locations within a single farm; parameters that could have contributed to the differences in quality attributes.

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148 The inability to detect differences in th e marketable life of Beit Alpha cucumbers grown in different seasons coul d be explained by the fact that all the produce used in these experiments was obtained from the same grower, grown in soilless media (composted pine bark) in commercial greenhouses in the same location with very little variation in production pract ices. Greenhouses reduce the environmental variability experienced throughout the year in open fields and provide a stable growing environment for the plants. Amr and Hadidi (2000) report that the ha rvest time had no effect on the chemical components of greenhouse-grown cucumbers and other vegetables while it had a significant effect on open-field cucumbers a nd other vegetables; the authors cite both light intensity and fluctuation as the decidi ng factor. Postharvest quality of horticultural crops is largely influenced by preharvest gr owing conditions such as temperature, light conditions, irrigation (Kang and Park, 1998; Altunlu and Gl, 2000; Lin and Jolliffe, 2000) and root climate (Tzel et al., 1997); a ll of which are regulated in the greenhouse growing environment (Maloupa and Gera sopoulos, 1997; zeker et al., 1997). Although not one of the initial parameters, is was noticed that percentage of culls at harvest varied between early and late harv ests. For each experiment, the commercially graded cucumbers were graded and sorted for a second time before setting up the experiment; more boxes of fruit were needed from the late harvest than from the early harvest to obtain the same am ount of research material.

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149 In early harvest experiments, less than 10% of the commercial product was culled before setting up the experiment, while in la te harvest experiments this figure ranged between 20 to 25% (data not shown). These fi gures represent the amount of produce that was culled due to mis-shaped fruit and transportation injury at the laboratory; the amount of produce culled at the packing station was not determined. External Color A seasonal variation in external color wa s observed at harvest; the October season had significantly higher hue angle values at harvest than the January and July season (Figure 5-6), however fruit from all three se asons experienced a decl ine in external hue angle values during storage. Higher hue angle va lues are reflected as a dark green color, while lower hue angle values are a lighter shad e of green. At harvest, the October season had a hue angle value of 130.4, while the July and January season had an external hue angle value of 128.9 and 123.7, respectively. Cucumber hue angle values fall between 90 (pure yellow) and 180 (pur e green). A decrease in hue angle values translated to changes in epidermal color. Cucumbers e xhibiting some incipient yellowing had hue angle values between 120 a nd 122, which during storage ge nerally progressed from the blossom-end (distal end) towards the stem-e nd (proximal end) of the fruit. Cucumbers became less green (hue angle values decreased) over time for all the three seasons but the seasons that had a higher hue angle at harvest, October (Figure. 5-7) and January (Figure. 5-8), ended the 18-day storage period with higher hue angl e values; 124.8 and 123.7, respectively. The July 2004 (Figure. 5-9) seas on which had the lowest hue angle values at harvest (123.7) ended the 18-day storage pe riod with an average hue angle value of 120.6 and showed yellowing of the epidermis at this point.

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150 Statistical differences in external hue a ngle values were also observed based on the time of harvest. Fruit from the early harv est had significantly lo wer hue angle values throughout the storage period than late harvest fruit (Figure. 5-10). Although significant differences in hue angle valu es were detected based on th e growing season and the time of harvest they did not transl ate into differences in the marketable life of the fruit.

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151 110.0 115.0 120.0 125.0 130.0 135.0 0369121518 Days in Storage (d) October-03 January-04 July-04 Figure 5-6. External color (hue angle ) of Beit Alpha-type cucumbers harvested during three different seasons and stored at 10 C for 18 d. Each season is an average of two harvests. Vertical lines repres ent the standard error from the mean, were not shown they fall within the marker size. Hue Angle ()

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152 110.0 115.0 120.0 125.0 130.0 135.0 0369121518 Days in Storage (d) Early October Late October Figure 5-7. External color (hue angle ) of Beit Alpha cucumbers harvested early and late in the October 2003 season and stored at 10 C for 18 d. Vertical lines represent the standard error from the mean, were not shown they fall within the marker size. Hue Angle ()

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153 110.0 115.0 120.0 125.0 130.0 135.0 0369121518 Days in Storage (d) Early January Late January Figure 5-8. External color (hue angle ) of Beit Alpha cucumbers harvested early and late in the January 2004 season and stored at 10 C for 18 d. Vertical lines represent standard error from the mea n, were not shown they fall within the marker size. Hue Angle ()

