Influence of Harvest Maturity and Pre-storage Conditioning on Quality of Melting and Non-melting Flesh Peaches

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Influence of Harvest Maturity and Pre-storage Conditioning on Quality of Melting and Non-melting Flesh Peaches
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1 online resource (230 p.)
Language:
english
Creator:
Kao,Ming-Wei S
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University of Florida
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Gainesville, Fla.
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Thesis/Dissertation Information

Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Horticultural Science
Committee Chair:
Brecht, Jeffrey K
Committee Co-Chair:
Williamson, Jeffrey G
Committee Members:
Chaparro, Jose
Huber, Donald J
Baldwin, Elizabeth A

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Subjects / Keywords:
heat -- maturity -- peach -- pectinmethylesterase -- polygalacturonase -- postharvest -- quality -- storage
Horticultural Science -- Dissertations, Academic -- UF
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Horticultural Science thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract:
Two melting flesh (MF) peach cultivars, 'Flordaprince' and 'TropicBeauty', and two non-melting flesh (NMF) peach cultivars, 'UFSun' and 'Gulfking', were sorted into different maturity groups (MG) at harvest based on peel ground color a* value (GCa*). The NMF cultivars harvested at different developmental stages generally produced higher climacteric ethylene at harvest and during ripening than the MF cultivars. The MF peaches were preclimacteric or at onset of the climacteric rise at harvest. The NMF cultivars can be harvested at more advanced developmental stages (MG 15-20) than the MF cultivars (MG 5-10) for immediate fresh market consumption due to the absence of rapid softening at late ripeness stage. The MF cultivars and NMF 'Gulfking' fruit intended for low temperature storage should be harvested at MG 0-10 for best quality when ripened, but NMF 'UFSun' needs to be harvested at a more advanced stage (MG 10-15) to avoid development of abnormal softening. A second study focused on the effect of different pre-storage conditioning treatments on maintenance of fruit quality during ripening at ambient temperature (20?C) or after low temperature storage condition (0?C). NMF 'UFSun' and NMF 'Delta' peaches at commercial harvest maturity were immersed for 30 min in water at 25?C (Control) or 46?C (HW), or in 25?C water containing 100 ?g/L 1-methylcyclopropene (1-MCP), or in 46?C water containing 100 ?g/L 1-MCP (HW x 1-MCP). It was found that 100 ?g/L 1-MCP was insufficient to inhibit fruit softening for both of those NMF cultivars. The experiment was repeated with higher 1-MCP concentrations based on the climacteric ethylene production rate of the fruit measured before the treatment. The results indicate the HW treatment alone was most potent in delaying fruit softening of the NMF peaches during ambient temperature storage. Although low temperature storage prolonged the inhibitory effect of 1-MCP, both HW and HW x 1-MCP treatments were more effective than 1-MCP application for firmness retention of the NMF peaches during ripening after low temperature storage.
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In the series University of Florida Digital Collections.
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Includes vita.
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Statement of Responsibility:
by Ming-Wei S Kao.
Thesis:
Thesis (Ph.D.)--University of Florida, 2011.
Local:
Adviser: Brecht, Jeffrey K.
Local:
Co-adviser: Williamson, Jeffrey G.

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1 INFLUENCE OF HARVEST MATURITY AND PRE STORAGE CONDITIONING ON QUALITY OF MELTING AND NON MELTING FLESH PEACHES By MING WEI SHERRY KAO A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2011

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2 2011 Ming Wei Sherry Kao

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3 To my family

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4 ACKNOWLEDGMENTS I am very grateful to both of my advisors, Dr. Jeffrey K. Brecht and Dr. Jeffrey G. Williamson, for their motivation, guidance, and support. I would like to thank Dr. Donald J. Huber for his assistance in solving problems associated with laboratory assays. I also would like to thank Dr. Jose Chaparro for establishing the peach journal cl ub, which helped me to keep up with the literature. I am very appreciative of Dr. Elizabeth A. Baldwin for her willingness to participate in my supervisory committee. I would like to thank Kim Cordasco, Paul Miller, James Lee and Adrian Berry for their ass istance in setting up my experiments both in the laboratory and peach orchard. Lastly, I would like to thank Bee Ling Poh, Angelos Deltsidis, Francisco Loayza, and Pei Wen Huang, for their kind help during my treatment days.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 8 LIST OF FIGURES ................................ ................................ ................................ ........ 13 ABSTRACT ................................ ................................ ................................ ................... 14 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 16 2 LITERATURE REVIEW ................................ ................................ .......................... 20 Origin and C ultivation ................................ ................................ .............................. 20 Fruit Growth and Development ................................ ................................ ............... 23 Peach Postharvest Physiology Climacteric Ripening ................................ ........... 26 Ethylene ................................ ................................ ................................ ........... 26 Respiration ................................ ................................ ................................ ....... 29 Compositional Changes ................................ ................................ ................... 30 Sugars ................................ ................................ ................................ ....... 30 Acids ................................ ................................ ................................ .......... 31 Pigments ................................ ................................ ................................ .... 32 Textural Changes ................................ ................................ ............................. 34 Cell Wall Modifications associated with Fruit Softening ................................ .... 35 Pectin methyl esterase (PME) ................................ ................................ .... 37 Polygalacturonase (PG) ................................ ................................ ............. 38 Chilling I njury ................................ ................................ ................................ .......... 40 Harvest Maturity ................................ ................................ ................................ ...... 42 Storage ................................ ................................ ................................ ................... 45 Temperature Management ................................ ................................ ............... 45 Atmosphere Modification ................................ ................................ .................. 46 Ethylene Control Inhibitors of Ethylene Biosynthesis ................................ ..... 47 Heat Treatment ................................ ................................ ................................ 47 Ethylene Control Inhibitors of Ethylene Action ................................ ............... 50 1 Methylcyclopropene (1 MCP) ................................ ................................ ........ 51 3 OP TIMUM HARVEST AND POSTHARVEST HANDLING PRACTICES FOR LOW CHILL, MELTING AND NON MELTING FLESH PEACH VARIETIES IN TROPICAL AND SUBTROPICAL CLIMATES ................................ ........................ 55 Overview ................................ ................................ ................................ ................. 55 Materials and Methods ................................ ................................ ............................ 58 Results and Discussion ................................ ................................ ........................... 61

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6 Effect of Maturity at Harvest on Physical and Chemical Characteristics .......... 61 Effect of Maturity and Ripening on Physical and Chemical Characteristics ...... 64 Optimum Harvest Ma turity Determination ................................ ......................... 68 Potential Maturity Indices Determination ................................ .......................... 71 Chapter Conclusion ................................ ................................ ................................ 72 4 RIPENING AND QUALITY DEVELOPMENT OF LOW CHILL SUBTROPICAL MELTING AND NON MELTING FLESH PEACH VARIETIES HARVESTED AT DIFFERENT MATURITIES ................................ ................................ ..................... 93 Ov erview ................................ ................................ ................................ ................. 93 Materials and Methods ................................ ................................ ............................ 96 Results and Discussion ................................ ................................ ......................... 102 Respiration and Ethylene Production ................................ ............................. 102 Quality Analysis ................................ ................................ .............................. 104 Enzyme Assays ................................ ................................ .............................. 106 Chapter Conclusion ................................ ................................ .............................. 109 5 EFFECT OF PRE STORAGE HOT WATER TREATMENT ALONE OR COMBINED WITH AQUEOUS 1 METHYCLCOPROPENE ON RIPENING OF NON MELTING FLESH PEACHES ................................ ................................ ...... 115 Overview ................................ ................................ ................................ ............... 115 Materials and Methods ................................ ................................ .......................... 118 Results and Discussion ................................ ................................ ......................... 125 Preliminary Study 1 Determination of Optimum Hot Water Temperature, 1 MCP Concentration, and Exposure time for Pre storage Conditioning Treatments ................................ ................................ ................................ .. 125 Preliminary Study 2 Effect of 1.5 Mg/L 1 MCP on Ripening of MF ............ 126 conditioned with HW, 1 MCP, or HW x 1 MCP at 20 C .............................. 127 Ethylene production and respiration rate ................................ ................. 127 Flesh firmness ................................ ................................ .......................... 130 Enzyme assays ................................ ................................ ........................ 131 Ground color and flesh color ................................ ................................ .... 134 Soluble solids content, titratable acidity, and pH ................................ ...... 135 Weight loss and decay ................................ ................................ ............. 136 Chapter Conclusion ................................ ................................ .............................. 137 6 EFFE CT of PRE STORAGE HOT WATER TREATMENT ALONE OR COMBINED WITH AQUEOUS 1 METHYCLCOPROPENE ON RIPENING OF NON MELTING FLESH PEACHES AFTER LOW TEMPERATURE STORAGE .. 155 Overview ................................ ................................ ................................ ............... 155 Materials and Methods ................................ ................................ .......................... 158 Results and Discussion ................................ ................................ ......................... 163

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7 Ethylene Production and Respiration Rate ................................ ..................... 163 Flesh Firmness, PME and endo PG Activities ................................ ................ 166 Ground Color, Flesh Color, and Weight Loss ................................ ................. 170 Soluble Solids Content, Titratable Acidity, pH ................................ ................ 172 Incidence of Decay and Pitting ................................ ................................ ....... 173 Chapter Conclusion ................................ ................................ .............................. 176 7 SUMMARY AND CONCLUSIONS ................................ ................................ ........ 196 LIST OF REFERENCES ................................ ................................ ............................. 206 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 230

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8 LIST OF TABLES Table page 3 1 physical and chemical characteristics of the least mature to most advanced fruit at harvest based on GCa* ................................ .................. 73 3 2 physical and chemical characteristics of least mature to most advanced fruit afte r 7 days at 20C based on GCa* ................................ ........... 73 3 3 physical and chemical characteristics of least mature to most advanced fruit after 14 days at 0C and 7 days at 20C based on GCa* ............ 74 3 4 physical and chemical characteristics of least mature to most advanced fruit at harvest based on GCa* ................................ ........................... 7 5 3 5 physical and chemical characteristics of least mature to most advanced fruit after 7 days at 20C based on GCa* ................................ ........... 75 3 6 physical and chemical characteristics of least mature to most advanced fruit after 14 days at 0C and 7 days at 20C based on GCa* ............ 76 3 7 physical and chemical characteristics of least mature to most advanced fruit at harvest based on GCa* ................................ ........................... 77 3 8 physical and chemical characteristics of least mature to most advanced fruit after 7 days at 20C based on GCa* ................................ ........... 77 3 9 physical and chemical characteristics of least mature to most advanced fruit after 14 days at 0C and 7 days at 20C based on GCa* ............ 78 3 10 physical and chemical characteristics of least mature to most advanced fruit at harvest based on GCa* ................................ ........................... 79 3 11 physical and chemical characteristics of least mature to most advanced fruit after 7 days at 20C based on GCa* ................................ ........... 79 3 12 physical and chemical characteristics of least mature to most advanced fruit after 14 days at 0C and 7 days at 20C based on GCa* ............ 80 3 13 physical and chemical characteristics of least mature to most advanced fruit at harvest based on GCa* in 2008 ................................ .............. 81 3 14 physical and chemical characteristics of least mature to most advanced fruit after 7 days at 20C based on GCa* in 2008 .............................. 82 3 15 physical and chemical characteristics of least mature to most advanced fruit after 14 days at 0C and 7 days at 20C in 2008 ........................ 83

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9 3 16 physical and chemical characteristics of least mature to most advanced fruit at harvest based on GCa* in 2008 ................................ .............. 83 3 17 physical and chemical characteristics of least mature to most advanced fruit after 7 days at 20C based on GCa* in 2008 .............................. 84 3 18 physical and chemical characteristics of least mature to most advanced fruit after 14 days at 0C and 7 days at 20C in 2008 ............... 85 3 19 physical and chemical characteristics of least mature to most advanced fruit at harvest based on GCa* in 2008 ................................ .............. 86 3 20 physical and chemical characteristics of least mature to most advanced fruit after 7 days at 20C based on GCa* in 2008 ............................. 87 3 21 physical and chemical characteristics of least mature to most advanced fruit after 14 days at 0C and 7 days at 20C in 2008 ........................ 88 3 22 physical and chemical characteristics of least mature to most advanced fruit at harvest based on GCa* in 2008 ................................ .............. 89 3 23 physical and chemical characteristics of least mature to most advanced fruit after 7 days at 20C based on GCa* in 2008 ............................. 89 3 24 physical and chemical characteristics of least mature to most advanced fruit after 14 days at 0C and 7 days at 20C in 2008 ........................ 90 3 25 Summary of optimum harvest maturities and the common maturity range between the two years for all cultivars ................................ ................................ 90 3 26 Correlation coefficient (r) between maturity groups and fruit qualities, and among fruit qualities at harvest for peaches in 2007 ................................ .......... 91 3 27 Correlation coefficient (r) between maturity groups and fruit qualities, and among fruit qualities at harvest for peaches in 2008 ................................ .......... 92 3 28 Two year summary of potential maturity indices for all cultivars, MF specific, or NMF specific ................................ ................................ ................................ ... 92 4 1 Mean fruit quality of MF and NMF peaches in three seasons after 5 days of storage at 20 C ................................ ................................ ................................ 113 4 2 Flesh firmness PME, and PG activities for MF and NMF peaches with initial GC a* at 20 C in 2007 ................................ ........................... 114 4 3 Flesh firmness PME, and PG activities of MF and NMF peaches with initial GC a* at 20 C in 2010 ................................ ............ 114

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10 5 1 peaches after 3 days at 20 C. ................................ ................................ ......... 138 5 2 Effect of 1 MCP concentration x exposure time on flesh firmness (N) of ................................ ....................... 138 5 3 Effect of pre storage HW and 1 MCP treatments on ethylene production and at 20 C ................................ ...... 139 5 4 Effect of pre storage HW and 1 MCP treatments on flesh firmness of ................................ ......... 140 5 5 after pre storage conditioning treatments ................................ ......................... 140 5 6 Effect of pre storage HW and 1 MCP treatments on ethylene production and ................................ ......... 142 5 7 Effect of pre storage HW and 1 MCP treatment on ethylene production and hes ................................ ............ 144 5 8 Effect of pre storage HW and 1 MCP treatments on flesh firmness (N) of ................................ ................................ ...... 145 5 9 storage conditioning treatments. ................................ ................................ ....... 146 5 10 Effect of pre storage HW and 1 peaches during ripening at 20 C ................................ ................................ ..... 147 5 11 storage conditioning treatments ................................ ................................ ........ 148 5 12 pre storage conditioning treatments ................................ ................................ 149 5 13 storage conditioning treatments ................................ ................................ ........ 150 5 14 pre storage conditioning treatments ................................ ................................ 151 5 15 storage conditioning treatments ................................ ................................ ........ 152 5 16 Incidence of decay of pre conditioned NMF peaches after 7 days of storage at 20 C ................................ ................................ ................................ ............. 153

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11 6 1 Effect of pre storage HW and 1 MCP treatments on ethylene production and ................................ ..................... 177 6 2 Effect of pre storage HW and 1 MCP treatments on ethylene production and ................................ ..................... 178 6 3 Effect of pre storage HW and 1 MCP treatments on ethylene production and ................................ ....................... 179 6 4 Effect of pre storage HW and 1 MCP treatments on ethylene production and ................................ ....................... 180 6 5 Effect of pre storage HW and 1 peaches in 2009 ................................ ................................ ............................... 181 6 6 Effect of pre storage HW and 1 peaches in 2010 ................................ ................................ ............................... 182 6 7 storage conditioning treatments in 2010 ................................ ................................ ............................ 183 6 8 Effect of pre storage HW and 1 peaches in 2009 ................................ ................................ ............................... 184 6 9 Effect of pre storage HW and 1 peaches in 2010 ................................ ................................ ............................... 185 6 10 storage conditioning treatments in 2010 ................................ ................................ ............................ 186 6 11 storage conditioning treatments in 2009 ................................ ................................ ............................ 187 6 12 storage conditioning treatments in 2010 ................................ ................................ ............................ 188 6 13 treatments in 2009 ................................ ................................ ........................... 189 6 14 storage conditioning treatments in 2010 ................................ ................................ ............................ 190 6 15 storage conditioning treatments in 2009 ................................ ................................ ............................ 191 6 16 storage conditioning treatments in 2010 ................................ ................................ ............................ 192

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12 6 17 storage conditioning treatments in 2009 ................................ ................................ ............................ 193 6 18 after pre storage conditioning treatments in 2010 ................................ ................................ ............................ 194 6 19 Incidence of decay of pre conditioned NMF peaches after 14 days of storage at 0C plus 5 7 days of ripening at 20C ................................ ........................... 195 6 20 Incidence of pitting of pre conditioned NMF peaches after 14 days of storage at 0C plus 7 days of ripening at 20 C in 2010 ................................ ................ 195

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13 LIST OF FIGURES Figure page 4 1 Respiration rate and ethylene production at 20C storage of different maturity groups of MF and NMF peaches in 2008 based on GCa*. ............................... 111 4 2 Respiration rate and ethylene production at 20C storage of different maturity groups of MF and NM F peaches in 2009 based on GCa*. ............................... 112 5 1 Effect of pre storage conditioning treatments on ethylene production and respiration rate s ................................ .................... 139 5 2 Ethylene production and respiration rate during ripening at 20 C after pre storage conditioning treatments in 2009 and 201 0 ............................ 141 5 3 Ethylene production and respiration rate during ripening at 20 C after pre storage conditioning treatments in 2009 and 2010 ............................ 143 5 4 Preclimacteric to climacteric ethylene production and respiration rate of NMF ................................ ................................ .............................. 154

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14 Abstract of Dissertation Presented t o t he Graduate School o f the University o f Florida in Partial Fulfillment of t he Requirements for t he Degree o f Doctor o f Philosophy INFLUENCE OF HARVEST MATURITY AND PRE STORAGE CONDITIONING ON QUALITY OF MELTING AND NON MELTING FLESH PEACHES By Ming Wei Sherry Kao Aug ust 2011 Chair: Jeffrey K. Brecht Co chair : Jeff re y G. Williamson Major: Horticultural Science s Flor daprince non different maturity groups (MG) at harvest based on peel ground color a* value (GCa*). T he NMF cultivars harvested at different developmental st ages generally produced higher climacteric ethylene at harvest and during ripening than the MF cultivars. The MF peaches were pre climacteric or at onset of the climacteric rise at harvest. The NMF cultivars can be harvested at more advanced developmental s tages (MG 15 20) than the MF cultivars (MG 5 10) for immediate fresh market consumption due to the absence of rapid softening at late ripeness stage. T intended for low temperature storage should be harvested at MG 0 10 for best quality 10 15) to avoid development of abnormal softening. A second study focused on the effect of different pre storage conditioning treatments on maintenance o f fruit quality during ripening at ambient temperature (20C) or after low temperature storage condition (0C)

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15 peaches at commercial harvest maturity were immersed for 30 min in water at 25 C (Control) or 46 C (HW), or in 25 C water containing 100 g/L 1 methylcyclopropene (1 MCP), or in 46 C water containing 100 g/L 1 MCP (HW x 1 MCP). It was found that 100 g/L 1 MCP was insufficient to inhibit fruit softening for both of those NMF cultivars. The e xperiment was repeated with higher 1 MCP concentrations based on the climacteric ethylene production rate of the fruit measured before the treatment. The results indicate t he HW treatment alone was most potent in delaying fruit softening of the NMF peaches during ambient temperature storage Although l ow temperature storage prolonged the inhibitory effect of 1 MCP b oth HW and HW x 1 MCP treatments were more effective than 1 MCP application for firmness retention of the NMF peaches during ripening after low temperature storage.

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16 CHAPTER 1 INTRODUCTION Peaches are one of the most popular fruits in the world because of their dessert like flavor and a long history of cultivation (Robertson et al., 1991; Li 1984). They can also be an important source of antioxidants for human nutrition (Tomas Barberan et al., 2001) Peaches ranked 6 th among 18 fruits in U.S. per capita consumption in 1997, higher than grapes (7 th ), cherries (16 th ), blueberries (17 th ), and cranberries (18 th ) that typically contain high polyphenol concentrations, but are underused in the average American diet (Vinson et al., 2001) Although peaches are flavorful and nutritious, the annual per person consumption of peach es (both fresh and canned) dropped from 13 lbs in the early 1970s to about 8.8 lbs by 2008 (Brunke et al., 2011) Fresh consumption was around 4.6 lbs in 2006 but increased to 5.5 lbs in 2008. Canned consumption decre ased from 7 lbs per person in the 1970s to 3.0 lbs per person in 2008. This suggests that consumers would like to incorporate fresh peach fruit in their diet more than the canned fruit. Lack of flavor and hard texture are two main complaints from consumer s about fresh peaches (Bruhn et al., 1991) Traditional peach cultivars (melting flesh types; MF) ripen quickly at ambient temperature and are extremely vulnerable to mechanical injuries after harvest due to extensive softening toward the end of ripening process. Thus, peaches grown for fresh consumption are harvested at (Cascales et al., 2005; Williamson and Sargent, 1999) These fru it are often immature and cannot ripen to have the same qualities as tree ripened fruit. To extend the postharvest life of peaches, immediate refrigeration at low temperature is necessary. The recommended storage temperature for most peaches is

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17 0 C for up to 2 or 3 weeks depending on the cultivar (Crisosto et al., 1999) Prolonged low temperature storage enhances the development of chilling injury (CI), which can result in peaches with poor flavor and dry and mealy texture ( Lurie and Crisosto, 2005 ) Immature and unripe peaches are more susceptible to chilling injury than ripe fruit. Another way to preserve the quality of peaches after harvest is to minimize ethylene production ei ther by blocking ethylene synthesis or action. Pre storage conditioning methods such as heat treatment (ethylene biosynthesis inhibitor) and 1 MCP application (ethylene action inhibitor) have the potential to be incorporated into commercial handling practi ces for peaches (Clemente Vitti et al., 2007; Kluge and Jacomino, 2002; Murray et al., 2007) A trend in peach breeding is to combine the ideal fresh mark et quality of MF peaches with the firmer texture of non melting flesh (NMF) peaches (Sherman et al., 1990) NMF peaches are generally used for canning since they are able to maintain their integrity throughout the high temperature retort treatment (Robertson et al., 1992 b ) They retain initial texture longer after harvest and soften gradually during ripening, thus decreasing the chance of physical damages from handling. A N MF fruit with MF flavor may attain maximum sensory qualities on the tree and would be more resistant to the mechanical damage and decay associated with excessive softening. Peach varieties that are suitable for growing in subtropical and tropical environm ents are continuously being released. Developing these low chill subtropical cultivars is advantageous because they provide a fresh supply of fruit for local markets and the potential to ship fruit for higher values to more distant markets where peach prod uction is not occurring (Rouse and Sherman, 2002) Although this deciduous fruit is

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18 becoming more popular in the subtropical and tropical regions, information on optimum harvest maturity, maturity indicators, and postharvest handling practices are limited, especially for the new NMF varieties. Using four, low chill, subtropical cultivars optimum harvest maturity based on ambient and low temperature storage conditions and to develop indices that can best predict fruit ma turity at harvest; and 2) to compare respiration rates and ethylene production for fruit harvested at different stages during ripening. The results indicate that the NMF cultivars can be harvested at more advanced stages than the MF cultivars for immediate fresh market consumption. The MF and NMF cultivars generally can be stored at 0 C for 2 weeks if harvested at lower maturity than those destined for immediate fresh market consumption. Harvest maturity for both peach types can be best predicted with grou nd color a* value and titratable acidity. The NMF peach cultivars harvested at different stages generally produced higher climacteric ethylene than the MF peaches at harvest and during ripening. evaluate if some pre storage conditioning methods, including hot water treatment, liquid 1 MCP application, a combination of the two, are effective to maintain quality, especially texture, of the fruit during ripening in ambient temperature storage (20C) and after low temperature storage (0C). The results suggest that HW treatment is more effective than 1 MCP treatment as a pre storage conditioning method for quality maintenance of NMF peaches at 20 C HW and HW x 1 MCP treatments have the potential to be used

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19 to control ripening of NMF peaches that are held in low temperature storage. 1 MCP treatment can be considered for cultivars that develop surface injury under heat stress.

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20 CHAPTER 2 LITERATURE REVIEW Origin and Cultivation Peach is native to China and its cultivation has been dated as early as 3,000 B.C (Li, 1984) The botanical name of peach, Prunus persica (L.) Batch, can be traced to Persia (Iran) (Bassi and M onet, 2008) It is believed that peaches were carried from China to Persia and quickly spread from there to Europe. The Spaniards first introduced peaches to America around 1565. The earliest cultivation was at St. Augustine, Florida and along the Savan nah River in Georgia. Around the same time, peaches brought by the Spaniards disseminated quickly among the Aztecs in Mexico. From Mexico, peaches spread to New Mexico, Arizona, and California. Eventually, commercial peach production in Californi a started around the mid 19 th century (Faust and Timon, 1995) According to the Food and Agriculture Organization (FAO) of the United Nations (FAO, 2009) China accounts for 50% of the world production of peaches and nectarines (a peach mutation lacking trichomes on the fruit) followed by Italy (10%), Spain (7%) and the USA (6%). In the USA, peaches are commercially produced in 23 states and the top four states are California, South Carolina, New Jersey and Georgia. California is a major producer of both fresh and processed peaches, while South Carolina New Jersey, and Georgia mainly produce fresh peaches. In 2009, the USA produced a total of 1,103,770 tons of peaches, 46% of which w ere destined for fresh consumption and 54% were for processing (NASS, 2010) Major processed peach products include canned and frozen fruit. Other products include peach concentrate, baby food, dry fruit, jam, and jelly (Siddiq, 2006)

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21 Peaches are generally pleasant to consumers due to dessert like characteristics developed during ripening (Robertson et al., 1991) They can also be an important source of antioxidants (Tomas Barberan et al., 2001) Vinson et al. (2001) presented data on per capita consumption of several fruits in 1997. Among 18 fruits, peach rank ed 6 th in per capita consumption, h igher than grapes (7 th ), cherries (16 th ), blueberries (17 th ), and cranberries (18 th ) that typically have high phenol ic concentrations but are underused in the average American diet. Melting (MF) and non melting flesh (NMF) are two types of peach fruit that are most commonly produced. Most fresh market peaches belong to the MF group. They NMF types that remain relatively firm. NMF peaches are generally used for canning since they are able to maintain their integrity throughout the high temperature retort treatment (Robertson et al., 1992 b ) MF cultivars carry the dominant allele of the (M) locus that controls flesh firmness while NMF cultivars possess a homozygous recessive (mm) allele (Peace et al., 2005) Various peach training systems are utilized in commercial orchards. Although the open vase system is the most popular, other training systems such as palmette, Y trellis, and slender spindle (fusetto), offer higher density planting, which can be more beneficial in certain orchards (Corelli Grappadelli and Marini, 2008) One of the major goals for any training and pruning system is to increase light interception without increasing vegetative growth potential (Grossman and DeJ ong, 1998) Light environment surrounding the fruit is able to positively influence fruit quality such as size,

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22 ground color (GC), firmness (softening), and sugar content (Lewallen and Marini, 2003; Marini et al., 1991) In the USA, the bulk of peach production areas are temperate, high chill locations with fruit available beginning in late May; hence, developing low chill subtropical cultivars is economically important because they provid e a fresh supply of fruit for local markets and the potential to transport fruit for higher values to more distant markets with no peach production at certain times of the year. The difference between high chill and low chill cultivars depends on the amoun temperature required during the winter dormancy before the resumption of growth in spring. The amount of chilling can be measured as chill units (CU) or chill hours, defined as 1 hour of exposure to an optimum air te mperature range (Richardson et al., 1974) Temperatures between 32 and 45 F (0 and 7.2 C ) are believed to be the optimum chilling temperatures for temperate zone peaches (Weinberger, 1950) In the South eastern USA low chill cultivars generally have less than a 500 chill hour requirement (Okie, 2004) North Carolina accumulates the largest number of chilling hou rs among the Southeastern states. The recommen ded varieties for North Carolina usually have a chilling requirement of 750 hours or greater (Parker and Werner, 1993) V arieties that require chilling between 500 750 h ours are considered medium chill in the Southeastern USA Low chill cultivars have been reported to set adequate crops after exposure to temperatures at or below 55 F (12.8 C ) (Rouse and Sherman, 2003) Low chill cultivars usually have a relatively short fruit development period (days from bloom to mature fruit), resulting in earlier harvests than the medium and high chill cultivars grown in temperate regions (Andersen et al., 2001) Low chill cultivars grown in

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23 sub tropical regions like Florida are also bred to withstand different climactic, disease, and pest pressures than higher chill cultivars grown in temperate regions. Fruit Growth and Developme nt Peach fruit growth has been described as a double sigmoidal curve since the work of Connors ( 1919) The double sigmoidal curve is separated into three stages. Stage I includes the first exponential growth phas e, which is characterized by rapid cell division and development of the endosperm. Endocarp sclerification or pit hardening occurs and rapid embryo development in Stage II, but little pericarp growth occurs. Stage II is followed by a second exponential gro wth phase characterized by rapid enlargement of primary focus of peach postharvest physiology research since fruit maturation, ripening, and senescence all occur durin g this stage. Cell division and cell expansion are both energy consuming process. Therefore, respiration rates are high during Stage I of fruit development, decreases through Stage II (pit hardening) and part of Stage III (second exponential growth phase), and rises gradually at the end of Stage III (Ramina et al., 2008). The primary cell wall grows in the expansion phase as fruit increases in size. The growing wall behaves like a network of inextensible cellulose microfibrils laterally linked together vi a a complex matrix of flexible polysaccharides (glycans and pectins) that may bind to cellulose and to each other (Cosgrove, 1999) According to Brummell et al. (2004) p ectins that are loosely attached to the wall through ionic calcium bonds increase in amount as peach fruit reaches full size. Pectins that are covalently attached to the wall are approximately half as much as those ionic bond pectins and the amount is fairly constant until early ripe. It is expe cted that the latter will decline with an

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24 increased of the former type of pectin in later stages. The amount of matrix glycans in the wall were relatively constant during the early developmental stages, with approximately 1/3 loosely bound to the wall and 2/3 tightly attached to the wall. The tightly bound matrix glycans decrease or are increase during ripening. Fruit maturation is a stage of development leading to the attainment of physiological or horticultural maturit y (Watada et al., 1984) Physiological maturity is defined as the stage of development at which a plant or plant part will continue ontogeny even if detached from the plant. A horticulturally mature commodity is defi ned as having reached a stage of development such that, after harvesting and postharvest handling, its quality will be at least the minimum acceptable to the ultimate consumer (Reid, 1992) For peaches, the horticultu ral maturity generally means when the fruit has reached or even passed the physiological maturity but has not undergone ripening (Delwiche and Baumgardner, 1983) In terms of postharvest physiology, a mature peach is generally referred to its horticultural maturity instead of physiological maturity. Ripening involves changes that transform the mature fruit into one that is ready to eat (Crisosto, 1994) These transformati ons can begin as early as the middle of the second exponential growth phase (Chalmers and Ende, 1975) to as late as when the exponential phase has plateaued (Kader and Mitchell, 1989) Tonutti et al. ( 1991) has further separated the ripening stage (Stage IV) from Stage III. Ethylene evolution is low and constant during development and generally begins to increase at Stage IV, reaching a pe ak that coincides with the last stage of peach fruit ripening.

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25 Level s of different sugars vary greatly during fruit growth in peaches. The sucrose concentration remains low in the early stages of development. A large amount of sucrose accumulates during Stage III but these molecules do not come from starch to su gar conversion as in fruits like apple and banana (Brady, 1993) Although young peach fruit tend to store some carbon as starch, this starch is used before the fruit enters Stage III. Glucose and fructose are present at similar concentrations throughout fruit development, and are the predominant soluble carbohydrates of mesocarp tissue during the early stages of growth. Thereafter, their contents decrease con current with the rise in sucrose concentration. Malate and citrate are the two major organic anions acids in peaches, but the ratio of the two from maturation to ripening is not constant, which reflects differential regulation of respiration at each developmental stage. Chapman et al. (1991) observed that during early development, the percentage of malic and citric peaches were similar. Malic acid increased and citric acid decreased in Stage III. At harvest maturity, malic acid composed about 50 60% of the total organic acid, citric (20 25%) and quinic (20 25%) being present in lesser quantities (Byrne et al., 1991) As an immature fruit transform s into a mature one, there is a slight incr ease in total phenolic compounds and total carotenoids (Kader et al., 1982) In peaches, the peel has higher concentration of phenolics than the flesh (Wang et al., 2010) These phen olic compounds have a role in the visual appearance (pigmentation and browning), taste (astringency), and health promoting properties (free radical scavengers) (Tomas Barberan et al., 2001) Peaches are rich in carotenoids cryptoxanthin (Caprioli et al., 2009 ) Chlorophyll content decrease s significantly during

PAGE 26

26 maturation parallel with an increase in caro tenoid content (Cascales et al., 2005) cryptoxanthin have been re ported to be the primary provita min A car ot enoids (Curl, 1959) Vitamin C, a natural antioxidant, is higher in concentration in mature than in immature peach fruit (Kader et al., 1982) The increase in total ascorbic acid along with increased maturity is c ontributed by a higher level of dehy d roascorbic acid (oxide form) (Camejo et al., 2010) indicating that more antioxidants are being used to offset oxidative stress brought by fruit ripening and senescence. Peach P ostharvest Physiology Climacteric Ripening Ethylene Ethylene is a gaseous plant hormone with numerous important roles in plant growth, development, and senescence. Its production increases during leaf abscission and flower senescence as well as during f ruit ripening. Furthermore, plants respond to environmental stimuli, such as touching, wounding, pathogen attack, and flooding with induction of ethylene production (Abeles et al., 1992) The biosynthetic pat hway of ethylene from methionine consists of three steps: (1) S adenosyl L methionine (SAM) synthetase catalyzes the conversion of methionine to SAM; (2) formation of 1 aminocyclopropane 1 carboxylic acid (ACC) from SAM via ACC synthase (ACS) activity; (3) conversion of ACC to ethylene by ACC oxidase (ACO) (Yang and Hoffman, 1984) Two systems are hypothesized to regulate ethylene production in higher plants. System 1 is responsible for producing the basal levels of et hylene detectable in all tissues, in which ethylene inhibits its own biosynthesis during the pre climacteric stage of fruit development. When development shifts from pre climacteric to climacteric System 2 is responsible for the upsurge in ethylene producti on in which ethylene biosynthesis

PAGE 27

27 becomes autocatalytic (McMurchie et al., 1972) The initiation of autocatalytic ethylene production is accompanied by increases in ACO and ACS gene expression (Giovannoni, 2001) Ethylene perception begins when ethylene binds to its receptor sites in the tissue and activates the downstream signal transduction. Treatment with ethylene hastens the ripening of climacteric fruit as a result o f the complete saturation of all the available receptor sites (Payasi and Sanwal, 2010) In Arabidopsis, ethylene is perceived by a family of five receptors: ETR1, ETR2, ERS1, ERS2 and EIN4 (Guo and Ecker, 2004) In peaches, PpETR2 is induced at the very early ste ps of climacteric and displays a ripening related expression pattern (Trainotti et al., 2006) PpETR1 and PpERS1 expression does not appear to be controlled by ethylene (Ziliotto et al., 2008) Ethylene binding to the ETRs further inactivates CTR1, a key negative regulator of the ethylene receptor complex (Kieber et al., 1993) EIN2 is the first positive regulator in the ethylene signaling cascade acting downstream from CTR1. Transcript accumulation of PpEIN2 has been associated with ripening peaches (Begheldo et al., 2008; Trainotti et al., 2006) The nuclear protein EIN3 is downstream of EIN2 and acts as a transcription factor that regulates the expression of its immediate target genes such as ethylene response factor (ERF) (Solano and Ecker, 1998) ERFs are proteins that specifically bind to GCC box in promoters of ethylene responsive genes and lead to the regulation of ethylene controlled gene expression (Guo and Ecke r, 2004) PpERF2 has been associated with peach fruit ripening and to the presence of ethylene (Trainotti et al., 2007)

PAGE 28

28 The ripening process of peaches, like other climacteric fruits such as tomato, avoca do, banana and apple, is regulated by System II ethylene for initiation and control of ripening (Lelievre et al., 1998) Ethylene production by peaches varies greatly from mature but unri kg 1 h 1 ) to ripe fruit (up to 160 kg 1 h 1 ) (Crisosto and Kader, 2004) In peach fruit, a gradient of ethylene concentration is established between epicarp and mesocarp during ripening. High rates of ACO activity in the epicarp disk was proposed to be responsible for the higher values of ethylene evolution (Tonutti et al., 1991) Haji et al. ( 2004) reported that varietal difference determines whether ethylene biosynthesis is initiated before or after softening begins. For example, in early softening MF completion of fruit enlargement and changes in GC, as well as the rapid rise in sugar conten t. Supported by Brovelli et al. (1998 b maturity was reached (based on GC and firmn ess) fruit did not stop increasing ethylene production starts after the fruit attain full size, complete sugar accumulation, and change GC from gre en to yellow. Tonutti et al. ( 1996) reported similar results with other MF cultivars. Another flesh typ e in peach produce any ethylene auto catalytically due to reduced expression of PpACS1 (Tatsuki et al., 2006) The stony hard trait is controlled by a single recessive gene ( hd ) which is inherited independently of the (M) locus (Haji et a l., 2005) Co nsequently, this type of peach do es not soften after harvest or even after the indicators for ripening such as GC, sugars and acids, have changed unless an external ethylene source is applied (Haji et

