<%BANNER%>

Effects of Laser Labeling on the storage quality of selected fresh fruits and vegetables.

Permanent Link: http://ufdc.ufl.edu/UFE0025064/00001

Material Information

Title: Effects of Laser Labeling on the storage quality of selected fresh fruits and vegetables.
Physical Description: 1 online resource (77 p.)
Language: english
Creator: Sood, Preeti
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: labeling, laser
Horticultural Science -- Dissertations, Academic -- UF
Genre: Horticultural Science thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Although in common practice since the 1990's, fruit labeling gained greater significance after 9/11 due to its potential relevance to food safety and bioterrorism. Labeling of fruits and vegetables is important for internal accounting, traceability and safety concerns. Most fruits and vegetables sold in the US are marked with non-permanent stickers or adhesive tags. These stickers usually contain names, identification numbers (three, four or five digit codes), country of origin, brands, and logos. They provide required information and help distinguishing among produce with similar appearance but a different quality value, resulting in a more efficient checkout process. Despite the many advantages, sticker labeling technology has several drawbacks. These adhesive labels are expensive to purchase and apply, and application equipment requires clean up after the season. In addition, produce are often left with glue residue on their surfaces after sticker removal, resulting in blemished fruits. An emerging technology called 'Laser Labeling' could be considered a desirable alternative to the existing labeling system. Not only is each piece of produce permanently coded, but the specific information can be stored electronically for any period of time. The technique involves a low energy carbon dioxide laser beam which vaporizes the epidermal cells and reveals the underlying cells, preferably with a contrasting color. Produce epidermis is marked with alphanumerical dot matrix characters formed by pinhole depressions (Drouilllard and Rowland, 1997). However, these depressions can promote water loss and increase the number of potential entry sites for decay-promoting organisms. The present study addresses the most vital of these postharvest concerns. The experiments were conducted to measure water loss, peel appearance, and potential decay in laser labeled citrus fruit namely 'Honey tangerine' (Citrus reticulata), 'Ruby Red' grapefruit (Citrus paradisi), tomato (Lycopersicon esculentum) and pepper (Capsicum annum) during storage. Laser labeled fruit stored at their respective optimum temperature and two relative humidities (i.e., 95% and 65% RH) for 3 to 5 weeks depending on the commodity, showed no increase in decay compared to non-etched control fruit, suggesting that laser labeling does not facilitate decay. This was confirmed by experiments where the spores of common postharvest pathogen (such as Penicillium digitatum in citrus and Geotrichum candidum in tomato and pepper) were coated on fruit surfaces before and after laser labeling. In either case, no decay was observed. Further, in agar plates which contain a lawn of P. digitatum spores, the laser labeling reduced germination of spores in contact areas. Water loss from etched areas and label appearance were determined during storage. Water loss from waxed and etched citrus peel declined to control levels after 24 hours in storage. Label appearance deteriorated slowly in citrus fruit as compared to tomato and pepper and was proportional to laser energy levels and ambient relative humidity. Waxing the laser labeled surface in citrus fruit reduced water loss by 35% to 94%, depending on the wax formulation used. This study concludes that laser labeling provides the produce industry a feasible alternative to adhesive sticker labeling without enhancing decay susceptibility.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Preeti Sood.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Etxeberria, Edgardo J.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0025064:00001

Permanent Link: http://ufdc.ufl.edu/UFE0025064/00001

Material Information

Title: Effects of Laser Labeling on the storage quality of selected fresh fruits and vegetables.
Physical Description: 1 online resource (77 p.)
Language: english
Creator: Sood, Preeti
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: labeling, laser
Horticultural Science -- Dissertations, Academic -- UF
Genre: Horticultural Science thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Although in common practice since the 1990's, fruit labeling gained greater significance after 9/11 due to its potential relevance to food safety and bioterrorism. Labeling of fruits and vegetables is important for internal accounting, traceability and safety concerns. Most fruits and vegetables sold in the US are marked with non-permanent stickers or adhesive tags. These stickers usually contain names, identification numbers (three, four or five digit codes), country of origin, brands, and logos. They provide required information and help distinguishing among produce with similar appearance but a different quality value, resulting in a more efficient checkout process. Despite the many advantages, sticker labeling technology has several drawbacks. These adhesive labels are expensive to purchase and apply, and application equipment requires clean up after the season. In addition, produce are often left with glue residue on their surfaces after sticker removal, resulting in blemished fruits. An emerging technology called 'Laser Labeling' could be considered a desirable alternative to the existing labeling system. Not only is each piece of produce permanently coded, but the specific information can be stored electronically for any period of time. The technique involves a low energy carbon dioxide laser beam which vaporizes the epidermal cells and reveals the underlying cells, preferably with a contrasting color. Produce epidermis is marked with alphanumerical dot matrix characters formed by pinhole depressions (Drouilllard and Rowland, 1997). However, these depressions can promote water loss and increase the number of potential entry sites for decay-promoting organisms. The present study addresses the most vital of these postharvest concerns. The experiments were conducted to measure water loss, peel appearance, and potential decay in laser labeled citrus fruit namely 'Honey tangerine' (Citrus reticulata), 'Ruby Red' grapefruit (Citrus paradisi), tomato (Lycopersicon esculentum) and pepper (Capsicum annum) during storage. Laser labeled fruit stored at their respective optimum temperature and two relative humidities (i.e., 95% and 65% RH) for 3 to 5 weeks depending on the commodity, showed no increase in decay compared to non-etched control fruit, suggesting that laser labeling does not facilitate decay. This was confirmed by experiments where the spores of common postharvest pathogen (such as Penicillium digitatum in citrus and Geotrichum candidum in tomato and pepper) were coated on fruit surfaces before and after laser labeling. In either case, no decay was observed. Further, in agar plates which contain a lawn of P. digitatum spores, the laser labeling reduced germination of spores in contact areas. Water loss from etched areas and label appearance were determined during storage. Water loss from waxed and etched citrus peel declined to control levels after 24 hours in storage. Label appearance deteriorated slowly in citrus fruit as compared to tomato and pepper and was proportional to laser energy levels and ambient relative humidity. Waxing the laser labeled surface in citrus fruit reduced water loss by 35% to 94%, depending on the wax formulation used. This study concludes that laser labeling provides the produce industry a feasible alternative to adhesive sticker labeling without enhancing decay susceptibility.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Preeti Sood.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Etxeberria, Edgardo J.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0025064:00001


This item has the following downloads:


Full Text

PAGE 1

1 EFFECTS OF LASER LABELING ON THE STORAGE QUALITY OF SELECTED FRESH FRUITS AND VEGETABLES By PREETI SOOD A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2009

PAGE 2

2 2009 Preeti Sood

PAGE 3

3 To my late grandmother Mrs. Vedvati Sood, my parents Mr. Subhash Chandra Sood and Mrs. Subhash Sood and my lovable brothers Prashant and Dhanvesh