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154 110.0 115.0 120.0 125.0 130.0 135.0 0369121518 Days in Storage (d) Early July Late July Figure 5-9. External color (hue angle ) of Beit Alpha cucumbers harvested early and late in the July 2004 season and stored at 10 C for 18 d. Vertical lines represent standard error from the mean, were not shown they fall within the marker size. Hue Angle ()

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155 110.0 115.0 120.0 125.0 130.0 135.0 0369121518 Days in Storage (d) Early Harvest Late Harvest Figure 5-10. Overall external color (hue angl e ) of Beit Alpha cucumbers harvested early and late in harvest season and stored at 10 C for 18 d. Each harvest time is an average of all three seasons. Vertical lin es represent standard error from the mean, were not shown they fall within the marker size. Hue Angle ()

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156 Yellowing of the peel has been reported as being the primary parameter to limit the marketable life of cucumbers (Lin and Jo lliffe, 1994). The peel color and chlorophyll content at harvest have theref ore also been proposed as indi cators of marketable life (Lin and Jolliffe, 2000) however it has been found to be of little reliability because color variations occur during storage in fruit with th e same initial color at harvest (Scouten et al., 2002). Furthermore the changes in peel color during storage may be in part independent to storage since it is influen ced by preharvest conditions (Scouten 1997) such as light intensity and quality as well as canopy char acteristics (Lin and Joliffe, 2000). Internal Color As with external color, a seasonal variati on in internal color or hue angle was also observed. Fruit from the July season, which had the lowest external hue angle values of all the three seasons, also had significantly lowe r internal hue angle values than fruit from the January or October season and also ended the storage period with significantly lower hue angle values than the other two seasons (T able 4-1). Initial hue angle values for the October 2003, January 2004 and July 2004 seasons were 113.5, 113.2, and 111.5, respectively and at the end of the 18-day storage peri od decreased to 108.8, 109.4 and 105.9, in the same order. The differences in hue angle were minor, in terms of absolute values, and did not affect the marketable life Internal color assessments are not included as part of the U.S. grade standards for greenhouse grown cucumbers and could not be correlated well with the overall quality of stor ed cucumbers. The effect of storage on the internal color could be important if the commodity was destined for fresh-cut products.

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157 Table 5-1. Internal hue angle of Beit Alpha cucumbers harvested during thr ee different growing seasons (October-2003, January2004 and July-2004) and stored at 10 C for 18 d. Each season consists of an early and late harvest. Storage Length (d) 0 3 6 9 12 15 18 Season Harvest Mean s Mean s Mean s Mean s Mean s Mean s Mean s October-03 Early 109.7 1.30109.53.05107.71.21110.80.88 107.81.41109.91.12108.42.40 Late 113.1 1.40111.21.45111.31.06106.50.95 108.53.26110.93.17106.32.50 January-04 Early 109.7 0.63114.91.43113.51.05114.80.93 109.51.74109.52.39108.81.30 Late 109.3 1.94112.62.81113.51.71112.31.20 111.71.37111.40.56106.30.99 July-04 Early 113.8 1.33113.40.92113.31.00113.61.14 111.90.67111.90.67105.11.20 Late 111.9 0.89111.20.53110.40.85114.30.57 114.91.12107.00.99106.51.10 Zn = 5

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Weight Loss The growing season had no effect on the ove rall weight loss of stored cucumbers. Although weight loss was initially higher in th e January season, these differences became indistinguishable from the other two seasons after 15 d in storage. Total weight loss for all the three seasons was betw een 2.82 to 3.02% after 18 d in storage with no significant differences among the three seasons (Table 4-2). Likewise, the time of harvest had no effect on the rate of weight loss of stored cucumbers. As with the different seasons, ther e were initial differences in weight loss with the early harvest having significantly highe r weight loss for the first 12 d in storage than the late season harvest. However, thes e differences became indistinguishable after 15 d in storage and at the end of the storag e period both the early harvest and the late harvest fruit had statistically similar weight loss rates. Fruit harvested early in the season had an average weight loss of 2.9% after 18 d in storage while fruit harvested late in the season lost an average of 3.4% after the same storage period; both values were statistically similar.