PAGE 29

29 al., 200 3) Stony hard (SH) peaches are useful for studying the regulation of ethylene on fruit ripening, especially on cell wall modification (softening). Ethylene can be both beneficial and deleterious in postharvest physiology. It is essential for the ripen ing of clima c teric fruits because without ethylene ripening does not proceed and the result is unpalatable fruit. However, once ripening is triggered by ethylene, the irreversible process can soon turn the beneficial aspects of ethylene for generating a hi gh quality product into over ripening and decay (Barry and Giovannoni, 2007) Thus, controlling the biosynthesis and action of ethylene during ripening in clima c teric fruits is a key point, but it may not be e nough for delaying postharvest deterioration. Both ethylene and developmental controls have been suggested to regulate clima c teric ripening. Transgenic and mutant tomato lines with inhibited ethylene biosynthesis or perception demonstrate that ACS expre ssion is initially induced during ripening by an unknown developmental signaling system (Barry et al., 2000) Hence, controlling both ethylene dependent and independent pathways involved in ripening can potentially le ngthen the postharvest life of many fruits and vegetables. Respiration Aerobic respiration, which involves the oxidative breakdown of certain organic substances stored in the tissues, supplies the energy required by horticultural products to support a my riad of metabolic processes. In peaches, the burst in respiration associated with climacteric ripening occurs simultaneously with the increased levels of System 2 ethylene production (Ferrer et al., 2 005; Madrid et al., 2000) The average respiration rate of peach fruit during ripening is classified as moderate when compared to other species (Wills et al., 2007) The respiration rate ( CO 2 production) at the

PAGE 30

30 climacteric peak has been reported to vary from 64 to 110 mg kg 1 h 1 at 20 C depending on the genotype (Crisosto and Kader, 2004) Marked differences in respiration rates have been observed in relation to th e duration of the fruit developmental cycle. Ventura et al. ( 1998) reported that cultivars with shorter developmental cycles (earlier harvest dates) had higher and more pronounced respiration rates at the climacteric peak. Compositional Changes Sugars, acids, salts, bitter compounds such as alkaloids or flavonoids, and aroma volatiles contribute greatly to the flavor in fruits and vegetable (Baldwin et al., 2007) However, these compounds may only be at the minimum acceptable level at harvest maturity of a commodity. Compositional changes during ripening increase the desirable flavor. In peaches, the sugar to acid ratio in ripe fruit plays a major role in consumer acceptance (Crisosto et al., 2006) The pigment changes during peach fruit ripening provide visual attraction and bo ost quality (Francis, 1995) Sugars The main sugars in a peach fruit at harvest maturity are sucrose, fructose, and glucose in a proportion of about 3:2:1 (Byrne et al., 1991) or 3:1:1 (Gnard et al., 2003) A rapid accumulation o f sucrose starts at the beginning of Stage III and peaks when ripening is initiated (Chapman et al., 1991; Vizzotto et al., 1996) The glucose:fructose ratio is about 1 during early Stage III a nd falls to 0.8 during ripening, showing that glucose is preferentially used for respiration during ripening (Souty et al., 1998) Peaches with high eating quality are considered to have relatively large amounts of fruc tose and low quantities of glucose and sorbitol (Brooks et al., 1993) because fructose is 3.0, 2.3, and 1.7 times sweeter than sorbitol, glucose, and sucrose,

PAGE 31

31 respectively (Kulp et al ., 1991) Although sugars are commonly thought to be synonymous with soluble solids content (SSC), salts, proteins, acids are also included in the measurement since SSC measures all the soluble solids dissolved in water. The sugar content of peach juice can be conveniently estimated using a refractometer. There is high consumer acceptance for peaches with high SSC (Crisosto et al., 2006) Overall, the SSC in mature nectarines and peaches should be in excess of 10% for acceptable quality (Beckman and Krewer, 1999; Kader and Mitchell, 1989) Acids Peach fruit undergoes a continuous accumulation of organic acids, mainly malic and citric acid, during development. These organic acids are used as respiratory substrat es (Etienne et al., 2002) A common method for measuring the level of the acids is by titration with sodium hydroxide (Jones and Scott, 1984) Titratable acidity (TA ) of peaches declines from Stage III to the end of ripening process (Bakshi and Masoodi, 2009; Kwon et al., 2007; Moing et al., 1999) Malic acid generally remain s constant throughout ripeni ng while citric acid either significantly increase s (Borsani et al., 2009) or decrease s (Robertson et al., 1991) depending on the peach genotype. The TA of the fruits in th e former case did not change significantly during the post harvest ripening process. Different acids can affect perception of sourness differently depending on their chemical structure. An increase in molecular weight can increase sourness perception whil e increasing carboxyl groups can decrease sourness (Hartwig and Mcdaniel, 1995) The concentration of acids correlates highly with sourness in ripe peaches (Crisosto et al., 2006 ) Although titratable acidity (TA) has been reported to play an important role in consumer acceptance for grapes (Crisosto and Labavitch, 2002) cherries (Crisosto et

PAGE 32

32 al., 2003) and kiwifruit (Marsh et al., 2004) SSC/TA ratio or pH can sometimes relate better to sourness perception than TA itself (Malundo et al., 2001) Peach cultivars can be further categorized by the level of TA into high acid and low acid (sub acid) cultivars. The high whereas the low populations tested (Crisosto et al., 2003) Moing et al. (1998) found 10 fold differences acid) peaches. Consumer acceptance for low acid was always greater than for hi gh acid cultivars regardless of fruit maturity (Iglesias and Echeverria, 2009) Pigments Color changes associated with ripening strongly influence visual and eating quality of fruits and vegetables (McGuire, 1992) Changes in color in many fruits involve loss of chlorophyll, synthesis of new pigments such as carotenoids and/or anthocyanins, and unmasking of other pigments that are formed previously during development (Ferrer et al., 2005) Martinez Madrid et al. (2000) reported that changes in peel GC and flesh color (FC) initiated around the same time during onset of peach fruit ripening but the changes in GC were more dramatic than in FC. Color can be measured objectively in the CIE (L*, a*, b*) color sphere using a (International Commission on Illumination). For all peach genotypes the chromaticity a value (green red) of the epidermal GC (GCa* value) increases the most with maturation and ripening, whereas the L* value (lightness, from black to white) and b* (yellow blue) value change only slightly (Delwiche and Baumgardner, 1985) Thus, the a* value has been suggested as the primary coordinate of change near harvest and has been

PAGE 33

33 described as a reliable color index of maturity for both MF and NMF peaches (Byrne et al., 1991; Delwiche and Baumgardner, 1983; Robertson et al., 1993) The FCa* value has been selected as a good maturity index for processing peaches (Fuleki and Co ok, 1976; Kader et al., 1982) Lessertois and Moneger ( 1978) showed that pigments of the mesocarp are the same as carotene, lutein, epoxylutein, violaxanthin and neoxant hin. The increase of FCa* value from negative to positive as maturity advances also denotes the loss of green color related to the disappearance of chlorophyll in the fruit flesh (Ferrer et al., 2005) Other color meas urements can be obtained from calculating hue a ngle (h; arctangent of b*/a*) and chroma [C*; (a* 2 + b* 2 ) ], an index analogous to color saturation or intensity (McGuire, 1992) In peaches, a sharper decline in h was found in peel than flesh and the C* of both r emained constant throughout ripening (Madrid et al., 2000) Evidence has been found to support ethylene regulation of color changes during the onset of peach fruit ripe ning (Amoros et al., 1989 ; Robertson et al., 1992a) For example, anoxia or 1 MCP treatments, which inhibit ethylene biosynthesis and ethylene perception, respectively, when applied at the precl imacteric stage, reduced the level of pigments in peaches (Mencarelli et al., 1998) Although Luchsinger and Walsh ( 1998) showed a good correlation between ethylene pr oduction and changes in GCa* values in Haji et al. ( 2004) and the GC a* va advanced without any application of ethylene.

PAGE 34

34 The results from transcriptome profiling of nectarines treated with 1 MCP indicated carotene hydroxylase was the earliest gene induced at the onset of ripening and appeared to be the only one among the selected targets that was significantly affected by 1 MCP (Ziliotto et al., 2008) Therefore, the accumulation pattern and abundance of specif carotene, and xanthophylls) induced by ethylene depended largely on the genetic background rather than the presence or not of the ethylene clima c teric at ripening. These results reinforce the hypothesis that both development and ethylene synergistically control peach fruit color development during ripening. Textural Changes One of the most important determinants of peach fruit quality and consumer acceptability is the transformation of texture from hard to soft during fruit ripening. MF peach cultivars lose firmness quickly once ripening is initiated, but NMF cultivars mainta in their textural integrity for a longer period of time; thus, NMF peaches can be harvested at a more advanced stage of ripeness and have a longer potential shelf life than the traditional MF cultivars (Byrne, 2002; Sherman et al., 1990) The texture differences of MF and NMF cultivars are controlled by a single gene with the NMF characteristic being recessive (Bailey and French, 1949) The limited softe ning of NMF cultivars during ripening coincides with their reduced capacity to degrade cell walls (Lester et al., 1994; Lester et al., 1996; Pressey and Avants, 1978 ) Furth ermore, the reduced capacity to degrade cell wall is not due to ethylene production since NMF fruit can produce higher levels of ethylene than MF fruit (Brovelli et al., 1999a) NMF cultivars are believed to have h igh potential for the fresh market, primarily because their improved firmness retention allows the harvest of NMF fruit to be delayed

PAGE 35

35 until ripening has begun. However, some NMF fruit have inherently superior flavor and aroma. In one study, the flavor of a NMF cultivar was rated higher than that of MF peaches when fruit were ripened at 20 C for 3 days following low temperature storage, and the firmer texture of the NMF cultivar did not appear to negatively impact consumer acceptance (Williamson and Sargent, 1999) While differences in pH, titratable acidity (TA), and soluble solids content (SSC) were detected among MF and NMF genotypes, no consistent grouping could be concluded based on the MF/NMF nature of the f ruit (Brovelli et al., 1999b ) f storage firmness, quality, and flavor compared to the current commercial MF cultivars gr own in the same region and having comparable harvest seasons (Beckman et al., 2008) These results indicate that NMF cultivars are a viable alternative to conventional MF cultivars and can be very beneficial to the e arly season shipping industry. Cell Wall Modifications associated with Fruit Softening Fruit softening is an intricate process that involves dissolution of the middle lamella, the primary determinant of intercellular adhesion, and disruption of the primar y cell wall, which is composed of rigid cellulose held together by a network of hemicellulose and pectin (Brummell and Harpster, 2001; Toivonen and Brummell, 2008) 2008). Brovelli et al. ( 1998a) observed that a similar anatomical structure of the mesocarp cells between unripe MF and NMF peaches. The middle lamella was well bonded between cells and the intercellular spaces were sharply defined. During fruit ripening, cells underwent separation and intercellular spaces ad opted the form of crevices among cells in MF fruit. Cells in NMF fruit retained good contact and showed less expansion of the intercellular spaces than that of the MF fruit

PAGE 36

36 The sequence of cell wall modifications in peaches from the end of maturation to the final melting phase of ripening has been described in detail by Brummell ( 2006) In the beginning of the softening process, pectin starts to lose galactose and arabinose side chains while depolymerization of h emicelluloses occurs; both processes continue until the end of ripening. As ripening progresses, pectin de methyl esterification precedes pectin solubilization. The final melting phase is achieved by pectin depolymerization. It is not clear why pectin depo lymerization begins relatively early in tomato and avocado but late in the ripening of MF peaches (Brummell et al., 2004; Huber and Odonoghue, 1993) In NMF peaches, the final melting phase is absent and the pectin undergoes little solubilization. Furthermore, the NMF peaches possess higher content of water insoluble pectin and higher capacity for calcium binding to this fraction compared to MF peaches, which generally have higher content of wat er soluble pectin as the fruit ripen (Karakurt et al., 2000b; Manganaris et al., 2006b) Progressive disassembly of the cell wall structural network is achieved by the concerted and synergist ic action of several different enzymes, in which the action of one family of cell wall modifying enzymes may mediate the activity of another, resulting in synchronized cell wall modification during fruit softening (Tra inotti et al., 2003) Pectin methyl esterase (PME) and polygalacturonase (PG) are believed to have important roles in peach fruit softening. For example, a common physiolo gical disorder of peaches related to cold storage is abnormal softening. This is r elated to an imbalanc e between PME and PG (Ben Arie and Lavee, 1971) The PME activity can increase, decrease, or remain unchanged during cold storage while PG activity is commonly inhibited ( Lurie and Crisosto, 2005 )

PAGE 37

37 Pectin methyl e sterase (PME) In plants, de novo synthesized pectin in Golgi is secreted into the cell wall in a highly esterified form (Mohnen, 2008) The degree of pectin esterification directly influences cell wall rigidity, gel forming ability, overall porosity, pH, and charge distribution (Carpita and Gibeaut, 1993; Grignon and Sentenac, 1991 ) Among cell wall changes during ripening fruit, pectins generally undergo the earliest modification (Li et al., 2010) PME (EC 3.1.1.11) is responsible for hydrolyzing the ester bond in the carboxymethyl groups of galacturonic residues of pectin, resulting in the release of methyl groups and exposure of carboxyl groups (Tijskens et al., 1999) De methy l esterification by the action of PME is a prelude to PG mediated pectin disassembly since the resulting pectin contains mainly homogalacturonan, the preferred substrate for PG (Wakabayashi, 2000) Thus, de methylesterification is an indispensable step for cell wall degradation. Muramatsu et al. ( 2004) observed that the activity of endo PG had little effect on solubilization of peach pectin derived from immature green fruit even though the enzyme was active. The rate of pectin solubilization acce lerated when active PME was added to the crude cell wall fraction with active endo PG. In MF peaches, PME activity increases sharply at an early stage of ripening and remains constant or decreases throughout the cell wall depolymerization phase (Brummell et al., 2004; Glover and Brady, 1995) PME mRNA expression also appeared to be highest at harvest and decrease during storage at 20 C (Zhou et al., 2000a) Two PME genes have been found in peaches and designated as PpPME1 and PpPME2 ( (Murayama et al., 2009) PpPME2 might be critical for fruit softening since ethylene

PAGE 38

38 (Murayama et al., 2009) However, ethylene application or 1 MCP treatment did not influence PME activity in other peaches stored at 20 C, which may reflect post translational regulation that is developmentally controlled (Girardi et al., 2005) Hayama et al. ( 2006a) also demonstrated that there was no significant difference in PME activity between ethylene treated SH PpPME1 expression was found to be fruit specific but the transcription was probab ly not ethylene mediated since up regulation of expression was observed during ripening of both MF and SH peaches stored in ethylene free air (Hayama et al., 2003) PME activity of NMF (Manganaris et al., 2006b) Polygalacturonase (PG) The role of PG in cell wall degradation during ripening has received broad attention. A rapid ris e in PG activity that parallels increased solubilization of pectic substances and progressive loss of flesh firmness is observed in many fruits during ripening (Li et al., 2010) Both endo PG (EC 3.2.1.15) and exo PG (EC 3.2.1.67) are found in ripening peaches. Ripening related exo PG activity is found in both MF and NMF peaches but an increase of endo PG activity is observed only in MF peaches. The reduced or undetectable endo PG mRNA accumulation and activity in ripening NMF peaches may be due to a partial or complete deletion of genes encoding endo PG (Callahan et al., 2004; Pr essey and Avants, 1978 ) Thus, endo PG is regarded as the key enzyme related to the textural difference between MF and NMF peaches. More detailed examinations of endo PG revealed that the endo PG activity of the MF cultivars increases gradually as the f ruit soften but the rate of increase in activity accelerates only

PAGE 39

39 when the fruit are already very soft (<20 N), suggesting that the initiation of softening is not associated with endo PG activity (Orr and Brady, 1993) T here are, to date, six PG genes that have been found in peaches and nectarines. The mRNA of PpPG2/PRF5 was found to substantially accumulate in late softening of (Lester et al., 1994) while eight NMF cultivars each had a deletion in at least one of their PpPG2 sequences (Callahan et al., 2004) The importance of PpPG2/PRF5 during ripening was confirmed by Murayama et al. (2009) who reported tha t PpPG2 was expressed throughout 7 days of storage at 20 C in MF ethylene treatment. Hence, it is likely that the transcription of PpPG2 corresponds to the ripening related endo PG (Lester et al., 1994) The levels of PpPG1 and PpPG3 are apparently regulated independently of ethylene since their expressions were barely detectable in MF and ethylene treated SH peaches during ripening. Altho ugh PG has been proposed as a major contributor to fruit softening, studies using antisense and overexpression technologies in several fruit species have revealed that PG is not the sole determinant of fruit softening ( Toivonen and Brummell 2008) Polyuron ide depolymerization was inhibited in antisense tomato expressing 1% of wild type PG activity and with reduced PG mRNA, but the fruit sustained almost normal pectin solubilization (Smith et al., 1990) In this case, th e reduction of PG mRNA and activity did not prevent fruit softening or the fruit remained just slightly firmer than the controls. Moreover, no significant effect on fruit softening was observed in mutant rin (ripening inhibitor) tomatoes that overexpressed PG to 60% of normal activity (Dellapenna et al., 1990; Giovannoni et al., 1989) In avocados, polyuronide

PAGE 40

40 solubilization occurs before the increase of PG activity, suggesting a PG indepen dent mechanism of pectin depolymerization. As a result, while PG is still proposed as the primary determinant for cell wall depolymerization, its activity alone is not sufficient to promote softening (Huber and Odonoghue 1993) Chilling Injury Chilling injury (CI), which is commonly called internal breakdown (IB) for peaches, is a physiological disorder due to stress from low temperature storage Internal breakdown is a primary factor that negatively influences cons umer acceptance of peaches (Stockwin, 1996) The consumer can easily recognize CI in peach fruit since the symptoms develop quickly upon transfer from chilling temperature to non chilling temper a ture (Lill et al., 1989) The development of CI can be affected by a combination of storage temperature and duration, fruit maturity, and genotype (Brovelli et al., 1998c; Ju and Duan, 2000) Although the recommended storage temperature for most peaches is 0 C peaches can develop CI when they are exposed to 0 C for 3 or more weeks. However, peaches develop CI symptoms faster and more intensely when stored between 2.2C to7. (Crisosto et al., 1999) Chilling injury can be directly related to the harvest maturity of peaches (Crisosto and Labavitch, 2002) Early ha rvest fruit are more susceptible to CI since they are presumably more likely to be immature than later harvest fruit (Ju et al., 2000). L ess mature fruit that have been exposed to chilling temperature are more likely to not ripen normally as a consequence of impaired ethylene synthesis (Obenland et al., 2008; Zhou et al., 2001) Chilling injury development has been suggested to affect the quality of MF cultivars more than NMF cultivars. MF peaches and less (Brovelli et al., 1998c)

PAGE 41

41 NMF peaches with CI were reported to have rubbery texture and off flavors such a s astringency, bitterness, and fermentative taste after ripening from cold storage (Karakurt et al., 2000a) These analyses demonstrated that NMF peaches have more genotypic advantages over MF peaches due to their slow softening rate and reduced CI susceptibility. Symptoms of CI in peach vary among genotypes and typically include flesh discoloration such as internal bleeding and flesh browning, abnormal softening, low aroma, and dry texture (i.e., mealiness). Flesh di scoloration and mealiness are the most frequently reported symptoms of CI (Murray et al., 2007) It is believed that flesh discoloration is related to tissue deterioration or senescence, which leads to changes in membr ane permeability. Consequently, phenolic substrates and polyphenol oxidase (PPO) are able to interact because they are no longer compartmentalized separately in the cell ( Lurie and Crisosto, 2005 ) Decreased activities o f both PG and PME accompanied with decreased levels of cell wall binding cations (primarily Ca 2+ ) were observed in the brown fleshed tissues (Manganaris et al., 2006a) Mealiness is hypothesized to be caused by t he interaction of extrace ll ul ar water with highly polymerized insoluble pectic substances that have low degrees of esterification and depolymerization. These insoluble pectic substances sequester water through the aid of cell wall Ca 2+ resulting in a gel like consistency in the middle lamella (Lurie et al., 2003; Zhou et al., 2000b) Reduc ed endo PG activity and enhanced or stable PME activity in low temperature stora ge have been observed in mealy tissues of peaches (Brummell et al., 2004; Zhou et al., 2000b) Furthermore, a dramatic decline in the arabinose (Ara) content of cell wall polysaccharides was detected in chilled peaches exhibiting mealy

PAGE 42

42 texture (Brummell et al., 2004) The relevance of PG and PME in the development of the CI in peach fruit was confirmed in a proteomic analysis (Nilo et al., 2010) Harvest Maturity The stage of development at which a peach fruit is harvested strongly affects its flavor components, susceptibility to mechanical injuries, resistance to moisture loss, resistance to pathogen invasio n, ability to ripen, and shelf life (Crisosto, 1994; Shewfelt et al., 1987) The physiological maturity and the horticultural maturity of a commodity can be distinct or overlapping with ea ch oth er. According to Watada et al. (1984), physiological maturity is defined as the stage of development at which a plant or plant part will continue ontogeny even if detached from the parent plant. For a climacteric fruit like peach, that means that it will be able to ripen normally. Horticultural maturity is defined as the stage of development when a plant or plant part possesses the minimum acceptable quality for utilization by consumers (Watada et al., 1984) For peaches, minimum horticultural matur ity coincides with physiological maturity because the harvested fruit must be able to complete ripening in order to be acceptable to consumers. However, a minimally mature peach fruit that is harvested prior to ripening initiation is likely to develop flav or, aroma and texture that are much inferior to that of a peach that was allowed to initiate ripening prior to harvesting. To ensure that a commodity will always be harvested at an optimum maturity, indices are developed and often can be used as standards for trade regulation. Crisosto (1994) suggested that a maturity index must ensure an acceptable eating quality and provide for adequate storage life for the commodity. Ideally, a maturity index should be easy to measure, objective, applicable to all growi ng conditions, and if possible, nondestructive (Crisosto, 1994) The common nondestructive maturity indices for

PAGE 43

43 peaches include size, fresh weight, and GC change; the destructive indices include flesh firmness, SSC, TA, pH and FC change. Determination of optimum harvest maturity for peaches, especially for MF cultiv ars, is crucial. Due to the fast softening characteristic of MF peaches, fruit are often harvested when the GC changes from green to yellow (firm mature or semi ripe stage) in order to have higher pack out, less spoilage, and to allow for long distance shi pment (Sherman et al., 1990) Growers tend to harvest fruit before it reaches the recommended maturity stage in order to meet the demand. Shewfelt et al. (1987) showed that out of 5 packing house s sampled, one pack ing house had 70% of fruit below color reference # 3, the minimum maturity standard adopted by both California Tree Fruit Agreement and South Carolina Peach Board (Delwiche et al., 1987) Therefore, these fruit ar e often not mature enough to develop good flavor like tree ripe fruit and frequently score low in consumer acceptance (Meredith et al., 1989) Crisosto ( 2002) indicated th at hard fruit, mealiness, lack of taste, and failure to ripen are the main reasons consumers do not eat more stone fruit. Ripe fruit have a short postharvest life, primarily because of rapid softening and because they are already approaching a senescent st age at harvest. The soft texture of ripe peaches renders them highly susceptible to mechanical injury and they are also more su s ceptible to fungal infection (Casals et al., 2010a) By the time such fruit reach the cons umer they may have become overripe, with poor eating quality including off flavors and irregular or mushy texture (Meredith et al., 1989) Many attempts have been made to determine the best maturity index for diff erent peach cultivars. Strong correlation between flesh firmness and ground color were found

PAGE 44

44 (Sims and Comin, 1963) firmness and the SSC/TA were reported to b e the best indicators of maturity (Salunkhe et al., 1968) Minimum quality criteria have been proposed for MF cultivars both at commercial harvest stage and ready to eat stage. Fruit at picking generally need to hav approximately 40 to 48 N (9 11 lbf) in flesh firmness for normal softening to occur. It is generally accepted that when peach fruit reach 8.8 13.2 N (2 3 lbf) in flesh firmness, 0.5 0.8% TA, greater than or equal to 10% SSC or a SSC/TA ratio of 15, the fruit are (Beckman and Krewer, 1999; Kader and Mitchell, 1989; Malakou and Nanos, 2005 ) The balance between TA and SSC are important to consumer acceptance. High acidity of peach fruit is not a negative quality attribute if balanced with the adequate amount of SSC at ripeness (Crisosto and Crisost o, 2005) Few attempts have been made to identify harvest indices for NMF peaches because differences in harvest maturity, peel ground color, and flesh firmness between MF and NMF cultivars complicate the use of existing peach maturity indices when app lied to the NMF cultivars. Robertson et al. ( 1993) found that size, weight, and CIE Lab a* values of the epidermis increased significantly during maturation for the three NMF cultivars measured. Despite the fact that GCa* value appears to be a universal maturity index for both MF and NMF genotypes, a different range of GCa* values or a different GCa* value threshold should be used for determining harvest timing o f NMF cultivars since they can be harvested at more advanced ripeness (Robertson et al., 1991) Furthermore, newer cultivars are more highly red colored with less visible GC than older cultivars, making assessment of GC more difficult. Flesh color can be used

PAGE 45

45 as a maturity index for NMF peaches when GC is not visible but destructive analysis is not practical for determining which fruit to harvest (Fuleki and Cook, 1976; Josan and Chohan, 1982; Kader et al., 1982) Brovelli et al. ( 1998b) identified cheek and blossom end firmness as potential indices common for both of the NMF flesh genotypes tested, b ut expert training was required for this method to be used. Clearly more work is needed to determine simple and reliable maturity indices for harvesting NMF peaches, especially when more new cultivars are released for commercial operations. Storage Temper ature Management Peaches are usually stored at low temperature s immediately after harvest because they ripen and deteriorate quickly at ambient temperature. As mentioned in the chilling injury section, storage at 0 C is better than 5 C for peaches in gene ral because CI symptoms develop faster and more intensely at 5 C (Crisosto et al., 1999) Higher degree of unsaturation in the plasma membrane and higher membrane fluidity were proposed as the main reasons for the e nhanced tolerance of peach fruit stored at 0 C relative to those stored at 5 C (Zhang and Tian, 2010) Therefore, temperatures between 1 to 0 C (30.5 to 32 F) are currently recommended to store peaches (Crisosto and Kader, 2004) It was reported that NMF peaches stored for 8 weeks (wk) at 0 C and subsequently ripened at 20 C showed no significant changes in physical characteristics for both immature and threshold mature (at physiological maturity) fruit except for a higher firmness compared to those ripened directly at 20 C (Robertson e t al., 1992 b ) Hue angle slightly decreased with storage time, which was ma inly attributed to the increase of GCa*. Weight of peaches of all maturity grades decreased significantly

PAGE 46

46 during storage probably due to dehydration. Brown rot development became an issue after 8 wk of low temperature storage. Similar to the NMF peaches reported by Robertson et al. (1992 b storage at 1 C C and the n ripened at 20 C were very similar to those stored at 2 wk (Lyon et al., 1993) Peach aroma and taste continuously decrease after peaches stored in 0 C for more than 4 wk. Atmosphere Modification Low O 2 and high CO 2 atmospheres were first shown to be beneficial to long term storage of apples by inhibiting the clima c teric r espiration (Kidd and C. West, 1934) The regulation may be directed towards the pathways involved in respirati on and the fermentative metabolism, presumably through its influence on the synthesis, degradation, inactivation and/or activation of the respective enzymes (Mathooko, 1996) Furthermore, high CO 2 has been shown to suppress ethylene action in apples by effectively inhibiting both ACS and ACO activity (Gorny and Kader, 1996) Thus, reduction of both clima c teric respiration and autocatalytic ethylene production can be achieved wi th high levels of CO 2 coupled with low levels of O 2 Consequently, modified (MA) or controlled atmosphere (CA) has been commonly used to improve the shelf life of fruit and vegetables (Kader et al., 1989) 3 5% CO 2 + 1 2% O 2 at 0 C were the original recommendation of CA conditions for peaches and nectarines (Kader, 1986) However, higher levels of CO 2 were found to delay appearance of CI symptoms better 3% O 2 + 10% CO 2 at 2 C for 15 days had improved juiciness, sweetness, perception of

PAGE 47

47 peach flavor, emission of arom a volatile compounds and sensory acceptance in comparison with fruit stored in cold air (Ortiz et al., 2009) Ethylene Control Inhibitors of Ethylene Biosynthesis ACC formation is critical for ethylene biosynthesis Although ACS is generally considered to be the rate limiting enzyme in the ethylene biosynthetic pathway, suppressing ACO activity by inhibitors are also effective in reducing ethylene production. Examples of ACS inhibitors include aminoethoxyviny lg l yc ine (AVG) and amino o xyacetic acid (AOA). Co 2+ aminoisobutyric acid (AIB), ethanol, and acetaldehyde vapors, are compounds that can depress ACO activity (Martinez Romero et al., 2007) In addition, heat treatments applied to apples and tomatoes prior to storage have been shown to inhibit ethylene synthesis, acting on both ACO and ACS activities, although ACS is less heat sensitive than ACO ( Lur ie 1998 ) Heat T reatment Heat is a type of abiotic stresses (Wang et al., 2003) Interestingly, the adaptive responses developed against th is type of abiotic stress are known to protect plants from other biotic o r abiotic stresses that can potentially lead to serious crop loss (Margosan et al., 1997; Serrano et al., 2004) Conditioning peach fruit using heat treatment before storage has the potential to reduce some of the major problems associated with low consumer acceptance. Heat treatment applied to peaches alone or combined with other treatments has been reported to reduce CI (Cao et al., 201 0; Murray et al., 2007) control postharvest decay (Casals et al., 2010b; Karabulut et al., 2010; Malakou and Nanos, 2005; Obenland et al., 2005 ) and delay softening (Budde et al., 2006; Steiner et al., 2006)

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48 Heat treatment is a pre storage conditioning method that utilizes a reversible temperature stress to stimulate a defense re action in plant tissues that is capable of protecting them from other stresses (Murray et al., 2007) been used to describe exposure to temperatures higher than 33 C (Li and Han, 1998) It is an ideal way to minimize chemical usage to control insect infestation and prolong postharvest life of peaches for food safety and environmental reasons (Serrano et al., 2004) Heat treatment is capable of causing the biological system to synthesize heat shock proteins (HSP), which have been suggested to induce plant resistance to CI by physical interaction with proteins or regulation of gene expression (Lurie, 1998; Zhou et al., 2002) For example, one HSP (VIS1) regulated by both high temperature and fruit ripening in tomatoes is proposed to act as a chaperone that binds reversibly to cell wall modifying enzymes and protect them from thermal denaturation (Ramakrishna et al., 2003) The altered gene expression patterns caused by the transient heat stress, including down regulation of ACS and ACO, are proposed to result in a reduction in cell wall catabolism, delaying normal fruit softening (Martinez and Civello, 2008) In heat treated MF peaches, PME was activated, resulting in production of more pectin carboxyl groups, while PG was inac tivated (Koukounaras et al., 2008) Although the activities of PME and PG in heat treated fruit were similar to that of the chilling injured fruit mentioned above, it was proposed that the retention of fir mness was caused by excess carboxyl groups of heat treated fruit bonding with endogen ous calcium to form Ca pectates, resulting in increased rigidity of the cell wall and middle lamella (Steiner et al., 2006). Baks hi and Masoodi ( 2010) reported that the decline in pectin (% of Ca pectate)

PAGE 49

49 was less in ripe, heat treated fruit, supporting the idea that the formation of Ca pectates in the cell wall and middle lamella restrict access and activities of cell wall degra dation enzymes such as PG. The most common postharvest heat treatments applied to fruits are hot water, hot water vapor, and hot air (Zhang et al., 2007) Heating by using radio frequency to control brown rot in p eaches and nectarines was also reported (Casals et al., 2010c) The internal temperature of peaches treated with hot water increases more rapidly than in fruit treated with hot moist air, due to the higher convective h eat transfer coefficient for water compared with air (Zhou et al., 2002) The most common temperatures applied to peaches to delay ripening are between 40 to 50 C and the length of application time varies from 10 min to 2 days (hot air) Peaches have been shown to tolerate hot water at 43 C for 24 min and 46C for 25 min without showing any external measurable injury (skin browning or pitting) (Malakou and Nanos, 20 05; Wells, 1971) Peaches heated at 50 C for 10 min, 4 h before fresh cut processing, had a significantly prolonged shelf life (Koukounara et al., 2008). These peach slices exhibited minimal changes in hue (h) and L* values in modified atmosphere packages (MAP). One possibility could be due to reduction in PPO activity (Bakshi and Masoodi, 2010). Firmness retention observed in peaches treated with hot air could be due to temporarily repressed ethylene synthesis and was suggested to be ripening related since heat treatments had no influence on f ruit firmness when ethylene production was already triggered (Budde et al., 2006). Fruit ripened after heat treatment were found to have positive qualities such as higher fructose content, lower total TA, and increased red pigments in the flesh and peel (Budde et al., 2006; Lara et al., 2009) or the changes

PAGE 50

50 were negligible (Obenland et al., 2005) On the contrary, when the stress applied is too extreme an d thus irreversible, heat treatment can lead to damages that can significantly affect the appearance and nutrition of the fruit such as causing substantial surface browning, increased total carotenoid loss, and lower chroma values of the flesh (Kerbel et al., 1985; Koukounaras et al., 2008; Steiner et al., 2006) Therefore, an optimum combination of temperature and exposure time must be determined specifically for e ach cultivar in order to avoid heat injuries that can possibly result in negative consumer acceptance. Ethylene Control Inhibitors of Ethylene Action Before the discovery of 1 methylcyclopropen e silver ions (applied as silver thiosulfate, STS) (Beyer, 1976) 2 ,5 norbornadiene (2,5 NBD) (Blankenship and Sisler, 1989) and diazocyclopentadiene (DACP) (Sisler and Blankenship, 1993) have been shown to successfully inhibit ethylene action. There are disadvantageous of these compounds. Silver ion cannot be used on foods since it is a heavy metal and a potential pollutant (Martinez Romero et al., 2007) Continuous application of 2,5 NBD in high concentration is required to inhibit ethylene perception Furthermore, the gas itself has a foul odor (Huber, 2008; Robbins et al., 1985) DACP is highly explosive and toxic (Sisler and Blankenship, 1993) 1 MCP is currently the most potent ethylene antagonist that can be applied on food crops The capacity of uniform delivery of 1 MCP to int act organs generates a major benefit over STS that required vascular access for uniform delivery, restricting its use to cut flowers (Huber, 2008) Other advantages of 1 MCP include low phytotoxicity, short expos ure period, and prolonged ethylene action inhib ition after a single exposure at relatively low concentrations (Sisler, 2006) Since 1 MCP has been used successfully to extend the postharvest life of various climacteric

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51 fruits including apple, avocado, banana, pear and tomato by inhibiting the onset and progression of ripening (Watkins, 2006) it has tremendous potential on extending postharvest life of peaches. Therefore, 1 MCP is discussed more in detail herein. 1 Methylcyclopropene (1 MCP) 1 MCP is an ethylene antagonist that competes with ethylene for its receptor and interacts with ethylene receptors by irreversible binding, thereby blocking ethylene dependent ripening responses (Sisler and Serek, 1997) Liguori et al. (2004) reported delayed flesh softening and extended shelf life with no inci dence of flesh browning or breakdown in MF peaches treated with 5L/L 1 MCP at 20 C or 0 C for 20 h. Kluge and Jacomino (2002) reported delayed flesh softening, less ground color loss and reduced incidence of fruit rot from Monilinia for preclimacteric pe aches treated with 100 nL/L 1 MCP at 20 C for 24 h. TA loss in peaches is generally inhibited by 1 MCP, but the influence of 1 MCP on respiration and SSC appear s to be cultivar dependent (Liguori et al., 2004) Transcr iptome analysis indicates that 1 MCP is capable of inhibiting genes associated with ripening in peach. Compared with samples at harvest, only nine genes appeared to be differentially expressed when peach fruit were sampled immediately after treatment with 1 L/L 1 MCP at 20 C for 24 h, while a total of 90 targets were up or down regulated in untreated fruit (Ziliotto et al., 2008). Reported effective gaseous 1 MCP concentrations for peaches vary greatly: from as low as 0.4 L/L (Liu et al., 2005) to 5 L/L (Liguori et al., 2004). However, 5 L/L is higher than the maximum concentration registered for use (Watkins 2006). Despite the fact that 1 MCP has been shown to be able to delay ripening in many climacteric fruit s, the inhibitory effect of 1 MCP on peaches is often transitory. For example, pre climacteric MF peaches (ethylene production rate of 0.4 nL/g FW/h and

PAGE 52

52 flesh firmness about 80 N) treated with 1 L/L 1 MCP gas for 12 h at 25 C began to soften only 1 2 days after the treatment ended (Rasori et al., 2002) Hayama et al. ( 2008) 1 L/L 1 MCP for 16 h at 25 C softened to a similar degree of flesh firmness as that of untreated fruit after 4 days of ripening at 20 C Although repeated 1 MCP applications on peaches were shown to be more effective in terms of softening inhibition than a single application (Liu e t al., 2005), it is difficult to apply repeated applications in a commercial operation. Application of 1L/L 1 MCP for 24 h at 20C had a relatively small effect on with r egard to gene expression and activities of the enzymes (PpACS1), regulators (PpCTR1), and receptors (PpETR1, PpERS1) involved in the ethylene biosynthetic and signal transduction pathways (Dal Cin et al., 2006) It was proposed that the ethylene receptors were regenerated within a short period of time after a single 1 MCP treatment (Mathooko et al., 2001) Another possibility is that the system 2 ethylene production in pe aches is regulated differently than in tomatoes and apples. PpACS1 might represent one crucial factor in the modulation of responses to 1 MCP application (Mathooko et al., 2001; Ziliotto et al., 2008). Expression of PpACS1 may be negatively regulated by et hylene, unlike the positively regulated LeACS2 and MdACS1 (Tatsuki, 2010) It is also possible that another hormone such as auxin (NAA) influences the PpACS1 expression more strongly than ethylene during ripening (Trainotti et al., 2007) The effectiveness of gaseous 1 MCP application appears to be limited by storage temperature, which can be a potential problem since low temperature storage is

PAGE 53

53 commonly required for peac hes. 1 MCP treated nectarine fruit stored at 25C had a longer shelf life than those stored at 4 C (Bregoli et al., 2005) The inhibition of softening was greater when peach fruit were 1 MCP treated and held at 20 C than when they were treated and held at 0 C before ripening at 20 C (Liguori et al., 2004). In some cases, use of 1 MCP on peaches has been associated with increased IB depending on the storage condition. It is possible that ethylene synthesis and action can be blocked by 1 MCP even after cold storage, subsequently leading to abnormal ripening and emergence of severe CI disorders such as IB (Dong et al., 2001; Fan et al., 2002; Gi rardi et al., 2005) Adding ethylene during cold storage was able to delay the development of mealiness (Zhou et al., 2001 ; Dong et al., 2001) These studies indicated that using g aseous 1 MCP to extend the shelf life of peaches after low temperature storage is currently limited. Liquid or spray formulations of 1 MCP have been developed recently, but this has not yet become commercially available for postharvest application. Aqueou s 1 MCP [ 1 MCP (aq ) ] application may have better potential than the gaseous application for postharvest purposes because it appears to be more efficient in inhibiting ripening and does not require tightly sealed rooms. Choi and Huber ( 2008) demonstrated that 1 MCP(aq) strongly delays ripening in both tomato and avocado fruit. Fruit immersed in 625 g/L 1 MCP (aq) for 1 min had all the examined ripening parameters strongly suppressed, including ethylene biosynthes is, respiration, softening, surface color changes, lycopene and PG accumulation. Manganaris et al. ( 2007) demonstrated the beneficial effects of MCP (aq) to delay ripening and control CI. They reported that plums immersed in 100 g/L of MCP (aq) for 5 min had

PAGE 54

54 reduced respiration and ethylene production, and better firmness retention. Furthermore, reduction in the activity of cell wall modifying enzymes such as PG, endo 1,4 Gal) were observed. The treated fruit that were ripened after being stored at 5 C for 10 days showed less flesh reddening, a CI symptom. In a more recent report, Manganari s et al. ( 2008) determined that 1 g/L of 1 MCP (aq) was the most effective rate to control ripening changes and extend shelf 1 MCP (aq) can be a potential pre storage conditioning m ethod for both MF and NMF peaches since it is more efficient compared to the traditional gaseous application and can be applied to stone fruit harvested after ripening has initiated.