PAGE 4

4 ACKNOWLEDGMENTS First and foremost, I would like to express my deepest thanks and gratitude to Dr. Edgardo Etxeberria, my committee chair, for providing me the opportunity to work on such an interesting project. I certainly feel myself fortunate enough to work with him and greatly appreciate all his guidance, encouragement and valuable advice he has given throu ghout my degree program. Many thanks to all my supervisory committee members, Dr. Steve Sargent, Dr. Mark Ritenour and Dr. Jan Narciso for serving on my committee and their help, support and valuable discussions towards the successful completion of thi s work. Special thanks to Chris Ference and James Holeton for helping me conduct my experiments. A huge appreciation for Pedro Gonzalez, my labmate for all his help whether it was fruit pick up, labeling, discussing current topics etc. I cannot be thankful enough to people at CREC, Paul Weikel, Tam Nyugen, John Henderson and Katherine Snyder for helping me in many ways. I express my thanks to Dr. Schumann for writing software which helped in assessing data. I am personally indebted to Greg Drouilliard, the inventor of the laser labeling machine as without his initiation this work would not have been conducted. I would also like to extend my special thanks to friends here in US especially Saurabh Morarka, Nicacio Cruz Huerta, and Desire Djidonou, and not to m ention my friends at CREC, Manjul Dutt and Karthik John Karrupiah for their help and support. Finally my deepest appreciation for my family members in India, my parents Mr. Subhash Chandra Sood and Mrs. Subhash Sood, my brothers Prashant and Dhanvesh for their love, motivation and support throughout my entire life. My thanks to friend Lovejot Chaudhary and her parents for their love and support till date.

PAGE 5

5 TABLE OF CONTENTS Page ACKNOWLEDGMENTS .................................................................................................................... 4 LIST OF TABLES ................................................................................................................................ 7 LIST OF FIGURES .............................................................................................................................. 8 LIST OF ABBREVIATI ONS ............................................................................................................ 11 ABSTRACT ........................................................................................................................................ 12 CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW ................................................................. 14 1.1 Fruit Anatomy and Classification .................................................................................... 15 1.2 Postharvest Concerns ........................................................................................................ 16 1.3 Trac eback ........................................................................................................................... 18 1.4 Produce Labeling............................................................................................................... 19 1.5 Laser Labeling ................................................................................................................... 21 2 EFFECTS OF L ASER LABELING ON THE QUALITY OF TANGERINES DURING STORAGE .............................................................................................................................. 25 2.1 Introduction ....................................................................................................................... 25 2.2 Materials and Methods ...................................................................................................... 25 2.2.1 Plant Material ........................................................................................................ 25 2.2.2 Exposure Time Selection ..................................................................................... 26 2. 2.3 Water Loss ............................................................................................................ 26 2.2.4 Effects of Waxes on Water Loss from Labeled Areas ....................................... 27 2.2.5 Peel Stability ......................................................................................................... 27 2.2.6 Decay Study .......................................................................................................... 28 2.2.7 Inoculation Study .................................................................................................. 28 2.3 Results and Discussion ..................................................................................................... 29 2.3.1 Water Loss ............................................................................................................ 30 2.3.2 Effects of Waxes on Water Reduction from Labeled Areas .............................. 31 2.3.3 Peel Stability ......................................................................................................... 32 2.3.4 Decay Study .......................................................................................................... 34 3 LASER ETCHING: A NOVEL TECHNOLOGY TO LABEL FLORIDA GRAPEFRUIT 37 3.1 Introduction ....................................................................................................................... 37 3.2 Materials an d Methods ...................................................................................................... 38 3.2.1 Plant Material ........................................................................................................ 38 3.2.2 Fruit Labeling ........................................................................................................ 38

PAGE 6

6 3.2.3 Select ion of Optimal Exposure Time .................................................................. 38 3.2.4 Determination of Water Loss ............................................................................... 39 3.2.5 Effect of Different Waxes on Water Loss from Labeled Areas ......................... 40 3.2.6 Peel Stability ......................................................................................................... 40 3.2.7 Decay Study .......................................................................................................... 41 3.2.8 Mold Inoculation Study ........................................................................................ 41 3.3 Results ................................................................................................................................ 42 3.3.1 Optimization of Exposure Time for Grapefruit Labeling .................................. 42 3.3.2 Measurements of Water Loss ............................................................................... 43 3.3.3 Effect of Waxes on Water Loss Retardation in Labeled Area ........................... 44 3.3.4 Peel Stability ......................................................................................................... 45 3.3.5 Decay Study .......................................................................................................... 47 3.4 Discussion .......................................................................................................................... 49 4 EFFECTS OF LASER LABELING ON THE POSTHARVEST STORAGE BEHAVIOUR OF TOMATO AND PEPPER FRUIT ........................................................ 53 4.1 Introduction ....................................................................................................................... 53 4.2 Materials and Methods ...................................................................................................... 54 4.2.1 Plant Material ........................................................................................................ 54 4.2.2 Fruit Labeling ........................................................................................................ 5 5 4.2.3 Selection of Optimal Exposure Time .................................................................. 55 4.2.4 Determination of Water Loss ............................................................................... 55 4.2.5 Peel Stability ......................................................................................................... 55 4.2.6 Decay Study .......................................................................................................... 56 4.2.7 Inoculation Study .................................................................................................. 57 4.3 Results ................................................................................................................................ 57 4.3.1 Optimum Exposure Time for Labeling ............................................................... 57 4.3.2 Measurements of Water Loss ............................................................................... 59 4.3.3 Peel Stability ......................................................................................................... 61 4.3.4 Decay Study .......................................................................................................... 65 4.4 Discussion .......................................................................................................................... 67 5 CONCLUSIONS ......................................................................................................................... 70 LIST OF REFERENCES ................................................................................................................... 73 BIOGRAPHICAL S KETCH ............................................................................................................. 77

PAGE 7

7 LIST OF TABLES Table page 2 1 Nine commercial waxes tested for water loss reduction from laser labeled areas ............. 27 2 2 Peel stability of laser labeled Honey Tangerine using 45s and stored at 10 oC and 65% RH ................................................................................................................................... 33 2 3 Peel stability of laser labeled Honey Tangerine using 45s and stored at 10 oC and 95% RH ................................................................................................................................... 33 2 4 Decay of non laser labeled and laser labeled Honey Tangerine using four different exposure time .......................................................................................................................... 34 3 1 Nine commercial waxes tested for water loss reduction from laser labeled areas ............. 40 3 2 Peel stability of laser labeled Ruby Red grapefruit using 45s and stored at 10 oC and 95% RH ............................................................................................................................ 46 3 3 Peel stability of laser labeled Ruby Red grapefruit using 45s and stored at 10oC and 65% RH ............................................................................................................................ 47 3 4 Decay of non las er labeled and laser labeled Ruby Red grapefruit using four different exposure time .......................................................................................................... 48 4 1 Peel stability of laser labeled tomato fruit stored at 12.5oC and 65% RH .......................... 61 4 2 Peel stability of laser labeled tomato fruit stored at 12.5oC and 95% RH .......................... 61 4 3 Peel stability of laser labeled pepper fruit stored at 7.5oC and 65% RH ............................ 63 4 4 Peel stability of laser labeled pepper fruit stored at 7.5oC and 95% RH ............................ 63 4 5 Decay of non laser labeled and laser labeled tomato fruit using four different exposure time .......................................................................................................................................... 65 4 6 Decay of non laser labeled and laser labeled pepper fruit using four different exposure time .......................................................................................................................................... 66