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159Table 5-2. Weight loss (%) of Beit Alpha cucumbers harvested during three different growing seasons (October-2003, January-200 4 and July-2004) and stored at 10 C for 18 d. Each season consists of an early and late harvest. Storage Length (d) 3 6 9 12 15 18 Season Harvest Mean s Mean s Mean s Mean s Mean s Mean s October-03 Early 0.3 0.04 0.6 0.39 1.2 0.67 1.5 0.78 1.8 0.90 2.4 0.85 Late 0.3 0.04 0.9 0.64 1.0 0.69 1.6 0.81 2.7 0.94 3.2 0.75 January-04 Early 1.0 1.04 1.8 0.99 2.1 1.10 2.5 1.27 2.5 1.37 3.1 1.05 Late 0.8 0.25 2.1 0.91 2.6 1.18 4.2 1.53 4.7 1.53 4.8 0.92 July-04 Early 0.8 0.56 1.5 0.57 2.1 0.84 2.3 0.92 2.5 0.96 2.9 0.85 Late 0.5 0.15 0.9 0.20 1.4 0.34 1.9 0.53 2.3 0.53 2.6 0.40 Z n = 30

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160 Firmness The growing season had no significant e ffect on the pulp firmness of Beit Alpha cucumbers during storage. Seasonal variations in pulp firmness were observed at harvest but did not affect the marketab le life of the fruit (Figure. 4-11). Depending on the season, mesocarp firmness either increased or remain ed stable during stor age but due to the variability during storage all seasons had statistically similar firmness values at the end of the 18-day storage period. Pulp firmness of fruit harvested in the October season decreased 13% while in storage (Figure. 412); from 15.6 N at harv est to 13.6 N after 18 d in storage while fruit from the January s eason, which had the lowest mesocarp firmness at harvest, experienced a 48% increase in pulp firmness or ‘toughening’ during the 18day storage period (Figure. 4-13). In comparis on, the pulp firmness of fruit from the July season was statistically unchanged during th e same storage period (Figure. 4-14). In cucumbers, an increase in firmness during storage has been associated with the concentration of CO2 in the storage atmosphere (Alt unlu and Gl, 1997). Differences of firmness at harvest as well as an increase in firmness or ‘tougheni ng’ in storage have been previously described in greenhous e-grown asparagus (B howmik et al., 2002). The harvest time (early in the harvest versus late in the harvest period) did not have an effect on the pulp firmness of Beit Alpha cucumbers during storag e (Figure. 4-15). Initial pulp firmness measurements were statis tically similar for both harvest periods (the average value for each harvest time is an av erage of the three seasons) and remained relatively stable during the st orage period independent of time of harvest. The early harvest fruit had an initial pulp firmness va lue of 13.8 N and it increased to 15.4 after 18 d of storage.

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161 On the other hand the late harvest fruit had an initial pulp firmness value of 13.6 and it increased to 14.5 after the same storag e period. Although different absolute values were obtained at different intervals in th e storage period, all th ese values were not statistically different to the initial pulp fi rmness values for both seasons; evidence that pulp firmness did not change significan tly during the 18-day storage period.

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162 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 0369121518 Length of Storage (d) Oct-03 Jan-04 Jul-04 Figure 5-11. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested during three different seasons and stored at 10 C for 18 d. Each season is an average of two harvests. Vertical lines repr esent standard error from the mean. Mesocar p Firmness ( N )

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163 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 0369121518 Length of Storage (d) Early October Late October Figure 5-12. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and late in the October 2003 season and stor ed at 10 C for 18 d. Vertical lines represent standard error from the mean. Mesocar p Firmness ( N )

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164 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 0369121518 Length of Storage (d) Early January Late January Figure 5-13. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and late in the January 2004 season and stor ed at 10 C for 18 d. Vertical lines represent standard error from the mean. Mesocar p Firmness ( N )

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165 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 0369121518 Length of Storage (d) Early July Late July Figure 5-14. Mesocarp firmness (Newtons) of Beit Alpha cucumbers harvested early and late in the July 2004 season and stored at 10 C for 18 d. Vertical lines represent standard error from the mean. Mesocar p Firmness ( N )