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55 CHAPTER 3 OPTIMUM HARVEST AND POSTHARVEST HANDLING PRACTICES FOR LOW CHILL, MELTING AND N ON MELTING FLESH PEACH VARIETIES IN T ROPICAL AND SUBTROPICAL CLIM ATE S Overview The bulk of peach production in the USA occurs in temperate, high chill locations with fruit available from late May through October. Developing low chill subtropical cultivars is economically important because they provide a fresh supply of fruit for loca l markets and the potential to transport fruit for higher values to more distant markets that have no peach production at the time (Rouse and Sherman, 2002) The traditional melting flesh (MF) cultivars are primarily g rown for fresh market whereas non melting flesh (NMF) cultivars are commonly grown for canning because the fruit maintain their integrity during the high temperature retort treatment (Robertson et al., 1992 b ) The main distinction between NMF and MF peaches is that the former lack the rapid loss of reduced capacity to degrade cell walls (Lester et al., 1994; 1996; Pressey and Avants, 1978 ) Early season peaches have a poor reputation among consumers. The major complaints are poor and inconsistent fruit textural quality and flavor (Beckman and K r ewer 1999). A common problem for traditional MF peaches is that the fruit are stage to minimize mechanical injuries, but consequently have considerably lower eating quality because these fruit have not completed or just rea ched physiological maturity at harvest (Cascales et al., 2005; Williamson and Sargent, 1999) A major goal of the University of Florida Prunus breeding program is to develop low chill NMF p eaches for fresh consumption with color, aroma, and flavor

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56 typical of MF cultivars while still possessing enough flesh firmness to prevent mechanical damage during postharvest handling (Sherman et al., 1990) Lit tle is known about the best harvesting procedures for NMF peaches and other low chill subtropical MF varieties that would result in fruit of satisfactory condition after handling and shipping. For peaches, horticultural maturity coincides with physiologica l maturity. Physiological maturity is defined as the stage of development at which a plant or plant part will continue ontogeny even if detached from the parent plant (Watada et al., 1984) Thus, peaches at horticultural maturity can continue ripening to develop high flavor characteristics; at the same time, the fruit is still firm enough to prevent bruising and premature softening during shipping and storage (Wells et al., 1989) Since NMF peaches can retain firm texture longer than MF peaches, standard harvest maturity of MF cultivars may not be suitable for the NMF cultivars. Many of the physical and chemical characteristics of maturing peaches, typically of the MF cu ltivars, have been studied in order to obtain suitable indices of harvest maturity. Ideally, a maturity index should be easy to measure, objective, applicable to all growing conditions, and if possible, nondestructive (Crisosto, 1994) Flesh firmness (Rood, 1957; Salunkhe et al., 1968) and peel ground color (Baumgardner and Delwiche, 1983; De lwiche and Baumgardner, 1985) have been suggested as reliable maturity indices for MF cultivars, while flesh color was suggested for NMF cultivars (Fuleki and Cook, 1976; Josan an d Chohan, 1982; Kader et al., 1982) Information on the maturity indices of fresh market NMF cultivars is currently limited because they are not traditionally used for fresh consumption. Furthermore, the newer cultivars are more

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57 highly red colored on th e skin making the assessment of the correct harvest maturity via peel ground color more difficult. Refrigeration is the most common practice to retard ripening and lengthen storage life of fruits and vegetables; however, low temperature can affect fruit q ualities in a negative way commonly known as chilling injury (CI). Although the recommended storage temperature for most peaches is 0 C fruit can develop CI when they are exposed to 0 C for 3 or more weeks. Symptoms are even more pronounced when the chill ing injured fruit are transferred from 1 or 2 weeks of storage at 2.2 C to 7.6 C (the (Crisosto et al., 1999) Flesh discoloration such as internal bleeding and flesh browning, abnormal softening, low aroma, and dry texture (i.e., mealiness) are typical symptoms of CI ( Lurie and Crisosto, 2005 ) The development of CI is usually related to a combination of storage temperature and durat ion, fruit maturity, and genotype (Brovelli et al., 1998a; Ju et al., 2000; Ju et al., 2000) It has been reported that symptoms were more severe in unripe than in ripe fruit (Ben Arie and Lavee, 1971) Chilling injury development has been suggested to affect the quality of MF cultivars more than NMF cultivars (Brovelli et al., 1998c) The purpose of thi s study was to investigate the changes of physical and chemical characteristics of the newer, low chill, MF and NMF varieties at harvest to aid in the development of indices for predicting the maturity of peaches. The second objective was to determine opti mum harvest maturity for each peach cultivar based on the effect of ripening and low temperature storage on fruit qualities.

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58 Materials and Methods Plant Materials During the spring seasons of 2007 and 2008, samples from two MF cultivars, harvested three times from the UF IFAS Plant Science Research & Education Unit (PSREU) at Citra FL. The harvest time was based on the development of 100 tagged fruit for each cultivar after fruit thinning and natural fruit drop. These fruit were randomly selected and considered as the representative population for each cultivar. Samples from the fo ur cultivars were harvested when 50%, 70%, and 90% of the tagged fruit reached commercial harvest stage (ground color change from green to yellow). For each harvest, a 50 fruit sample from four trees was sorted according to ground color (subjective) and fr uit diameter. Ten fruit were used for destructive analyses immediately after harvest. The remaining fruit were divided into two groups of 20 for two storage treatments. The first group was stored (ripened) at 20 C for 7 days in 2007 and 5 days in 2008. The second group was stored at 0 C for 14 days, and then ripened at 20 C for 7 days in 2007 and 5 days in 2008. After storage and ripening, non destructive analyses (fresh weight, size, peel blush and ground color), and destructive analyses (flesh color, firmness, soluble solids content, total sugars, pH and titratable acidity) were performed. Relative humidity (RH) of both storage conditions ranged from 83 to 97%. Size, Fresh Weight, and Peel Blush Determination Fruit size was determined by measuring th e diameter midway between the stem and blossom end with a vernier caliper. Peel blush (PB) was subjectively measured by estimating the total percentage of each fruit that was red. Fresh weight (FW) of individual fruit was recorded using a weighing balanc e. Measurements of size, FW, and

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59 PB were taken at harvest (initial) and after ripening from each storage condition (final). were determined in 2008 for samples stored dir ectly at 20 C WL was calculated by subtracting the final FW of the fruit from the initial FW. The difference obtained was divided by the initial FW and converted to percentage by multiplying by 100. The SL calculated by subtracting the final PB from the initial PB. In addition, weight loss was measured immediately after 14 days of low temperature storage in 2008 (WL m). Color Determination Ground color (GCa*) and flesh color (FCa*) were objectively measu red using a reflectance colorimeter (Minolta CR 400, Konica Minolta, Japan) and expressed as C.I.E. a* values (green red) since a* value increases with increasing maturation and ripening both in the peel (Delwiche and Baumgardner, 1985) and in the flesh ( Kader et al., 1982; Robertson et al., 1991). Ground color was measured on the greenest portion of the peel. Flesh color was measured after removing a small section of the epidermis on two sides of each fruit at the equator on the cheeks using a potato peel er. Changes C or 0 C storage treatments minus the initial a* values. Compositional Analysis Fruit were sliced, pitted, and pureed in a Waring blender for 1 min. After the s lurry was centrifuged (20 min; 15,000 x g n ; 4 C ), the clear solution was used to determine soluble solids content (SSC) and titratable acidity (TA). SSC was measured with a temperature compensated digital refractometer (model ABBE Mark II, Cambridge Instru ments Inc, U.S.A) and expressed as percent FW. TA was determined by titration

PAGE 60

60 (model 719 S. Titrino, Metrohm, Switzerland). A 0.1N sodium hydroxide solution was used to titrate 6 g of peach juice until pH 8.2 was reached. The TA was expressed as percent ma lic acid. The juice pH was measured using the same equipment for TA determination. Total soluble sugar (TS) determination was performed using the phenol sulfuric assay (Dubois et al., 1956) modified as follows: 5 L of extracted sample was diluted with 5 mL of 80% ethanol. Further dilution was performed if the concentration of the sample was out of the range of the standard curve. A 500 L aliquot of the diluted sample was added to 500 L of 5 % phenol solution (Fisher Scientific, New Jersey, USA; certified grade) then vortexed. Then 2.5 mL of concentrated sulfuric acid (Fisher Scientific; certified ACS grade) w as added to the mixture and vortexed. The mixture was left for 10 min at room temperature for color development. The absorbance of the sample at 490 nm was read on a microplate with glucose (Fisher Scientific, New Jersey, USA; certified ACS grade) as the s tandard. Total sugar was expressed as a percentage of FW. Flesh Firmness Determination Flesh firmness was measured with an Instron Universal Testing Instrument (Model 4411 C8009, Canton, MA, USA) that applie d a compressive force from a 50 kg load cell. A convex tip probe (Magness Taylor type), 7.9 mm in diameter, was attached to the load cell moving at a speed of 12 cm/min. Flesh firmness was measured on two sides of each fruit at the equator on the cheeks without peel and expressed as the maximum bioyiel d force (N).

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61 Statistical Analysis Since differences in the physical and chemical characteristics for all the cultivars were not noticeable among the three harvests, the data for all harvests were pooled together for statistical analysis. Samples were divi ded into 7 maturity groups (MG) in 2007, ranging from the least mature to most mature based on GCa* measurements. varieties had broader ranges of GCa* than in 2007. D ata were analyzed by the General Linear Model (GLM) program of the Statistical Analysis System (SAS) (SAS Institute, Cary, NC). One way Analysis of Variance (ANOVA) was used to detect significant differences at the 5% level among the MG for each cultivar. The le ast significant difference (LSD) test was used for mean separation. Correlation coefficients (r) were obtained both at 1% and 5% level of significance. Results and Discussion Effect of M aturity at H arvest on P hysical and C hemical C haracteristics Ground color (GCa*) and flesh color (FCa*) increased significantly as maturity increased for all the cultivars ( Table 3 1 3 4, 3 7, 3 10, 3 13, 3 16, 3 19, 3 22 ). A change of negative a* value to positive a* value represents the increase of orange and red coloration and decrease of green. Therefore, peaches accumulate orange and red pigments while losing chlorophyll as maturity advances. The percentage of the fru it surface covered by red blush or peel blush (PB) is an important quality indicator to the consumer. The current U.S. Standard for Grades of Peaches includes minimum PB as a requirement for the U.S. Fancy and U.S. No. 1 Extra grades (AMS, 2004) The PB of Table 3 7 3 19 f was not ( Table 3 10 3 22 ). The significance of PB development related to maturity in

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62 both MF cultivars varied between the 2 years. The consistent pattern of PB development within the NMF cultivars in both years suggests that this trait is genetically regulated in the NMF cultivars and m ay be influenced more by the environment in the MF cultivars. A minimum of 60% red blush is considered to be sufficient for new varieties in the UF br eeding program and would score as 7 on a 10 point scale ( Beckman et al., 2008) commercial harvest stage in Gainesville, FL were reported to have 70, 80, and 80% red blush, respectively (Rouse et al., 2004) The report ed % red blush was only observed in blush in 2008 ( Table 3 22 ). Regardless of maturity, all the cultivars achieved 90 g FW and 57 mm size in 2007 ( Table 3 1 3 4, 3 7, 3 10 ), the most common size sold in the early season market ( Beckman et al. 2008). Smaller fruit size was observe d in 2008 for all the cultivars although Table 3 16 ). Since all the cultivars were affected, climate, crop load, and time of thinning were possible reasons that may have contributed to smaller fruit size in 2008 (Drogoudi et al., 2009) FW and size were highly correlated for both MF and NMF cultivars in both years ( Table 3 26 3 27 ). Therefore, as the FW increases the fruit also expands in size. T he softening pattern was different between MF and NMF cultivars as the fruit started to ripen. Fruit o f the MF cultivars were very firm until they reached MG 10 to15 ( Table 3 1 3 4 ) in 2007 and MG 20 to 25 in 2008 ( Table 3 13 3 1 6 ). Flesh firmness softening cultivars decreased relatively slowly as maturity increased ( Table 3 7 3 10 3 19 3 22 ).

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63 size in 2007, ( Table 3 1 3 10 ) similar to the result reported by (Brovelli et al., 1998b) This indicates that cell wall synthesis and cell wall degradation may overlap each other when the fruit switches from the pre climacteric to the climacter ic stage of development (Rose and Bennett, 1999) In peaches, different isozymes of expansins are suggested to be responsible for loosening the cell wall during this overlapping phase (Hayama et al., 2003; Hayama et al., 2006a; Hayama et al., 2006b) Up regulation of cellulose synthase catalytic subunit expression during this period demonstrates that newly synthesized cellulose can be in tegrated into the cell wall while fruit softening progresses (Trainotti et al., 2003) Soluble solids content (SSC) was generally not affected by maturity for all the cultivars. It was possible that most of these fruit had already reached physiological maturity at harvest. Secondly, there might be large variations of SSC within the MG since fruit at different positions within the canopy showed significant differences in SSC (Mitchell et al., 199 0 ). 11% SSC at harvest ( Table 3 1 3 13 13% SSC ( Table 3 4 3 1 6 ), which was similar and higher than the values reported by Karakurt et al. ( 2000b) 12% SSC at harvest ( Table 3 10 3 19 3 22 ). Total soluble sugar (TS) was usually no different among the MG for both MF and NMF peaches. This implies that the quan tity of sugars in peaches does not vary significantly throughout the latter stages of development although the types m ay differ. The main sugars in peach fruit at harvest maturity are sucrose, fructose, and glucose, with sucrose being dominant (Byrne et al., 1991; Gnard et al., 2003) It is possible that

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64 while sucrose decreases, glucose and fructose increase during ripening, thus maintaining a constant TS level (Borsani et al., 2009) SSC/TA generally increased as maturity increased for all of the cultivars. Since SSC was not significantly different among the MG, the increase in SSC/TA was due to a gradual decrease of TA along with advanced maturity. The pH either year ( Table 3 1 3 13 (Brovelli et al., 1998c) (Moing et al., 1998) The major amino acid in peach flesh, nd r eases (Moing et al., 1998) Effect of M aturity and R ipening on P hysical and C hemical C haracteristics Color changes associated with ripening strongly influence visual and eating quality of fruits and vegetables (McGuire 1992). Significant increase s in ground color change observed in all the cultivars, especially the least mature fruit, after ripening for 7 d at 20 C (Table 3 2, 3 5, 3 8, 3 11, 3 14, 3 17, 3 20, 3 23 ). This resu lt agrees with Robertson et al. (1993) who reported that immature fruit (Maturity 1) had the most increase in a* on the skin color and the mature fruit (Maturity 3) had the least increase after ripening. Ripening induced higher a* in flesh color (FCa*) in all the cultivars thus fruit flesh became more red and orange. Maturity did not significantly either year ( Table 3 8 3 20 ), demonstrating that synthesis and accumulation of pigments in the flesh of this cultivar cease earlier th an in ed more green color in

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65 the flesh than did the direct ripening at 20 C was only measured in 2008 ( Table 3 14 3 17, 3 20, 3 23 significantly affected by maturity in any of the cultivars. The changes were often close to zero, suggesting that the red pigment is n ot synthesized postharvest. The changes were also random, indicating that this subjective method is not a reliable indicator of fruit maturity The WL and SL after storage for 7 d at 20 C were only determined in 2008 ( Table 3 14, 3 17, 3 20, 3 23 ). The WL and SL were similar among the MG. The WL for 12%, similar to the value reported by (Robertson et al., 1990 b ) 9% WL. Shrinkage in size was generally around 5% or less. The NMF cultivars maintained texture better than the MF cultivars after ripening. The MF fruit were very soft ( 5N) after ripening regardless of maturity ( Table 3 2 3 5 3 14 3 17 ). The NMF cultivars were approximately 3 5 times firmer than the MF types ( Table 3 8 3 11 3 20 3 23 ). Levels of SSC and TS were generally not affected by maturity and ripening, simila r to the results reported by Byr ne et al (1991). consumer acceptance (Crisosto et al., 2006) In general, SSC/TA and pH increased while TA dec reased after ripening compared to the values measured at harvest. Maturity had a significant effect on these chemical characteristics. Fruit in more advanced MG generally had higher SSC/TA, indicating that fruit harvested at more advanced stages had a swe eter taste than those in the lower MG after ripening. Robertson et al. ( 1993) reported that threshold mature (maturity 2) fruit ripened for 7 d

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66 at 20C had significantly higher attribute scores for fruity, peachy, sweet, and juicy and had greater overall acceptability than the less mature peaches. Effect of Maturity and Storage on Physical and Chemical Characteristics Slight increases in GCa* were observed in all the cultivars after ripening following low temperature storage relative to ripening directly at 20 C ( Table 3 3 3 6, 3 9, 3 12 ) Robertson et al. ( 1992 b ) did not find any changes in GCa* in fruit stored for 8 weeks at 0 C and subsequently ripened. Low temperature had a major impact on FCa* of both NMF cultivars ( Table 3 12 3 2 1 3 2 4 ). The FCa* increased markedly compared to fruit ripened directly at 20 C ( Table 3 11 3 20 3 23 ). It has been reported that total carotenes and xanthophylls increased in three NMF cultivars and decreased in MF C (Karakurt et al., 2000b) Since no browning was observed, this development was not considered to be related to CI. The WL for all the cultivars was more severe after cold temperature storage compared to ambient temperature storage and was independent of the degree of maturity. Longer period of storage was the main reason that fruit lost more weight after ripening following cold temperature storage, presumably due to de hydration (Lyon et al., 1993) fruit shrank about 5 10% in size after ripened following 0 C storage in both years ( Table 3 3 3 12 3 15 3 21 3 24 and 10% in 2008) and shrank approximately 5% in size ( Table 3 6 3 18 ). Weight loss was also determined immediately after the fruit were transfer red from 0 C to 20 C in

PAGE 67

67 2008 (WL m was similar to that of fruit ripened at ambient temperature, and was approximately half of the total WL. Therefore, fruit lost about 3 5% of their initial weight ea ch week under the 0 C storage condition. temperature flesh firmness as those stored directly at 20 C Low temperature Table 3 8 3 9 ). er after ripening following low temperature storage compared to those ripened directly at ambient temperature storage ( Table 3 20 3 21 ). This a bnormal softening pattern indicated that less mature fruit had greater susceptibility to CI (Fernandez Trujillo and Artes, 1997) Fruit with abnormal softening appeared to be similar in color and composition to other fruit in the nearby MG. Robertson et al. ( 1992 b ) reported similar observations. In their study, NMF peaches had no significant changes in physical characteristics after ripening except firmness, which increased during 8 weeks of storage at 0 C plus 6 d of ripening at 20 C regardless of maturi ty. Since only one NMF cultivar was affected by low temperature in this study, it is difficult to conclude that chilling affects the quality of MF more than NMF genotypes as suggested by (Brovelli et al., 1998c) Fruit SSC and TS were not significantly affected by maturity and the values determined after low temperature storage were similar to those of fruit ripened directly at ambient temperature for all the cultivars. After ripening from the l ow temperature stora ge, most fruit in lower MG were able to attain SSC/TA of 15, the minimum

PAGE 68

68 acceptable quality standard for ripe fruit (Kader and Mitchell, 1989; Robertson et a l., 1990 a ) This indicates that more organic acids are being consumed during the prolonged storage period, resulting in even lower TA and higher pH compared to fruit ripened directly at 20 C This was a beneficial aspect of low temperature storage if no CI developed. A wider maturity range can be used with low temperature storage because the fruit with lower maturity will have enough time to develop an acceptable flavor compared with those ripened directly at 20 C Optimum Harvest M aturity D etermination to 13.2 N. Other minimum quality standards for ripe fruit include TA > 0.8%, and 10 11% SSC or 15% SSC/TA (Kader and Mitchell, 1989; Robertson et al., 1990 a ; Kader et al., 1989) Typically, consumer acceptance is controlled by the interaction between TA and SSC rather than SSC alone (Crisosto and Crisosto, 2005) After ripening directly at 20 C or to Table 3 2 3 5 3 14 3 17 ). In because softening was not initiated ( Table 3 1 ) and fruit attained SSC/TA of 17.02 after ripening at 20 C ( Table 3 2 ). MG 5 to10 were suitable for low temperature storage (Table 3 3 ). MG< 5 contained high TA (Table 3 3 ) with SSC/TA less than 15 and thus was not recommended for low temperature storage. MG 10 to 20+ was not a suitable range for either storage condi tion because the fruit were already too soft at harvest (Table 3 1 ). In 2008, fruit from different MG were separated into two groups based on flesh firmness ( Table 3 13 ). Fruit harvested between MG <0 to 20 had enough firmness (approximately 45 N) to allow softening to occur during storage. These fruit possessed

PAGE 69

69 desirable flavor after ripening at 20 C (i.e. 11% SSC, <0.8% TA, and >15 SSC/TA) ( Table 3 14 ). MG < 0 was not recommended for low temperature storage due to persistence of h igh TA after ripening ( Table 3 15 ). both storage conditions. Fruit of MG < 0 might be too immature, still having TA > 0.80% after ripening directly at 20 C or foll owing storage at 0 C ( Table 3 5 3 6 ). Similar to firmness at harvest in 2008 ( Table 3 16 ). MG 5 to 20 was selected as the ideal range for fresh market use mainly because of the acceptable TA ( Table 3 17 ). A wider range ( Table 3 18 ). Since NMF peac hes soften relatively slowly compared to the MF types, peaches with flesh firmness less than 45 N were considered suitable for both fresh and distant markets. A critical bruising threshold for NMF peaches was proposed by (Metheney et al., 2002) Out of the sample population, only 1 percentile of bruises greater than 100 mm 2 reported to have flesh firmness of 14 N at harvest maturity (Rouse et al., 2004) Therefore, flesh firmness around 14 N was considered as the standard firmness for fresh market NMF peaches. Fruit with flesh firmness around 27 N were generally considered best for distant markets in th ideal for fresh consumption since they ripened to have high SSC/TA ( Table 3 8 ). MG ( Table 3 25 ) because fruit within this maturity range were un able to soften to the same extent as those ripened directly at 20

PAGE 70

70 C ( Table 3 8 ) Thus, only fruit at more advanced stages, i.e., MG 10 20+, were suitable for low temperature storage. Abnormal softening also occurred in low temperature in 2008 ( Table 3 21 ). MG 5 to15 was a better range for low temperature storage in 2008 since the flesh firmness at harvest was greater than the critical bruising threshold ( Table 3 19 ) and those fruit were able to attain SSC/TA of 20 after ripening ( Table 3 21 30+ were recommended for fresh consumption due to their high quality developed after ripening ( Table 3 20 ). The ideal harvest maturity for was MG 15+ in 2007 ( Table 3 11 ) and MG 10 25+ in 2008 ( Table 3 20 ) because these fruit had flesh firmness around 14 N at harvest and had the preferred quality suggested by (Leonard et al., 1961) Leonard et al., (1961) found that SSC/TA above 25 and acidity below 0.5% in fresh clingstone peaches resulted in canned fruit with good flavor. MG 0 to15 in 2007 ( Table 3 12 ) and MG <0 to 10 ( Table 3 24 ) appeared to be the optimum harvest maturity stage for low temperatures storage due to their suitable firmness at harvest ( Table 3 10 3 22 ). Based on the results from this 2 year study, the optimum harvest maturities associated with direct ripening or for ripening after low temperature storage for both MF and NMF cultivars are summarized in Table 3 25 The common MG shows the overlappi ng optimum maturity stages between 2007 and 2008. NMF peaches destined for fresh consumption can be picked at more advanced stages than MF peaches. MF peaches must be picked at an earlier maturity to avoid handling soft fruit that are prone to mechani cal injuries. For both MF varie

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71 destined for low temperature storage can be picked at less mature stages than those CI, they must be har vested at more advanced stage s to avoid abnormal softening. Potential Maturity Indices Determination High correlations of GCa* with maturity (GC MG) were found in all the cultivars over the 2 years (r = 0.98 to 0.99) ( Table 3 26 3 27 3 28 ), confirming that GCa* is a good indicator of ground color changes for both MF and NMF types (Delwiche and Baumgardner, 1985) FCa* was highly correlated with MG in both MF cultivars and in in 2007 and 2008 ( Table 3 26 3 27 ). This result was unanticipated since FC has been suggested as a maturity index for NMF peaches when GC is not visible; however, it was correlated with both MF cultivars but only one NMF cultivar in this s tudy (Fuleki and Cook, 1976; Kader et al., 1982) Consistent correlation of size and Table 3 26 3 27 ). This positive consumer perception depends primarily on external qualities such as size and appearance (Iglesias and Echeverria, 20 09) High correlations were found between MG and firmness (MG Firm) and GCa* and firmness (GC Firm) for both MF and NMF cultivars in Year 2007 (Table 3 26 ). The results agree with (Brovelli et al., 1998b) who demonstrated the importance of firmness as a potential maturity index, even in NMF genotypes. However, the correlations of MG Firm and GC Firm were only observed in MF in 2008 ( Table 3 27 3 28 ), confirming that the firmness is the most consistent maturity indicator for MF types (Byrne et al., 1991; Sims and Comin, 1963)

PAGE 72

72 The TA was inversely correlated with MG in both 2007 and 200 8 ( Table 3 26 3 27 ), indicating that TA can be used as a reliable maturity index for both MF and NMF peaches ( Table 3 28 ). The pH was highly correlated with TA in both NMF peaches and Table 3 26 3 27 ). Fruit pH may be a better maturity index for NMF peaches than TA since it can be easily measured in the field. Chapter Conclusion This study demonstrates that NMF peaches do not need to be harvested at the same maturity as MF peaches. NMF peaches for fresh consumption can be picked at storage stud y shows that 2 weeks of 0 C storage are not enough to induce severe CI in peaches but can induce minor symptom like abnormal softening. Low temperature storage can actually be beneficial for fruit harvested at less mature stages because it provides time fo r the fruit to develop proper flavor. Varieties that are susceptible to CI should be harvested at more advanced stages. Finally, the results of this study suggest that GCa* and TA are reliable maturity indicators of low chill subtropical MF and NMF cultivars. GCa* is preferred over TA since it is easy to measure and non destructive. TA may be used as a supplementary indicator if fruit is covered with blush. FCa* may be used as a s econdary indicator for the MF cultivars while pH may be used specifically for the NMF cultivars

PAGE 73

73 YEAR 2007 Table 3 1 p hysical and chemical characteristics of the least mature to most advance d fruit at harvest based on GCa* Fruit were obtained when 50%, 70%, or 90% of tagged fruit reached commercial harvest stage Maturity g roup (GC a*) GC (a*) FW (g) Size (mm) PB (%) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 8.81 g 87.23 c 50.76 b 23.00 c 7.85 b 68.45 a 10.00 a 1.07 a 9.40 3.60 4.58 5 to 0 3.20 f 92.30 bc 52.71 b 40.00 bc 3.97 b 60.14 a 9.64 ab 1.04 ab 9.33 3.72 5.17 0 to 5 2.26 e 106.26 abc 55.60 ab 70.00 a 2.35 b 59.07 a 10.7 7 a 1.01 ab 10.83 3.80 5.61 5 to 10 7.22 d 101.12 abc 53.83 b 67.50 a 2.02 b 65.57 a 10.23 a 0.92 bc 11.19 3.72 5.47 10 to 15 13.00 c 124.62 ab 61.10 a 87.50 a 4.62 a 31.56 b 10.65 a 0.74d 11.92 4.02 5.91 15 to 20 17.95 b 111.78 abc 57.13 ab 66.67 ab 4.96 a 4.91 c 7.83 c 0.74d 10.59 3.88 4.26 20+ 24.81 a 129.69 a 61.27 a 80.00 a 9.12 a 4.18 c 8.40 bc 0.78 cd 10.76 3.82 5.60 Significa nce * * * * NS NS NS = Signi ficant NS = Non significant Values with different letters were significantly different at Table 3 2 physical and chemical characteristics of least mature to most advance d fruit after 7 days at 20 C based on GCa* Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity group (GCa*) (a*) FC (a*) Firmness (N) SSC (%) TA (%) SSC/TA pH TS (%) 14.05 a 6.36 c 4.39 a 11.27 1.07 a 10.97 e 3.82 d 5.02 5 to 0 15.40 ab 8.96 abc 3.37 bc 11.25 0.80 bc 14.82 de 4.10 bc 6.01 0 to 5 13.06 ab 7.83 bc 3.49 b 11.17 0.88 b 12.93 de 3.96 cd 5.48 5 to 10 13.43 ab 11.29 a 2.90 cd 10.80 0.68 cd 17.02 cd 4.25 ab 5.91 10 to 15 11.88 ab 9.91 ab 2.64 de 10.50 0.50 e 21.45 ab 4.42 a 5.44 15 to 20 10.35 b 10.11 ab 2.49 de 10.58 0.57 de 19.26 bc 4.37 a 5.25 20+ 5.43 c 11.08 a 2.18 e 12.14 0.52 de 24.31 a 4.37 a 7.01 Significance * NS * NS = S NS = n on significant Values with different letters were significantly different at

PAGE 74

74 Table 3 3 physical and chemic al characteristics of least mature to most advance d fruit after 14 days at 0 C and 7 d ays at 20 C based on GCa* Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) (a*) WL ( %) SL (%) ( %) FC (a*) Firmness (N) SSC ( % ) TA (%) SSC/TA pH TS (%) 19.60 a 23.28 9.65 5.25 a 9.80 4.38 a 12.94 0.98 a 13.58 e 3.95 c 7.19 5 to 0 18.04 a 23.63 9.77 2.50 ab 11.45 3.33 cd 11.90 0.79 b 16.54 de 4.21 b 7.65 0 to 5 17. 85 a 19.65 7.53 0.00 ab 10.85 3.41ab 11.48 0.65 bc 17.77 cd 4.29 b 9.05 5 to 10 15 .58 a 23.15 10.55 3.33 ab 11.04 2.43 bcd 12.08 0.60 c 20.79 bc 4.30 b 7.48 10 to 15 8.53 b 21.67 9.60 4.17 ab 11.07 2.94 bcd 12.01 0.56 cd 22.26 b 4.40 ab 8.98 15 to 20 8.81 b 22.46 8.81 6.43 b 11.97 2.34 cd 10.93 0.53 cd 20.42 bc 4.40 ab 6.30 20+ 3.37 c 21.86 9.30 10.89 b 10.22 2.36 d 11.94 0.42 d 28.35 a 4.57 a 7.74 Significance NS NS NS NS * NS = S ignif NS = n on significant Values with different letters were significantly different at

PAGE 75

75 Table 3 4 physical and chemical characteristics of least mature to most advance d fruit at harvest based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) GC (a*) FW (g) Size (mm) PB (%) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 6.37 e 105.51 c 56.23 b 31.67 d 3.70 d 80.18 a 12.51 1.13 a 11.13 b 4.07 bc 7.32 5 to 0 2.16 d 120.83 bc 58.13 b 69.00 bc 1.26 bc 62.23 b 12.02 1.12 a 11.09 b 4.02 ab 8.02 0 to 5 0.86 d 132.08 b 60.65 ab 50.00 cd 4.83 b 57.29 b 12.65 0.99 b 12.82 b 3.71 c 10.03 5 to 10 8.05 c 142.93 ab 63.20 ab 30.00 d 3.39 b 58.01 b 12.80 1.04 ab 12.35 b 4.07 ab 9.07 10 to 15 12.53 b 137.30 b 59.60 b 65.00 bc 14.50 a 3.89 d 11.20 0.56 c 12.49 b 3.94 bc 7.63 15 to 20 15.73 b 120.19 bc 61.15 ab 75.00 ab 5.40 b 47.81 c 12.40 1.02 ab 12.12 b 3.91 bc 10.03 20+ 28.35a 166.52 a 67.88 a 93.00 a 13.48 a 3.88 d 13.02 0.51 c 25.45 a 4.24 a 9.76 Significance * * * NS * NS = S NS = n on significant Values with different letters were significantly different at Table 3 5 Tropic Beauty physical and chemical characteristics of least mature to most advance d fruit after 7 days at 20 C based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) (a*) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 12.56 a 9.56 c 4.04 a 13.39 1.19 a 11.47 e 4.08 7.42 b 5 to 0 13.61 a 12.03 b 3.44 ab 13.44 1.00 a 13.42 de 4.15 7.09 b 0 to 5 11.09 a 12.86 ab 3.54 ab 13.21 0.76 cd 16.86 cde 4.15 7.67 b 5 to 10 12.97 a 11.74 bc 3.00 bc 13.22 0.79 c 17.74 cd 4.25 8.19 b 10 to 15 7.36 b 14.80 a 2.97 bc 13.75 0.58 e 20.70 bc 4.36 12.10 a 15 to 20 7.99 bc 13.37 ab 2.76 c 14.23 0.62 de 27.20 a 4.31 7.02 b 20+ 3.51 c 11.86 bc 2.90 bc 12.35 0.51 e 25.13 ab 4.21 7.58 b Significance * NS * NS * = S NS = n on significant Values with different letters were significantly different at

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76 Table 3 6 physical and chemic al characteristics of least mature to most advance d fruit after 14 days at 0C and 7 d ays at 20 C based on GCa* Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) (a*) WL % SL% ( %) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 16.77 a 14.68 ab 6.20 0.83 13.47 3.74 14.45 a 1.05 a 14.15 d 4.32 bc 6.91 5 to 0 15.99 a 14.33 abc 5.09 3.33 12.99 3.20 13.85 ab 0.83 b 16.86 cd 4.28 c 7.72 0 to 5 13.70 ab 14.99 a 5.50 2.86 12.27 3.58 14.10 a 0.76 b 17.81 cd 4.40 bc 8.37 5 to 10 11.58 b 12.55 c 4.12 4.50 13.33 3.16 12.55 bc 0.55 c 22.63 bc 4.40 bc 7.35 10 to 15 7.89 c 13.44 abc 4.67 4.29 13.81 3.25 13.63 ab 0.52 cd 27.54 ab 4.29 c 9.33 15 to 20 4.89 c 12.35 c 3.43 2.50 11.71 3.57 13.35 abc 0.46 de 31.63 a 4.63 a 10.91 20+ 0.46 d 12.67 bc 4.50 7.78 12.36 3.36 12.11 c 0.40 e 30.08 a 4.54 ab 7.79 Significance * NS NS NS NS * * NS = S NS = n on significant Values with different letters were significantly different at