PAGE 8

8 LIST OF FIGURES Figure page 1 1 Laser labeling machine .......................................................................................................... 22 1 2 Laser Labels. A) Laser labeled pepper. B) Etched pear ..................................................... 22 2 1 Shrinkage rating scale ranges from 0 (no shrinkage) to 5 (total label collapse) ................ 28 2 2 A group phot ograph of labels etched using increasing exposure times .............................. 30 2 3 Surface area covered by 100 dots etched with exposure times ranging from 30 s to 140 s ..................................................................................................................................... 30 2 4 Water loss associated with labels etched usin g four different exposure times ................... 31 2 5 Percentage decrease in evaporation rate resulting fr om wax application on labeled areas ......................................................................................................................................... 31 2 6 Evaporation from unwaxed laser label, waxed laser label (using Carnuba 505), and control (n o label) during 7 d storage ..................................................................................... 32 2 7 Peel stability of etched fruit (45 s) during storage at 10 oC and 65% RH ........................ 33 2 8 Peel stability of laser labeled fruit (45 s) during storage at 10 oC and 95% RH .............. 33 2 9 Deca y of labeled fruit in storage. Fruit were labeled with four exposure times and stored at 10 C and 95% RH. ................................................................................................. 35 2 10 Fungal spores were spread on agar plates and laser labeled at 45 s (A) and laser labeling of 72 h grown hyphae (B) ....................................................................................... 35 2 11 Combined data from Figure 2 3 and 24 showing water loss and label exposure time and the oval area includes all readable labels ....................................................................... 36 3 1 Shrinkage rating scale for laser labeled Ruby Red grapefruit peel. Scale ranges from 0 (no shrinkage) to 5 (total labe l collapse) ........................................................................... 41 3 2 A group photograph of labels etched on Ruby Red grapefruit using different exposure times/energy levels. ................................................................................................ 42 3 3 Relationship between exposure time (30 to 140 s) and laser labeled surface area (covered by 100 dots) of Ruby Red grapefr uit .................................................................. 43 3 4 Water loss from laser labeled Ruby Red grapefruit peel usin g four different exposure times ........................................................................................................................................ 44

PAGE 9

9 3 5 Percentage decrease in the rate of water loss from laser labeled Ruby Red grapefruit peel by different commercial waxes compared to unwaxed label. ..................................... 44 3 6 Water loss from unwaxed label, waxed (carnuba) label and control Ruby Red grapefruit (no label) during 7 d storage at 10 C (50.0 F). ................................................ 45 3 7 Peel shrinkage of etched Ruby Red grapefruit during storage at 10 C (50.0 F) and 95% relative humidity. ........................................................................................................... 46 3 8 Peel shrinkage of etched Ruby Red grapefruit during storage at 10 C (50.0 F) and 65% relative humidity. ........................................................................................................... 47 3 9 Total decay of labeled Ruby Red grapefruit in storage. Fruit were labeled using 4 exposure times (35 s, 45 s 85 s and 120 s) at ambient temperature and stored at 10 C (50.0 F) and 95% relative humidity. ......................................................................... 48 3 10 Fungal hyphae grown for 72 h on potato dextrose agar. A) after a lawn of spores was laser labeled at 45 s, B) laser labeling of 72 h grown hyphae ........................................... 49 4 1 Shrinkag e rating scale for laser labeled tomato peel. Scale ranges from 0 (no shrinkage) to 5 (total label collapse). .................................................................................... 56 4 2 Shrinkage rating scale for laser labeled pepper peel. Scale ranges from 0 (no shrinkage) to 5 (total label collapse). .................................................................................... 56 4 3 A group photograph of laser labels on tomato fruit using different exposure times/energy levels. ................................................................................................................ 58 4 4 A group photograph of labels etched on pepper fruit using different exposure times/energy levels. ................................................................................................................ 58 4 5 Relationship between exposure time (30 to 120 s) and laser labeled surface area (covered by 100 dots) of tomato fruit. .................................................................................. 59 4 6 Relationship between exposure time (30 to 120 s) and laser labeled surface area (covered by 100 dots) of pepper fruit. .................................................................................. 59 4 7 Water loss from laser labeled tomato fruit peel using four different exposure times. ..... 60 4 8 Water loss from laser labeled pepper fruit peel usin g four different exposure times ........ 60 4 9 Peel shrinkage of laser labeled tomato fruit during storage at 12.5C (55 F) and 95% relative humidity. ................................................................................................................... 62 4 10 Peel shrinkage of laser labeled tomato fruit during storage at 12.5 C (55 F) and 65% relative humidity. ................................................................................................................... 62 4 11 Peel shrinkage of laser labeled pepper fruit during storage at 7C (45 F) and 95% relative humidity. ................................................................................................................... 63

PAGE 10

10 4 12 Peel shrinkage of laser labeled pepper fruit during storage at 7C (45 F) and 65% relative humidity .................................................................................................................... 64 4 13 Unwaxed and waxed laser labeled tomato fruit during storage. ......................................... 64 4 14 Total decay of labeled tomato fruit in storage. ..................................................................... 66 4 15 Total decay of labeled pepper fruit in storage. ..................................................................... 66

PAGE 11

11 LIST OF ABBREVIATIONS CO2 Carbon Dioxide P.L.U. Price Look Up RH Relative Humidity

PAGE 12

12 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EFFECTS OF LASER LABELING ON THE STORAGE QUALITY OF SELECTED FRESH FRUITS AND VEGETABLES By Preeti Sood August 2009 Chair: Edga rdo Etxeberria Major: Horticultural Sciences Although in common practice since the 1990s, fruit labeling gained greater significance after 9/11 due to its potential relevance to food safety and bioterrorism. Labeling of fruits and vegetables is important for internal accounting, traceability and safety concerns. Most fruits and vegetables sold in the US are marked with non -permanent stickers or adhesive tags. These stickers usually contain names, identification numbers (three, four or five digit codes), country of origin, brands, and logos. They provide required information and help distinguishing among produce with similar appearance but a different quality value resulting in a more efficient checkout process. Despite the many advantages, sticker labeli ng technology has several drawbacks. These adhesive labels are expensive to purchase and apply, and application equipment requires clean up after the season. In addition, produce are often left with glue residue on their surfaces after sticker removal, res ulting in blemished fruits. An emerging technology called Laser Labeling could be considered a desirable alternative to the existing labeling system. Not only is each piece of produce permanently coded, but the specific information can be stored electron ically for any period of time. The technique involves a low energy carbon dioxide laser beam which vaporizes the epidermal cells and reveals the underlying cells, preferably with a contrasting color. Produce epidermis is marked with alphanumerical dot matrix