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166 0 2 4 6 8 10 12 14 16 18 0369121518 Length of Storage (d) Early Harvest Late Harvest Figure 5-15. Overall mesocarp firmness (New tons) of Beit Alpha cucumbers harvested early and late in harvest season and stor ed at 10 C for 18 d. Each harvest time is an average of all three seasons. Verti cal lines represent standard error from the mean. Mesocar p Firmness ( N )

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167 Conclusions The growing season and time of harvest ha d no significant effect on the marketable life of greenhouse-grown Beit Alpha cucumber s. On average, all three seasons had similar marketable life and stored well for 15 to 18 d at 10 C. Although differences in certain attributes could be detected at di fferent intervals in the storage period, these differences did not translate in to differences in marketable life. Greenhouse production of Beit Alpha cucumbers allows growers to ha ve a year-round supply of cucumbers with no significant variation in quality aspects such as firmness, inte rnal color, weight loss and most important marketable life.

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168 CHAPTER 6 CONCLUSIONS Beit Alpha-type cucumbers maintained ma rketable quality for 15 to 18 d when stored in rigid, ventilated cl amshells at 10 C and ~90% relative humidity. The clamshells provided protection from two shelf life-lim iting factors; dehydrat ion and mechanical injury. Humidity levels inside the clamshells reached ~90 % and remained at that level during the storage period, prot ecting the cucumbers from excessive weight loss without promoting pathogenic infection (the cucumbers were surface sanitized ). The rigidity of the clamshells protected the cucumbers from bruising that would have resulted if the cucumbers had been stored in bulk and under pr essure from other layers of cucumbers. Beit Alpha-type cucumbers are sensi tive to ethylene and exposure to concentrations as low as 1 ppm resulted in the deterioration of quality. Ethylene reduced the marketable of Beit Alpha cucumbers between 20 and 60% depending on the ethylene concentration in the storage atmosphe re and the duration of exposure. European-type cucumbers were also affect ed by ethylene and the protective shrinkwrap did not mitigate the effect of ethylene although it protected the fruit from weight loss. European cucumbers retained acceptable appearance for up to 9 d when exposed to ethylene and did not respond different when the ethylene concentra tion in the storage atmosphere was increased from 1 to 10 ppm. Determining the effect of ethylene by a ppearance alone, proved to be misleading since changes in appearance were secondary and developed after the effect of ethylene was reflected on other parameters such as el ectrolyte leakage. A reliable assessment of

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169 the quality of the product, especially if it is suspected to have been exposed to stressful conditions such as ethylene, should involve the assessment of parameters such as electrolyte leakage and firmness. Beit Alpha-type cucumbers grown in gr eenhouses did not exhibit remarkable differences in quality assessments during th e storage period. The growing season and the time of harvest did not have an effect on the shelf life of cucumbers; an indication that cucumbers grown in greenhouses do not show intr a or interseasonal va riations in quality.

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170 APPENDIX A APPEARANCE RATING SCALE FOR STORED CUCUMBERS Rating Description Remarks 9 Field Fresh Dark green color, waxy appearance, turgid 7 Good Minor defects are present but not objectionable. Slight shriveling of the stem end, firm (doesnÂ’t yield when flexed) 5 Fair Slight yellowing is evident, stem-end and blossom end shriveling is moderate 3 Unmarketable Pale yellow external color, severe water loss (shriveling, leathery skin), severe shriveling of the stem and blossom ends. 1 Inedible Adapted from Dr. Jeffrey Brecht, University of Florida.

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171 APPENDIX B ISOTONIC MANNITOL CONCENTRATION -50.0 -40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0 0.00.10.20.30.40.50.60.70.80.91.0 Mannitol Concentration (M) Appendix B. Weight change, as a percent of initial weight, of mesocarp cores of Beit Alpha cucumbers immersed in different con centrations of mannito l bathing solution for four hours. Vertical bars represent standa rd error from the m ean, were not shown standard error falls within the marker size. Weight Change (%)

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183 BIOGRAPHICAL SKETCH Alfredo Villalta was born in Tegucig alpa, Honduras, in 1979. He obtained his associateÂ’s degree in tropical agriculture fr om Zamorano University (Escuela Agricola Panamericana) in Tegucigalpa, Honduras, in 1999 and a Bachelor of Science degree from the University of Florida in 2001.