PAGE 77

77 Table 3 7 p hysical and chemical characteristics of least mature to most advance d fruit at harvest based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) GC (a*) FW (g) Size (mm) PB (%) FC (a value) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 7.53 g 98.32 55.05 35.5 c 0.82 d 53.67 a 9.93 1.03 a 9.64 c 3.83 bc 4.69 5 to 0 3.25 f 124.60 60.80 39.5 bc 3.59 cd 49.00 a 10.30 0.98 ab 10.55 bc 3.79 c 5.70 0 to 5 1.96 e 127.99 60.90 60 .0 abc 3.76 cd 42.65 a 10.25 0.94 ab 10.92 bc 3.82 bc 5.15 5 to 10 5.76 d 120.67 60.0 0 50 .0 bc 14.26 ab 22.89 b 8.20 0.74 ab 11.12 abc 4.22 a 6.08 10 to 15 13.76 c 152.46 65.03 50 .0 bc 7.00 bcd 17.60 b 11.55 0.78 ab 16.01 a 4.04 ab 6.49 15 to 20 17.44 b 142.67 63.34 74 .0 ab 9.52 abc 25.46 b 9.63 0.73 ab 13.13 abc 3.99 abc 5.20 20+ 29.07 a 137.61 63.55 93.5 a 17.65 a 18.74 b 10.85 0.71 b 15.29 ab 4.02 abc 6.00 Signi ficance NS NS * NS * NS = S NS = n on significant Values with different letters were significantly different at Table 3 8 physical and chemical characteristics of least mature to most advance d fruit after 7 days at 20 C based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit reached commercial h arvest stage Maturity g roup (GC a*) (a*) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 20.10 a 10.53 20.76 a 10.65 0.83 a 13.46 c 4.21 b 7.81 5 to 0 16.99 ab 12.31 18.25 ab 11.34 0.64 b 17.44 bc 4.30 b 7.55 0 to 5 14.02 bc 11.18 16.05 ab 9.54 0.58 bc 17.04 c 4.41 b 5.33 5 to 10 14.50 bc 11.65 13.98 bc 9.88 0.46 cd 22.89 ab 4.64 a 7.91 10 to 15 9.59 c 12.96 9.18 c 10.13 0.40 d 26.43 a 4.67 a 6.74 15 to 20 4.10 d 14.34 10.12 c 9.88 0.39d 26.36 a 4.71 a 5.04 20+ 2.22 e 13.49 10.28 c 9.30 0.40 d 23.43 a 4.68 a 5.65 Significance NS NS * NS = S ignificant differences detected NS = n on significant Values with different letters were significantly different at

PAGE 78

78 Table 3 9 physical and chemic al characteristics of least mature to most advance d fruit after 14 days at 0C and 7 d ays at 20 C based on GCa* Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) (a*) WL ( %) SL ( %) ( %) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 22.39 a 20.76 8.77 a 12.06 a 12.07 d 26.26 a 11.72 ab 0.76 a 15.75 c 4.31 d 7.24 5 to 0 20.57 a 22.43 8.85 a 11.25 a 18.51 bc 23.31 a 12.50 a 0.62 ab 21.20 b 4.46 bcd 6.95 0 to 5 15.41 b 20.16 9.13 a 2.67 a 15.35 cd 19.96 a 11.24 ab 0.65 ab 18.22 bc 4.44 cd 7.13 5 to 10 12.74 b 16.28 6.88 ab 10.0 0 ab 17.79 bc 20.94 a 10.78 bc 0.52 bc 21.17 b 4.51 bc 7.09 10 to 15 6.04 c 16.02 4.82 ab 6.00 bc 23.26 ab 11.97 b 7.80 d 0.37 cd 21.07 b 4.80 a 4.51 15 to 20 3.71 c 12.90 2.44 b 1.67 abc 25.07 a 12.31 b 11.35 ab 0.46 cd 25.50 a 4.64 ab 8.18 20+ 2.60 d 15.75 4.07 ab 11.3 0 c 23.43 ab 9.11 b 9.53 c 0.36 d 27.36 a 4.82 a 5.66 Significance NS * * * * NS = S NS = n on significant Values with different letters were significantly different at 0.05

PAGE 79

79 Table 3 10 p hysical and chemical characteristics of least mature to most advance d fruit at harvest based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit reached commercial harvest stage Maturity g roup (GC a*) GC (a*) FW (g) Size (mm) PB (%) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 7.78 f 95.72 b 54.40 b 40.83 0.07 c 47.02 a 11.13 0.87ab 12.89 3.86 de 6.49 5 to 0 2.55 ef 102.16 b 55.93 b 69.00 3.88 bc 42.37 ab 11.75 0.99 a 11.99 3.82 e 8.68 0 to 5 2.84 de 91.68 b 53.35 b 54.00 8.45 b 23.43 bc 10.30 0.58 cd 17.77 4.19 b 6.00 5 to 10 9.02 cd 116.92 ab 58.77 ab 67.33 6.92 b 21.54 bc NA NA NA NA NA 10 to 15 13.17 bc 123.42 ab 58.30 ab 85.00 24.89 a 32.74 abc 10.10 0.70 bc 14.48 3.99 cd 6.08 15 to 20 18.65 b 159.18 a 65.10 a 75.00 7.80 b 17.95 c 9.00 0.59 cd 15.63 4.08 bc 5.46 20+ 30.27 a 156.25 a 65.90 a 90.00 9.77 b 13.77c 9.10 0.35 d 25.95 4.41 a 11.89 Significance * NS * NS NS NS = Significant NS = n on significant Values with different letters were significantly different at Table 3 11 Gulfking physical and chemical characteristics of least mature to most advance d fruit after 7 days at 20 C based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) (a*) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 17.45a 9.60 18.01 a 11.83 0.67 a 18.24 c 4.29b 10.84 a 5 to 0 13.74ab 12.23 20.51 a 10.46 0.50 b 20.94 c 4.45b 7.43 abc 0 to 5 12.92b 11.94 19.83 a 10.37 0.52 b 19.97 c 4.46b 6.91 abc 5 to 10 15.61ab 11.70 16.49 ab 9.95 0.35 c 28.54 ab 4.71a 4.89 abc 10 to 15 5.64c 17.71 12.98 ab 8.05 0.37 c 22.36 bc 4.79a 4.89 c 15 to 20 6.89c 12.91 14.09 ab 10.84 0.39 c 28.95 ab 4.77a 6.48 bc 20+ 0.85d 13.03 8.70 b 11.54 0.35 c 33.74 a 4.74a 9.31 ab Significance NS NS * * = Significant NS = n on significant Values with different letters were significantly different at

PAGE 80

80 Table 3 12 physical and chemic al characteristics of least mature to most advance d fruit after 14 days at 0C and 7 d ays at 20 C based on GCa* Fruit were obtained when 50%, 70%, or 90% of tagged fruit reached commercial harvest stage Maturity g roup (GC a*) (a*) WL ( %) SL ( %) ( %) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 18.71 a 19.37 ab 7.21 10.25 ab 13.99 b 18.71 12.18 0.71 a 18.04 c 4.28 c 7.70 5 to 0 18.28 a 21.33 a 7.91 22.00 a 20.87 ab 23.83 11.88 0.57 b 21.54 bc 4.50 bc 6.56 0 to 5 18.67 a 20.22 ab 7.28 2.17 b 23.51 a 18.76 11.37 0.49 bc 23.72 abc 4.54 b 9.25 5 to 10 8.49 b 16.40 bc 3.94 6.25 ab 20.60 ab 17.61 9.75 0.48 bc 19.97 c 4.56 ab 6.51 10 to 15 8.26 b 14.78 c 4.71 0.00 b 26.54 a 12.74 9.68 0.36 c 27.32 ab 4.77 a 6.86 15 to 20 9.43 b 19.89 ab 7.65 1.17 b 22.99 a 17.70 11.70 0.40 c 28.94 a 4.59 ab 8.53 20+ 0.88 c 16.34 bc 4.89 7.00 ab 26.83 a 12.31 11.47 0.41 c 28.40 a 4.55 ab 8.25 Signi ficance * NS * NS NS * NS = Significant NS = n on significant Values with different letters were significantly different at

PAGE 81

81 YEAR 2008 Table 3 13 p hysical and chemical characteristics of least mature to most advance d fruit at harvest based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) GC (a*) FW (g) Size (mm) PB (%) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 2.48 g 73.10 b 52.50 b 72.50 1.77 abc 45.48 a 10.30 0.89 a 11.57 d 3.83 6.21 0 to 5 3.18 f 73.50 b 53.67 b 55.00 1.25 c 50.42 a 10.03 0.79 ab 12.72 cd 3.88 4.93 5 t o 10 NA NA NA NA NA NA NA NA NA NA NA 10 to 15 14.08 e 70.49 b 51.33 b 63.33 0.62 bc 43.53 a 10.73 0.71 bc 15.42 bc 3.95 5.41 15 to 20 17.47 d 81.12 b 55.55 ab 65.00 3.66 ab 42.49 a 11.05 0.64 bc 17.79 ab 3.96 8.14 20 25 23.42 c 86.42 ab 56.63 ab 66.67 3.27 ab 19.27 b 9.77 0.60 cd 14.69 bcd 3.95 5.10 25 30 27.19 b 116.28 a 61.39 a 75.00 5.99 a 14.03 b 10.44 0.66 bc 16.10 cd 3.89 5.56 30+ 32.37 a 81.48 b 54.52 ab 85 .00 6.09 a 7.03 b 10.50 0.47 d 21.36 a 4.12 5.77 Sig nificance * NS * NS * NS * = Significant NS = n on significant Values with different letters were significantly different at

PAGE 82

82 Table 3 14 physical and chemical characteristics of least mature to most advance d fruit after 7 days at 20 C based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) (a*) WL ( %) SL ( %) ( %) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 10.56 a 10.54 3.64 17.50 6.89 b 5.37 a 11.75 ab 0.77 a 15.33 3.80 c 7.14 0 to 5 5.55 ab 12.30 5.65 2.50 5.96 b 3.43 bc 12.40 a 0.67 ab 18.72 3.90 bc 8.27 5 to 10 7.87 ab 10.65 4.09 17.86 6.95 b 3.60 b 11.24 ab 0.58 bc 19.21 3.89 bc 7.20 10 to 15 8.46 ab 10.41 3.88 10.63 6.72 b 3.74 b 10.91 b 0.54 c 19.89 4.22 ab 7.00 15 to 20 5.69 ab 9.79 3.65 12.0 0 6.79 b 2.96 bc 10.94 b 0.52 c 21.64 4.21 ab 6.22 20 25 4.46 abc 10.03 3.34 4.55 8.78 ab 2.92 bc 11.33 ab 0.52 c 22.67 4.25 ab 6.76 25 30 3.86 bc 10.91 4.11 10.63 9.33 ab 2.85 bc 11.10 ab 0.47 c 24.21 4.28 a 5.64 30+ 0.69 c 10.91 3.90 8.25 11.52 a 2.39 c 11.81 ab 0.50 c 23.48 4.31 a 7.34 Significance NS NS NS * * NS NS = Significant NS = n on significant

PAGE 83

83 Table 3 15 physical and chemic al characteristics of least mature to most advance d fruit after 14 days at 0C and 7 d ays at 20 C based on GCa* Fruit were obtained when 50%, 70%, or 90% of tagged fruit reached commerci al harvest stage Maturity group (GC a*) (a*) WL m (%) WL (%) SL (%) ( %) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 13.03 a 13.41 21.08 10.78 5.00 8.76 ab 3.11 b 14.30 0.97 a 14.80 c 4.00 c 8.48 0 to 5 14.09 ab 10.70 17.78 7.89 0.00 7.32 b 5.58 a 12.40 0.63 bc 19.80 bc 4.28 ab 6.96 5 to 10 9.14 abc 10.24 17.79 6.18 3.13 9.51 a b 4.87 a 13.38 0.70 b 19.27 bc 4.18 bc 7.89 10 to 15 10.31 abc 9.75 17.08 7.96 0.00 11.07 ab 2.72 b 12.20 0.58 bcd 21.34 bc 4.30 ab 5.85 15 to 20 8.49 bcd 10.10 17.46 7.02 0.00 10.37 ab 2.87 b 12.46 0.55 bcd 23.29 ab 4.26 ab 6.57 20 25 5.82 cd 8.46 15.74 6.17 10.0 10.12 ab 2.58 b 11.91 0.48 cd 25.23 ab 4.38 ab 6.44 25 30 4.11 de 9.21 16.11 6.13 5.00 11.69 ab 2.54 b 11.82 0.50 cd 24.03 ab 4.34 ab 6.41 30+ 0.76 e 9.65 17.91 6.20 2.41 13.28 a 2.14 b 12.89 0.44 d 30.69 a 4.49 a 8.48 Significance NS NS NS * NS * NS = Significant NS = n on significant Table 3 16 p hysical and chemical characteristics of least mature to most advance d fruit at harvest based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity group (GCa*) GC (a*) FW (g) Size (mm) PB (%) FC (a*) Firmness (N) SSC (%) TA (%) SSC/TA pH TS (%) 4.61 g 79.10 54.95 58.75 3.00 c 63.02 a 12.53 0.89 a 14.25 3.90 4.52 0 to 5 2.00 f 100.41 58.81 68.13 1.74 bc 45.88 a 12.69 0.84 a 15.70 3.98 5.67 5 to 10 7.11 e 97.36 58.10 73.75 2.63 bc 53.56 a 12.88 0.78 a 15.68 3.93 5.93 10 to 15 1 2.93 d 92.20 57.80 83.75 4.33 ab 49.66 a 12.90 0.78 a 15.42 3.79 6.14 15 to 20 1 7.82 c 110.62 61.77 78.33 6.14 ab 38.63 a 12.62 0.71 a 18.51 4.03 5.80 20 25 24.9 5 b 128.02 64.40 80.00 11.33 a 9.23 b 13.35 0.70 ab 19.38 3.78 6.73 25+ 26.70 a 103.32 57.10 70.00 4.56 ab 4.27 b 12.3 0.57 b 25.38 4.27 6.58 Significance NS NS NS * NS NS NS NS = Significant NS = n on significant

PAGE 84

84 Table 3 17 TropicBeauty physical and chemical characteristics of least mature to most advance d fruit after 7 days at 20 C based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) (a*) WL ( %) SL ( %) ( %) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 8.56 ab 8.08 4.29 0.33 6.70 c 4.80 a 13.37 0.94 a 14.54 e 3.93 c 6.66 0 to 5 9.81a 6.76 2.90 1.00 7.92 bc 3.53 b 12.48 0.80 ab 15.62 de 4.04 bc 6.60 5 to 10 8.50 abc 9.54 4.15 3.64 8.79 abc 3.61 b 13.31 0.75 bc 18.82 cde 4.12 abc 6.51 10 to 15 5.90 c 8.81 5.17 5.71 9.54 ab 3.07 bc 13.61 0.62 cd 22.59 bc 4.25 ab 8.52 15 to 20 6.24 bc 9.40 3.66 10.00 9.50 ab 3.47 bc 12.92 0.63 cd 21.17 cd 4.24 ab 6.82 20 25 1.65 d 9.77 5.23 4.29 9.56 ab 3.08 bc 13.63 0.51 d 29.16 a 4.34 a 7.13 25+ 0.45 d 7.80 3.27 8.57 10.95 a 2.46 c 12.77 0.49 d 27.93 ab 4.34 a 8.05 Significance NS NS NS * NS * NS = Significant NS = n on significant

PAGE 85

85 Table 3 18 TropicBeauty physical and chemic al characteristics of least mature to most advance d fruit after 14 days at 0C and 7 d ays at 20 C based on GCa* Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity group (GC a*) (a*) WL m (%) WL (%) SL (%) ( %) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 13.10 a 6.06 9.17 bc 3.17 b 1.18 9.80 3.60 a 13.14 0.69 a 20.43 b 4.26 c 5.96 0 to 5 11.03 a 6.87 9.77 bc 2.63 bc 1.11 11.07 3.21 ab 13.76 0.65 ab 22.81 b 4.25 c 7.22 5 to 10 10.48 a 5.97 8.72 bc 1.81 bc 0.56 10.65 3.34 a 13.27 0.53 abc 26.14 b 4.33 bc 5.98 10 to 15 9.07 a 8.52 12.94 a 5.43 a 0.00 11.72 3.57 a 13.13 0.48 bcd 27.45 b 4.47 b 7.24 15 to 20 4.23 b 6.56 10.41 ab 2.67 bc 0.91 11.75 3.20 ab 12.64 0.47 bcd 28.56 b 4.50 b 5.99 20 25 4.16 b 6.24 7.55 c 0.66 c 1.67 10.20 2.67 ab 11.80 0.46 cd 27.25 b 4.52 ab 5.99 25+ 0.97 c 6.38 9.51 bc 2.93 b 2.86 13.62 2.34 b 12.91 0.33 d 45.11 a 4.72 a 6.34 Significance NS * NS NS NS * NS = Significant differences det NS = n on significant

PAGE 86

86 Table 3 19 p hysical and chemical characteristics of least mature to most advance d fruit at harvest based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) GC (a*) FW (g) Size (mm) PB (%) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 0 2.82 i 80.88 54.97 58.33 bc 0.21 c 38.15 a 11.53 0.95a 12.12 3.82 5.81 0 to 5 1.89 h 83.73 57 .00 85 .00 ab 7.15 bc 17.78 c 13 .00 0.76abc 17.15 4.11 7.07 5 to 1 0 6.37 g 95.46 57.93 55.00 c 5.46 bc 35.94 ab 10.07 0.77ab 13.44 4.02 4.90 10 to 15 12.07 f 74.47 52.65 75.00a bc 4.88 bc 35.92 ab 12.45 0.90a 13.91 3.98 5.58 15 to 20 17.48 e 87.83 56.53 60.00 bc 8.69 abc 22.14 c 11.60 0.59bc 17.60 4.07 5.19 20 25 22.02 d 94.42 57.13 67.50 abc 10.48 ab 18.52 c 12.02 0.55bc 18.56 4.13 6.00 25 30 28.46 c 90.38 56.40 83.00 abc 17.34 a 18.37 c 10.52 0.48c 19.41 4.30 5.81 30 35 31.48 b 91.58 56.10 85.00 ab 10.41 ab 26.83 bc 11.60 0.58bc 16.86 4.04 3.81 35 + 36.02 a 95.63 57.40 89.00 a 9.70 ab 22.84 c 11.20 0.59bc 19.47 4.12 4.85 Sign i f icance NS NS * NS NS NS NS = Significant NS = n on significant

PAGE 87

87 Table 3 20 physical and chemical characteristics of least mature to most advance d fruit after 7 days at 20 C based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit reached commercial harvest stage Maturity g roup (GC a*) (a*) WL ( %) SL ( %) ( %) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 9.71 ab 13.04 5.32 5.00 8.65 16.67 9.70 c 0.75 a 12.91 c 4.25 a 5.07 0 to 5 13.98 a 12.18 5.05 2.50 10.85 20.75 11.15 bc 0.73 a 15.92 bc 3.70 c 6.43 5 to 10 12.96 a 12.42 5.12 2.50 10.11 10.80 11.20 bc 0.77 a 14.70 bc 4.22 b 4.29 10 to 15 5.33 bc 14.38 3.76 0.71 11.70 16.71 13.60 a 0.61 ab 23.61 abc 4.36 ab 8.57 15 to 20 5.06 bc 12.36 5.04 0.38 11.84 16.45 11.36 bc 0.46 bc 24.18 abc 4.55 ab 5.38 20 25 3.10 b 13.24 5.56 0.63 12.00 13.98 12.33 abc 0.49 bc 25.68 ab 4.55 ab 6.37 25 30 1.59 b 11.94 4.63 5.00 14.21 18.05 12.32 ab 0.50 bc 20.20 abc 4.46 ab 6.59 30 35 0.06 cd 11.64 3.86 1.80 14.36 17.45 10.87 bc 0.46 bc 26.34 ab 4.45 ab 6.45 35 + 4.56 d 13.00 4.58 2.30 12.31 18.08 12.00 ab 0.39 c 31.87 a 4.67 a 6.93 Significance NS NS NS NS NS * * NS = Significant NS = n on significant

PAGE 88

88 Table 3 21 physical and chemic al characteristics of least mature to most advance d fruit after 14 days at 0C and 7 d ays at 20 C based on GCa* Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity group (GC a*) (a*) WL m (%) WL (%) SL (%) ( %) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 17.23 a 10.77 18.04 7.46 1.25 10.91 c 13.07 c 11.73 bc 0.81 a 15.55 d 4.25 d 5.04 bc 0 to 5 16.89 a 11.24 21.57 9.44 5.00 14.87 bcd 26.26 a 10.33 c 0.58 bc 17.91 d 4.31b cd 4.11 c 5 to 10 14.84 a 14.76 24.81 6.83 1.25 16.82 abc 21.10 b 11.95 bc 0.60 b 20.00 cd 4.37 cd 5.13 bc 10 to 15 9.67 b 9.68 18.63 6.71 6.43 14.00 cd 17.47 bc 12.66 abc 0.63 b 20.71 bcd 4.41 bcd 6.01 bc 15 to 20 5.56 bc 9.50 19.54 5.98 1.50 19.40 ab 14.86 c 13.66 ab 0.51 bc 26.67 abc 4.58 abc 7.15 ab 20 25 7.46 b 9.60 19.01 6.39 7.22 21.20 a 16.60 bc 11.12 bc 0.43 c 27.74 a 4.74 a 5.68 bc 25 30 1.95 cd 9.69 18.99 5.84 10.00 18.45 abc 16.90 bc 11.99 bc 0.44 c 27.86 a 4.70 ab 6.51 bc 30 35 1.29 d 9.40 19.50 8.46 11.29 17.73 abc 16.11 bc 15.40 a 0.56 bc 27.43 ab 4.45 abcd 9.66 a 35+ 6.46 e 8.78 18.86 6.74 0.17 21.62 a 14.97 c 13.05 abc 0.48 bc 27.64 a 4.49 abcd 6.97 ab Significance NS NS NS NS * * * * = Significant NS = n on significant

PAGE 89

89 Table 3 22 p hysical and chemical characteristics of least mature to most advance d fruit at harvest based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity g roup (GC a*) GC (a*) FW (g) Size (mm) PB (%) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 5 to 10 8.16 e 83.71 b 53.36 bc 90.80 12.04 29.38 a 12.54 a 0.70 a 17.99 4.00 c 6.98 10 to 1 5 13.40 d 105.00 a 58.42 a 95.00 13.40 20.85 b 11.88 a 0.60 b 19.93 4.11 bc 6.40 15 to 20 16.79 c 89.65 b 55.65 ab 92.70 14.90 19.80 bc 11.59 a 0.54 c 21.68 4.19 b 6.26 20 25 22.82 b 85.08 b 53.43 bc 86.17 18.48 13.75 c 9.62 b 0.42 d 22.68 4.49 a 5.81 25+ 26.98 a 57.28 c 50.20 c 85.75 16.03 18.17 bc 7.30 c 0.35 e 21.36 4.58 a 3.79 Significance * NS NS * NS NS = Significant NS = n on significant Values with different letters were significantly Table 3 23 physical and chemical characteristics of least mature to most advance d fruit after 7 days at 20 C based on GCa*. Fruit were obtained when 50%, 70%, or 90% of tagged fruit reached commercial harvest stage. Maturity g roup (GC a*) (a*) WL ( %) SL ( %) ( %) FC (a*) Firmness (N) SSC (% ) TA (%) SSC/TA pH TS (%) 19.83 a 7.49 3.54 2.50 7.29 b 11.32 11.00 a 0.73 a 15.14 b 4.18 c 5.45 ab 0 to 5 12.68 b 8.63 2.32 0.25 10.94 ab 15.24 11.88 a 0.52 b 23.06 ab 4.39 bc 6.92 a 5 to 10 10.22 c 12.80 2.21 2.86 12.03 ab 14.46 11.01 a 0.44 c 24.93 ab 4.46 bc 6.41 a 10 to 15 8.41 d 13.71 3.48 2.00 19.19 a 12.75 12.20 a 0.39 d 31.23 a 4.48 bc 7.35 a 15 to 20 6.22 e 11.26 4.01 3.00 17.51 a 12.74 10.35 a 0.33 e 31.79 a 4.65 ab 5.78 ab 20 25 4.29 f 11.65 4.25 0.22 17.62 a 13.50 8.81 ab 0.27 f 32.95 a 4.90 a 4.46 ab 25+ 3.09 g 11.22 8.99 30.00 19.03 a 8.938 6.2 0 b 0.23 g 26.50 a 5.04 a 2.90 b Sig nificance NS NS NS NS * * * = Significant NS = n on significant

PAGE 90

90 Table 3 24 Gulfking physical and chemic al characteristics of least mature to most advance d fruit after 14 days at 0C and 7 d ays at 20 C based on GCa* Fruit were obtained when 50%, 70%, or 90% of tagged fruit r eached commercial harvest stage Maturity group (GCa*) (a value) WL m (%) WL (%) SL (%) ( %) FC (a*) Firmness (N) SSC (%) TA (%) SSC/TA pH TS (%) 18.67 a 6.29 13.08 2.74 bc 3.75 16.23 b 19.73 12.18 ab 0.65 a 18.94 d 4.24 e 5.71 bc 0 to 5 14.84 b 5.80 13.47 1.55 c 5.36 19.69 b 16.46 12.49 ab 0.56 b 22.32 cd 4.29 de 6.62 abc 5 to 10 12.63 c 6.90 15.99 5.17 abc 1.29 16.84 b 16.08 12.89 a 0.51 c 25.36 bcd 4.42 d 6.73 ab 10 to 15 9.66 d 8.66 18.42 3.32 bc 1.27 27.38 a 15.63 12.85 a 0.44 d 29.38 bc 4.58 c 7.02 a 15 to 20 7.74 e 6.14 16.22 3.36 bc 1.14 26.21 a 14.73 12.43 ab 0.39 e 31.69 ab 4.61 c 7.05 a 20 25 5.21 f 7.84 18.94 6.43 ab 3.29 28.61 a 13.60 10.16 b 0.33 f 30.57 b 4.85 b 4.96 bc 25+ 2.50 g 9.05 20.73 8.49 a 0.83 26.88 a 13.15 10.18 b 0.27 g 39.45 a 5.08 a 4.75 c Significance NS NS NS NS * * * = Significant NS = n on significant Table 3 25 S ummary of optimum harvest maturities and the common maturity range between the two years for all cultivars Storage at 20C for 7D Storage at 0C for 14D Plus 20C for 7D Cultivar Year 2007 Year 2008 Common Maturity Range Year 2007 Year 2008 Common Maturity Range MG 5 10 MG < 0 to 20 MG 5 10 MG 5 to 10 MG 0 20 MG 0 10 MG 0 to 10 MG 5 20 MG 5 10 MG 0 to 10 MG < 0 to20 MG 0 10 MG 5 20+ MG 10 to 35+ MG 10 20 MG 10 20+ MG 5 15 MG10 15 MG 15 20+ MG 10 25+ MG 15 25 MG 0 to 15 MG <0 to 10 MG 0 10

PAGE 91

91 Table 3 26 Correlation coefficient (r) between maturity groups and fruit qualities and among fruit qualities at harvest for both MF and NMF peaches in 2007 Year 2007 MF NMF Significant at MG GC(0.99) MG GC(0.98) MG GC(0.98) MG GC (0.99) MG FW(0.90) GC FC(0.92) MG PB(0.88) MG FW(0.91) MG Size(0.87) FW Size(0.93) MG Firm( 0.90) MG Size (0.9) MG FC(0.98) Size FC(0.94) MG TA( 0.93) GC Mass(0.99) MG Firm( 0.90) FC Firm( 0.97) GC Peel(0.91) GC Size (0.9) MG TA( 0.92) Firm TA(0.98) GC TA( 0.88) FW Size (0.99) GC FW(0.91) FW Size(0.99) Firm TA(0.93) GC Size(0.88) FC TA( 0.90) TA pH(0.97) GC FC(0.98) Firm TA(0.96) SSC/TA pH (0.97) GC Firm( 0.90) GC TA( 0.92) FW Size(0.99) FW PB(0.90) FW FC(0.95) Size PB(0.89) Size FC(0.94) PB SSC/TA(0.92) FC Firm( 0.93) FC TA( 0.92) Firm TA(0.87) Significant at MG PB(0.82) MG Size(0.82) MG FW(0.79) MG PB(0.86) GC PB(0.82) MG FC(0.90) MG Size(0.82) MG Firm ( 0.85) FW Firm( 0.81) MG Firm( 0.91) MG FC(0.84) MG SSC( 0.91) FW TA( 0.87) MG TA( 0.90) MG SSC/TA(0.85) MG TA( 0.83) FW pH(0.82) GC Mass(0.80) GC Size(0.78) GC Peel (0.9) Size Firm( 0.81) GC Size(0.87) GC FC(0.83) GC Firm( 0.85) Size TA( 0.87) GC Firm( 0.88) GC Firm( 0.86) GC SSC( 0.9) Size pH(0.86) GC TA( 0.89) GC SSC/TA(0.87) GC TA( 0.86) PB FC(0.82) GC SS/TA(0.79) FW Firm( 0.76) FW PB (0.76) PB TA( 0.73) FW FC(0.89) FW SSC/TA(0.86) FW SSC( 0.85) PB pH(0.85) FW SSC/TA(0.83) Size Firm( 0.78) Size PB (0.76) FC pH(0.76) Size SSC/TA(0.86) Size SSC/TA(0.86) Size SSC( 0.82) Firm SSC(0.77) FC TA( 0.94) FC Firm( 0.84) Firm SSC(0.91) TA pH( 0.83) FC SSC/TA(0.86) FC pH (0.78) Firm pH ( 0.90) SSC/TA pH(0.78) Firm SSC/TA( 0.85) TA SSC/TA( 0.91) Firm pH( 0.83) TA pH( 0.84)

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92 Table 3 27 Correlation coefficient (r) between maturity groups and fruit qualities, and among fruit qualities at harvest for both MF and NMF peaches in 2008 Year 2008 MF NMF Significant at MG GC(0.98) MG GC(0.99) MG GC(0.99) MG GC(0.99) MG Firm( 0.93) MG Firm( 0.91) MG TA( 0.80) MG TA( 0.99) MG TA( 0.93) MG TA( 0.96) GC TA( 0.82) MG pH(0.98) MG SSC/TA(0.83) MG SSC/TA(0.88) FW Size(0.88) GC TA( 0.99) GC FC(0.82) GC Firm( 0.90) FC TA( 0.92) GC pH(0.99) GC Firm( 0.89) GC TA( 0.94) FC SSC/TA(0.86) FW Size(0.97) GC TA( 0.94) GC TS(0.89) FC pH(0.94) Firm SSC/TA( 0.96) FW Size(0.97) FW Size(0.94) Firm TA(0.80) SSC pH( 0.96) TA SSC/TA( 0.91) FW FC(0.94) Firm SSC/TA( 0.92) SSC TS(0.97) TA pH( 0.91) Size FC(0.90) Firm pH( 0.83) TA pH( 0.99) SSC/TA pH(0.92) Firm TA(0.89) TA SSC/TA( 0.90) Firm SSC/TA( 0.91) TA pH( 0.84) TA SSC/TA( 0.95) SSC/TA pH(0.87) Significant at MG FC(0.86) MG FC(0.80) MG FC(0.74) MG SSC( 0.94) GC FC(0.822) MG TS(0.87) MG SSC/TA(0.76) MG TS( 0.90) GC SSC/TA(0.84) GC FW(0.77) GC FC(0.77) Size PB(0.90) GC pH(0.75) GC FC(0.85) GC SSC/TA(0.77) FC Firm( 0.93) GC SSCTA(0.79) GC SSC/TA(0.84) FW TA( 0.72) FC SSC/TA(0.93) PB FC(0.85) FW Firm( 0.76) FC Firm( 0.76) SSC TA(0.95) PB Firm( 0.78) FW TS(0.77) pH TS( 0.88) FC Firm( 0.87) PB FC(0.79) SSC TS(0.76) FC TS( 0.81) Firm TS( 0.81) SSC pH( 0.82) TA TS( 0.80) Table 3 28 Two year summary of potential maturity indices for all cultivars, MF specific, or NMF specific based on the c orrelation coefficient (r) between maturity groups and fruit qualities, and among the fruit qualities at harvest Year All Cultivar MF Specific NMF Specific 2007 MG GC MG FC MG PB MG Firm GC FC Firm pH MG TA GC FW TA pH MG Size FC Firm Firm TA FC Size GC TA FC FW GC Firm FC TA GC Size FW Size 2008 MG GC MG Firm Firm SSC/TA MG TA MG SSC/TA TA pH GC TA MG FC FC Firm FW Size GC Firm FC SSC/TA GC SSC/TA TA SSC/TA

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93 CHAPTER 4 RIPENING AND QUALITY DEVELOPMENT OF LOW CHILL SUBTROPICAL MELTING AND NON MELTING FLESH PEACH VARIETIES HARVESTED AT DIFFERENT MATURITIES Overview Growing high quality peaches ( Prunus persica (L.) Batch) i.e., with good flavor and fruit size, is appealing to homeowners, landscapers, and commercial fruit growers located in the tropical and sub tropical regions of the U.S. (Rouse et al., 2006) P eaches adapted to tropical and sub tropical climates have a low chilling requirement for fruit set (less than 250 chill units) and, in Florida, ripen in a market window when peaches from other areas of the U.S. are not availabl e. Supplied of f ruit fro m Chile usually are depleted before early market Florida peaches mature (about early April) and the earliest higher chill peach cultivars from Georgia, Carolina and California appear after they ripen (Rouse and Sherman, 2 002) .Therefore, growing low chill peach cultivars in Florida may be economically advantageous. Early season peaches suffer from relatively low soluble solids content (SSC). Thus, fruit growers generally rely on c ultural practices to improve the fruit quality (Mercier et al., 2009) Moreover, the traditional melting flesh ( MF ) peaches become extremely triggered T hus they need to be harvested stage to minimize mechanical injuries, but consequently have considerably lower eating quality than tree ripened fruit (Cascales et al., 2005; Delwiche and Baumgardner, 1983; Williamson and Sargent, 1999) Developing non melting flesh (NMF) peach cultivars that are traditionally used for canning with the flavor and external red color of MF peaches is desirable because the relatively slow softening characteristics of NM F peaches will allow growers to pick the fruit at a riper stage, thus

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94 provi di ng eating quality for consumers without sacrificing shipping ability (Beckman et al., 2008) Ripening initiation of p eaches is regulated by System II ethylene. In peaches, the burst in respiration associated with climacteric ripening coincides with the increased levels of System II ethylene production (Ferrer et al., 2005; Madrid et al ., 2000) Peaches have a moderate respiration rate during ripening relative to other horticultural commodities (Wills et al., 2007) It was reported that peach cultivars with shorter developmental cycle s ( earlier ha rvest dates ) had higher and more pronounced respiration rate s at the climacteric peak (DeJong et al., 1987) T here are no clear distinctions between the sensory aspects of MF and NMF peaches after normal ripening except texture (Brovelli et al., 1999 b ) The dominant (M) allele controls the flesh firmness of MF cultivars, while the allele of NMF cultivars is homozygous recessive (mm) (Peac e et al., 2005) This genetic difference in texture translates into a reduced capacity for cell wall degradation in the NMF fruit, which could be attributed to either a partial or complete deletion (Callahan et al., 2004 ; Pressey and Avants, 1978 ) or mutation (Morgutti et al., 2006) of the endo polygalacturonase (endo PG) gene. Endo PG (E.C. 3.2.1.15) is a cell wall modification enzyme that randomly cleaves specific pectin molecules (homogalacturonans) and effectively reduces their molecular size (Pressey 1978) Since endo PG mRNA is highly expressed after the ethylene climacteric rise and the increased enzyme activity is accompanied by increases in water soluble pectin during the melting phase (Orr and Brady, 1993; Pressey and Avants, 1978 ) endo PG is regarded as the primary enzyme responsible for peach softening (Lester et al., 1994; 1996)

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95 In contrast to endo PG, exo PG (PG, E.C. 3.2.1.67) removes monomer units from the non reducing end s of the pectin chain s and has a minimal effect on the size of the macromolecule (Pre ssey and Avants 1978). E xo PG activity in NMF peaches can be similar or higher than in MF peaches during ripening (Manganaris et al., 2006a; 2006 b; Pressey and Avants, 1973; 1978b) Two forms of exo PG in the mesocarp tissue of ripe MF peaches were distinguished, and increased enzyme activity occurred only when the mesocarp tissue was very soft (Downs and Brad y, 1990) Therefore, exo PG may not have an important role in the initiation or promotion of fruit softening during ripening but it may act together with endo PG to produce the MF texture (Orr and Brady 1993). Based on previous research, a direct rela tionship between endo PG and peach softening may be assumed; however, antisense RNA work in transgenic tomato did not support a direct relationship between endo PG and softening (Carrington et al., 1993) Incre ased endo PG activity in tomato fruit was found to occur mostly during the final Furthermore, ripening inhibition of avocados using 1 methylcyclopropene (1 MCP) also show ed that endo PG is not required for the extensive softening that occurs in ripening avocado fruit (Jeong et al., 2002) Another enzyme that may affect cell wall degradation during ripening is pectin methylesterase (PME; E. C 3.1.1.11) PME activity is required to initiate pectin degradation (Li et al., 2010) by hydrolyzing the ester bond in the carboxymethyl groups of galacturonic residues of pectin, resulting in the release of methyl groups and exposure of carboxyl groups (Tijskens et al., 1999) PG has no substrates with which to

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96 react until demethylesterification occurs (Fischer and Bennett, 1991) PME activity has been shown to increase sharply at an early stage of peach ripening and remains constant or decreases throughout t he cell wall depolymerization phase in MF cultivars (Brummell et al., 2004; Glover and Brady, 1995) peaches was reported to be significantly lower than that of MF (Manganaris et al., 2006b) Compositional changes during ripening increase the desirable flavor of peaches Assessment of fruit quality after ripening is important because consumers ultimately wi ll taste the ripened fruit and make decisions regarding repeat purchases base on this experience. Currently, there is little information available on the qualities of the low chill peaches after ripening, especially for the NMF cultivars that have been rec ently released. Thus, t he objective of the this study was to characterize the ripening of low chill, subtropical MF and NMF peach cultivars during storage at 20 C based on their respiration rates and ethylene production rates when harvested at various dev elopmental stages; 2) to quantify the qualities of the fruit objectively after postharvest ripening at 20 C for 5 days; and, 3) to investigate the relationship between cell wall modifying enzymes and softening of MF and NMF cultivars via measurement of PM E and PG activities during ripening. Materials and Methods Plant Materials In 2007 2008, and 2009 two MF cultiv the peach collection at the UF Plan t Science Research & Education Center at Citra, Florida and a group of 100 marker fruit from four trees for each cultivar were tagged after fruit thinning and natural

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97 fruit drop. These fruit were randomly selected and considered to be representative of the population of each cultivar During later stages of fruit development, as the fruit approached full size, the marker fruit were monitored visually for changes in peel ground color (GC). When the peel GC of 50% of the marker fruit changed from green to yellow, the peel GC (C.I.E. L*, a*, and b* val ues) of all 100 marker fruit were objectively measured using a reflectance colorimeter (Minolta CR 400, Konica Minolta, Japan). Ground color was measured on the greenest portion of the peel. For all peach g enotypes, the chromaticity (gre en red) of the epidermal GC (GCa* ) increases the most with increasing maturation and ripening, whereas L (lightness) and b* (yellow blue) values change only slightly with maturation and ripening (Delwiche and Baumgardner, 1985) Three fruit per tree (12 fruit per cultivar) with GCa* that was within one standard deviation of the 100 marker fruit were harvested. The harvested fruit were subjectively separated into different maturity groups (MG) according to their GC and ripened at 20 C for 5 days. Since PG activity is expected to be higher at more advanced ripeness stages, at least 9 fruit from each of the four cultivars with initial GC a* together from thre e harvest s in 2007. In 2010, fruit collected from one harvest of pair of cultivars had initial GC a* pair had a* values < 15. All of the f ruit were ripened at 20 C for 5 days before firmness measurements and tissue collection. Fruit tissue was diced and stored at 30 C until enzyme analyses were conducted.