PAGE 13

13 characters formed by pinhole depressions (Drouilllard and Rowland, 1997). However, these depressions can promote water loss and increase the n umber of potential entry sites for decay promoting organisms. The present study addresses the most vital of these postharvest concerns. The experiments were conducted to measure water loss, peel appearance, and potential decay in laser labeled citrus fruit namely Honey tangerine ( Citrus reticulata ), Ruby Red grapefruit (Citrus paradisi ), tomato ( Lycopersicon esculentum ) and pepper ( Capsicum annum ) during storage. Laser labeled fruit stored at their respective optimum temperature and two relative humidit ies (i.e., 95% and 65% RH) for 3 to 5 weeks depending on the commodity, showed no increase in decay compared to non-etched control fruit, suggesting that laser labeling does not facilitate decay. This was confirmed by experiments where the spores of commo n postharvest pathogen (such as Penicillium digitatum in citrus and Geotrichum candidum in tomato and pepper) were coated on fruit surfaces before and after laser labeling. In either case, no decay was observed. Further, in agar plates which contain a la wn of P. digitatum spores, the laser labeling reduced germination of spores in contact areas. Water loss from etched areas and label appearance were determined during storage. Water loss from waxed and etched citrus peel declined to control levels after 2 4 hours in storage. Label appearance deteriorated slowly in citrus fruit as compared to tomato and pepper and was proportional to laser energy levels and ambient relative humidity. Waxing the laser labeled surface in citrus fruit reduced water loss by 35% to 94%, depending on the wax formulation used. This study concludes that laser labeling provides the produce industry a feasible alternative to adhesive sticker labeling without enhancing decay susceptibility.

PAGE 14

14 CHAPTER 1 INTRODUCTION AND LIT ERATURE REVIEW Fresh fruits and vegetables have been a part of the human diet in all cultures (Willis, et al., 1998). The nutritional importance of fresh fruits and vegetables was first recognized in England during the early part of the17th century for the ability of citrus to cure the scurvy disease among the naval personnel. Their complete nutritional benefits were not known until recently however. Most fruits and vegetables are high in water content (80 90% of fresh weight) and low in protein and fat content. Carbohydrates content in fruits and vegetable is low except in certain starchy vegetables, for example cassava, potato, sweet potato, sweet corn and fruits such as dates. Lipids comprise less than 1% of most fruits and vegetables and are associated with cell membranes and the protective cuticular surface layer Fruits and vegetables are also rich sources of certain vitamins, especially beta carotene (precursor of vitamin A) and vitamin C (ascorbic acid). Approximately 95% of the human dietary vitamin C comes from fruits and vegetables. Fruits, such as citrus, strawberry and kiwifruit, are outstanding sources of this vitamin. All vegetables contain small amounts of the B -complex vitamins, but their nutritive value is attributed mainly to beta carotene, vitamin C and folic acid. The most abundant mineral found in fruits and vegetables is potassium followed by calcium. Minerals like magnesium, iron and phosphorus are also present at substantial levels. Their high water and fiber content helps in digestion and utilization of foods. Fruits and vegetables are good sources of naturally occurring antioxidants that may help protect against free radicals and oxidative damage, thereby lowering cancer and cardiovascular disease risk (Cao et al., 1996; Cohen et al., 2000). These antioxidants include vitamin C, glucosinolates, flavonoids carotenoids and polyphenolics (Larson, 1988). For example limonin and nomilin in citrus fruits are believed to help inhibit the development of certain forms of cancer (Lam and Hasegawa, 1989; Miller et al., 1989). Many studies have

PAGE 15

15 stated that a frequent intake of cruciferous vegetables, such as broccoli, cauliflower, and cabbage, could also be helpful in protecting against cancer (De Long et al., 1986, Zhang et al., 1995). Avocado is a very rich sourc e of monounsaturated fats (50 75%) and recent studies reported the benefits of avocado with respect to heart diseases. The United States Department of Agriculture food pyramid or 5 A DayFor Better Health dietary program suggests 2 servings of fruits an d 3 servings of vegetables every day per individual (Center for Nutrition Policy and Promotion, 2000). World fruits and vegetable production is estimated around 388 MT and 486 MT respectively, with China being the worlds largest producer of both fruits an d vegetables followed by India. According to FAO, China contributes nearly 50% of the worlds vegetable production and 16% of the fruit production. India accounts for about 8% of the worlds fruit production and 15% of the total vegetable production. US is a dominant player in the international trade of fruits and vegetables and accounts for about 25% of world trade. As far as production within the US, California leads by producing more than 50% of the all fruits and vegetables. Florida is the second larges t producer with 8% and 14% of the US vegetable and fruit production respectively (NASS, 2000). In general, production of fruits and vegetable crops worldwide has increased over the past few years. 1 1 Fruit Anatomy and Classification Botanically, fruit is defined as a ripened or mature ovary including seeds and other associated plant plants such as the receptacle (e.g.,strawberry), bracts (e.g., apple) and peduncle (e.g., pineapple). Fruits can be classified various ways. Based on th e growing conditions, fruits are divided into temperate, tropical and sub -tropical types. Temperate fruits are grown in places with distinctly cold winter. These are suited to higher elevations and can withstand frost such as apple, plum, peach and pear. T ropical fruits require moist warm climate and can bear dry

PAGE 16

16 weather (e.g., banana, mango, guava, papaya). Fruits such as citrus, grapes, loquat etc., are sub tropical in nature. These fruits are grown in between temperate and tropical climates, and can with stand low temperature and frost but only for short period. Based on their respiration patterns and ethylene production during maturation and ripening, fruits and vegetables are categorized as either climacteric or non climacteric (Biale, and Young, 1981). The term climacteric was first used in apples for the characteristic rise in the respiration rate that accompanies maturation and ripening (Kidd and West, 1924). The ripening process of climacteric fruits (e.g., apple, banana, mango) is accompanied by a peak in respiration and a simultaneous burst of ethylene production (Giovannoni, 2004). When exposed to exogenous ethylene, climacteric fruits undergo autocatalytic ethylene production. On the contrary, non climacteric fruits (e.g., citrus, strawberry) do not show increased ethylene production and respiration during ripening (Knee et al., 1977). Vegetables in general are divided into three main groups: 1) seeds and pods; 2) flowers, buds, stems and leaves; and 3) bulbs, roots and tubers. Some immature frui t (cucumber, zucchini, beans) and ripe fruit types (tomato, avocado, capsicum, egg plant) are also consumed as vegetables. 1 2 Postharvest Concerns Fresh fruits and vegetables are living tissues and therefore highly perishable in nature. They continue their bi ological processes after harvest and subject to changes (Kader, 2002). Their quality rapidly deteriorates after harvest. During handling and transportation, these fresh commodities are subjected to impact, compression, vibration, bruising, low/ high temper ature, humidity conditions and pathological attacks. These may lead to loss in the quantity and quality of these fresh commodities between harvest and consumption. The magnitude of these postharvest losses is higher in developing countries (20 50%) than in developed countries (5 25%) depending on the commodity, cultivar, infrastructure and handling practices. These losses