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98 Ethylene Production and Respiration Rate Determination In 2008, respiration rate (CO 2 production) and ethylene production were monitored in a static system consisting of 550 ml glass containers with air tight lids containing individual fruit that were sealed for 0.5 h before 1 ml headspace gas samples were withdrawn fo r gas chromatograph (GC) injection. The CO 2 was determined by GC using a thermal conductivity detector with a molecular sieve column. Ethylene was measured by GC with a photoionization detector and activated alumina column. Certified gas standards were use d to determine the concentration of CO 2 and ethylene. Measured concentrations of CO 2 and ethylene were converted into rates of production by calculation based on the mass of fruit in a jar, the void volume, and the duration of sealing. Respiration rate and ethylene production were monitored every day for 5 days at 20 C In 2009, an ethylene and CO 2 gas analyzer ETH 1010 (Fluid Analytics, Inc., West Linn, Oregon) was used to measure respiration rate and ethylene production. One to two fruit were sealed in a 2.735L Plexiglas container connected to the device. Five replicate measurements per sample were made. Quality Analysis Ground and flesh color d etermination Ground color (GCa*) and flesh color (FCa*) were objectively measured using a reflectance colorime ter (Minolta CR 400, Konica Minolta, Japan) and expressed as C.I .E. a* values (green red) since a* value increases the most with increasing maturation and ripening of peaches, both in the peel (D elwiche and Baumgardner, 1985) and the flesh (Fuleki and Cook, 1976; Kader et al., 1982; Robertson et al., 1991) Ground color was measured on the greenest portion of the peel. Flesh color was measured after removing a small (circa 2 cm diameter) patch of peel.

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99 Flesh f irmness d etermination Flesh firmness was measured with an Instron Universal Testing Instrument (Model 4411 C8009, Canton, MA, USA) that applied a compressive for ce from a 50 k g load cell. A convex tip probe (Ma g ness Taylor type), 7.9 mm in diameter, was attached to the load cell moving at a speed of 12 cm/min. Flesh firmness was measured at the fruit equator on two sides on the cheeks without peel and expressed as the bioyield force (N). Following color and firmness measurements, fruit samples were placed in quart size (17.7cm x 20.3cm) zipper locking plas ti c freezer bags and stored at 30 C for later compositional analyses Soluble s olids c ontent, t itratable a cidity and t otal s ugar d eterminations Frozen fruit tissues were pureed in a Waring blender for 1 min. The resulting slurry was centrifuged (20 min; 15,000 g n ; 4 C ) and the clear supernatant was used to determine soluble solids content (SSC) and titratable acidity (TA). The SSC was measured with a temperature compensated digital refractometer (model ABBE Mark II, Cambridge Instruments Inc, U.S.A) and expressed as per cent FW. The TA was determined by titration (model 719 S. Titrino, Metrohm, S witzerland) of 6 .0 g of juice plus 50 mL of water with 0.1N sodium hydroxide solution until pH 8.2 was reached and the TA was expressed as percent malic acid. The pH of the diluted juice was determine d automatically by the Titrino equipped with a pH electr ode. Total soluble sugar (TS) measurement was performed using the phenol sulfuric assay (Dubois et al., 1956) modified as follows : 5 L of extracted juice was diluted with 5 mL of 80% ethanol. Further dilution was performed if the concentration of the sample was out of the range of the standard curve A 500 L aliquot of the diluted sample was added to 500 L of 5 % phenol solution (Fisher Scientific, New Jer sey, USA; certified

PAGE 100

100 grade) and vortexed. Next, 2.5 mL of c oncentrated sulfuric acid (Fisher Scientific; certified ACS grade) was slowly added to the mixture and vortexed. The mixture was left for 10 min at room temperature for color development. The absorbance of the sample at 490 nm was read on a microplate with glucose (Fisher Scientific, New Jersey, USA; certified ACS grade) as the standard. Total sugar in the juice was expressed as a percentage. Enzyme Assays Preparation of c ell free p rotein e xtract Enzyme extracts were prepared similarly to the method of Jeo ng et al. (2002). Partially thawed mesocarp tissue (15 g) was homogenized with 25 mL of ice cold 95% ethanol for 1 min in an Omnimixer (Model GLH 01, New town, CT, USA) and centrifuged at 15,000 g n for 10 min at 4 C The supernatant was discarded and t he pellets were resuspended in 25 mL of ice cold 80% ethanol for 1 min and centrifuged again at 15, 000 g n for 10 min at 4 C The pellets were transferred to 10 mL of 50 mM Na acetate buffer, pH 5, containing 0.5 M NaCl, for 30 min in an ice cold water bath followed by centrifugation 15, 000 g n for 10 min at 4 C The resulting supernatant was analyzed for enzyme activities. Total soluble protein in the supernatant was measured using the bicinchoninic acid method with bovine serum albumin as the standard (Smith et al., 1985) Pectinmethylesterase a ctivity d etermination Pectinmethylesterase (PME, E.C. 3.1.1.11) was measured using modifications of the method of (Jeong et al., 2002). A 1% (w/v) solution of 93 % esterified citrus pectin (Sigma Chemical Co., St. Louis, MO, USA) was prepared in 0.1 M NaCl and adjusted to pH 7.5 with dilute NaOH. A 0.01% solution of bromothymol blue was prepared in 0.003

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101 M potassium phos ph ate buffer pH 7.5. A 166 L volume of 1% c itrus pectin was mixed with 12 L of 0.01% bromothymol blue and 70 L of water, and the pH adjusted to 7.5 with dilute NaOH. The reaction was initiated by adding 6 L of the cell free protein extract that had been adjusted to pH 7.5 with dilute NaOH. The d ecrease in A 620 over a 10 min reaction time was A 620 mg 1 protein min 1 Polygalacturonase a ctivity d etermination E ndo PG (E.C. 3.2.1.15) activity was assayed by mixing 250 L of enzyme extract with 250 L of 0.5% polygalacturonic acid (from orange peel, Sigma Chemical Co., St. Louis, MO, USA) in 50 mM Na acetate buffer (pH 4.4) and incubated at 30 C for 16 h (Pressey and Avants, 1973) For measurement of exo PG (E.C. 3.2 .1.67) activity, 250 L of enzyme extract was mixed with 250 L of 0.5% polygalacturonic acid in 50 mM Na acetate buffer (pH 5.5) containing 2 mM CaCl 2 and incubated at 30 C for 16 h. Uronic acid (UA) reducing groups released were measured using the met hod of Milner and Avigad (1967) with mono D galacturonic acid as the standard. One unit of activity was defined as 1 g galacturonic acid produced mg 1 protein h 1 Statistical Analysis The General Linear Model program of the Statistical Analysis System (SAS) (SAS Institute, Cary, NC) w as used. One way Analysis of Variance (ANOVA) was used to detect significant differences at the 5% level among the cultivar s and between years Since there were in general, no significance difference s after ripening among the MGs for the qualities listed in Table 4 1 all of the data were combined for analysis. The least significant difference (LSD) test was used for mean separation.

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102 Results and Discussion Respiration and Ethylene Production In 200 climacteric rise at the time of harvest as shown by increased respiration and ethylene production measured after harves t (Fig. 4 1A to 4 1D; Fig. 4 2A to 4 2D). The ethylene production me asured at harvest indicates that the MF cultivars only required low levels of ethylene to initiate ripening, since the fruit were apparently producing minimal amounts of ethylene on the tree. Fruit from different MGs were generally not significantly diffe rent in respiration rate and ethylene production for both MF cultivars. The peak levels of ethylene and CO 2 production in peaches were reported to occur around the same time (Amoros et al., 1989) This was only observ ed on Day 4 of storage of MG 5 to 10 in 2008 (Fig. 4 1C, 4 1D ) and Day 3 for Fig. 4 2A, 4 2B) The ethylene product ion rates similar to values reported by (Brovelli et al., 1999a) but higher than the rates in 2009. The ethylene production measured during ripening at 20 C in 200 8 was in accordance with (Brovelli et al., 1999 b ) in both 2008 and 2009 were higher than previously reported values, the trends were comparable (Brovelli et al., 1998b) For NMF peaches with GCa* values of 10 to 15 and 20 to 25 were post climacteric at the time of harvest in 2008 indicating that fruit from the more advanced MGs were producing climacteric ethylene wh ile ripening on the tree (Fig. 4 1E, 4 1F ). In 2009, post climacteric ethylene production was not observed on any Fig. 4 2E, 4 2F) which suggests a possible difference in harvest maturity

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103 be tween the two years The least mature fruit (GCa* 0 to 5) had peak ethylene production on Day 3 while other MG had the peaks on Day 2. Climacteric respiration peaked approximately 1 to 2 days after maximum ethylene production was reached (Fig. 4 2E). For N MF fruit in the lower MGs (GCa* < 15) had higher respiration rates than the most mature fruit (GCa* 20 to 25) in 2008 (Fig. 4 1G). The respiration climacteric of fruit with GCa* of 20 to 25 was 1 day in advance (Day 2) of the less mature fruit, which had their climacteric peaks delayed until Day 3. Fruit with GCa* of 20 to 25 had significantly lower ethylene production than fruit from the other MGs during storage (Table 4 range reached the post climacteric GCa* > 20 had their respiration climacteric on Day 1, 2 days earlier than the fruit from lower MG (Fig. 4 2G), indica ting that the fruit were quickly approaching the post climacteric stage. The ethylene climacteric occurred between Day 2 and Day 3 after harvest, similar to results in 2008 (Table 4 t with GCa* of 5 t o 10 reached their maximum respiration rate and ethylene production on the tree prior to harvest since they were already at the post climacteric stage during storage (Table 4 2G, 4 2H). In summary, t he respiration rate s w ere similar for MF and NMF p eaches, but the ethylene production was usually higher in the NMF cultivars during ripening. Similar results have been reported, confirming that the NMF trait in peaches is not related to low ethylene production (Brovelli et al., 1999a ; Haji et al., 2001; Manganaris et al., 2006b) The MF cultivars were mostly pre climacteric or at onset of ripening reg ardless

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104 of the different MG at harvest. The more advanced NMF peaches had already started the ripening process on the tree and became post climacteric during storage. The results from a previous experiment (Chapter 3) indicate that peaches destined for fre sh market should be harvested when the GCa* reaches 5 to 10 for MF fruit harvested within a GCa* range of 5 to 10 were at the beginning of the climacteric rise with very low ethylene production, while both NMF peach cultivars were further along on the climacteric rise. This is expected, because MF cultivars have been selected by breeders so that the optimum harvest maturity occurs when softening has not ye t been initiated. Since NMF peaches soften relatively slowly, the fruit can be harvested when ripening has already been initiated. Based on the results of this study, to 25 to GCa* 15 to 20 to avoid fruit that are approaching the post climacteric phase. At the postclimacteric developmental stage, fruit are over ripe and more susceptible to decay caused by pathogens (Gradziel, 1994) Qu ality Analysis G round color (GCa*) increased tremendously after 5 days of storage (Table 4 1). In peaches, the increase in a* denotes an increase in red carotenoid pigments and a loss of green color that is related to t he disappearance of chlorophyll in t he skin or flesh of the fruit (Ferrer et al., 2005; Madrid et al., 2000) The initial GCa* and final GCa* of indicat ing that this MF cultivar generally has more green color and less red pigment accumulation in the peel than the other cultivars that were included in this study. MF

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105 appeared to be less red. Flesh firmness and flavor composition were compared to the minimum eating qualities of MF peaches stated in the literature. MF peaches at eating ri pe stages should be close to 13 N flesh firmness, 0. 5 0.8% TA, and at least 10% SSC or SSC/TA 15 (Beckman and Krewer, 1999; Malakou and Nanos, 2005) Currently, there are no minimum eating qual ities defined for NMF peaches although it is known that a ripe NMF fruit may soften to around 16 N in firmness ( Lurie and Crisosto, 2005 ) As was expected, the MF cultivars in this study became extremely soft during st orage (flesh and the NMF cultivars retained greater flesh firmness longer than the MF cultivars. Both NMF cultivars maintain ed flesh firmness of 12 to 17 N after ripening for 5 days at 20 C years of this study (11.50 (10 (9 10%). Interestingly, the higher TA of the MF cultivars was balanced by higher SSC, while the lower TA of the NMF cultivars was balan ced by lower SSC. As a result, an SSC/TA of more than 15 was consistently observed in the NMF cultivars but was only achieved in the MF cultivars in two out of three years (2008 and 2009), indicating that the NMF cultivars may have higher consumer accep tance than MF peaches after ripening (Williamson and Sargent 1999) Consumer s favorably among the cultivars studied because it had the highest SSC/TA due to it having the lowest TA. Consumers reportedly prefer low acid over the high acid cultivars regardless of fruit maturity (Iglesias and Echeverria, 2009)

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106 The pH was significantly different between the MF and NMF peaches. The MF cultivars consistently had lower pH than the NMF cultivars after ripening. It has been shown that pH can sometimes relate better to sourness perception than TA in mangoes (Malundo et al., 2001) Hence, the MF cultivars would be expected to be perceived as more sour than the NMF cultivars. The TS concentrations were similar among the four cultivars in 2008 and 2009, but all were significantly less than the SSC. Sucrose fructose, and glucose are the main sugars in peaches, with sucrose being the dominant sugar at harvest (Byrne et al., 1991; Gnard et al., 2003) The TS is generally lower than the SSC because SSC can also include solutes that are not sugars such as pigments, salts, proteins, and acids. Furthermore it is possible that a lcohol soluble substan ces present in ripe peaches including pigments lipids and proteins, react with the concentrated sulfuric acid in the TS assay and therefore may significantly interfere with the absorbance reading (Ashwell, 1957) Enzyme Assays In 2007, MF differed from the other MF cultivar in having a higher level of endo PG activity than the two NMF cultivars after being stored at 20 C for 5 days (Table 4 2 ). In 2010, endo PG activity was significantly higher in MF Table 4 3 ). The NMF cultivar PG activity that was similar to the MF cultivar in 2007 approximately five A similar pattern was observed in 2010. T here were no differences in endo PG activity Since MF and NMF cultivars can have similar endo PG activities, lack of endo PG mRNA

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107 accumulation as suggested by Callahan et al. (2004) may not fully explain the delayed softening characteristic of NMF peaches. This confirms the report of Morgutti et al (2006), who observed that peach fruit with essentially the same flesh firmness (46 N) showed barely detectable accumulation of endo It may also be possible that the standard firmne ss measurement procedure using a Magness Taylor type probe, which was developed for MF peaches, does not accurately measure the different texture of NMF peaches. Exo sign ificantly diffe rent after storage in 2007 ( Table 4 2 significantly higher exo PG activities were not significantly different between Tabl e 4 3 ). These results demonstrate that the exo PG activit y of NMF fruit can be similar or higher than that of MF fruit after ripening (Pressey and Avant s 1978; Manganaris et al. 2006). When comparing the endo PG and exo PG activities for each cultivar, MF peaches appeared to have higher endo PG activity than exo PG activity, except for NMF UFSun appeared to have higher exo PG than e ndo PG activity in 2007 ( Table 4 2 ) a nd the reverse in 2010 ( Table 4 3 ). Therefore, it may be possible for ripe NMF peaches to have lower, similar or higher exo PG activity than endo PG activity. The PME activity after ripening was significantly higher in both MF cultivars than in the tw o NMF cultivars in 2007 ( Table 4 2 ), which was si milar to the results reported by Manganaris et al. (2006 ). However, this relationship was only observed between MF

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108 Table 4 3 cultivars after ripening cannot be explained by PME activity which differed significantly It is possible that the PME determination in this study was not performed at the period of development when the enzyme is most active. PME is most active during the early stage of ripening and remains constant or decreases throughout the cell wall depolymerization phase (Glover and Brady 19 95; Brummell et al., 2004 ). Porter et al. ( 2000) reported that there was no apparent relationship between PME activity and major changes in firmness for low vs high chill, or MF vs NMF peaches from the mature green developmental stage to the early stages of fruit ripening. Ortiz et al. nectarines had a similar trend during ripening but there was no apparent coin cidence for either enzyme with the melting phase of fruit softening. PG and PME activities were highest at the mature unripe stage and declined noticeably during the melting phase (late climacteric), but slowly regained activities as fruit became over ripe This may be indicative of a situation such that once ripening is initiated in MF fruit, the onset of events is irreversible, leading to the extensive, melting softening. It may also be possible that the presence of different PG and/or PME isozymes that c ontribute to the total activity of each enzyme measured masks the activity of individual softening related isozymes. The result would be that the changes in overall PG or PME enzyme activities would not correlate with the changes in flesh firmness. This w as observed in tomatoes galactosidase Gal) activity, which was due to three forms of the enzyme. During tomato ripening, the sum of their activities remained

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109 relatively constant, but the levels of the individual forms of Gal changed markedly (Pressey, 1983) Only one of the Gal forms was correlated with softening. Different rates of softening in different fruit are contributed to inherent differences in composition and in the na ture of the cell wall polysaccharides and other cell wall structural components (Li et al., 2010) Manganaris et al. (2006) reported that MF peach fruit underwent greater loss of neutral sugars, especially arabinose (Ar a) and galactose (Gal), than NMF peaches during ripening. This is supported by Yoshioka et al. ( 2010) who observed that pectin solubilization and loss of neutral sugars, Ara and Gal, occurred to a limited exten d in NMF peaches compared to that of MF peaches. G alactosyl and arabinosyl containing side chains on pectin backbones are thought to control pore size in the cell wall, thus limiting the accessibility of the pectin to pectolytic hydrolases and thereby protecting cell wall polysaccharides from extensive depolymeriz ation (Brummell and Harpster, 2001; Brummell, 2006) The loss of Ara arabinofuranosidase (ARF) activity from the pre climacteric to cl imacteric stage in MF peaches (Brummell et al., 2004; Carolina Di Santo et al., 2009; Santo et al., 2009) nectarines that the highest Gal activity occurs in mature but unripe fruit and a loss of Gal from cell wall material is followed immediately afterwards together with a significant decline in fruit firmness (Ortiz et al., 2010) H Gal may be related to the difference in texture between MF and NMF peaches more directly than PME and PG activities. Chapter Conclusion The low

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110 climacteric or at onset of ripening. NMF fruit harvest ed at different maturities generally had started ripening on the tree and the fruit were at more advanced ripeness stages and some became post climacteric potential to be perceived as having higher sensory quality by consumers due to higher SSC/TA than the MF cultivars. PME and PG activities determined after ripening appeared to have no direct relationship with softening in either MF and NMF peaches.

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111 Year 2008 Ethylene Production ( L C 2 H 4 /kgh ) Respiration Rate ( mg CO 2 /kgh ) Figure 4 1.Respiration rate and ethylene production at 20 C storage of different maturity groups of peaches in 2008 based on GCa*. Days at 20 C A B C D E F G H

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112 Year 2009 Ethylene Production ( L C 2 H 4 /kgh ) Respiration Rate ( mgCO 2 /kgh ) Figure 4 2. Respiration rate and ethylene production at 20C storage of different maturity groups of peaches in 2009 based on GCa*. Days at 20 C A B C D E F G H

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113 Table 4 1 Mean fruit quality of MF and NMF peaches in three seasons after 5 days of storage at 20 C except initial GCa*, which was determined at harvest Year MF MF NMF NMF Initial GCa* y 2007 2.66ab 9.30a 0.48b 6.65a 2008 22.97a 8.68c 14.48b 17.49b 2009 12.72a 6.38b 14.16a 12.72a Final GCa* y 2007 17.13b 21.55a 15.54b 15.9b 2008 28.57a 17.56c 21.35b 23.87b 2009 24.25a 15.92b 23.27a 21.61a FC (a* value) y 2007 7.32b 12.81a 12.43a 12.95a 2008 8.62c 10.28bc 12.43b 15.92a 2009 2.61c 9.11a 8.04ab 6.08b Firmness (N) y 2007 3.78b 3.32b 17.03a 14.56a 2008 3.37c 3.86c 12.66b 17.27a 2009 2.41b 2.76b 13.99a 12.74a SSC (Brix) y 2007 9.73b 11.49a 9.01bc 8.83c 2008 10.82b 12.80a 9.99b 10.38b 2009 11.16b 12.55a 11.08bc 10.04c TA (%) y 2007 0.75a 0.83a 0.60b 0.42c 2008 0.62a 0.64a 0.47b 0.33c 2009 0.51b 0.70a 0.40c 0.39c SSC/TA y 2007 13.04c 14.07bc 15.40b 21.54a 2008 17.89b 20.97b 21.58b 31.55a 2009 22.16bc 18.16c 29.86a 25.49ab pH y 2007 NA NA NA NA 2008 4.23b 4.24b 4.55a 4.68a 2009 4.11b 4.00b 4.64a 4.56a TS (%) y 2007 6.97b 9.78a 9.37a 7.60b 2008 x 4.42 5.59 5.06 5.18 2009 6.70a 6.37a 5.96ab 5.29b X = N o significant differences of total sugar among the cultivars in 2008 y = S

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114 Table 4 2 Flesh firmness and cell wall modification enzyme activities for MF and NMF peaches with initial GC a* after 5 days of storage at 20 C in 2007 Cultivar PME a ctivity (units) m Endo PG activity (units) g Exo PG activity (units) g Flesh f irmness (N) 0.57a 0.67 bc 0.73 b 2.34 b 0.42b 2.86 a 2.17 a 2.86 b 0.11c 0.24 c 0.32 b 11.40 a 0.11c 1.17 b 0.63 b 10.77 a * * m = 1 unit of PME activity = A 620 mg 1 protein min 1 g = 1 unit of PG activity = 1 g galacturonic acid mg 1 protein h 1 = S ignificant NS = n on significant Table 4 3 Flesh firmness and cell wall modification enzyme activities of MF and NMF peaches with initial GC a* values 15 and after 5 days of storage at 20 C in 2010 Cultivar Initial GC a* < 15 PME a ctivity (units) m Endo PG activity (units) g Exo PG activity (units) g Flesh f irmness (N) 0.50 1.96 0.86 2.89 0.43 0.98 0.74 8.62 Significance ( p NS NS Cultivar Initial GCa* PME a ctivity (units) m Endo PG activity (units) g Exo PG activity (units) g Flesh f irmness (N) 0.66 1.38 0.30 2.97 0.19 1.48 1.06 8.03 Significance ( p NS * m = 1 unit of PME activity = A 620 mg 1 protein min 1 1 unit of PG activity = 1 g galacturonic acid mg 1 protein h 1 = S ignificant NS = n on significant

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115 CHAPTER 5 EFFECT OF PRE STORAGE HOT WATER TR EATMENT ALONE OR COMBINED WITH AQUEOUS 1 METHYCLCOPROPENE ON RIPENING OF NON MELTING FLESH PEACHES Overview Ripening is a part of development that transforms a low quality fruit into one with acceptable eating texture, attractive color, pleasant aroma and flavor, and various health promoting phytochemicals. Among these quality attributes, fruit texture is pivotal in terms of its relationship to consumer preference, fruit storability, transportability, shelf life, and pathogen resistance (Li et al., 2010) Traditional melting flesh (MF) peaches have dessert like qualities after ripening but have to be harvested at to avoid over softening during distribution (Cascales et al., 2005; Williamson and Sargent, 1999) Consequently, the flavor is sacrificed because these fruit are too immature to be ripened with desirable qualities. Newer varieties of non melting flesh (NMF) peaches, which have h istorically been use for canning, have become more popular fresh market peaches due to their slower rate of softening as well as terminal firmness retention at the full ripe stage compared with the MF varieties. NMF peaches can be left on the tree longer t o achieve maximum quality and still have sufficient firmness to be handled successfully during shipping and long term storage due to this trait (Sherman et al., 1990) Controlling the irreversible ripening proces s is crucial for reducing distribution loss and supplying high quality fruit to consumers. As a climacteric fruit, peach ripening is promoted by ethylene (Lelievre et al., 1998) Pre storage hot water and 1 methylc ylopropene (1 MCP) applications have been reported separately to maintain postharvest quality of MF peaches by lowering ethylene production (Kerbel et al., 1985;

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116 Liguori et al., 2004) but no studi es have been conducted with NMF varieties harvested at more advanced developmental stages than those typically utilized for MF varieties. higher than 33 C (Li and Han, 1998). H eat treatment is an attractive approach to minimize chemical usage in controlling insect infestation and prolonging the postharvest life of the fruit (Serrano et al., 2004) It extends storability and marketing of fru it by inhibiting ripening, inducing plant resistance to chilling injury (CI), and reducing external skin damage during storage (Lurie, 1998; Paull and Chen, 2000) Under certain conditions, heat sho ck may be induced by heat treatment, resulting in delay of normal fruit softening, possibly due to disruption of mRNA synthesis and stability or protein synthesis and degradation of essential enzymes such as those responsible for ethylene biosynthesis (i.e ., ACC oxidase and ACC synthase) and cell wall catabolism (i.e., polygalacturonase) (Lurie, 1998; Martinez and Civello, 2008) The most common application methods include hot water, hot wat er vapor, and hot air. Water is the preferred medium for most applications since it is more efficient than air in transferring heat (Zhou et al., 2002) Typical treatments usually consist of dipping fruit in 43 49 C wat er from several minutes to 2 hours (Fallik, 2004) 1 Methylcyclopropene (1 MCP), an ethylene action inhibitor, prevents ripening in climacteric fruits such as apple, banana, pear, plum, tomato, and avocado (Blankenship and Dole, 2003; Watkins, 2006) 1 MCP is traditionally applied in gaseous form, which requires incubating the fruit in a tightly sealed room on the order of 24 h at 20 C. Effective gaseo us 1 MCP concentrations for delaying softening of MF peaches have been reported to range from 100ppb to 5ppm (Kluge and Jacomino 2002; Liguori et al.,

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117 2004). Liquid formulated 1 MCP has been recently developed and appeared to be as efficient in inhibiting ripening as the gaseous method for avocado (Choi and Huber, 2008) MCP to delay ripening and control CI. They reported that plums immersed in 100 ppb of 1 MCP for 5 min had reduced respiration and ethylene production, and better firmness retention than untreated fruit, which could be related to the reduction in the activity of cell wall modifying enzymes. No information on ripening inhibition of peach fruit using liquid formulated 1 MCP can be found currently. Endo and exo polygalacturonase (PG) are pectin hydrolyzing enzymes that have been shown to increase in transcription and activity at the same time when degradation of pectin molecules occurs during ripening (Downs and Brady, 1990; Lester et al., 1994) Endo PG is regarded as the key enzyme related to the textural difference between MF and NMF varieties ( Pressey and Avants, 1978 ) Ripened MF peaches have higher or similar levels of endo PG activity compared to exo PG activity, whereas ripened NMF peaches possess high exo PG activity but very low endo PG activity. Partia l or complete deletion of gene encoding endo PG may be responsible for the reduced or lack of endo PG mRNA accumulation and enzyme activity in NMF peaches (Callahan et al., 2004; Lester et al., 19 96) De methylesterification by the action of pectin methylesterase (PME) is a prelude to PG mediated pectin disassembly since the resulting pectin after PME action contains mainly homogalacturonan, the preferred substrate for PG (Wakabayashi, 2000) For MF peaches, PME activity increases sharply at an early stage of ripening and remains constant or decreases throughout the cell wall depolymerization phase (Brummell et al.,

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118 2004; Glover and Brady, 1995) (Manganaris et al., 2006b) The objective of this study was to evaluate the effectiveness of pre storage hot water and liquid formulated 1 MCP treatment alone or combined in inhibiting ripening of NMF peaches. We hypothesized that hot water combined with 1 MCP may be more potent than either treatment alone in delaying softening by altering the activities of PME and PG, maintaining fruit qualities such as ground color (GC), flesh color (FC), soluble solids content (SSC), and titratable acidity (TA), a nd reducing weight loss (WL) and incidence of decay. Materials and Methods Preliminary Study 1 Determination of Optimum Hot Water Temperature, 1 MCP Concentration, and Exposure time In 2008, a batch of commercial harvest maturity (peel GC changed from green to slightly yellow ) was obtained from California and divided into two groups. One group was used to determine the optimum temperature and exposure time for hot water (HW) treatment and the other group was used to determ ine the optimum aqueous 1 MCP (AF x RD 038, AgroFresh, Inc.) concentration and exposure time. For both groups, four peaches were used to determine the initial flesh firmness. The rest were divided into four sub groups of temperatures (25, 43, 46, and 50 C ) for HW treatments or 1 MCP concentrations (0, 100, 500, and 1000 g/L), which were all applied using 25 C water. Each sub group was immersed for 1, 5, 10, 20, or 30 min. The treated fruit were air dried before being placed on trays in a 20 C

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119 storage roo m. The trays of fruit were inserted into 30 x 45 mil thickness unsealed plastic trash can liners to prevent moisture lost. All the fruit were ripened directly at 20 C for 3 days and flesh firmness was determined immediately after storage. Preliminary St udy 2 Effect Of 1.5 Mg/ L 1 MCP On Ripening of MF September Peaches Alone o r Combined w ith HW Treatment The firmness data indicated that the 1 MCP concentration (100 g/L) applied to during the first year of the 2 year study described below was not effective in inhibiting fruit softening; therefore, a higher 1 MCP concentration (1.5 mg/L) was tested before the start of the second Florida harvest season. Since there were no NMF peaches peaches from Chile were used in this study. A batch of 720 fruit at minimum maturity was divided into 4 treatment groups before storage at 20 C. The fruit were immersed for 30 min in water at 25 C (Control) or 46 C (HW), or immersed in 25 C water containing 1.5 mg/L aqueous 1 MCP, or 46 C water containing 1.5 mg/L aqueous 1 MCP (HW x 1 MCP). The fruit GC, FC, flesh firmness, WL ethylene production and respiration rate were measured on 3 replications of 10 fruit during 5 days of storage. Two Year Study on Ripening of NMF Peaches Pre conditioned with HW, 1 MCP, or HW x 1 MCP at 20 C Plant m aterial In May of peaches were commercially harvested from Punta Gorda, FL (peel GC was yellow ; ) In June of 2009 and 2010, were commercially harvested from Mershon, GA when the peel GC started t o change from green to yellow and the diameter was 64mm Peaches of both cultivars were transported to the University of Florida in Gainesville, FL by air conditioned vehicle. In 2009, fruit were peaches

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120 immersed for 30 min in water at 25 C (Control) or 46 C (H W), or immersed in 25 C water containing 100 g/L aqueous 1 MCP or 46 C water containing 100 g/L aqueous 1 MCP (HW x 1 MCP). Zipper lock bags were used in all treatments to trap off gas released by 1 MCP when it was introduced to water. Fruit were sto red at 20 C for 5 days after the treatment. In 2010, the 1 MCP concentration was increased to 1.5 mg/L or 1.5 ppm for MCP concentration used in the previous year (100 g/L) did not inhibit fruit softening. All the f ruit were stored at 20 C for 7 days. Respiration rate, ethylene production, and physical characteristics (GC, F C, flesh firmness, WL) were measured on all of the fruit in both years. Due to the failure of 1 MCP to produce softening inhibition during the first year of study chemical characteristics (SSC, TA, pH) and PME and PG activities were measured only on the control and HW fruit in 2009 but on all the fruit in 2010. Incidence of decay was determined at the end of the ripening period for all the fruit in both years. In a separate experiment during the second year of study, ethylene production and pre climacteric to climacteric stages in order to better understand the ripeness stage of the fruit from the main experiment when 1 MCP was applied. The samples were obtained from the UF Plant Science Research and Education Unit at Citra, FL. A batch of 15 fruit was harvested with green GC and an average size of 82 g. The fruit were divided i nto 3 replications and stored at 20 C until Day 8. Ethylene production and respiration rate were measured every other day in order to construct curves for the

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121 respiratory and ethylene climacterics to use for comparison with the ethylene productions and res piration rates of the fruit from the main experiment. Ethylene p roduction and r espiration r ate d etermination In 2009, a gas analyzer ETH 1010 (Fluid Analytics, Inc., West Linn, Oregon) with an infrared detector for CO 2 measurement and a gold catalyst det ector for ethylene measurement was used to measure respiration rate and ethylene production. 10 Fruit were equally divided into five replicatio n s and fruit of each replication were sealed in a 2.735L container that was connected to the device. In 2010, eth ylene production and respiration rate for each treatment were monitored using a static system consisting of three, 18.9 L glass jars each containing 10 fruit. The jars were sealed for 15 min before 5 mL headspace gas samples were withdrawn. The concentrati ons of gases were determined using a Varian gas chromatograph (GC) (CP 3800, Middelburg, The Netherlands) equipped with a Valco valve system (Houston, Texas, USA). Ethylene was 100 mesh) a nd a Pulse Discharge Helium Ionization Detector (PDHID) was used for detection. Measured concentrations of ethylene were converted into rates of production based on the mass of fruit in a jar, the void volume, and the duration of sealing. Physical c haracteristics Ground and f lesh c olor d etermination GC and FC were determined using a reflectance colorimeter that measured in C.I.E. L*, a*, b* values (Minolta CR 400, Konica Minolta, Japan). The shade of color, which is best described by hue angle (h; arctangent of b*/a*), can often change after postharvest treatment (McGuire, 1992) Therefore, GCh; and FCh; were presented in

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122 this study. GC was measured on the greenest portion of the peel. FC was measured afte r removing a small (circa 2 cm diameter) patch of peel. Flesh f irmness d etermination Flesh firmness was measured with an Instron (Model 1132) that applied a compressive force from a 50 kg load cell. A convex tip probe (Magness Taylor type), 7.9 mm in dia meter, was attached to the load cell and the force applied with the probe moving at a speed of 12 cm/min. Flesh firmness was measured on the cheeks of the fruit at the fruit equator on both sides with peel removed and was expressed as the bioyield force ( N). Following color and firmness measurements, fruit samples were placed in quart size ( 17.7 cm x 20.3 cm ) zipper locking, plas ti c freezer bags and stored at 30 C for later compositional analyses. Weight loss d etermination Weight loss (WL) was calculated by subtracting the final (after storage) fresh weight of the fruit from the initial fresh weight and dividing the difference by the initial fresh weight. The resulting values were converted to percentage by multiplying by 100. Chemical c haracter istics Soluble s olids c ontent, t itratable a cidity, and pH d etermination Frozen fruit tissues were pureed in a Waring blender for 1 min. The resulting slurry was centrifuged (20 min; 15,000 g n ; 4 C ) and the clear supernatant was used to determine SSC and TA. The SSC was measured with a temperature compensated digital refractometer (model ABBE Mark II, Cambridge Instruments Inc, U.S.A) and expressed as per cent FW. TA was determined by titration (model 719 S. Titrino, Metrohm, Switzerland) of 6.0 g of juic e plus 50 mL of water with 0.1N sodium hydroxide solution until pH 8.2 was reached and the TA was expressed as percent malic acid. The

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123 pH of the diluted juice was determine d automatically by the Titrino equipped with a pH electrode. Enzyme a ssays Preparati on of c ell free p rotein e xtract Enzyme extracts were prepared similarly to the method of Jeong et al. (2002). Partially thawed mesocarp tissue (15 g) was homogenized with 25 mL of ice cold 95% ethanol for 1 min in an Omnimixer (Model GLH 01, New town, CT USA) and centrifuged at 15,000 g n for 10 min at 4 C The supernatant was discarded and the pellets were resuspended in 25 mL of ice cold 80% ethanol for 1 min and centrifuged again at 15, 000 g n for 10 min at 4 C The pellets were transferred to 10 mL of 50 mM Na acetate buffer, pH 5, containing 0.5 M NaCl, for 30 min in an ice cold water bath followed by centrifugation 15,000 g n for 10 min at 4 C The resulting supernatant was analyzed for enzyme activities. Total soluble protein in the supernatant was measured using the bicinchoninic acid method with bovine serum albumin as the standard (Smith et al., 1985) Pectinmethylesterase a ctivity d etermination Pectinmethylest erase (PME, E.C. 3.1.1.11) was measured using modifications of the method of (Jeong et al., 2002) A 1% (w/v) solution of 93% esterified citrus pectin (Sigma Chemical Co., St. Louis, MO, USA) was prepared in 0.1M NaCl a nd adjusted to pH 7.5 with dilute NaOH. A 0.01% solution of bromothymol blue was prepared in 0.003M potassium phosphate buffer, pH 7.5. A 166 L volume of 1% citrus pectin was mixed with 12 L of 0.01% bromothymol blue and 70 L of water on a microplate, a nd the pH adjusted to 7.5 with dilute NaOH. The reaction was initiated by adding 2 L of the cell free protein extract adjusted to pH 7.5 with dilute NaOH. The decrease in A 620

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124 over a 10 min reaction time A 6 20 mg 1 protein min 1 Polygalacturonase a ctivity d etermination In 2009, e ndo PG (E.C. 3.2.1.15) was assayed by mixing 250 L of enzyme extract with 250 L of 0.5% polygalacturonic acid (from orange peel, Sigma Chemical Co., St. Louis, MO, USA) in 50 mM Na acetate buffer (pH 4.4) and incubated at 30 C for 16 h (Pressey and Avants, 1973) Exo PG (E.C. 3.2.1.67) activity was assayed by adding 250 L of enzyme extract to 250 L of 0.5% polygalacturonic acid in 50 mM Na acetate buffer (pH 5.5) containing 2 mM CaCl 2 and incubating at 30 C for 16 h In 2010, the endo PG assay was amended by using 100 L of enzyme extract with 400 L of 0.5% polygalacturonic acid. The purpose was to reduce concentration of NaCl to approxima tely 0.15M to maximize PG activity in vitro (Huber and Lee1989). Uronic acid (UA) reducing groups released were measured using the method of Milner and Avigad (1967) with mono D galacturonic acid as the standard. One unit of activity was defined as 1 g galacturonic acid produced mg 1 protein h 1 Statistical Analysis Randomized complete design was utilized in Preliminary Study 1 and o ne way ANOVA was used to detect significant differences among the treatments. Preliminary Study 2 and studies associated with ripening of NMF peac hes were conducted using a randomized complete design with a factorial arrangement of treatments. When a significant difference was detected in ethylene production, respiration rate, and flesh firmness, the data were ana lyzed by two way ANOVA to examine the influence of HW (factor A), 1 MCP (factor B), and A x B interaction at both p 1 and p Differences among the treatments were analyzed by LSD at p

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125 Results and Discussion Preliminary Study 1 Determination of Optimum Hot Water Temperature, 1 MCP Concentration, and Exposure time for Pre storage Conditioning Treatments significantly different among various temperatures o nly for fruit immersed in water for 5 min and 30 min ( Table 5 1 ). However, the control fruit immersed for 5 min were firmer than the other treated fruit; therefore, 5 min was not considered to be an effective HW exposure time. HW, 1 MCP, and HW x 1 MCP fruit had better firmness retention than the control fruit when t he exposure time was increased to 30 min. Abnormal texture was found in fruit immersed in 50 C water for 30 min because flesh firmness after storage (53.39 N) was actually greater than the initial value measured before the treatment (46.89 4.13 N). Inte rnal damage might have occurred for fruit treated with this combination of temperature and exposure time (Paull and Chen, 2000) Fruit immersed in 43 C or 46 C water for 30 min were firmer than those immersed at oth er temperatures without showing any external injuries. Therefore, the 46 C for 30 min treatment was selected as the maximum temp x time combination tolerated and was subsequently used in later experiments to delay softening of NMF peaches. fruit immersed in 1 MCP solutions of 100 to 1000 g/L for 5 min and 30 min retained greater flesh firmness than the control fruit ( Table 5 2 ). Fruit treated with different 1 MCP concentrations showed similar flesh firmness after storage indicatin g that the lowe st 1 MCP concentration applied ( 100 g/L) was sufficient to inhibit ripening. The 100 g/L of 1 MCP for 30 min treatment was chosen to be the optimum combination in this study because the exposure time could be kept constant for further inve stigations when HW was combined with the 1 MCP treatment.

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126 Preliminary Study 2 Effect o f 1.5 Mg/ L 1 MCP on Ripening o f MF September Peaches alone Or combined w ith HW Treatment Ethylene was significantly reduced by both the HW and 1 MCP treatments and the combined HW x 1 MCP treatment fruit had the lowest ethylene level (Fig. 5 1A). The ethylene production at the climacteric peak (Day 3) was reduced by 20%, 60%, and 80% for 1 MCP HW, and HW x 1 MCP fruit respectively. The average initial ethylene h approximately 17% of the peak value. Therefore, 1.5 mg/L of 1 MCP was enough to saturate the ethylene recepto rs when the fruit were at the beginning of the climacteric Respiration rates were generally similar among the treatments and appeared to be post climacteric after Day 3 ( Fig. 5 1B), indicating that the treated fruit were functioning normally, like the con trol fruit, in terms of the climacteric. HW and 1 MCP significantly reduced ethylene production throughout the ripening period, but did not affect respiration rate ( Table 5 3 ). Flesh firmness was significantly maintained at higher levels than th e control by the HW and 1 MCP treatments ( Table 5 4 ). HW and HW x 1 MCP fruit had greater flesh firmness than the control fruit on Day 0. The effect of 1 MCP application on softening inhibition was observed on Day 1 when the control fruit started this effect of 1 MCP lasted throughout the ripening period. The melting phase for the HW, 1 MCP, and HW x 1 MCP fruit was delayed until Day 3. Interestingly, the ANOVA indicated that HW was the dominant factor regulating flesh f irmness in the beginning of the ripening period whereas 1 MCP became dominant during the melting phase. An interaction effect of HW 1 MCP was only observed on last day of storage.

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127 The HW, 1 MCP, and HW x 1 MCP treatments did not inhibit peel color devel opment (GCh ) even though the fruit ethylene production was significantly suppressed ( Table 5 5 Fig 5 1A). This suggests that peel color development may be induced by very low levels of ethylene and that the process may be irreversible once tri ggered. All of the pre conditioned fruit had significantly lower FCh than the non treated fruit on Day 3 and Day 5, indicating that both HW and 1 MCP may have favored either loss of chlorophyll or synthesis of carotenoids, or both, in the flesh of MF values were similar among the treated and non treated fruit ( Table 5 5 ). Therefore, WL probably had little effect on fruit firmness. Two Year Study on Ripen re conditioned with HW, 1 MCP, or HW x 1 MCP at 20 C Ethylene p roduction and r espiration r ate E thylene synthesis is reversibly inhibited in fruit exposed to high temperatures (Paul and Chen, 2000). This was evident in this study for both HW treated NMF cultivars. Ethylene production was first suppressed by HW then recovered to similar ( Fig. 5 2A, 5 3A) or higher ( Fig. 5 2B, Day 5) levels than the control for fruit. The reversible nature of the ethylene biosynthesis was probably related to the restoration of enzymes involved in the ethylene biosynthesis pathway such as ACC oxidase (ACO) and S adenosylmethion ine synthetase 2 (SAMS) (Lara et al., 2009) Ethylene production by HW entire ripening period ( Fig. 5 3B). The r espiration rate of HW fruit on Day 1, dropped to a lower level on Day 3, and recovered to a similar level on Fig. Effect of treatments on respir peaches

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128 Day 5 in 2009 ( Fig. 5 2C). In 2010, the respiration rates of HW treated and control Fig. 5 peaches immediately following HW treatment could be attributed to the cyanide insensitive pathway (Inaba and Chach in, 1989; Kruse et al., 2011) The respiration rate of HW ( Fig. 5 3C and 5 3D). In 2009, 1 MCP treatment (100 g/L) significantly reduced ethylene production and respirat climacteric rise ( Fig. 5 2A, 5 MCP In 2010, the 1 MCP concentration was increased to 1.5 mg/L or 1.5 ppm for MCP concent ration did not inhibit fruit softening and 1.0 ppm (the current registered c oncentration for apples in U.S. it was reported to have only a transient effect on peaches (Dal Cin et al., 2006) The initial ethylen e production (before HW or 1 approximately 17% of the peak value determined in 2009. The initial ethylene was about 42 L which was similar to the maximum level detected in 2009. Therefore, the 1 MCP concentration was increased to 5.0 mg/L extending shelf life of early season peaches and nectarines (Liguori et al., 2004) 1.5 mg/L 1 MCP significantly lowered the climacteric peaks of both ethylene production and Fig. 5 2B, 5 2D) instead of delaying the peak as

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129 observed for 1 hes (Fan et al., 2002) 5 mg/L 1 MCP was ripening ( Fig. 5 3C, 5 3D). The response of peach respiration rate to 1 MCP has been previousl y reported to be cultivar dependent (Liguori et al 2004). It has been shown that the tra nscription of ethylene receptor transcripts in peaches and nectarines resumed within a short period of time after a single 1 MCP application (Mathooko et al., 2001; Mathooko et al., 2004; Ziliotto et al., 2008) resultin g in restoration of the ability of the fruit to respond to ethylene when the same concentration of 1 ly redundant (Klee, 2002) normal ripening can still occur if the concentration of 1 MCP applied is too low to saturate all the receptor sites. Greater production of ethylene during recovery from 1 MCP treatment was no t observed in this study in contrast to a previous report for peach (Rasori et al., 2002) HW x 1 MCP treatment was effective in suppressing ethylene production by vels in this were generally the lowest ( Fig. 5 2A, 5 2B, 5 3A, 5 3B). This was possibly due to interactions between HW and 1 MCP (Table 5 6 5 7 ) such that ethylene biosynthesis was suppressed by HW (Lurie, 1998; Lurie and Crisosto, 2005 ) and ethylene action was blocked by 1 MCP. The respiration rate of HW x 1 MCP treated fruit for both NMF cultivars was affected more by 1 MCP treatment because the respiratory patterns of the fruit f rom the 1 MCP and

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130 HW x 1 MCP treatments closely resembled each other during storage regardless of the concentrations applied. Flesh f irmness HW treatment was more effective than 1 MCP treatment in promoting firmness retention for both NMF cultivars ( Table 5 8 5 10 sensitive to HW treatment because softening was delayed throughout the ripening effective in delaying softe ning of peaches that were already producing autocatalytic ethylene, contrary to the results reported by Budde et al. (2006) who found that heat treatments have no influence on fruit firmness when ethylene production is already triggered. The temporarily along with prolonged softening inhibition (Fig 5 2A, 5 2B and Table 5 8 ) suggests that HW stress may inhibit cell wall catabolism by regulating both ethylene dependent (i.e., 1 MCP responsiv e) and ethylene independent pathways (Hayama et al., 2006b) The low concentration of 1 MCP (100 g/L) applied in 2009 did not inhibit uced throughout the ripening period ( Table 5 8 Fig 5 with 1.5 mg/L 1 MCP solution retained their flesh firmness for only 1 day after the treatment, suggesting that a higher concentration or repeated applicati on of 1 MCP may need to be used to prolong the effect (Liu et al., 2005) ( Table 5 8 ). The transitory firmness retention in 1 MCP treated peach fruit could be attributed to the level of internal ethylene before 1 MCP treatment. For example, 1.5 mg/L 1 MCP were at the beginning of the climacteric rise.

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131 were further along on the climacte ric rise when the same concentration of 1 MCP was applied in 2010 ( Fig 5 4 ) and the fruit firmness was maintained for only 1 day ( Table 5 8 ). On the contrary, Fan et al. (2002) reported that early harvested MF fruit showed little response to 1 M CP treatment compared to late harvested fruit although the latter had higher ethylene production than the former. MCP did not maintain initial flesh firmness, which could be attributed to the non suppressed ethylene pr oduction (Table 5 10 Fig 5 3A). Treatment with 5 mg/L 1 MCP significantly rapidly than the control fruit by Day 3 (Table 5 11 ), demonstrating that the effect of cultivar was greater than that of 1 MCP. Softening inhibition in HW x 1 MCP treated fruit was mainly attributed to the influence of HW treatment since similar softening patterns were observed in the fruit from the HW a nd HW x 1 MCP treatments ( Table 5 8 5 10 ). This effect did not last as long as anticipated. As soon as the effect of 1 MCP appeared, fruit quickly softened to the same degree as the control fruit. 1 MCP treatment seemed to counteract the eff ect of HW treatment without increased ethylene production. Enzyme a ssays Cell wall degradation during fruit ripening is intricately coordinated by different enzyme activities. PME and PG activity are crucial to modification of pectin molecules during peach fruit softening (Muramatsu et al., 2 004) It has been shown that the maximum PG activity of HW treated Mei fruit ( Prunus mume known as Japanese apricot, was delayed instead of being repre ssed when softening was inhibited (Luo, 20 06) The peak PME activity of HW treated Mei fruit was also delayed and with a reduced magnitude than in the control fruit. In this study, delayed

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132 peak endo PG activity was only observed in HW 2009 ( Table 5 9 ) and HW 5 11 ) and the PG activity of both was higher than that of the control fruit. Interestingly, significantly higher PME activity was detected in HW HW and HW PG activity that occurred on the same day as the control fruit and with similar magnitudes. Maximum PME activit y of HW tre 1) and HW 2009 (Day 3) occurred in advance of the control fruit maximum PME and the levels were slightly reduced. Higher PME activity has been reported in fresh cut peaches treated with HW a few hours before processing (Koukounaras et al., 2008; Steiner et al., 2006) It is believed that the exces s carboxyl groups of heat treated fruit generated by the higher PME activity bond with endogenous calcium to form Ca pectates This hypothesis was supported by the lower decline in pectin (% of Ca pectate) found in ripe, heat treated fruit (Bakshi and Masoodi, 2010) The loss of neutral sugar side chains during the heat treatment may also lead to closer packing of the pectin strands (Ben Shalom et al., 1993). Consequently, the rigidity of the cell wall and middle lamella would be increased and in turn restrict access by cell wall degradation enzymes. Therefore, the peak endo PG activity would be delayed and the endo PG activity would be higher, just as observed in HW treated 2010, possibly due to accumulation of enzyme that could only gain access to substrate when the fruit recovered from the HW treatment. Alternatively, the rigidity of the cell wall

PAGE 133

133 and middle lamella can be built up more rapidly if the max imum PME activity is shifted to earlier stages of ripening by HW treatment. This could explain the firmness retention observed for HW addition, there were no significant differences in exo PG activity between the control and HW treated fruit of both NMF cultivars in 2009 and the exo PG levels were constant throughout ripening. Therefore, exo PG was probably not directly related to softening of NMF peaches ( Table 5 9 5 11 ). 1 MCP MCP treatment in 2010 (Day 0), which was 3 days in advance of that of the control fruit. The peak endo PG activity occurred on the same day as the control fruit (Day 1) ( Table 5 9 ). 1 MCP PG activity (Day 5) on the same day as the control fruit (Table 6b). The endo PG activity was similar, but PME activity was significantly higher. The higher PME activity induced by 1 MCP was associated with greater softening observed on Day 3 (Table 5 10 ). High 1 MCP concentration (5 mg/L) completely suppressed endo until Day 3 (Fig 5 3B, Table 5 11 ), indicating a positive relationship between ethylene production and endo PG activity as reported by Hayama et al. ( 2006a) However, the absence of endo PG activity did not correspond to inhibition of fruit softening. Morgutti et al. ( 2006) reported the NMF phenotype does not seem to be caused by a large deletion of the endo PG gene. Furthermore, analysis of cell wall polysaccharides showed that pectins might be solubilized durin g ripening of NMF peaches without substantial de polymerization (Yoshioka et al., 2011) These results suggest that NMF cultivars do not depend on endo PG activity for cell wall degradation.

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134 Statistical analysis ind icated that interaction of HW and 1 MCP effects had a major influence on PME and PG activities for HW x 1 MCP treated fruit of both cultivars. Therefore, no consistent trends could be delineated when HW x 1 MCP treated fruit were compared to the control fr uit. The opposite effect of HW and 1 MCP on endo PG activity was observed on Day 1 in 2010 (Table 5 11) The endo PG activity of HW x 1 MCP MCP fruit. Ground color and flesh c olor Compared with the c MCP, or HW x 1 MCP had significantly higher or similar GCh by the end of the ripening period in 2009 and 2010, respectively (Table 5 12 ). The higher GCh indicated that the peels of the pre conditioned fruit were less yellow or greener than the control fruit. Thus, the treatments were either effective in delaying the breakdown of chlorophyll or delayed the synthesis of carotenoids, or both. The FCh among the treatments (Table 5 12 ). HW and HW x 1 MCP had similar effects on GCh and FCh changes during 5 13 ). Fruit from both treatments had significantly lower GCh by Day 3 and lower FCh by the end of the ripening period compared with the control fruit. Therefore, HW treatment was able to accelerate either the breakdown of chlorophyll or the development of carotenoids in both the peel and the MC P as the control when a low 1 MCP concentration was applied, but had lower GCh by the end of the ripening period when a high 1 MCP concentration was applied.

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135 Soluble s olids c ontent, t itratable a cidity, and pH Frui t SSC was generally not affected by HW treatment for both NMF cultivars (Table 5 14 and Table 5 1 5 ), which is in agreement with the reported results (Budde et al., 2006; Malakou and Nanos, 2005) It was suspected that the higher respiration rate immediately following the HW treatment as observed in HW 2009 (Fig. 5 2C) could have resulted in breakdown of organic acids, which would lead to lower levels of malate and citrate in the fruit tissue (Lara et al. 2009). Since there were no significant differences in TA between HW and control fruit in 2009 (Table 5 14 ), organic acid metabolism or the amount of acids consumed was insignificant compared to the losses during storage. HW treated and HW x 1 MCP maintained higher TA and lower pH than control fruit by Day 5 in 2010 (Table 5 14 ) HW cantly lower TA than the control fruit on both Day 0 and Day 5 in 2010 (Table 5 1 5 ), indicating that regeneration of organic acids was inhibited or slowed. The reduction in TA caused by HW stress may be a favorable effect since consumer acceptance is repo rtedly always greater for low acid than for high acid peach cultivars regardless of fruit maturity (Iglesias and Echeverria, 2009) 1 MCP treatment had no effect on the SSC of both NMF cultivars (Table 5 14 5 1 5 ). 1 MCP was most effective in delaying the breakdown of organic acids as indicated by the highest level of TA on Day 5 found in both NMF cultivars after 1 MCP treatment in 2010 (Table 5 14 ). Similar results were observed for MF peaches treated with gas eous 1 MCP (Liguori et al., 2004) and for plums treated with aqueous 1 MCP (Liguori et al., 2004; Manganaris et al., 2007) to 1 MCP, the TA of HW x 1 MCP MCP fruit

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136 (Table 5 14 MCP. Thus, HW x 1 fruit had a similar level of TA as the HW treated fruit (Table 5 15 ). Weight loss and d ecay The WL of control and HW generally similar (Table 5 12 ), confirming the results reported by Obenland and Carroll ( 2000) Moreover, HW treated fruit of both NMF cultivars in this study did not have greater WL than the control fruit, which does not support the assertion that HW treatment increases WL in peaches due to removal of trichomes at higher temperature (Bakshi et al., 2006; Phillips and Austin, 1982) In fact, 1 MCP WL by the end of the storage period in 2009 than the HW 5 13 ). conditioned with HW or HW x 1 MCP had less incidence of decay than the control fruit in both years (Table 5 1 6 treatments had higher incidence of decay in some cases. It is possible that the natura l openings and barely or entirely sealed with rearranged natural wax components present on the cuticle, thus limiting sites of fungal penetration into the fruit. The sealing of cracks or natural openings by HW treatment has been shown to lead to significantly reduced WL (Fallik et al., 1999; Fallik et al., 2000) and may also reduce entry routes for pathogenic microorganisms (Fallik, 2004) Similar results have been reported on HW treated citrus, sweet peppers, Galia melons, tomatoes, and cactus pears (Fallik, 2004; Schirra et al., 1999) HW treatment can also act directly on the pathogen (cell damage) and indirectly on the fruit host (induction of resistance mechanisms) to suppress incidence of decay (Casals et al., 2010b)

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137 The control and 1 MCP treat ed fruit of both NMF cultivars had similar WL, usually by the end of the ripening period (Table 5 12 5 13 ). 1 MCP treated fruit of both NMF cultivars had lower incidence of decay in 2009 and similar incidence as the control fruit in 2010 (Table 5 1 6 ). The high concentration of 1 MCP applied in 2010 did not increase the severity of fruit decay as seen in strawberries (Ku et al., 1999) and avocados (Adkins et al., 2005) It has been reported that brown rot incidence, sporulating area, and production of conidia per fruit are higher on commercially mature peach fruit as compared with immature fruit (Holb and Schnabel, 2008) Maturity difference s could not explain the lower decay that occurred in 2009 because the fruit were riper at the beginning of the storage period in 2009 than in 2010 based on the timing of the ethylene climacteric rise immediately after the treatment (Fig 5 2A, 5 3A). Chap ter Conclusion HW treatment alone is a more effective pre storage conditioning method than 1 MCP or HW x 1 MCP in terms of delaying normal fruit softening of NMF peaches. Aqueous 1 MCP concentration greater than 5 mg/L may be required to prolong firmness retention in NMF peaches. The cultivar effect greatly dominated the response of the peaches used in this study towards HW and 1 MCP treatment. PME activity may have a more dominant role than PG in cell wall modification during ripening of NMF fruit.

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138 Preliminary Study 1 Determining Optimum HW Temperature, 1 MCP, and Exposure time for Pre storage Conditioning Treatments Table 5 1 Ef fect of temperature x exposure ti peaches after 3 days at 20 C. Temp/Time 1 min 5 min 10 min 20 min 30 min 25 C 34.66 39.03a 44.60 36.88 32.81c 43 C 36.02 26.42b 34.40 44.90 42.88b 46 C 32.54 27.05b 36.46 44.54 43.27b 50 C 26.87 32.70ab 37.77 42.13 53.39a Temp = t emperature Table 5 2 Effect of 1 MCP concentration x exposure t ime on flesh firmness (N) of Conc /Time 1 min 5 min 10 min 20 min 30 min 0 g/L 31.01 21.79b 34.31 34.73 21.05c 100 g/L 42.59 41.82a 39.89 38.43 43.09ab 500 g/L 42.81 42.47a 44.77 43.15 46.49a 1000 g/L 39.73 39.10a 41.59 41.89 37.47b Conc = concentration

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139 Preliminary Study 2 Effect of 1.5mg/L 1 MCP alone or combined with HW Table 5 3 Effect of pre storage HW and 1 MCP t reatment s on ethylene production and Ripening p eriod (d) 0 1 3 5 Ethylene p roduction (L C 2 H 4 ) Factor A (HW) ** ** ** ** Factor B (1.5 mg/L 1 MCP) ** ** ** ** A x B NS ** NS NS Respiration r ate (mg CO 2 ) Factor A (HW) NS NS NS NS Factor B (1.5mg/L 1 MCP) NS ** NS NS A x B NS NS NS NS = Significant at p ** = Significant at p NS = n on significant Figure 5 1. Effect of pre storage conditioning treatments on ethylene production (A) and respiration rate (B) of L C 2 H 4 /kgh mg C O 24 /kgh Days at 20 C Days at 20 C A B

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140 Table 5 4 Effect of pre storage HW and 1 MCP treatments on flesh firmness of Ripening p eriod (d) 0 1 3 5 Firmness (N) Control 13.92b 6.92b 4.19b 3.79b HW 23.79a 18.89a 4.73ab 4.26a 1 MCP (1.5 mg/L) 17.58b 14.16a 5.42a 4.58a HW x 1 MCP 24.04a 13.76a 5.36a 4.43a Significance Factor A (HW) ** NS NS Factor B (1 MCP) NS NS ** ** A x B NS NS * = Significant at p ** NS = n on significant Table 5 5 C after pre storage conditioning treatments Ripening p eriod (d) 0 1 3 5 GC h Control 85.63 84.98 82.71 79.62 HW 87.42 85.25 82.29 78.90 1 MCP 86.90 83.47 80.79 81.05 HW x 1 MCP 86.78 82.50 82.23 79.55 Significance NS NS NS NS FC h Control 89.78 90.34 90.43a 89.81a HW 90.34 89.19 87.96b 85.34b 1 MCP 90.43 88.75 87.14b 86.17b HW x 1 MCP 89.81 89.61 88.18b 86.45b Significance NS NS * WL (%) Control 0 3.59 4.91 6.31 HW 0 2.47 3.61 5.13 1 MCP 0 1.64 1.94 5.31 HW x 1 MCP 0 2.41 2.74 3.36 Significance NS NS NS NS = Significant at p NS = n on significant

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141 conditioned with HW, 1 MCP, or HW x 1 MCP at 20 C L C 2 H 4 /kgh mg C O 24 /kghr peaches mg C O 2 /kgh Days at 20 C A B C D Figure 5 C after pre storage conditioning treatments.

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142 Table 5 6 Effect of pre storage HW and 1 MCP treatments on ethylene production and Year 2009 2010 Ripening p eriod (d) Ripening p eriod (d) 0 1 3 5 0 1 3 5 7 Ethylene Production (L C 2 H 4 ) Ethylene Production (L C 2 H 4 ) Factor A (HW) ** ** NS NS Factor A (HW) ** ** NS ** Factor B (100 g/L 1 MCP) NS ** ** ** Factor B (1.5 mg/L 1 MCP) * ** ** A x B NS ** NS NS A x B NS NS ** ** Respiration Rate (mg CO 2 ) Respiration Rate (mg CO 2 ) Factor A (HW) NS NS NS Factor A (HW) NS NS NS NA Factor B (100 g/L 1 MCP) ** NS * Factor B (1.5 mg/L 1 MCP) ** NS ** NS NA A x B NS NS NS A x B ** NS NS ** NA = Significant at p ** = Significant NS = n on significant NA = not available

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143 L C 2 H 4 /kgh mg C O 2 /kgh Figure 5 C after pre storage conditioning treatments Days at 20 C A B C D

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144 Table 5 7 Effect of pre storage HW and 1 MCP treatment on ethylene production and Year 2009 2010 Ripening p eriod (d) Ripening p eriod (d) 0 1 3 5 0 1 3 5 7 Ethylene p roduction (L C 2 H 4 ) Ethylene Production (L C 2 H 4 ) Factor A (HW) ** ** NS NS Factor A (HW) ** NS NS ** ** Factor B (100 g/L 1 MCP) NS NS NS NS Factor B (5.0 mg/L 1 MCP) ** ** ** ** ** A x B NS NS NS NS A x B NS NS NS ** Respiration r ate (mg CO 2 ) Respiration r ate (mg CO 2 ) Factor A (HW) NS ** NS NS Factor A (HW) NS NS ** ** ** Factor B (100 g/L 1 MCP) ** NS NS Factor B (5.0 mg/L 1 MCP) NS NS ** ** ** A x B ** NS A x B NS NS ** ** ** = Significant at p ** = Significant NS = n on significant

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145 Table 5 8 Effect of pre storage HW and 1 MCP treatments Year 2009 2010 Ripening p eriod (d) Ripening p eriod (d) 0 1 3 5 0 1 3 5 7 Firmness (N) Firmness (N) Control 8.23b 9.90a 7.30b 6.83bc Control 26.08 17.34c 14.28b 12.61c 13.69b HW 10.90a 9.33a 9.76a 8.97a HW 27.89 25.1 0 a 19.63a 18.19a 19.77a 1 MCP (100 g/L) 9.23b 8.02b 8.37b 5.67c 1 MCP (1.5 mg/L) 27.22 21.29b 15.38b 14.94b 14.58b HW x 1 MCP 11.38a 9.42a 10.16a 7.20b HWx1 MCP 30.56 23.39ab 19.02a 17.13a 16.44b Significance Significance Factor A (HW) NS * Factor A (HW) NS * * Factor B (1 MCP) NS NS Factor B (1 MCP) NS NS NS NS NS A x B NS NS NS NS A x B NS NS * = Significant at p ** = Significant NS = n on significant

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146 Table 5 9 after pre storage conditioning treatments Year 2009 2010 Ripening p eriod (d) Ripening p eriod (d) 0 1 3 5 0 1 3 5 7 PME Activity (Unit) m PME Activity (Unit) m Control 0.17 0.35 0.44 0.43 Control 0.38b 0.96 1.60a 0.62ab 0.59ab HW 0.37 0.36 0.3 0 0.71 HW 0.34b 1.13 0.50b 0.19c 0.78a Significance NS NS NS 1 MCP ( 1.5 m g /L) 1.7 0 a 0.74 0.72b 0.32bc 0.49b HW x 1 MCP 0.23b 0.84 1.34a 0.93a 0.40b Endo PG Activity (Unit) y Significance NS * Control 0.78 0.57 0.32 0.7 0 HW 1.41 2.07 1.36 1.91 Endo PG Activity (Unit) y Significance NS * NS Control 0.34b 0.77 0.58 0.47 0.5 0 HW 0.36b 0.62 0.16 1.1 0 0.18 Exo PG Activity (Unit) y 1 MCP (1.5 m g /L) 0.32b 0.52 0.45 0.38 0.21 Control 0.62 1.23 0.98 0.99 HW x 1 MCP 1.13a 0.8 0 0.22 0.55 0.2 0 HW 1.27 1.71 1.14 1.41 Significance NS NS NS NS Significance NS NS NS NS m A 620 mg 1 protein min 1 y =1 unit of PG activity = 1 g galacturonic acid mg 1 protein h 1 = Significant at p NS = n on significant

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147 Table 5 10 Effect of pre storage HW and 1 MCP treatments Year 2009 2010 Ripening p eriod (d) Ripening p eriod (d) 0 1 3 5 0 1 3 5 7 Firmness (N) Firmness (N) Control 33.21 21.36b 17.50b 14.91 Control 44.99b 41.23b 25.22b 18.92 15.52 HW 33.47 33.27a 28.44a 16.43 HW 48.43ab 47.21a 28.42a 20.01 15.48 1 MCP (100 g/L) 35.89 24.16b 17.69b 14.33 1 MCP (5 mg/L) 45.13b 33.34c 22.57c 17.49 14.48 HW x 1 MCP 29.24 33.36a 16.79b 14.74 HW x 1 MCP 50.82a 43.76b 26.51ab 20.78 17.15 Significance Significance Factor A (HW) NS * NS Factor A (HW) * NS NS Factor B (1 MCP) NS NS NS Factor B (1 MCP) NS * NS NS A x B NS NS NS A x B NS NS NS NS = Significant at p ** = Significant NS = n on significant

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148 Table 5 11 after pre storage conditioning treatments Year 2009 2010 Ripening p eriod (d) Ripening p eriod (d) 0 1 3 5 0 1 3 5 7 PME Activity (Unit) m PME Activity (Unit) m Control 0.6 0 0.83 0.25 1.28 Control 1.51 1.5 0 1.66b 1.48 2.66 HW 0.82 0.8 0 0.89 0.26 HW 1.2 0 0.71 2.35ab 2.17 2.12 Significance NS NS * 1 MCP (5 mg/L) 1.86 1.6 0 3.15a 0.55 0.4 0 HW x 1 MCP 1.36 2.42 2.02b 1.42 2.37 Endo PG Activity (Unit) y Significance NS NS NS NS Control 1.93 0.38 0.36 1.35 HW 1.62 0.86 0.65 0.71 Endo PG Activity (Unit) y Significance NS NS Control 0.13 0.63 0.38 0.82 0.28b HW NA 0.37 0.73 1.02 1.19a Exo PG Activity (Unit) y 1 MCP (5 mg/L) NA NA 0 .00 0.48 0.26b Control 1.09 0.72 0.58 0.48 HW x 1 MCP NA 0.16 0.44 0.5 0 0.64ab HW 1.04 1.06 1.06 1.43 Significance NS NS Significance NS NS NS NS m A 620 mg 1 protein min 1 y =1 unit of PG activity = 1 g galacturonic acid mg 1 protein h 1 = Significant NS = n on significant NA = no enzyme activity detected

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149 Table 5 12 after pre storage conditioning treatments Year 2009 2010 Ripening p eriod (d) Ripening p eriod (d) 0 1 3 5 0 1 3 5 7 GC h GC h Control 70.32 66.41c 65.82b 65.18b Control 86.07 83.54b 78.13 71.1 0 72.09 HW 70.94 68.45bc 70.42a 68.21ab HW 85.91 86.34ab 78.04 74.88 72.73 1 MCP (100 g/L) 68.77 70.09ab 71.10a 70.05a 1 MCP (1.5 m g /L) 88.58 89.26a 78.47 75.55 69.53 HW x 1 MCP 68.89 71.89a 69.67a 71.16a HW x 1 MCP 89.62 85.20b 74.17 72.55 69.51 Significance NS * Significance NS NS NS NS FC h FC h Control 77.90 77.45 74.05c 78.21 Control 80.97 79.93b 80.4 0 a 80.33 83.89 HW 76.62 76.76 76.94b 75.28 HW 83.08 82.14a 79.17a 78.27 81.51 1 MCP (100 g/L) 77.92 75.85 77.57ab 76.46 1 MCP (1.5 m g /L) 84.10 79.27b 74.58c 78.38 80.49 HW x 1 MCP 76.98 78.18 79.90a 75.28 HW x 1 MCP 80.74 80.28b 76.87b 81.76 82.95 Significance NS NS NS Significance NS * NS NS WL (%) WL (%) Control 0.00 2.24 7.94 8.79 Control 0.00 1.76c 4.94 8.48 13.3 HW 0.00 2.34 6.96 8.05 HW 0.00 1.85b 4.72 8.22 13.6 1 MCP (100 g/L) 0.00 2.34 6.96 8.05 1 MCP (1.5 m g /L) 0.00 1.96a 5.32 9.00 13.1 HW x 1 MCP 0.00 2.32 6.62 10.4 0 HW x 1 MCP 0.00 1.80bc 5.34 8.15 13.1 Significance NS NS NS Significance NS NS NS NS = Significant at p NS = n on significant

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150 Table 5 13 after pre storage conditioning treatments Year 2009 2010 Ripening p eriod (d) Ripening p eriod (d) 0 1 3 5 0 1 3 5 7 GC h GC h Control 88.17 87.49 81.55 77.65 Control 89.17b 88.67a 87.04a 79.77 80.92a HW 86.70 86.36 81.11 75.99 HW 89.64b 85.73b 82.64c 81.42 81.04a 1 MCP (100 g/L) 86.39 85.78 81.66 78.90 1 MCP (5.0 mg/L) 92.39a 88.57a 86.13ab 82.76 77.68b HW x 1 MCP 88.29 83.92 79.66 73.93 HW x 1 MCP 89.79b 88.63a 83.83bc 80.76 80.44a Significance NS NS NS NS Significance * NS FC h FC h Control 76.22 78.89bc 77.67 77.37 Control 88.39 88.4 0 88.41 87.47 87.13a HW 70.81 87.65a 80.79 80.28 HW 88.53 87.76 88 .00 86.77 85.26c 1 MCP (100 g/L) 71.90 80.85b 83.03 84.91 1 MCP (5.0 mg/L) 88.73 87.93 88.62 88.09 86.46ab HW x 1 MCP 80.85 73.56c 85.60 79.92 HW x 1 MCP 88.4 0 88.15 87.69 86.54 85.81bc Significance NS NS NS Significance NS NS NS NS WL (%) WL (%) Control 0.00 1.28a 6.47a NA Control 0.00 NA 3.15a 5.07 11.8 0 HW 0.00 0.94b 3.52b 6.55b HW 0.00 NA 1.31b 3.95 6.55 1 MCP (100 g/L) 0.00 1.16ab 4.08b 8.88a 1 MCP (5.0 mg/L) 0.00 NA 1.20b 4.06 9.32 HW x 1 MCP 0.00 1.30a 7.44a 10.36a HW x 1 MCP 0.00 NA 1.34b 2.81 4.47 Significance NS * Significance NS NS NS = Significant at p NS = n on significant NA = n ot ava il able

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151 Table 5 14 after pre storage conditioning treatments Year 2009 2010 Ripening p eriod (d) Ripening p eriod (d) 0 1 3 5 0 1 3 5 7 SSC ( % ) SSC ( % ) Control 13.33 12.83 13.67 12.58 Control 10.6 0 10.53a 10 .0 0 10.73 10.7 0 HW 13.90 12.90 12.53 12.67 HW 10.97 10.27ab 9.77 10.27 9.7 0 Significance NS NS NS NS 1 MCP (1.5mg/L) 10.47 9.27b 9.97 10.73 10.8 0 HW x 1 MCP 10.7 0 10.93a 9.4 0 10.85 10.7 0 Significance NS NS NS NS NS TA (%) TA (%) Control 0.31 0.30 0.21 0.21 Control 0.64 0.60ab 0.48b 0.39c 0.32 HW 0.29 0.28 0.26 0.25 HW 0.64 0.58b 0.47b 0.48b 0.36 Significance NS NS NS NS 1 MCP (1.5mg/L) 0.64 0.62a 0.54a 0.53a 0.34 HW x 1 MCP 0.65 0.64a 0.46b 0.51ab 0.36 Significance NS * NS pH pH Control 4.77 4.93 5.27 5.19 Control 4.08 4.16 4.35 4.54a 4.87 HW 4.88 4.98 5.05 5.13 HW 4.07 4.11 4.3 0 4.34b 4.74 Significance NS NS NS NS 1 MCP (1.5mg/L) 4.14 4.12 4.24 4.31b 4.77 HW x 1 MCP 4.02 4.09 4.31 4.3 0 b 4.8 0 Significance NS NS NS NS = Significant at p NS = n on significant

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152 Table 5 15 after pre storage conditioning treatments Year 2009 2010 Ripening p eriod (d) Ripening p eriod (d) 0 1 3 5 0 1 3 5 7 SSC (% ) SSC ( % ) Control 10.53 9.93 8.87 10.67 Control 10.17ab 10.63 10.13 10.33 9.65 HW 10.80 9.57 10.43 7.80 HW 9.47b 9.97 10.47 9.97 9.83 Significance NS NS NS NS 1 MCP (5 mg/L) 10.23ab 10.10 10.27 10.2 0 9.63 HW x 1 MCP 10.63a 9.87 10.03 10.3 0 9.73 Significance NS NS NS NS TA (%) TA (%) Control 0.66 0.48 0.43 0.47 Control 0.45b 0.47 0.52 0.49a 0.45 HW 0.60 0.59 0.47 0.42 HW 0.40c 0.45 0.46 0.44ab 0.42 Significance NS NS NS NS 1 MCP (5 mg/L) 0.54a 0.48 0.48 0.51a 0.45 HW x 1 MCP 0.48b 0.46 0.43 0.41b 0.42 Significance NS NS NS pH pH Control 3.97 4.10 4.28 4.37 Control 4.12b 4.07 4.09 4.08c 4.28 HW 4.01 3.96 4.30 4.42 HW 4.26a 4.17 4.15 4.21ab 4.29 Significance NS NS NS NS 1 MCP (5 mg/L) 4.03c 4.06 4.08 4.09bc 4.22 HW x 1 MCP 4.08bc 4.15 4.21 4.28a 4.29 Significance NS NS NS = Significant at p NS = n on significant

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153 Table 5 1 6 Incidence of decay of pre conditioned NMF peaches after 7 days of storage at 20 C Year 2009 2010 Cultivar Decay (%) Decay (%) Control 11.7 52.1 Control 11.0 22.0 HW 17.0 18.8 HW 24.0 4.0 1 MCP (1.5 mg/L) 5.0 29.2 1 MCP (5 mg/L) 12.2 24.0 HW x 1 MCP 22.0 6.3 HW x 1 MCP 18.3 0. 6

PAGE 154

154 Days at 20 C Ethylene Production (L C 2 H 4 /kgh ) Respiration Rate (mg CO 2 /kgh ) Figure 5 4. Preclimacteric to climacteric ethylene production and respiration production rate at the time when HW and 1 MCP treatments were applied in 2010.