PAGE 17

17 can be reduced by implementing proper handling and storage techniques. Proper postharvest management facilitates the continuous and timel y supply of fresh fruits and vegetables. The deterioration of fresh commodities can be the result of physiological breakdown due to natural ripening, water loss, temperature injury, or invasion by pathogens (Thompson et al., 1998). These harvested fresh co mmodities exhibit enhanced respiration and ethylene production. Respiration is a process by which organic compounds are broken down into simple sugars and further with a release of heat ATP and energy resulting in reduced nutritional quality as well. Withi n the range of 4o to 35oC every 10 oC rise in temperature causes 2 3 fold increase in the respiration rate thereby shortening the shelf life of the commodity (Pittenger, 2002). Fresh commodities are stored at low temperature to slow down respiration and senescence which in turn lengthen the postharvest shelf life ( Kader, 2002). Since fresh horticultural commodities vary in composition, morphology (roots, stems, leaves, flowe rs, fruits) and physiology, t hey have different postharvest requirements and recom mendations for maintaining maximum postharvest shelf life. Storage life can vary from < 2 weeks to > 16 weeks depending on the commodity. For example, green onions can be stored for less than 2 weeks as compared to dried onions which can be held at 0 oC for 8 10 weeks. Citrus fruits in general can be stored for moderate period s of time. Grapefruit can be stored for 6 8 weeks at 12 15 oC and 90 95% RH. Fully ripe tomatoes can be stored optimally for 3 5 days at 7 10 oC and 8595% RH, in contrast to matu re green which can be kept for 14 days at 12.5 15 o C. Storage of peppers at 7.5 oC is best for maintaining maximum shelf life of 3 5 weeks. Fresh horticultural crops are a package of water. Water loss equates to loss in saleable weight, textural quality (softening, flaccidity, loss of crispiness, juiciness) and nutritional quality. Weight loss of only 5 % can make the fresh produce appear wilted or shriveled and may render

PAGE 18

18 them unmarketable. However, high (RH) (90 95%) in conjunction with low temper ature and low surrounding air velocity helps in reducing wa ter loss. In general, fruits store best at 85 to 95% RH and vegetables at 90 to 98% RH in order to retain freshness. Besides holding the produce at high humidity, transpiration or water loss can be reduced by applying waxes and other surface coatings or wrapping with plastic films. Fruits that are normally waxed include citrus, apples, pear, avocado, cucumber, tomato and pepper (Baldwin, 1994). Packaging is one of the most important postharvest trea tments required for marketing of fresh produce. It also plays a crucial role in preventing deterioration losses and improving shelf life of produce. More than 1,500 types of packages are used for produce in the US. Packaging material includes corrugated f iber board boxes, plastic trays, mesh bags, woven sacks, stretch films, shrink wrapping etc. Commodities such as potatoes, onions, citrus, sweet corn are packed in mesh bags. Besides making attractive displays for supermarket, these bags provide adequate v entilation for produce. Plastic bags (polyethylene films/wraps) are commonplace in packi ng fresh fruits and vegetables such as w rapping of an individual stalk of cauliflower, cabbage, and lettuce. High value produce items such as berries (strawberry, blueb erry, raspberry), small fruits and datil peppers are most often packed in clamshells. Besides being inexpensive, clamshells provide great protection to the produce and make a very pleasing consumer package. 1 3 Traceback The Center for Disease Control and Pr evention (CDC) estimated that food borne diseases causes approximately 76 million cases illnesses, 350,000 hospitalizations and 5,000 deaths annuall y in US. Produce is considered a leading vehicle of foodborne illnesses and was responsible for more than half of illnesses associated with foodborne outbreaks between 1998 and 2004. From 19952006, 22 produce outbreaks have been reported in the US Hepatitis cases by consumption of green onions from Mexico in 2003 and Salmonella outbreak of 2004 in Roma

PAGE 19

19 toma toes led to deaths of thousands. Furthermore, in 2006, 205 cases of E. coli O157:H7 illnesses transmitted by bagged spinach were reported in 26 states. The same year, Salmonella outbreaks linked to tomatoes accounted for the death of thousands. Salmonella is the most common bacterial agent causing food borne illness. Approximately, 1.4 million illnesses and 600 deaths are caused by Salmonella each year in US (Mead, et al., 1999). In 2005, US Center for Disease Control and Preventions Emerging Infectious Pr ogram under the Food-borne Diseases Active Surveillance Network reported 6471 confirmed cases of Salmonella (Center for Disease Control and Prevention, 2006). However, difficulty in tracing the source of tainted food items stifled the investigation of thes e past outbreaks. Due to the difficulties in tracing back produce, more emphasis has been lately placed on traceability and other food safety concerns of the fresh produce industry. Traceability is the ability to trace food items back to their source (gr owers, packers) and through all commercial channels. It is considered as good agricultural practices (GAP) and intended to minimize the liability and preventing occurrence of food security problems. (Center for Food Safety and Applied Nutrition,1998). O wing to the current food safety concerns, track and trace systems for the product in international trade, particularly in sea and air freight are becoming increasingly important. There is a need for high quality identification (labeling) and information sy stems. 1 4 Produce Labeling In 2002, US congress passed the Public Health Security and Bioterrorism Preparedness and Response Act, also known as Bioterrorism Act. The purpose of the Act was to protect the countrys food supply against the intentional contam ination. Section 305 of this Act specifies the requirement for labeling of products including produce. Since then price look up (P.L.U.) labeling of produce has become commonplace. Price look up (P.L.U.) labeling of the fresh

PAGE 20

20 fruits and vegetables has ga ined marked attention in the United States over the last decade. PLU codes are normally used on items that are sold in loose state or bunch (for example, an individual orange or bunch of greens). The PLU index coding contains four digit identification number developed by the Produce Electronic Board (PEIB) to identify the variety of fruit and vegetables (PEIB, 1995). This board was established to upgrade the electronic data collection and communication of fresh produce sales (Etxeberria et. al., 2006). S o far, the most commonly used labeling system consists of adhesive tags/stickers applied to individual fruit and vegetable on the packing line (Varon and Paddock, 1978). The first fruit label is dated back in 1929 and was created by a British company Elder s & Fyffes Ltd. (Anonymous). Produce labeling started with the labeling of bananas. Labeling of oranges, grapefruit, tomatoes, pepper and others with individual stickers is accomplished by passing the individual fruit beneath a cassette of gummed labels a pplied with gentle pressure. The PLU stickers usually contain names, identification number (three, four or five digit code), country of origin, brands and logos. These are helpful for grocery clerks, making it easy to distinguish among produces with simila r appearance, but a different quality value As a consequence, sticker labeling also saves time at the checkout counter. Despite the many advantages, sticker labeling technology has several drawbacks. Besides being expensive, these stickers require c lean up after the season, as they gummed up along the packingline. Fruits are often left with glue residue on its surface after sticker removal resulting in blemished fruits. In addition, these stickers are not permanent and can be detached at any postharv est handling stage. It is also not possible to make P.L.U. number changes in a timely manner.