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155 CHAPTER 6 EFFECT OF PRE STORAGE HOT WATER TR EATMENT ALONE OR COM BINED WITH AQUEOUS 1 METHYCLC OPROPENE ON RIPENING OF NON MELTING FLESH PEACHES AFTER LOW TEMPERATURE STOR AGE Overview Peaches can be separated into different types based on their texture. Melting flesh (MF) peaches soften excessively toward the end of ripening. Thus, they have to be (AMS, 2004; Cascales et al., 2005; Delwiche, 1987) Non melting flesh (NMF) peaches soften relatively slowly and are characterized by the on the tree longer to develop maximum flavor while still possessing sufficient fle sh firmness for storage and shipping (Sherman et al., 1990) Changes in flesh firmness are associated with extensive modification in cell wall structure and composition during fruit ripening, which is achieved by synergistic actions of related enzymes (Toivonen and Brummell, 2008) Pectin methylesterase (PME) activity peaks early in peach ripening and remains constant or decreases throughout the mid and full ripe sta ges (Brummell et al., 2004; Glover and Brady, 1995) PME removes methylester groups from pectin molecules, which are subsequently depolymerized by the action of polygalacturonase (PG) during the melting phase (Orr and Brady, 1993; Wakabayashi, 2000) .The limited softening of NMF cultivars is related to their deficiency of endo PG mRNA accumulation and enzyme activity compared to MF cultiv ars (Callahan et al. 2004; Lester et al., 1994; 1996; Pressey and Avants, 1978 ) Peaches ripen quickly at room temperature. Thus, immediate storage at 0 C after harvest is necessary. However, peaches can develop chilling injury (CI) when they are exposed to 0 C for 3 or more weeks (Crisosto et al., 1999) However, CI symptoms

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156 develop most rapidly and intensel y when peaches are stored between 2.2 C and 7.6 C ( Lurie and Crisosto, 2005 ) Symptoms of CI in peaches vary among genotypes and typically include flesh discoloration, such as internal bleeding and flesh browning, abnorm al softening, reduced aroma, and dry or grainy texture (i.e., leatheriness or mealiness). Mealiness is the most frequently reported symptom of CI in MF peaches (Brovelli et al., 1998c; Murray et al. 2007) NMF peaches with CI are reported to have rubbery texture, higher incidence of flesh bleeding, and off flavors such as astringency, bitterness, and fermentative taste (Cantin et al., 2010; Karakurt et al., 2000a; Robertson et al., 1992 b ) CI in peaches has been associated with reduced endo PG activity and enhanced or stable PME activity during low temperature storage (Ben arie and Sonego, 1980; Brummell et al., 2004; Nilo et al., 2010; Zhou et al., 2000a) Pre storage heat treatment has been shown to reduce CI in many fruits and vegetables, which may be relate d to induction of heat shock proteins (Lurie, 1998) The than 33 C (Li and Han, 1998). Heat treatment is also capable of suppressing postharvest decay (Casals et al., 2010b; Malakou and Nanos, 2005; Obenland and Carroll, 2000) and texture change in MF peaches th rough down regulation of enzymes involved in ethylene biosynthesis (Budde et al., 2006; Martinez and Civello, 2008; Steiner et al., 2006) As a result, firmness reten tion in heat treated fruit may be due to inhibited synthesis of ethylene dependent cell wall hydrolytic enzymes such as endo PG (Jin et al., 2009; Lurie, 1998) The most common application methods are hot water (HW), hot water vapor, and hot air (Zhang et al., 2007) The internal temperature of peaches treated with HW increases more rapidly than in fruit treated with hot air, due to the

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157 higher convective heat t ransfer coefficient for water compared with air (Zhou et al., 2002) Applying 1 methylcylopropene (1 MCP), an ethylene action inhibitor, to MF peaches has been shown to be effective in suppressing deterioration of fruit quality during ripening although the impact is usually transient (Watkins, 2006) 1 MCP is traditionally applied in gaseous form, but its usage has been limited by low temperature storage. In one report, gaseous 1 MCP lost its efficacy in nectarines stored at 4 C for 3 days (Bregoli et al., 2005). Furthermore, 1 MCP can induce greater incidence of CI in peaches and nectarines stored in low temperature for more than 3 weeks (Bregoli et al., 2005; Dong et al., 2001; Fan et al., 2002) An aqueous 1 MCP formulation has been recently developed and is relatively efficient in controlling fruit ripening (Choi and Huber, 2008) The effect of aqueous 1 MCP treatment may not be influenced by low found to maintain better fruit quality after ripening following 10 days of 0 C or 5 C sto rage (Manganaris et al., 2007) Currently, no studies have been conducted to investigate the quality of NMF peaches pre conditioned with either HW or aqueous 1 MCP and ripened after low temperature storage Since both pre conditioning methods have been shown to be effective on MF peaches, the combined treatment (HW x 1 MCP) may be more beneficial in preventing CI and regulating fruit ripening. The objective of this study is to evaluate the effect of combini ng HW and aqueous 1 MCP treatments with low temperature storage on shelf life extension of NMF peaches.

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158 Materials and Methods Plant Material from Punta Gorda, FL when fruit were harvested from Mershon, GA when the peel GC started to transform from green to yellow and the diamet er was greater or equal to 64mm Peaches of both cultivars were transported to the University of Florida in Gainesville, FL by air conditioned vehicle. In 2009, 280 fruit per cultivar were separated into 4 treatments. Fruit were immersed for 30 min in water at 25 C (Control) or 46 C (HW), or immersed in 25 C water containing 100 g/L of aqueous 1 MCP (1 MCP), or 46 C water containing 100 g/L of aqueous 1 MCP (HW x 1 MCP). Zipper lock bags were used in all treatments to trap off gas released by 1 MCP when it was introduced to water. The temperature x exposure time and 1 MCP concentration x exposure time combinations w ere chosen based on their effect on firmness retention in a preliminary study (Chapter 5) Following the pre conditioning treatments, fruit were stored at 0 C for 14 days before ripening at 20 C for 5 days. For w temperature storage was not collected. Data collection on ripening fruit started 12 h after they were transferred from 0 C to 20 C In 2010, the experiment was repeated with 840 fruit per cultivar. Results in 2009 showed that 100 g/L 1 MCP did not inhi bit fruit softening of both cultivars. Furthermore, the inhibitory effect of 1.0 ppm (1,000 g/L; the current registered concentration for apples in U.S.) was reported to be transient (Dal Cin et al., 2006) Th erefore, the aqueous 1

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159 (1.5 ppm). peaches at 20 C approximately 17 % of the peak value determined at 20 C in 2009. at 20 C which was similar to the peak level detected at 20 C in climacteric peaches, the 1 MCP concentration was increased to 5.0 mg/L or 5.0 ppm, a concentration that has been identified as optimal for extending the shelf life of early season peaches and nectarines (Liguori et al., 2004) Following the pre conditioning treatments, all of the f ruit in 2010 were stored at 0 C for 14 days before ripening at 20 C for 7 days. Respiration rate, ethylene production, and physical characteristics (ground color, flesh color, weight loss) were measured in both years. Since 1 MCP treatment was unable to inhibit fruit ripening in 2009, chemical characteristics (soluble solids content, titratable acidity, and pH) and activities of PME and endo PG were only measured in 2010. Incidence of decay was determined at the end of the ripening period in both years. Incidence of pitting was only recorded in 2010. Ethylene Production and Respiration Rate Determination In 2009, a gas analyzer ETH 1010 (Fluid Analytics, Inc., West Linn, Oregon) with an infrared detector for CO 2 measur ement and a gold catalyst detector for ethylene measurement was used to measure respiration rate and ethylene production. 10 Fruit were equally divided into five replicatio n s and fruit of each replication were sealed in a 2.735L container that was connected to the device. In 2010, ethylene production and respiration rate for each treatment were monitored using a static system consisting of three 18.9 L glass jars each containing 10 fruit. The jars were sealed for 15 min before

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160 5 mL headspace gas sam ples were withdrawn. The concentrations of gases were determined using a Varian gas chromatograph (GC) (CP 3800, Middelburg, The Netherlands) equipped with a Valco valve system (Houston, Texas, USA). Ethylene was separated on a molecular sieve column (Ulti 100 mesh) and a Pulse Discharge Helium Ionization Detector (PDHID) was used for detection. Measured concentrations of ethylene were converted into rates of production based on the mass of fruit in a jar, the void volume, and the du ration of sealing. Physical Characteristics Ground color (GC) and f lesh Color (FC) d etermination GC and FC were determined using a reflectance colorimeter that measured in C.I.E. L*, a*, b* values (Minolta CR 400, Konica Minolta, Japan). The shade of col or, which is best described by hue angle (h; arctangent of b*/a*), can often change after postharvest treatment (McGuire, 1992) Therefore, GCh and FCh were presented in this study. GC was measured on the greenes t portion of the peel. FC was measured after removing a small (circa 2 cm diameter) patch of peel. Flesh f irmness d etermination Flesh firmness was determined with an Instron (Model 1132) that applied a compressive force from a 50 kg load cell. A convex tip probe (Magness Taylor type), 7.9 mm in diameter, was attached to the load cell and the force applied with the probe moving at a speed of 12 cm/min. Flesh firmness was measured on the cheeks of the fruit at the fruit equator on both sides with peel rem oved and was expressed as the bioyield force (N). Following color and firmness measurements, fruit samples were p laced in quart size (17.7cm x 20.3cm) zipper locking, plastic freezer bags and stored at 30 C for later compositional analyses.

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161 Weight l oss ( WL) d etermination WL was calculated by subtracting the final (after storage) fresh weight of the fruit from the initial fresh weight and dividing the difference by the initial fresh weight. The resulting values were converted to percentage by multiplying by 100. Chemical Characteristics Soluble solids content (SSC), t itrat able acidity (TA), and pH d etermination Frozen fruit tissues were pureed in a Waring blender for 1 min. The resulting slurry was centrifuged (20 min; 15,000 g n ; 4 C ) and the clear supe rnatant was used to determine SSC and TA. The SSC was measured with a temperature compensated digital refractometer (model ABBE Mark II, Cambridge Instruments Inc, U.S.A) and expressed as percent FW. TA was determined by titration (model 719 S. Titrino, Me trohm, Switzerland) of 6.0 g of juice plus 50 mL of water with 0.1N sodium hydroxide solution until pH 8.2 was reached and the TA was expressed as percent malic acid. The pH of the diluted juice was determined automatically by the Titrino equipped with a pH electrode. Enzyme Assays Preparation of cell free protein e xtract Enzyme extracts were prepared similarly to the method of Jeong et al. (2002). Partially thawed mesocarp tissue (15 g) was homogenized with 25 mL of ice cold 95% ethanol for 1 min in an O mnimixer (Model GLH 01, New town, CT, USA) and centrifuged at 15,000 g n for 10 min at 4 C The supernatant was discarded and the pellets were resuspended in 25 mL of ice cold 80% ethanol for 1 min and centrifuged again at 15, 000 g n for 10 min at 4 C The pellets were transferred to 10 mL of 50 mM Na acetate buffer, pH 5, containing 0.5 M NaCl, for 30 min in an ice cold water bath

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162 followed by centrifugation 15, 000 g n for 10 min at 4 C The resulting supernatant was analyzed for enzyme activities. Total soluble protein in the supernatant was measured using the bicinchoninic acid method with bovine serum albumin as the standard (Smith et al., 1985) Pectinmethylesterase (PME) activity d etermination PME (E.C 3.1.1.11) activity was measured using modifications of the method of (Jeong et al., 2002) A 1% (w/v) solution of 93% esterified citrus pectin (Sigma Chemical Co., St. Louis, MO, USA) was prepared in 0.1M NaCl and adj usted to pH 7.5 with dilute NaOH. A 0.01% solution of bromothymol blue was prepared in 0.003M potassium phosphate buffer, pH 7.5. A 166 L volume of 1% citrus pectin was mixed with 12 L of 0.01% bromothymol blue and 70 L of water on a microplate, and the pH adjusted to 7.5 with dilute NaOH. The reaction was initiated by adding 2 L of the cell free protein extract adjusted to pH 7.5 with dilute NaOH. The decrease in A 620 over a 10 min A 620 mg 1 protein min 1 Endo p olygalacturonase (Endo PG) activity d etermination Endo PG (E.C. 3.2.1.15) activity was assayed by mixing 100 L of enzyme extract with 400 L of 0.5% polygalacturonic acid (from orange peel, Sigma Chemical Co., St. Louis, MO, USA) in 50 mM Na acetate buffer (pH 4.4) and incubating at 30 C for 16 h (Pressey and Avants, 1973) Uronic acid (UA) reducing groups released were measured using the method of Milner and Avigad (1967) with mono D galactur onic acid as the standard. One unit of activity was defined as 1 g galacturonic acid produced mg 1 protein h 1

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163 Incidence of Decay and Pitting Incidence of decay was calculated by dividing the total number of decayed fruit by the total number of fruit. The resulting value was converted to percentage by multiplying by 100. The same calculation was used to determine the percentage of pitted fruit. Statistical Analysis The study was conducted by randomized complete design with a factorial arrangement of treatments The data were analyzed by two way ANOVA. Significant influence of HW (factor A), 1 MCP (factor B), and A x B interaction at both p 0 1 and p were only shown for ethylene production, respiration rate, and flesh firmness. Differences among the treatments were determined by LSD at p Results and Discussion Ethylene Production and Respiration Rate Ripening of all fruit wa s slowed during low temperature storage as evident by reduced ethylene biosynthesis and respiration rate. The impact of HW treatment was (Table 6 1 6 3 ) or induced in 2010 (Table 6 4 ) on Day 0 Ethylene suppression in HW fruit may be due to reduced ACC oxidase (ACO) activity more than ACC synthase (ACS) activity (Lurie 1998; Giradi et al., 2005). HW ly exhibited higher ethylene production than the control fruit of the same cultivar during low temperature storage (Table 6 3 6 4 ), which could be a protective mechanism against CI. Inhibition of ethylene can increase severity of CI and application of ethylene during low temperature storage can decrease the percentage of woolly fruit, as shown for nectarines (Dong et al., 2001) Immediate suppression of ethylene production following 1 MCP treatment was only observed in 2010 when higher

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164 1 MCP concentrations were applied to both NMF cultivars (Table 6 2 6 4 ). Higher concentrations of 1 MCP w ere also more persistent in inhibiting ethylene production throughout low temperature storage. The persistent effect of 1 MCP may be due to irreversible binding to ethylene receptors and inhibition of ACO activity (Mathooko et al., 2001; Sisler and Serek, 1997) Since response to 1 MCP has been related to the internal ethylene level of fruit (Zhang et al., 2009) the internal ethylene levels of both NMF cultivars might be too high to be overcome by the concentration of 1 MCP applied in 2009. Interestingly, HW x 1 MCP fruit followed a similar pattern of ethylene production as 1 MCP fruit (Table 6 1 6 2 6 3 ). Therefore, 1 MCP treatment was more likely responsible for inhibiting ethylene production than HW treatment at low temperature. An initial increase in the respiration rate of HW on Day 0 in 2010, but respiration declined to the level of the non treat ed fruit by the first week of low temperature storage (Table 6 2 ). The temporary increase in respiration rate induced by heat stress may be attributed to the cyanide insensitive pathway (Inaba and Chachin, 1989) Si nce the fruit were able to recover, it was assumed that the temperature x exposure time of the HW treatment did not cause irreversible damage. Temporary increase in respiration rate during low temperature storage was detected in 1 14 (Table 6 2 6 4 ), which could be related to the high 1 MCP concentrations applied. Liguori et al., 2 production when fruit were treated with 5 or 20 L/L 1 MCP at 0 C for 20 h relative to those treated with 0.5 or 1 L/L 1 MCP. Respiration rate of HW x 1

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165 the 1 MCP fruit during low temperature storage in both years regardless of the concentrations of 1 MCP applied (Table 6 1 6 2 6 3 6 4 ). Ethylene biosynthesis quickly resumed when the peaches were transferred from 0 C to 20 C for ripening. In 2009 and 2010, peak ethylene production of HW treated were 15% and 7% lower respectively (Table 6 1 6 2 ). Peak ethylene production of HW treated in 2010 (Table 6 3 6 4 ). Low concentration of 1 MCP did not affect ethylene production on for 6 1 6 3 ). 1 MCP treatment fruit when higher concentrations were applied (Table 6 2 6 4 ). HW x 1 MCP treatment was most promising in inhibiting ethylene biosynthesis of both NMF cultivars during fruit ripening at 20 C following low temperature storage in both years. from low temperature storage (Table 6 1 6 2 ). HW rate than the control fruit upon transfer to 20 C as well as a delayed respiration peak in 2009 (Table 6 1 ). The climacteric respiration peak of HW tr on the same day as that of the control fruit in both years but the magnitudes were approximately 40% lower (Table 6 3 6 4 ). According to Lurie (1998), the climacteric respiration peak can be decreased or increased as w ell as advanced or delayed depending on the temperature and length of exposure of a heat treatment.

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166 1 MCP treatment generally lowered the peak respiration of both cultivars (Table 6 2 6 3 6 4 ). Similar behaviors were observed in 1 MCP treated plums and apricots ripened following 10 days of storage at 0 C (Dong et al., 2002; Manganaris et al., 2007) HW x 1 MCP fruit followed a similar respiration pattern as HW trea ted fruit during ripening, when the concentration of 1 MCP applied was too low to have an impact on both NMF cultivars (Table 6 1 6 3 ). Respiration rate of HW x 1 MCP fruit was similar to that of 1 MCP fruit (Table 6 2 ) or at a n intermediate level between 1 MCP and HW fruit as shown in HW x 1 (Table 6 4 ) when higher 1 MCP concentrations were applied. Flesh Firmness, PME and endo PG Activities In 2009, HW MCP, HW x 1 MCP treatments softened to a similar degree by the first week of low temperature storage (Table 6 5 ). Firmness retention in HW treated fruit might be attribut ed to the persistent reduction of ethylene biosynthesis since temporary reduction of ethylene by 1 MCP (Day 7) did not correlate with a firmer texture (Table 6 1 6 5 ). Upon removal from low temperature storage, HW treated fruit initially maintaine d better firmness than fruit from the 1 MCP and HW x 1 MCP treatments. However, HW x 1 MCP treated fruit retained the same firmness until Day 17 when the HW treated fruit had already softened to the level of the control fruit (Table 6 5 ). Softening inh ibition was more prominent when a higher concentration of 1 (Table 6 6 ). This could be the reason for the prolonged firmness retention that occurred in HW x 1 all the treatments had no effect on firmness retention during low temperature storage in 2009, while HW treatment was most effective in 2010 (Table

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167 6 8 6 9 ). Furthermore, during ripening in 2010, but not in 2009 (Table 6 8 6 9 ). This could be related to the difference in maturity of fruit in those two years (Budde et al., 2006). 1 MCP was relatively concentration of 1 MCP was only capable of retaining firmness for 1 day after removal from low temperature storage (Table 6 9 ). In 2010, the inhibitory effect of 1 MCP lasted 6 6 6 9 ), demonstrating that sensitivity to 1 MCP is cultivar dependent. Repeated 1 MCP applications on peaches may be able to maintain suppression of ripening longer (Liu et al., 2005) Firmness retention may be explained by changes in PME and PG activities. PME and PG activity were affected differently in the two NMF cultivars. Similar to the results reported in Zhou et al. (2000) and Ben Arie and Sonego (1980), PME activity increased in 6 7 by the first week of low temperature storage (Table 6 10 ). Proteomic analysis indicated that PME protein increased to a higher level after peaches were stored at 4 C for 3 weeks than when the fruit were ripened immediately after harvest (Nilo et al., 2010). In this study, PME activity dropped to a lower level by the second week of low temperature storage for both cultivars (Table 6 7 6 10 ). PME activity of 6 7 ), decreased activity during mid ripening (Day 17) and decreased thereafter (Table 6 10 ). It has been shown that t he PME activity of juicy peach fruit after 2 weeks of storage at 5 C and

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168 subsequent ripening is low compared to mealy fruit, which tend to maintain the same level of PME activity (Brummell et al., 2004) In thi s study, the increased PME activity of by the end of ripening period (Table 6 6 ). The abnormal texture may be attributed to leatheriness since NMF peaches are less likely to develop mealiness (Brovelli et al., 1998c; Cantin et al., 2010; Ju and Duan, 2000) High PME activities of HW treated and HW x 1 detected during ripening (Table 6 7 ). PME has been demonstrated to be more active at higher temperatures ( Koukounaras et al., 2008; Steiner et al., 2006) It is hypothesized that after methoxy groups are released from galacturonic acid residues by the action of PME, the carboxyl groups may complex with free cations, particularly endogenous Ca 2+ (Steiner et al., 2006). The subsequent increase in Ca pectate may result in a more rigid then increased again. It was 2 fold higher than that of the control fruit by Day 21 (Table 6 7 C for 12 h had higher flesh mealiness index after 5 weeks of storage at 0 C (Jin et al., 2009) The abnormal increase in flesh firmness of HW ruit by the end of storage in 2010 could have reflected a change in texture from normal to rubbery (Table 6 6 ). Since HW x 1 MCP fruit softened normally, peak PME activity was simply delayed to Day 21 (Table 6 6 6 7 ). Higher PM E activities were not detected in HW treated and HW x 1 6 9 6 10 ). The data suggests that the mechanisms underlying the preservation of flesh firmness deviated greatly between these two NMF cultivars.

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169 Surprisingly, high PME activity was also detected in 1 MCP during ripening (Table 6 7 ). Hence, regulation of cell wall modification during ripening of peaches may have been similar between 1 MCP and HW tr eatments. 1 MCP treated than the control fruit by Day 21 (Table 6 6 6 7 ), suggesting that those fruit did not develop rubbery texture like the control and HW treated fruit (Giradi et al., 2005). Therefore, 1 MCP treatment may be capable of preventing certain chilling related (DeEll et al., 2008) Low temperature stora ge has a more pronounced effect on protein synthesis and activity of endo PG than it does on PME in peaches (Girardi et al., 2005; Nilo et al., 2010). Endo temperature storage ( Table 6 7 ). Endo and HW x 1 MCP treatments recovered by Day 17 while endo PG in 1 MCP treated fruit rapidly recovered on Day 15 (Table 6 7 ). Endo detectable, but decreased consistently during low temperature storage (Table 6 10 ). Endo PG activity in HW treated and HW x 1 completely by Day 7 and Day 15 (Ta ble 6 10 ). Endo PG activity was detected on Day 15 in 1 MCP treated fruit, but was slightly lower than that of the control fruit. Delaying the increase in activity of endo PG could be the mechanism responsible for firmness retention in HW treated and H W x 1 not increased, the HW and HW x 1 MCP treatments may have regulated endo PG at the transcriptional level via ethylene inhibition. Interestingly, endo PG activity of control eased throughout ripening, a trend that is the opposite of MF

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170 peaches (Brummell et al., 2004) The rapid recovery of endo PG activity in 1 MCP treated fruit upon removal from low temperature storage for both cultiv ars might be associated with the minor (Table 6 2 ) or no (Table 6 4 ) suppression of ethylene biosynthesis in those fruit. It has been shown that ACS1 expression and activity are not affected by 1 MCP in ripening peaches (Dal Cin et al., 2006) and A CS1 may be a key factor in the modulation of responses to 1 MCP application (Ziliotto et al., 2008) Ground Color, Flesh Color, and Weight Loss peaches during low temperature storage in 2009 (Table 6 11 ) but significantly delayed the changes by Day 14 in 2010 (Table 6 12 ). A decrease in GCh in the range measured in these experiments denotes an increase in orange or red coloration of the s kin T he control fruit gradually became more orange during ripening while the HW treated and HW x 1 6 11 ) and Day 19 in 2010 (Table 6 12 ). 1.5 mg/L 1 MCP was required to inhibit GCh change 6 12 ). GCh of all pre was similar to that of control fruit in low temperature storage (Table 6 13 6 14 ). During ripening of changes were transiently inhibited by HW, 1 MCP, and HW x 1 MCP treatments in 2009 (Table 6 13 ) or not affected in 2010 (Table 6 14 ). Both cultivars developed localized slight red coloration naturally in the flesh as fruit senescence proceeded. HW treatment increased the intensity and area of red coloration but no browning was observed in the flesh. This alteration was reflected by the decreased FCh of HW fruit by the end of the ripening period of both cultivars in 2009 (Ta ble 6 11 6 13 ). Flesh reddening has been shown in heat treated fruit ripened

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171 directly at room temperature; therefore, this feature has been proposed to be associated with alteration of ethylene biosynthesis (Budde et al. 2005; Murray et al., 2007) 1 MCP 2010 (Table 6 12 ), a symptom associated with inhibition of ethylene production after low temperature storage (Dong et al., 200 1) It has been shown that PAL activity and accumulation of anthocyanin are generally reduced by 1 MCP (Jiang et al., 2001; Manganaris et al., 2007) The induction of red coloration i n this study might be attributed to the recovery of ethylene biosynthesis. Therefore, it was only evident toward the end of ripening. HW x1 MCP was the most significant treatment in inhibiting FCh changes 6 12 ). The F Ch values were significantly different 2010, but the differences in flesh color were most likely too small to be detected visually. It has been reported for peaches and nectarines that a h difference of 2.5 units or greater is required for consumers to be able to perceive a color difference (Obenland et al., 2005) HW treatment increased WL in both NMF cultivars. HW treated and HW x 1 MCP l and 1 MCP trea ted fruit by Day 19 in 2009 (Table 6 13 ). Transiently higher WL of HW x 1 peaches was observed in 2010, but the WL difference quickly disappea red as ripening progressed (Table 6 14 ). In contrast, HW Day 14 to 17 in 2010 but eventually reached the same level of WL as the control fruit by Day 19 (Table 6 12 ). The WL characteristics of each NMF cultivar after HW treatment may have been caused by different rearrangements of epicu ti cular wax (Lopez

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172 Castaeda J. et al., 2010) 1 MCP treated fruit had WL that was similar to the control fruit regardless of the concentration of 1 MCP applied (Table 6 11 6 12 6 13 6 14 ), in agreement with the results of Manganaris et al. (2008) for 'Harrow Sun' plums. Soluble So lids Content, Titratable Acidity, pH In 2009, HW Day 19 (Table 6 15 ), but a similar effect was not observed for HW (Table 6 17 ). Others have also reported that HW treatment can either have no effect or slightly increase the SSC of ripened peaches (Malakou and Nanos, 2005; Obenland et al., 2005) In 2010, HW treated and H W x 1 than the control fruit on Day 15 (Table 6 16 showed a reverse trend (Table 6 18 ). Higher SSC may be attributed to increases in glucose and fructose because the sucrose level of peaches is not affected by heat treatment (Lara et al., 2009) No consistent trend was observed for SSC of 1 MCP 6 16 ). Upon removal fr om low temperature storage, 1 MCP similar to HW treated and HW x 1 MCP treated fruit. 1 peaches during low temperature storage or ripening (Table 6 18 ). TA of the control fruit was maintained throughout low temperature storage, then decreased gradually during ripening for both cultivars (Table 6 15 6 16 6 17 6 18 ). HW t by Day 19 in 2009 (Table 6 15 ), but the opposite trend was observed in 2010 (Table 6 16 ). The higher SSC and lower TA that developed as a consequence of HW treatment may have SSC/TA (51.68) on Day 19 in 2009 (Table 6 15 ). The SSC/TA for minimum accept ability

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173 of MF peaches at the eating ripe stage is 15 or greater (Beckman and Krewer, 1999; Malakou and Nanos, 2005) The decrease in TA and accumulation of SSC suggest that organic acids may be p referred over sugar as respiratory substrate in heat treated fruit temperature storage and ripening (Table 6 17 ). In 2010, TA of HW treated and HW x uit gradually decreased during low temperature storage, which corresponded with an increase in pH, while no changes occurred in both control and 1 MCP treated fruit (Table 6 18 ). Although the TA of HW treated and HW x 1 MCP atistically higher than that of control fruit by Day 21, the differences were probably too small to be noticed by the consumer. 1 MCP was the most effective treatment in delaying the changes of TA and pH of both cultivars during ripening (Table 6 16 6 18 ); however, the effect was more MCP treated fruit may be attributed to the suppressed ethylene production and, consequently, reduced respiration rate (Table 6 2 6 4 ) (Girardi et al., 2005). As ripening progresses, the pH of the fruit generally increases as the TA decreases. The rise in pH was accelerated by HW x MCP treatment in both cultivars (Day 17) (Table 6 16 6 18 ). This could be related to the higher r espiration rates in those treatments that were observed during low temperature storage (Table 6 2 6 4 ). Incidence of Decay and Pitting HW treatment was (Table 6 19 ). The rearrangement of e p icuticular waxes under high temperature conditions partially or entirely seals the natural openings and barely visible cracks in the epidermis, thus limiting sites of fungal penetration into the fruit (Fallik et al., 1999; Fallik

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174 et al., 2000) HW treatment can also act directly on the pathogen (cell damage) and indirectly on the fruit host (induction of resistance mechanisms) to suppress incidence of decay (Casals et al., 2010b) However, if the temperature and exposure time is not tissues (Lo pez Castaeda J. et al., 2010) HW x 1 MCP treatment was also capable of greater than that of fruit from HW treatment (Table 6 19 ). This data suggests that 1 MCP can in duce infection when applied at high temperature. It is possible that differences in skin composition between the two NMF peaches may contribute to the differences in responsiveness to 1 MCP that were observed. Inhibition of ripening by 1 MCP was very tran MCP concentration used for the former was 3 times more than for the latter. Recently, it has been shown that an intact apple absorbs gaseous 1 MCP at a relatively slow rate compared to a peeled apple (Huber et al., 2010) Secondly, hydrophobic compounds such as lignin, high methoxy pectins and oil have high sorption for 1 MCP. Hence, the hydrophobicity of the peel may naturally influence sor ption rate and affect access of 1 MCP to the internal tissue (Choi and Huber, 2009) Limited diffusion across the peel tissue may also be responsible for the observed transient effect of 1 omato fruit partially exposed to aqueous 1 MCP had a more acute ripening inhibitory effect in the external (epidermal) tissues compared with internal tissues (Choi and Huber, 2008) Pitting was observed only on HW treated and HW x 1 MCP treated fruit of both cultivars (Table 6 20 ). Low temperature storage did not induce pitting on peaches in

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175 these experiments since it was not found on the control fruit of either cultivar (Table 6 20 ). Pitting was also not observed on 1 MCP treated fruit, indicating that it was caused by high temperature exposure. Pitting did not correlate with incidence of decay as 6 19 6 20 ). HW treated and HW x 1 M CP HW x 1 MCP treated fruit compared with 17% of the HW treated fruit. It has been shown that non grapefruit increases when the fruit are initially exposed to low humidity then transferred to a high humidity environment (Alferez et al., 2003; 2010) The low humidity environment results in negative turgor pr essure in exposed fruit compared to positive turgor pressure of freshly harvested fruit. Based on these previous reports, it was likely that the HW conditioning in this study predisposed the peach fruit to lose more water after the treatment, such as the 6 13 ), which caused a decrease in turgor pressure of the epidermal cells due to dehydration. Apparently, 1 MCP exacerbated the effect of high temperature. Thus, the combined treatment caused higher incidence of pi tting (Table 6 20 ). Fruit pitting may be related to localized programmed cell death because a cysteine protease gene has been identified with peel pitting of navel oranges (Fan et al., 2009; Vaux and Korsmeyer, 1999; Xu and Chye, 1999) Coincidently, peach fruit treated with hot air at 39 C for 3 days also showed increased gene expression of cysteine protease (Lara et al., 2009). Overall, pitting renders fruit unmarketable, but i t can be potentially reduced by adding sodium chloride in the water (Obenland and Aung, 1997)

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176 Chapter Conclusion Pre storage HW and HW x 1 MCP treatments were more effective than aqueous 1 MCP application in delaying softening of NMF peaches ripened after low temperature storage. Prevention of postharvest decay by HW treatment was cultivar dependent. exposure time used for the HW t reatment in this study as evidenced by less pitting. Pre MCP may be a better postharvest practice to maintain fruit quality for this cultivar.