PAGE 21

21 1 5 Laser Labeling Laser labeling is a technology where low -energy CO2 lasers beam (10,600 nm) (Drouilllard and Rowland, 1997) is used to mark a produce. The genera l etching process is similar to the one used in electronics manufacturing and medical treatments and explained by Hecht (1994). The laser labeling is a sterile, non-contact, high speed, efficient method which provides a sharply defined permanent mark. Lase r beam etches the outermost pigment layer of the produce skin to reveal a contrasting sub-layer. Etched markings are formed in dot matrix pattern letters and numbers, each dot created by pinhole depressions (Etxeberria et al., 2006). The laser labeling app aratus has an articulating arm with an optical head attached to it (Figure 1 1) and can be positioned at a variety of positions related to the piece of produce. The laser head emits a high intensity and controlled light beam which is directed along a prede termined path to etch the epidermis of the produce. The mark is produced by vaporizing the wax portion of the skin and desiccating the underlying cell layers under where the high intensity beam contacts the skin. The contact time of the beam is yet limited to reduce or prevent transfer of heat energy or thermal degradation or breakdown of the underlying tissues. The whole system is controlled by a programmable electronic interface, which is a high speed programmable logic controller (PLC). The graphic int erface create files to store specific equipment settings required for different varieties of fruit, different PLU codes, and other related information. Such settings of the equipment allow the system to sense differences in surface texture and color and ma ke necessary adjustments. In order to operate the laser labeling machine, the user enters the desired code and system parameters using a keypad. The PLC uses this input and the one from the attached external sensors to make the necessary calculations and adjustments in order to emi t laser beam. The system can etch PLUs, trace codes, and date and time stamps in 14 different languages; it can

PAGE 22

22 also convert any kind of image into a matrix that can be printed. The processing speed of the laser labeling machine is up to 17 fruits per second. It can be used in various fruits and vegetables such as cucumber, pepper, potato, avocado, tomato, apple, citrus, pear, watermelons and even onions (whose epidermis is only 18 m deep) (Figure 1 2A and Figure 1 2B). For fruits such as citrus that do not have good contrast, FDA approved food coloring is used for contrast enhancement. Figure 1 1 Laser labeling machine A B Figure 1 2 Las er Labels A ) Laser labeled pepper. B) Etched pear Other advantages of this laser technique are that the label are permanent, do not require additional adhesives, and labeling information can be stored electronically for any period of Laser output User interface Articulating arm

PAGE 23

23 time. In the long run, laser system offers production cost cutting as we ll. The machine requires little or no supervision, thereby reducing operating cost to a greater extent. Furthermore, these labels do not create any clutter, leave no glue residues on the produce surface, and above all, offers the potential to track and tra ce the origin of the produce. The system is more flexible as PLU information can be changed number of times before labeling the fruit. Furthermore, the laser labels are environment friendly. The barriers to the acceptance of this technology are the presump tions that it is not safe and may leads to early produce decay, as pinhole depressions make the surface more susceptible to water loss, potential pathogen attack and other postharvest losses. Water loss from harvested fruit occurs continuously and may be r esponsible for loss of quality and marketability of fruit. The natural cuticular wax layer of citrus fruit protects against water loss. Laser labeling pinholes rarely penetrate beyond the third layer of epidermal and/or underlying cells. Underlying tissue s deposit additional wax, lignin and phenolic suggesting a self healing process as noticed previously in avocado and tomato (Exteberria et.al, 2006). Brown (1973) also reported lignin deposition in the injured citrus peel. Significant deposition of lignin was noticed around the wounds inoculated with Geotrichum candidum in lemon peel (Baudoin and Eckert, 1985). Some changes were observed at the wound and in surrounding peel tissues after 1 -4 days of wounding in satsuma mandarins (Kinay et al., 2005). The l ignin like material (L -LM) is induced by wounding of fruit in cucumber (Walter et al., 1990) and impedes the hyphal penetration of Penicillium in lemons (Stange and Eckert, 1994). The effectiveness of natural cuticular barrier diminishes by the soaking, wa shing and brushing of the fruit during packinghouse operations. Therefore, commercial wax coating is applied to the fruits to compensate the loss of natural protection. In addition, waxes applied for

PAGE 24

24 other reasons such as reduction of water loss, improved appearance and some level of protection against decay. The composition and properties of a typical self -polishing, fungicide -containing water wax was described by Newhall and Grierson (1955). In general the rate of water loss from waxed fruit is comparable to unwashed fruit. Commercial use of waxes is extensive for fruits, especially apples and citrus, and some vegetables such as tomatoes, melons and cucumbers. Limited use is observed in asparagus ( Asparagus officinalis ) peppers, carrots, radish, potatoes, squash and turnip (Baldwin, 1994). Produce may be exposed to pathogens both prior to harvest in the field and also after harvest while handling, storage and transit. Most pathogens required wounds or other unprotected areas to enter the fruit tissue. Laser labeling disrupts the natural protective barrier seemingly creating open wounds. Studies on anatomical, morphological and physical aspects of the laser labeling cavities states that the cells underlining etch depression increase phenolic and lignin dep osits in their walls (Etxeberria et al., 2006) yet the degree of protection has not been investigated. The microbial community of bacteria and yeasts on the surfaces of fruit and vegetables can influence the development of postharvest rots of fruit and vegetables (Blakeman, 1985; Spurr, 1994). Although it was shown previously that the alphanumeric codes produced by the laser beams do not support the infiltration and survival of spoilage organism like Salmonella spp. on tomato surface (Yuk et. al., 2007) l ittle additional information is available regarding the decay of laser labeled fruits. The present study addresses potential complications brought about by microflora population and various other postharvest losses on the laser labeled fruit in comparison to non laser labeled.

PAGE 25

25 CHAPTER 2 EFFECTS OF LASER LAB ELING ON THE QUALITY OF TANGERINES DURING STORAGE 2 1 Introduction Citrus is th e major fruit crop of Florida. The state contributes nearly 58% of all U.S. tangerine production, 78% of w hich goes to the fresh market. With the possibility of bioterrorism and other economic concerns, labeling of fresh market produce has become increasingly r elevant in the last few years. In addition to making check -out easier, labeling helps with the trac king and traceability of the pr oduce. Laser labeling is emerging as an alternative to traditi onal stickers/adhesive labels. With this method, a low energy CO2 beam creates pinhole depressions into the product surface that forms the alphanumeric label infor mation (Drouilliard and Rowland, 1997). However, these pinhole depressions disrupt the protective barrier of the produce and can potentially become entry sites for decay organisms and sites for enhanced water loss, despite the significant amounts of wax a nd lignin deposited by surrounding and underlying cells (Etxeberria et al., 2006). Little information is available on the impact of this new technology on the overall quality of the labeled produce, especially its effect on water loss and decay during s torage. The present study investigates the effects of laser labeling on the quality of Honey tangerine (Citrus reticulata Blanco) during storage. 2 2 Materials and Methods 2 2 1 Plant Material Honey tangerine ( Citrus reticulata Blanco) fruit was purchased in October 2008 from Haines City CGA, Haines City, Fla. after commercial washing and waxing. Fruit was labeled using a low energy CO2 laser labeling machine (Model XY mark 10, Sunkist Growers Inc., Fontana, Calif.) at the Citrus Research and Education center in Lake Alfred as described earlier (Etxeberria et al., 2006).

PAGE 26

26 2 2 2 Exposure Time Selection A label code M1 was etched on fruit surfaces using 18 different exposure times corresponding to 30 s to 140 s label duration (Etxeberria et al., 2006). The energy level used was the recommended 0.000752 W/dot. To enhance resolution, labels were dyed with fruit based black color. Five replicates per exposure time were used. Images of the dyed label were taken using a Canon Powershot S31S digital camera mounted on a Wild Heerbrugg 165083 stereoscope. Surface area altered by the label was measured using an Image Processing Software. Total area was calculated based on number of pixels within the area covered by the laser depressions with 1 pixel corresponding to 50 m2. 2 2 3 Water Loss Water loss from the fruit surface was measured using a modified leaf porometer ( Decagon Devices, Pullman, Wash. ). To estimate water loss as a function of exposure time, an etched rectangle of 7 x 8 dots matrix pattern was used for eac h of four exposure times, namely low (35 s), commercially recommended (45 s), medium (85 s ), and high (120 s). The modified leaf porometer was placed on the top of the treate d area immediately after laser labeling until a stable reading was obtained. Water vapor diffusion from fruit and vege tables was calculated using Eq. 2 -1 based on Ficks law where water vapor flux density or evaporation rate is the product of vapor conductance (gv) and the difference between vapor concentration at the evaporating surface (Cvs) and water vapor concentration in atmosphere (Cva). Values are expressed as mmol m2 sec1. The modified leaf porometer (Decagon Devices, Pullman, Wash.) estimates the value for water vapor conductance (gv) which can be computed in the equation below to obtain evaporation rate. F = gv (Cvs Cva) (2 1)

PAGE 27

27 Vapor concentration was calculated using Eq. 2 2 where ea is the vapor pressure (kPa) which is a function of temperature, and pa is the atmospheric pressure (kPa) (information courtesy of Dr. Doug Cobos, Decagon Devices, Inc., Pullman, Wash.). Cv = ea / pa (2 2) 2 2 4 Effects of Waxes on Water Loss from Labeled Areas Nine different commercial waxes were tested for moisture loss reduction from the labele d area. Fruit were labeled using a single exposure time ( 45 s) and wax applied using a painters brush. Evaporation rate measurements of the labeled surface were determined before and after waxing along with control (no label on fruit). Each experiment was replicated 30 times. The second part of the experiment followed water loss from the waxed etched area during storage. Half of the total number of etched rectangles (2 rectangles per 30 fruit) were waxed with one of the waxes tested (highest reductio n in water loss) and kept at 10 oC and 95% RH for 7 d. Daily measurements of evaporation rate of the waxed label, unwaxed label, and control (no label on fruit) were carried out with the porometer. Table 2 1 Nine commercial waxes tested for water loss reduction from laser labeled areas Names of waxes Names of Manufacturers Deco shellac Deco, Monrovia, CA Carnuba 505 Deco, Monrovia, CA Carnuba + TBZ Deco, Monrovia, CA Carnuba 231 Deco, Monrovia, CA Carnuba blend Deco, Monrovia, CA Citrus wax shellac HDH Agriproducts, Tavares, FL HDH Carnuba HDH Agriproducts, Tavares, FL Pace Carnuba Pace International, Visalia, CA Organic Carnuba Pace International, Visalia, CA 2 2 5 Peel Stability The label Florida citrus was etched on the fruit using 45 s for exposure time, and fruit kept at 10 oC in two different relative humidity levels (i.e., 65% and 95% RH) for 4 weeks. Five

PAGE 28

28 replicates (1 replicate = 1 box = 60 fruit) per exposure time and control (nonlabeled fruit) were used. Weekly examination of the label appearance and surrounding area was done. Peel stability was determined on the basis of a visual rating scale according to the shrinkage of the skin around labe l as follows: 0 (no shrinkage), 1 (very low), 2 (low), 3 (medium), 4 (high), and 5 (very high) (Figure 2 1). For better visualization, we show the scale using grapefruit. Figure 2 1 Shrinkage rating sc ale ranges from 0 (no shrinkage) to 5 (total label collapse) 2 2 6 Decay Study Fruit were labeled using the commercially suggested exposure time ( 45 s) and stored for 5 weeks at 10 oC and 95% RH. Five replicates of labeled and control (nonlabeled fruit) (1 replicate = 1 box = 60 fruit) were used. Fruit were examined weekly for decay. 2 2 7 Inoculation Study Experimental areas on the fruit were subjected to four treatments. The four treatments were: 1) inoculation of fruit prior to labeling, 2) inoculation after labeling, 3) inoculation on waxed label, and 4) waxing of inoculated label. Fruit were inoculated with a spore suspension of Penicillium digitatum Link (105) was used as in oculum. Inoculum was prepared by growing P. digitatum Link on potato dextrose agar (BD/Difco, Sparks, MD) plates for 7 d. One hundred microliters of sterile 0.1% Tween 20 was placed on the plate surface and the spores were liberated from the colony and pla ced in sterile phosphate buffer (0.1%; 7.2 pH). Spore

PAGE 29

29 concentration was determined by counting cells with a hemocytometer (Hausser Scientific, Horsham, PA). Inoculum was adjusted to 105 cells /mL. Inoculation was carried out by spreading a thin layer of spore suspension onto the fruit peel before and after labeling using a sterilized small brush. Inoculation was carried out by applying a thin layer of spore suspension over the experimental areas using a painters brush. Inoculated fruit was stored at 10 oC and 95% RH for 3 weeks and examined for decay weekly. Labeling was done using one exposure time (45 s). Thirty replicates consisting of one fruit each were used for all four treatments. In a separate experiment, Penicillium spore suspension was sp read on potato dextrose agar plates (BD/Difco, Sparks, Md.) The plates were laser labeled and observed under the microscope immediately and 72 h after labeling. Each experiment was repeated five times. 2 3 Results and Discussion The visual effect of inc reasing laser labeling exposure time on tangerine peel is shown in Figure 2 2. At the lowest possible exposure time of 30 s, the label was faint and hardly visible, whereas at the highest exposure time of 120 s, the etch markings merged into solid lines Calculations of laser etched surface area were done using Image processing software. In general, the area covered by the etched markings increased with increase in exposure time (Figure 2 3). The rate of peel surface area disruption declined at higher exposure times as etch markings began to merge. Etched markings created with 45 s exposure time were selected as the best among all energy levels on the basis of visual appearance and area covered. This exposure time (45 s) creates less surface disrup tion while generating readable code. However, from F igure 2 2 and 2 3, higher exposure times create darker labels without significantly increasing peel disruption.