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177 Table 6 1 Effect of pre storage HW and 1 MCP treatments peaches during 14 days of storage at 0 C plus 5 days of ripening at 20 C in 2009 Year 2009 Storage days (0 C ) Ripening days (20 C ) 0 7 14 14.5 15 17 19 Ethylene production (L C 2 H 4 ) Control 15.26a 19.91a NA 96.67a 162.0ab 107.7ab 79.82ab HW 5.62c 2.95c NA 22.65c 139.0b 122.7a 73.54b 1 MCP (100 g/L) 16.28a 7.84b NA 76.39b 176.2a 120.5ab 93.14a HW x 1 MCP 11.17b 6.19b NA 19.04c 94.04c 101.8b 87.84a Significance Factor A (HW) ** ** NA ** ** NS NS Factor B (1 MCP) ** ** NA ** NS ** A x B ** NA ** ** NS NS Respiration rate (mg CO 2 ) Control 29.71a 68.31a NA 183.3a 138.3b 161.5a 234.8a HW 22.73b 29.49c NA 148.4b 197.5a 153.2b 168.1c 1 MCP (100 g/L) 32.22a 43.44b NA 187.3a 159.0b 164.9a 184.9bc HW x 1 MCP 29.05a 52.43b NA 145.9b 148.1b 142.2c 220.4ab Significance Factor A (HW) ** ** NA ** ** ** NS Factor B (1 MCP) NS NA NS NS NS A x B NS ** NA NS ** ** = Significant at p ** = Significant at p NS = Non significant NA = not available

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178 Table 6 2 Effect of pre storage HW and 1 MCP treatments peaches during 14 days of storage at 0 C plus 7 days of ripening at 20 C in 2010 Year 2010 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 21 Ethylene production (L C 2 H 4 ) Control 5.29a 5.63a 6.14 83.96a 251.6a 131.7a 101.6b HW 5.34a 5.24b 6.07 67.88b 235.1a 129.1a 117.5a 1 MCP (1.5 mg/L) 4.38c 4.77c 5.79 61.64c 155.1b 110.9ab 86.46c HW x 1 MCP 4.77b 4.93bc 5.97 28.40d 120.5c 91.83b 69.63d Significance Factor A (HW) NS NS ** NS NS Factor B (1 MCP) ** ** NS ** ** ** ** A x B NS NS ** NS NS ** Respiration rate (mg CO 2 ) Control 84.52b 86.37 88.60b 304.5a 290.3a 214.0 264.0 HW 96.13a 76.46 87.39b 302.0a 301.0a 219.3 240.8 1 MCP (1.5 mg/L) 70.82c 63.89 93.85a 264.5b 225.3b 264.5 323.5 HW x 1 MCP 82.30b 99.48 96.83a 247.7c 236.5b 250.3 283.8 Significance Factor A (HW) ** NS NS NS NS NS Factor B (1 MCP) ** NS ** ** ** NS NS A x B NS NS NS NS NS NS NS = Significant at p ** = Significant at p NS = n on significant

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179 Table 6 3 Effect of pre storage HW and 1 MCP treatments during 14 days of storage at 0 C plus 5 days of ripening at 20 C in 2009 Year 2009 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 Ethylene production (L C 2 H 4 ) Control 3.30a 0.83b 0.29c 30.98a 61.99a 49.98 HW 0.86d 2.11a 1.02a 14.29b 47.78b 51.85 1 MCP (100 g/L) 2.69b 0.83bc 0.41b 13.43b 44.94b 60.81 HW x 1 MCP 1.88c 0.63c 0.34bc 6.55c 27.49c 53.10 Significance Factor A (HW) ** ** ** ** ** NS Factor B (1 MCP) NS ** ** ** ** NS A x B ** ** ** ** NS NS Respiration rate (mg CO 2 ) Control 21.17a 11.88c 14.57b 78.74a 144.6 0 a 97.57 HW 19.83a 27.49a 26.27a 78.28ab 92.98c 85.25 1 MCP (100 g/L) 16.71b 15.03b 11.45c 49.22c 120.5 0 b 114.2 0 HW x 1 MCP 16.84b 14.41b 12.12bc 72.90b 83.11c 92.71 Significance Factor A (HW) NS ** ** ** ** NS Factor B (1 MCP) ** ** ** ** ** NS A x B NS ** ** ** NS NS = Significant at p ** = Significant at p NS = n on significant

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180 Table 6 4 Effect of pre storage HW and 1 during 14 days of storage at 0C plus 5 days of ripening at 20C in 2010 Year 2010 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 21 Ethylene production (L C 2 H 4 ) Control 4.43bc 8.84a 4.50b 187.5a 97.35a 312.1a 288.1a HW 5.28a 7.87a 5.04ab 188.9a 92.99a 222.3b 234.0b 1 MCP (5 mg/L) 4.28c 4.91b 4.73b 156.2b 83.88b 226.7b 191.9c HW x 1 MCP 4.84ab 7.41a 5.64a 182.5a 63.93c 213.9b 185.3c Significance Factor A (HW) ** NS ** NS ** NS Factor B NS ** ** ** ** ** A x B NS NS * NS Respiration rate (mg CO 2 ) Control 68.73b 71.92c 64.40 184.6 196.9a 217.1a 250.2a HW 69.68b 71.04c 63.54 195.0 155.7c 162.5c 172.5b 1 MCP (5 mg/L) 74.90b 80.15b 60.17 186.3 153.2c 180.5b 206.1ab HW x 1 MCP 86.17a 88.39a 69.04 206.7 185.0b 177.7bc 181.9ab Significance Factor A (HW) NS NS NS NS ** ** Factor B (1 MCP) ** ** NS NS NS NS A x B NS NS NS ** ** NS = Significant at p ** = Significant at p NS = n on significant

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181 Table 6 5 Effect of pre storage HW and 1 MCP trea tmen t g 14 days of storage at 0 C plus 5 days of ripening at 20 C in 2009 Year 2009 Storage days (0 C ) Ripening days (20 C ) 0 7 14 14.5 15 17 19 Firmness (N) Control 23.47a 16.54bc NA 11.53b 12.27b 11.84ab 9.82 HW 17.18b 27.69a NA 20.41a 13.68ab 10.10b 10.30 1 MCP (100 g/L) 16.25b 13.24c NA 12.77b 12.73b 10.00b 10.46 HW x 1 MCP 20.53ab 18.61b NA 14.29b 16.70a 14.05a 11.10 Significance Factor A (HW) NS ** NA ** NS NS Factor B (1 MCP) NS ** NA NS NS NS NS A x B ** NS NA ** NS ** NS = Significant at p ** = Significant at p NS = Non significant NA = not available

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182 Table 6 6 Effect of pre storage HW and 1 MCP treatments g 14 days of storage at 0 C plus 7 days of ripening at 20 C in 2010 Year 2010 Storage days (0 C ) Ripening days (20 C) 0 7 14 15 17 19 21 Firmness (N) Control 29.35 26.40b 29.26 28.77 19.35c 13.63c 14.74ab HW 28.88 29.57a 31.25 28.02 19.48c 14.70bc 17.86a 1 MCP (1.5 mg/L) 29.94 28.87a 29.87 28.71 22.43b 15.38b 13.01b HW x 1 MCP 28.26 29.85a 29.35 32.03 25.48a 19.91a 18.50a Significance Factor A (HW) NS ** NS NS ** ** Factor B (1 MCP) NS NS NS ** ** NS A x B NS NS NS NS ** NS = Significant at p ** = Significant at p NS = Non significant

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183 Table 6 7 peaches durin g 14 days of storage at 0 C plus 7 days of ripening at 20 C after pre storage conditioning treatments in 2010 Year 2010 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 21 PME Acti vity (Unit) m Control 0.33 1.02 0.81 1.23 0.37b 0.44b 1.18bc HW 0.46 1.28 0.9 0 0.85 4.30a 1.13b 2.47ab 1 MCP (1.5 mg/L) 0.63 1.53 0.34 1.32 3.95a 2.21a 0.40c HW x 1 MCP 0.63 1.6 0 0.62 0.71 0.66b 0.75b 3.35a Significance NS NS NS NS * Endo PG Activity (Unit) y Control 1.15 NA NA NA 0.75 1.44 0.86 HW 0.74 NA NA NA 1.09 0 .00 1.66 1 MCP (1.5 mg/L) 0.4 0 0 .00 NA 0.87 0.8 0 0.94 0.73 HW x 1 MCP 0.46 NA 0.12 NA 0.5 0 0.8 0 0.65 Significance NS NS NS NS m A 620 mg 1 protein min 1 y =1 unit of PG activity = 1 g galacturonic acid mg 1 protein h 1 = Significant at p NS = n on significant NA = no enzyme activity detected

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184 Table 6 8 Effect of pre storage HW and 1 MCP treatments g 14 days of storage at 0 C plus 5 days of ripening at 20 C in 2009 Year 2009 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 Firmness (N) Control 34.07 28.77 34.98 27.00b 25.38 23.43 HW 36.62 33.13 35.85 36.15a 20.86 20.41 1 MCP (100 g/L) 35.02 31.66 32.49 26.11b 25.31 20.93 HW x 1 MCP 35.51 30.38 28.34 30.30b 26.72 22.66 Significance Factor A (HW) NS NS NS ** NS NS Factor B (1 MCP) NS NS NS NS NS NS A x B NS NS NS NS NS NS = Significant at p ** = Significant at p NS = n on significant

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185 Table 6 9 Effect of pre storage HW and 1 MCP treatments g 14 days of storage at 0 C plus 7 days of ripening at 20 C in 2010 Year 2010 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 21 Firmness (N ) Control 47.17 45.66b 49.81ab 44.6c 35.50b 23.58b 16.46b HW 50.54 47.12a 50.99a 48.82b 34.63bc 30.18a 22.48a 1 MCP (5.0 mg/L) 51.31 47.62a 46.47bc 52.1a 34.51c 23.63b 17.16b HW x 1 MCP 48.77 45.77b 45.59c 52.51a 36.73a 25.46a 20.02a Significance Factor A (HW) NS NS NS ** ** Factor B (1 MCP) NS NS ** ** NS ** NS A x B NS ** NS ** ** NS = Significant at p ** = Significant at p NS = n on significant

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186 Table 6 10 PME and PG activities of g 14 days of storage at 0 C plus 7 days of ripening at 20 C after pre storage conditioning treatments in 2010 Year 2010 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 21 PME Activity (Unit) m Control 0.99 1.34 0.67 0.27 1 .00 0.36b 0.32 HW 1.23 0.17 0.28 0.31 0.75 0.34b 0.49 1 MCP (5 mg/L) 1.24 0.27 0.86 0.59 0.65 0.69a 0.39 HW x 1 MCP 1.21 0.95 0.67 0.6 0 0.85 0.22b 0.28 Significance NS NS NS NS NS NS Endo PG Activity (Unit) y Control 1.44a 0.8 0 0.24 0.55 0.45 0.41 0.23 HW 0.87ab NA 0.48 NA 0.06 0.25 0.21 1 MCP (5 mg/L) 0.46b 0.04 0.95 0.32 0.28 0.37 0.67 HW x 1 MCP 0.24b 0 .00 0.04 NA 0.28 NA 0.32 Significance NS NS NS m A 620 mg 1 protein min 1 y =1 unit of PG activity = 1 g galacturonic acid mg 1 protein h 1 = Significant at p NS = n on significant NA = no enzyme activity detected

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187 Table 6 11 g 14 days of storage at 0 C plus 5 days of ripening at 20 C after pre storage conditioning treatments in 2009 Year 2009 Storage days (0 C ) Ripening days (20 C ) 0 7 14 14.5 15 17 19 GCh Control 66.62 72.06 NA 66.30c 70.31b 69.57 69.66 HW 68.57 69.63 NA 70.70ab 73.48a 70.08 68.92 1 MCP (100 /L) 68.00 69.62 NA 68.23bc 69.88b 68.16 67.19 HW x 1 MCP 70.33 73.77 NA 72.53a 72.57ab 70.84 68.43 Significance NS NS * NS NS FCh Control 79.49 77.81 NA 80.76 78.13 77.15 77.03a HW 79.54 81.85 NA 80.47 77.19 73.07 64.04b 1 MCP (100 /L) 78.90 79.89 NA 77.83 78.82 76.06 75.30a HW x 1 MCP 80.91 81.43 NA 82.09 80.49 73.05 76.02a Significance NS NS NS NS NS WL (%) Control 0.00 0.21 NA 1.08 3.06 5.30 9.33 HW 0.00 0.23 NA 1.41 2.97 5.74 9.05 1 MCP (100 /L) 0.00 0.16 NA 0.97 2.97 5.20 9.15 HW x 1 MCP 0.00 0.34 NA 1.67 3.26 4.82 8.39 Significance NS NS NS NS NS NS = Significant at p NS = non significant NA = not available

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188 Table 6 12 g 14 days of storage at 0 C plus 7 days of ripening at 20 C after pre storage conditioning treatments in 2010 Year 2010 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 21 GCh Control 88.10a 85.80 79.35c 75.19b 76.88bc 68.26c 69.48 HW 89.79a 85.19 83.22b 75.97b 74.87c 74.43a 72.44 1 MCP (1.5 mg/L) 89.15a 84.40 86.01a 87.02a 81.43a 70.53bc 70.63 HW x 1 MCP 84.99b 83.00 85.52a 85.11a 80.85ab 71.73b 70.9 0 Significance NS * * NS FCh Control 78.47 83.41b 81.83c 81.91c 76.18b 75.48b 76.95a HW 80.26 83.83b 85.07a 82.54bc 75.62b 74.91b 76.67a 1 MCP (1.5 mg/L) 78.8 0 82.22c 83.25b 83.63a 75.33b 69.24c 70.13b HW x 1 MCP 79.83 86.21a 85.50a 82.98ab 82.37a 78.03a 75.12a Significance NS * * * WL (%) Control 0.00 6.82 13.74ab 15.89a 19.22a 20.56 21.36 HW 0.00 5.16 11.16b 13.10b 15.92b 18.43 20.71 1 MCP (1.5 mg/L) 0.00 7.44 14.74a 16.60a 19.67a 20.97 22.84 HW x 1 MCP 0.00 6.83 14.28a 16.17a 20.11a 22.79 26.12 Significance NS NS * NS NS = Significant at p NS = n on significant

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189 Table 6 13 g 14 days of storage at 0 C plus 5 days of ripening at 20 C after prestorage conditioning treatments in 2009 Year 2009 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 GCh Control 88.17 86.17 85.28 81.66b 80.39 77.36a HW 86.70 88.32 87.28 85.06ab 80.23 78.96a 1 MCP (100 g /L) 86.39 84.10 87.07 86.17a 83.29 76.99ab HW x 1 MCP 88.29 88.84 87.10 86.48a 80.91 74.28b Significance NS NS NS NS FCh Control 88.50 87.28 88.21ab 86.58 85.59a 78.09a HW 85.60 88.27 88.40a 87.03 70.43c 61.55b 1 MCP (100 g /L) 87.61 88.19 89.23a 85.95 80.51ab 74.96a HW x 1 MCP 86.82 86.77 86.13b 85.29 78.30b 76.29a Significance NS NS NS * WL (%) Control 0.00 1.72 3.20 4.18 5.17 8.02b HW 0.00 1.65 3.08 4.02 6.99 10.61a 1 MCP (100 g /L) 0.00 1.56 2.97 3.60 6.41 7.81b HW x 1 MCP 0.00 1.50 2.95 3.90 7.16 10.08a Significance NS NS NS NS NS * = Significant at p NS = n on significant

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190 Table 6 14 g 14 days of storage at 0 C plus 7 days of ripening at 20 C after pre storage conditioning treatments in 2010 Year 2010 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 21 GCh Control 92.14 90.92 91.58 91.98 84.58 81.30 79.34b HW 91.57 92.38 90.50 90.20 82.58 81.32 81.34a 1 MCP (5.0 mg/L) 91.24 90.93 91.77 89.26 84.98 79.88 79.13b HW x 1 MCP 91.40 90.43 91.54 90.54 83.95 80.54 78.91b Significance NS NS NS NS NS NS FCh Control 87.81d 87.85 88.51b 88.64 86.44 86.24a 86.28 HW 89.36a 88.42 90.06a 88.89 85.37 85.97a 86.15 1 MCP (5.0 mg/L) 89.03b 88.26 88.50b 89.25 86.42 82.58c 85.34 HW x 1 MCP 88.66c 88.24 88.01c 89.88 86.05 84.70b 85.95 Significance NS NS NS NS WL (%) Control 0.00 1.84 3.91b 4.54b 7.02ab 8.63 11.31 HW 0.00 1.76 3.72b 4.47b 6.08b 7.46 11.71 1 MCP (5.0 mg/L) 0.00 1.23 3.20b 4.84b 5.29b 6.48 9.69 HW x 1 MCP 0.00 2.32 5.26a 6.31a 8.01a 9.7 0 8.04 Significance NS NS * NS NS = Significant at p NS = n on significant

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191 Table 6 15 g 14 days of storage at 0 C plus 5 days of ripening at 20 C after pre storage conditioning treatments in 2009 Year 2009 Storage days (0 C ) Ripening days (20 C ) 0 7 14 14.5 15 17 19 SSC (%) Control 11.30 10.45 NA 13.90 12.30 12.65 12.30 HW 12.90 12.80 NA 11.00 11.30 12.65 13.05 Significance NS NS NS NS TA (%) Control 0.441 0.498 NA 0.330 0.302 0.262 0.238 HW 0.392 0.530 NA 0.427 0.283 0.244 0.224 Significance NS NS NS NS NS pH Control 4.52 4.40 NA 4.55 4.52 3.90 4.88 HW 4.54 4.46 NA 3.95 4.99 4.69 5.28 Significance NS NS NS NS = Significant at p NS = n on significant NA = not available

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192 Table 6 16 g 14 days of storage at 0 C plus 7 days of ripening at 20 C after pre storage conditioning treatments in 2010 Year 2010 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 21 SSC (%) Control 9.15c 11.37a 10.45 12.50a 11.53 11.40a 12.03 HW 11.60a 10.60b 10.77 10.95b 11.47 11.50a 13.13 1 MCP (1.5mg/L) 10.27b 9.95c 11.47 10.75b 11.30 11.80a 12.67 HW x 1 MCP 11.35a 11.50a 11.30 11.23b 10.73 10.43b 12.77 Significance * NS NS NS TA (%) Control 0.61 0.59ab 0.60c 0.70a 0.52b 0.46c 0.39b HW 0.63 0.53b 0.63bc 0.56c 0.54b 0.51b 0.44a 1 MCP (1.5mg/L) 0.70 0.65a 0.68a 0.58bc 0.66a 0.55a 0.44a HW x 1 MCP 0.64 0.59ab 0.67ab 0.62b 0.54b 0.49bc 0.47a Significance NS * * * pH Control 4.05 4.06 4.15a 4.02c 4.16c 4.40a 4.51 HW 4.07 4.15 4.15a 4.21a 4.22b 4.29c 4.55 1 MCP (1.5mg/L) 4.04 4.06 4.06b 4.14b 4.17bc 4.26c 4.52 HW x 1 MCP 4.07 4.17 4.13a 4.17ab 4.30a 4.35b 4.57 Significance NS NS * * NS = Significant at p NS = n on significant

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193 Table 6 17 g 14 days of storage at 0 C plus 5 days of ripening at 20 C after pre storage conditioning treatments in 2009 Year 2009 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 SSC (%) Control 10.13 10.73 10.40 10.13 8.93 10.30 HW 10.80 10.67 10.40 10.10 9.60 11.20 Significance NS NS NS NS NS NS TA (%) Control 0.52 0.55 0.59 0.47 0.42 0.43 HW 0.58 0.5 0.55 0.48 0.52 0.36 Significance NS NS NS NS NS pH Control 3.97 4.10 4.28 4.34 4.17 4.10 HW 4.01 3.96 4.30 4.37 4.14 4.18 Significance NS NS NS NS NS NS NS = non significant

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194 Table 6 1 8 14 days of storage at 0 C plus 7 days of ripening at 20 C after pre storage conditioning treatments in 2010 Year 2010 Storage days (0 C ) Ripening days (20 C ) 0 7 14 15 17 19 21 SSC (%) Control 10.30 10.70a 11.00 10.55b 10.80 10.25 10.85 HW 9.45 10.80a 10.13 11.00ab 10.70 10.60 10.20 1 MCP (5.0 mg/L) 10.00 10.65a 10.75 10.40b 9.90 10.30 10.55 HW x 1 MCP 10.47 9.67b 10.53 11.33a 10.87 10.57 10.57 Significance NS NS NS NS NS TA (%) Control 0.52a 0.52 0.57a 0.47b 0.47ab 0.44 0.46b HW 0.44b 0.51 0.49b 0.49b 0.43b 0.46 0.47ab 1 MCP (5.0 mg/L) 0.52a 0.52 0.55a 0.55a 0.49a 0.42 0.48a HW x 1 MCP 0.52a 0.45 0.43c 0.49b 0.45bc 0.43 0.48a Significance NS * NS pH Control 4.03b 3.92b 3.95d 4.06a 4.11b 4.15 4.16 HW 4.21a 4.09a 4.08b 4.04a 4.007b 4.19 4.21 1 MCP (5.0 mg/L) 4.00b 3.97b 4.02c 3.96b 4.10b 4.15 4.27 HW x 1 MCP 4.04b 4.13a 4.22a 4.03a 4.20a 4.16 4.32 Significance * * NS NS NS = non significant

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195 T able 6 1 9 Incidence of decay of pre conditioned NMF peaches after 14 days of storage at 0C plus 5 7 days of ripening at 20C Year 2009 2010 Cultivar Decay (%) Decay (%) Control 5.0 31.3 Control 8.8 8.8 HW 16.3 3.1 HW 15.0 2.1 1 MCP (100 g/L) 7.5 25.0 1 MCP (1.5 or 5 mg/L) 8.3 10.4 HW x 1 MCP 17.5 6.3 HW x 1 MCP 12.5 5.8 Table 6 20 Incidence of pitting of pre conditioned NMF peaches after 14 days of storage at 0 C plus 7 days of ripening at 20 C in 2010 Cultivar Pitting (%) Control 0 0 HW 17 10 1 MCP 0 1 HW x 1 MCP 52 24

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196 CHAPTER 7 SUMMARY AND CONCLUSI ONS In the first study of this work, the effects of maturity, ripening and low temperature storage on peach fruit quality were explored with the aim to determine the optimum harvest maturity and maturity indices for low chill, subtropical MF and NMF peach (MG) at harvest bas ed on their initial ground color a* value (GCa*). Fruit quality factors were determined after ripening at 20 C for 1 week or following storage at 0 C for 2 weeks. The changes in peel GC and flesh color (FC) of both the MF and NMF cultivars from green to red or orange as harvest maturity advanced or during fruit ripening were indicated by the increases in a* values. Larger increases in the FCa* of both NMF cultivars were detected during ripening following 0 C storage than during 20 C storage. Since no brow ning was observed, this feature was not considered to be a symptom of chilling injury (CI). The flesh firmness of the MF cultivars dropped markedly began, but the flesh firmness of the NMF cultivars decreased relatively slowly as ripening progressed. The NMF peaches were approximately 3 to 5 times firmer than the MF peaches when both were at the full ripe stage. Cell wall synthesis and degradation b peaches were most susceptible to CI since abnormal softening occurred in fruit of that cultivar from the lower MG after ripening following low temperature storage.

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197 Th e soluble solids content (SSC) and total sugar (TS) of all the cultivars were generally little affected by harvest maturity and ripening. The SSC content varied SSC/TA increa sed as harvest maturity advanced and during ripening for all of the cultivars, primarily due to gradual decreases in titratable acidity (TA). Most of the fruit in SSC/TA f to (Beckman and Krewer, 1999; Kader and Mitchell, 1989) Thus, the prolonged low temperature storage period may have actual ly been beneficial to taste quality by increasing the perceived sweetness of those peaches that were not susceptible to CI. Optimum harvest maturity of the MF and NMF cultivars was defined based on their initial flesh firmness and fruit quality after ripe ning at 20 C either immediately after harvest or following 0 C storage. MF cultivars usually require an initial flesh firmness of at least 45 N to prevent excessive softening during shipping and to allow proper softening after transfer to ambient tempera ture for ripening (Beckman and Krewer, 1999; Kader and Mitchell, 1989) Initial flesh firmness levels of 14 N and 27 N were considered to be suitable for NMF peaches destined for local and dista nt markets, respectively (Metheney et al., 2002; Rouse et al., 2004) Flesh firmness of 8.8 to 13.2 N, recommended for ripe MF fruit, but also considered appropriate for ripe NMF fruit when selecting the range of ideal harvest maturity (Kader et al., 1982; Robertson et al., 1990 a )

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198 The results of this study suggest that NMF peaches for fresh (i.e., local) consumption can be harvested at more advanced stages (MG 15 20) than MF peaches (MG 5 1 15) than the other three cultivars (MG 0 10) to avoid CI in low temperature storage. The maturity indices for all of the cultivars were developed based on linear correlations between fruit mat urity and fruit quality factors determined at harvest. The GCa* and TA were the most reliable maturity indicators for all of the cultivars. The FCa* can used as a secondary indicator for MF peaches while pH can be used specifically for NMF cultivars when t he peel GC is not visible due to excessive peel blush coverage. Ethylene production and respiration rates of these MF and NMF peaches harvested at different developmental stages were measured during 5 days at 20 C The NMF peaches generally produced ethyl ene at higher rates than the MF peaches at harvest because the latter were mostly pre climacteric or at onset of ripening when harvested at appropriate maturity stages. Thus, the ripening process for the NMF cultivars had started prior to harvest and the fr uit at more advanced stages could quickly become post climacteric during ripening. Peaches at the post climacteric stage are more prone to physical damages and decay than less ripe fruit because they may already be to refore, the optimum harvest maturity for NMF peaches intended for immediate consumption should be selected to avoid fruit that are either immature or at the full ripe stage. Examination of endo polygalacturonase (endo PG), exo PG, and pectin methylestera se (PME) activities of both MF and NMF cultivars was carried out after 5 days of storage at 20 C The endo PG activities were similar for the MF and NMF

PAGE 199

199 cultivars although the texture of the two types was significantly different. The exo PG and PME activit ies did not correlate with the flesh firmness of either MF and NMF cultivars. Therefore, PG and PME activities may not be directly related to peach fruit softening, at least as it was measured in this study. In a second study, I focused on the potential use of different pre storage conditioning methods, including hot water treatment, aqueous 1 methylcyclopropene application (1 MCP), or a combination of the two, on quality maintenance of NMF peaches during ripening at 20 C or following low temperature (0 C ) storage. Results from a preliminary study showed that a NMF cultivar treated with 46 C water for 3 0 min or 25 C water containing 100 g/L 1 MCP for 30 min had the best firmness retention among other combinations after ripening at 20 C for 3 days. Thus, N C (Control) or 46 C (HW) water, or 25 C water containing 100 g/L 1 MCP (1 MCP), or 46 C water containing 100 g/L 1 MCP (HW x 1 MCP). Tw o trends of ethylene production were observed in th e HW treated fruit of both cultivars during ripening at 20 C for 1 week or following 2 weeks of 0 C The ethylene production of the HW treated fruit was initially suppressed, then recovered to a level similar to the control fruit, or it was suppressed thro ughout the entire ripening period. It has been reported that CI in nectarines is linked to inhibition of ethylene synthesis after prolonged low temperature storage (Dong et al., 2001) HW maintain ed higher ethylene production than the other cultivars during low temperature storage, which could help protect the fruit from CI. An immediate rise in respiration rate of HW

PAGE 200

200 conditions. The temporary rise in respiration rate after the HW treatment may be attributed to the cyanide insensitive respiratory pathway (Inaba and Chachin, 1989) The peak respiration rates of the HW treated NMF peaches were delayed, reduced, or a combination of the two during ripening in both storage conditions. Treatment with 100 g/L 1 MCP reduced ethylene production and respiration rate during ripening at 20 C T his suggests that sensitivity to 1 MCP is cultivar dependent, which may be related to the differences in terms of ratio, expression pattern, and turnover of the ethylene receptors, and mechanisms leading to altered chemical binding of 1 MCP (Cin et al., 2006; Ziliotto et al., 2008) Since1 00 g/L 1 MCP was unable to inhibit softening of both NMF cultivars during ripening at 20 C or following low temperature storage, 1.5 mg/L 1 MCP was applied to been investigated on a MF cultivar obtained from California. In addition, 5.0 mg/L 1 MCP was applied to climacteric ethylene production mea sured in freshly harvested fruit before the treatments were applied. When those high concentrations of 1 MCP were applied, the reduction of ethylene biosynthesis during ripening of both NMF cultivars at 20 C storage or following 2 weeks of 0 C storage was generally prolonged, but the response in terms of respiration rate was cultivar dependent. The HW x 1 MCP treatment was the most effective pre storage conditioning method for suppressing ethylene production and respiration rate of both NMF cultivars duri ng ripening for both storage conditions. The ethylene production and respiration rate of the HW x 1 MCP treated fruit either was similar to that of the 1 MCP treated fruit or

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201 was at an intermediate level between that of the 1 MCP treated and HW treated fru it. This suggests that the ethylene signaling pathway may be more important than the ethylene biosynthesis pathway in controlling the ripening process of peaches. The HW treatment was more effective than the 1 MCP treatment in delaying the softening of t he NMF peaches during ripening at 20 C or following low temperature storage. The effect of cultivar dominated the response of the NMF peaches to the HW treatment. For example, softening inhibition of HW throughout 5 days of storage at 20 C whereas the effect lasted only 3 days in HW ethylene production in HW inhibition during ripening at 20 C suggests that HW stress may inhibit cell wall catabolism by regulating both ethylene dependent (i.e., 1 MCP responsive) and ethylene independent pathways (Hayama et al., 2006b) The 1.5 mg/L 1 MCP treatmen day, while the 5 mg/L 1 Hence, repeated 1 MCP applications or even higher 1 MCP concentrations may be necessary to achieve prolonged firm ness retention of these cultivars. The effect of 1 MCP was more significant when it was combined with low temperature storage. The MCP, respectively, persisted 4 days and 1 day m ore during ripening after low temperature storage relative to 20 C storage. The HW x 1 MCP treatment was more effective than the HW treatment in retaining MCP were equally effective in

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202 retaining the firmn The softening inhibition of both NMF cultivars during ripening at 20 C could be mainly attributed to the influence of the HW treatment. In contrast, following low temperature storage, firmness retention was due to the strong interaction between HW and 1 MCP. Transient reduction or promotion of weight loss (WL) by all the tr eatments during ripening at 20 C and by the HW and HW x 1 MCP treatments following 0 C storage were found in both cultivars. However, the differences in WL between the HW and 1 MCP treatments and the control fruit generally became non significant as ripeni ng progressed. Therefore, WL differences cannot be used to explain the texture differences created by those treatments in the two NMF peach cultivars. Peak PME activity in the HW treated fruit of both cultivars either occurred earlier or the magnitude was higher than that of the control fruit during ripening at 20 C or following low temperature storage. Those earlier peak or relatively high PME activities may be related to the firmer texture of the HW treated fruit due to promotion of bonding between endogen ous Ca 2+ and pectin in the cell wall and middle lamella (Koukounaras et al., 2008; Steiner et al., 2006) However, a delay in peak endo PG activity occurred in the HW fru it of both cultivars during ripening in both storage conditions. This could be attributed to inhibition of mRNA synthesis and/or restriction of the enzyme to access the reaction site. The exo PG activities of both cultivars were not affected by the HW trea tment. Different patterns of PME and PG activities were observed for the two NMF peach cultivars treated with 1 MCP during ripening in both storage conditions. The peak PME activity of 1 MCP treated fruit PME

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203 activity was either advanced or the magnitude was higher than that of the control fruit. The peak endo PG activity in 1 MCP in the control fruit and with same magnitude. The peak PME activity for 1 M CP treated C but was delayed following low temperature storage. The peak endo PG activity of 1 MCP hese results suggest that PME may be more important than endo PG in regulating cell wall PG sup ported by the HW x 1 MCP treated fruit in that the treatment only delayed the PME peaches during ripening following low temperature storage. Both HW and 1 MCP treatme nts inhibited changes of hue in the peel (GCh) and flesh (FCh ) of the NMF cultivars while the control fruit exhibited constant decline in h during ripening at 20 C or following low temperature storage. However, the same treatments accelerated red color development in both the peel and flesh as shown by significant decreases in GCh and FCh. Red coloration in the flesh was intensified by 2 weeks of 0 C storage compared to 20 C storage in both HW treated and 1 MCP treated fruit although no browning occurr ed, which would indicate CI. Since flesh reddening has been proposed to be associated with alteration of ethylene biosynthesis (Murray et al., 2007; Budde et al. 2005; (Dong et al., 2001) the induction of red coloratio n observed in this study may be attributed to the recovery of ethylene biosynthesis (Jiang

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204 et al., 2001; Manganaris et al., 2007) Surprisingly, HW x 1 MCP was the most effective treatme nt in inhibiting GCh and FCh changes during both storage conditions. The TA and pH of both NMF cultivars were affected more significantly than the SSC by all the treatments. The pH of the NMF peaches was generally inversely related to TA. The TA exhibit ed no consistent response to HW treatment during ripening in either storage condition. The reduction of TA that sometimes occurred in response to HW stress may be favorable since consumer acceptance was found to be always greater for nectarine cultivars wi th lower TA regardless of fruit maturity (Iglesias and Echeverria, 2009) 1 MCP delayed the changes in TA and pH of both cultivars during ripening at 20 C and after removal from 0 C storage. This impact was more pers istent MCP treatment was as effective as the other treatments in delaying changes of TA of both NMF cultivars, but the influence of HW or 1 MCP was inconsistent. The HW and HW x 1 MCP treatments reduced peaches after ripening in both storage conditions. This is in agreement with some previous reports in which it was proposed that HW treatment of peaches causes rearrangement of e p icuticular waxes, and this restricts fungal penetration into the fruit by sealing the natural openings and cracks in the epidermis (Fallik et al., 1999; Fallik et al., 2000) The HW treatment might also act di rectly on the pathogen (cell damage) and indirectly on the fruit host (induction of resistance mechanisms) to suppress incidence of decay (Casals et al., 2010b) The 1 MCP treated fruit of both NMF cultivars generally had levels of decay that were similar to the control fruit after ripening immediately at

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205 20 C or at 20 C following low temperature storage. Therefore, it can be concluded that 1 MCP had no effect on preventing decay regardless of the concentration applied Pitting developed during ripening following low temperature storage and was mainly found on HW treated and HW x 1 MCP treated fruit, but not on the control or 1 MCP treated fruit; therefore, pitting was induced by HW treatment during ripening following low temperature storage. It is unclear if the pitting that was observed was damage from HW or if it was CI related pitting exacerbated by the HW treatment. Different decay patterns in the two NMF peach cultivars treated with HW or HW x 1 MCP leads to the h ypothesis that skin composition of peaches may contribute to the responsiveness to 1 MCP treatment (Choi and Huber, 2009) Limited diffusion of 1 MCP across the epidermal tissue may also account for the transient ef fect of 1 MCP (Choi and Huber, 2008) In conclusion, HW treatment was the most effective conditioning method for both NMF when they were ripened at 20 C immediately after h arvest. Both HW and HW x 1 Due to the high incidence of decay and pitting, aqueous 1 MCP was a better pre ipening following low temperature storage.

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206 LIST OF REFERENCES Abeles, F.B., P.W. Morgan, and M.E. Saltveit. 1992. Ethylene in plant biology. 2nd ed. Academic Press, San Diego. Adkins, M.E., P.J. Hofman, B.A. Stubbings, and A.J. Macnish. 2005. Manipulating avocado fruit ripening with 1 methylcyclopropene. Postharvest Biol. Technol. 35:33 42. Alferez, F., M. Agusti, and L. Zacarias. 2003. Postharvest rind staining in Navel orang es is aggravated by changes in storage relative humidity: effect on respiration, ethylene production and water potential. Postharvest Biol. Technol. 28:143 152. Alferez, F., B. Alquezar, J.K. Burns, and L. Zacarias. 2010. Variation in water, osmotic and turgor potential in peel of 'Marsh' grapefruit during development of postharvest peel pitting. Postharvest Biol. Technol. 56:44 49. Amoros, A., M. Serrano, F. Riguelme, and F. Romojaro. 1989. Levels of ACC and physical and chemical parameters in peach de velopment. J. Hortic. Sci. 64:673 677. AMS. 2004. United States Standards for Grades of Peaches. United States Department of Agriculture, Washington, D.C.Jan 13, 2011. < ht tp://www.agmrc.org/media/cms/peaches_4EFAEFAA6947E.pdf >. Andersen, P.C., W.B. Sherman, and J.G. Williamson. 2001. Low chill peach and nectarine cultivars from the University of Florida breeding program: 50 years of progress. Proc. Fla. State Hort. Soc. 1 14:33 36. Ashwell, G. 1957. Colorimetric analysis of sugars. Methods Enzymol. 3:73 105. Bailey, J.S. and A.P. French. 1949. The inheritance of foliage characteristics in the peach. Mass. Agr. Exp. Stat. Bul. 452:11 12. Bakshi, P. and F.A. Masoodi. 20 09. Effect of various storage conditions on chemical characteristics and processing of peach cv. 'Flordasun'. J. Food Sci. Technol 46:271 274. Bakshi, P. and F.A. Masoodi. 2010. Effect of pre storage heat treatment on enzymological changes in peach. Journal of Food Science and Technology Mysore 47:461 464. Baldwin, E.A., A. Plotto, and K. Goodner. 2007. Shelf life versus flavour life for fruits and vegetables: how to evaluate this complex trait. Stewart Postharv. Rev. 3:1 10.

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209 Brummell, D.A. and M.H. Harpster. 2001. Cell wall metabolism in fruit softening and quality and its manipulation in transgenic plants. Plant Mol. Biol. 47:311 340. Brummell, D.A., V. Dal Cin, S. Lurie, C.H. Crisosto, and J.M. Labavitch. 2004. Cell wall m etabolism during the development of chilling injury in cold stored peach fruit: association of mealiness with arrested disassembly of cell wall pectins. J. Exp. Bot. 55:2041 2052. Brunke, H., M. Chang, and D. Huntrods. 2011. Peach Profile. AgMRC, Iow a St ate UniversityJan 14, 2011. < http://www.agmrc.org/commodities__products/fruits/peach_profile.cfm >. Budde, C.O., G. Polenta, C.D. Lucangeli, and R.E. Murray. 200 6. Air and immersion heat treatments affect ethylene production and organoleptic quality of 'Dixiland' peaches. Postharvest Biol. Technol. 41:32 37. Byrne, D.H. 2002. Peach breeding trends: A world wide perspective. Acta Hort. 592:49 59. Byrne, D.H., A .N. Nikolic, and E.E. Burns. 1991. Variability in sugars, acids, firmness, and color characteristics of 12 peach genotypes. J. Amer. Soc. Hort. Sci. 116:1004 1006. Callahan, A., R. Scorza, C. Bassett, M. Nickerson, and F. Abeles. 2004. Deletions in an en dopolygalacturonase gene cluster correlate with non melting flesh texture in peach. Functional Plant Biology 31:159 168. Camejo, D., M.C. Marti, P. Roman, A. Ortiz, and A. Jimenez. 2010. Antioxidant system and protein pattern in peach fruits at two matur ation stages J. Agric. Food Chem. 58:11140 11147. Cantin, C., C. Crisosto, E. Ogundiwin, T. Gradziel, J. Torrents, M. Moreno, and Y. Gogorcena. 2010. Chilling injury susceptibility in an intra specific peach Prunus persica (L.) Batsch progeny. Postharvest Biol. Technol. 58:79 87. Cao, S., Z. Hu, Y. Zheng, and B. Lu. 2010. Synergistic effect of heat treatment and salicylic acid on alleviating internal browning in cold stored peach fruit. Postharvest Biol. Technol. 58:93 97 Carprioli, I.. M. Lafuente, M. J. Rodrigo, and F. Mencarelli. 2009. Influence of postharvest treatments on quality, carotenoids, and abscisic acid content of stored "Spring Belle" peach ( Prunus persica ) fruit. J. Agric. Food Chem. 57:7056 7063.

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230 BIOGRAPHICAL SKETCH Ming Wei S herry Kao was born in 1982, the third of five children of Hung Chi Kao and Shu Mei Kao. Sherry was born in Taiwan and moved to Canada with her family when she was 11 years old. She completed her B achelor of S cience in b iochemistry at the University of Waterloo, Ontario, Cana da. She got interested in postharvest physiology of fruits and vegetables during her senior year in colleg e and thus decided to h orticultur al s ciences. In 2004, she received her M aster of S cience in h orticulture from Auburn University, Auburn, Alabama. Soon after graduat ing from Auburn University, she began her work towards a doctorate degree in the Horticultural Sciences Department at the University of Florida under the direction of Dr. Jeffrey K. Brecht and Dr. Jeff re y G. Williamson. She received her Ph.D. from the University of Florida in the summer of 20 11.