PAGE 30

30 Figure 2 2 A group photograph of labels etched using increasing exposure times Figure 2 3 Surface area covered by 100 dots etched with exposure times ranging from 30 s to 140 s Each point represents an average of five replicates. Ver tical lines represent SE 2 3 1 Water Loss Moisture content is one of the important factors determining the marketable quality of produce. Fruit and vegetables start losing moisture immediately after harvest (Ben Yehoshua and Rodov, 2002). However, laser -gener ated etched markings are physical pinholes penetrating through the cuticle and into the epidermis rendering the produce surface more susceptible to water loss than non etched surfaces. There was a sharp increase in the rate of water loss between the 35 and 45 s exposure times (Figure 2 4). The difference in the rate of water loss was less pronounced at higher exposure times.

PAGE 31

31 Figure 2 4 Water loss associated with labels etched using four different expo sure times. Each bar represents an average of 20 samples 2 3 2 Effects of Waxes on Water Reduction from Labeled Areas Natural waxes on the epidermis play a vital role in retaining moisture in fruit and vegetables (Kader, 2002). The openings created by laser l abeling disrupt the natural waxy coating on the surface of produce. In this experiment, all nine commercial waxes that were applied helped in reducing water loss by sealing the etched area. However, significant differences in the capability of these waxe s to prevent water loss were observed. Among all waxes, three reduced water loss by >80%, with Carnauba 505 resulting in the highest protection (86% reduction in water loss) (Figure 2 5). Figure 2 5 Percentage decrease in evaporation rate resulting from wax application on labeled areas. Each wax was tested on 30 separate labels b a a a 0 2 4 6 8 10 35 45 85 120 Evaporation rate (mmol. m 2 sec 1 ) Energy (s) LSD3.08 a a ab ab b ab b b 0 10 20 30 40 50 60 70 80 90 100 % Decrease in evaporation rate Waxes a

PAGE 32

32 Rate of water loss from unwaxed labeled areas declined with time of storage. There was a sharp decline in the rate of water loss 24 h after labeling, which continued to decrease before reaching a constant value (Figure 2 6). Water loss from waxed labeled (using Carnuba 505) areas was nearly equal to control unlabeled areas, which confirms the importance and necessity of waxing the fruit after labeling. Figure 2 6 Evaporation from unwaxed laser label, waxed laser label (using Carnuba 505), and control (no label) during 7 d storage. Each point represents 30 samples. Verti cal lines represent SE 2 3 3 Peel Stability The rate of water loss from fruit depends upon the vapor pressure deficit between the commodity and surrounding air, which is influenced by temperature and relative humidity. Relative humidity has a direct effect on rate of moisture loss from produce (Forbes and Watson, 1992). Fruits are commonly stored at labels at both 65 and 95% RH, began to show low levels of shrinkage within a week (Figure 27 and 2 8). Degr ee and percent fruit showing visible signs of shrinkage on the label increased with storage time, exposure time (data not shown), and was inversely proportional to RH. However, even at the end of 5 weeks, labeled fruit peel at 95% RH had minimal shrinkage 0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 24 0 24 48 72 96 120 144 Evaporation rate (mmol/m 2 sec) Time after labeling (h) Unwaxed label Waxed label Control

PAGE 33

33 Table 2 2 Peel stability of laser labeled Honey Tangerine using 45s and stored at 10 oC and 65% RH Percentage of total fruit Time after labeling (weeks) 1 (very low) 2(low) 3(medium) 4(high) 5(very high) 1 5.28 1. 66 0 .32 0 0 2 6.3 3.66 0 .66 0 0 3 2.64 5. 28 2.98 0 .32 0 4 2.96 4.64 4.62 1.96 0 Figure 2 7 Peel stability of etched fruit (45 s) during storage at 10 oC and 65% RH Table 2 3 Peel stability of laser labeled Honey Tangerine using 45s and stored at 10 oC and 95% RH Percentage of total fruit Time after labeling (weeks) 1 (very low) 2(low) 3(medium) 4(high) 5(very high) 1 1.28 0.32 0 0 0 2 2.6 0.66 0 0 0 3 0.98 1.96 0 0 0 4 1.64 1.96 0 .64 0 .32 0 Figure 2 8 Peel stability of laser labeled fruit (45 s) during storage at 10 oC and 95% RH 0 5 10 1 2 3 4 % of total fruit Storage after labeling (weeks) 1 (very low) 2 (low) 3 (medium) 4 (high) 5 (very high) 0 5 10 1 2 3 4 % of total fruit Storage after labeling (weeks) 1(very low) 2 (low) 3 (medium) 4 (high) 5 (very high)

PAGE 34

34 2 3 4 Decay Study Citrus fruits are relatively non perishable and can be stored for long periods. Tangerine, in general, can be stored at 5 8 oC at 90 95% RH for 2 6 weeks (Arpaia and Kader, 2006). Decay of citrus fruit in storage is one of the major factors responsible f or postharvest losses. Citrus fruits in storage are vulnerable to various decay organisms such as fungi (e.g., Penicilium spp.) and bacteria (Kader, 2002). Laser labeled fruit held at 10 C and 95% RH conditions showed no decay around etched area (Figure 2 9). All decay during the storage period was independent from the labeled areas, the most common being stem end rot. In the present study, decay rate of the fruits labeled with all the four exposure times were similar to the control (non-labeled fr uit) which confirms that laser labeling does not enhance decay (Figure 2 9). These results are in accordance with those of Yuk et al. (2007) where laser labeling did not facilitate Salmonella infiltration and survival in tomato. Table 2 4 Decay of non laser labeled and laser labeled Honey Tangerine using four different exposure time Total Decay (%) Time after labeling (weeks) Control 35 s 45 s 85 s 1 20 s 1 0 0 0 0 0 2 0 0 0 0 0 3 5 7.5 5.31 5 6.87 4 8.12 10.62 11.25 9.37 10.62 5 14.06 15.62 15.62 15.31 15.62 In a separate experiment, fruit were inoculated before and after laser labeling with a suspension of P. digitatum (105). In fruit inoculated prior to and after labeling, no symptoms of decay appeared after 3 weeks in storage. When viewed under the microscope, laser labeling appeared to prevent spore germination as indicated by the lack of fungal growth at the points of

PAGE 35

35 laser impact (Figure 2-10A). The laser also destroyed mycelial strands after germination as demonstrated in Figure 2-10B. Figure 2-9. Decay of labeled fruit in storage. Fruit were labeled with four exposure times and stored at 10 C and 95% RH. Each point represents an average of five boxes, each containing 50 fruits. There was no d ecay associated with the laser label Figure 2-10. Fungal spores were spread on agar plates and laser labeled at 45 s (A) and laser labeling of 72 h grown hyphae (B) The results obtained in the present study dem onstrate that the epidermal openings created by the laser labeling do not promote decay in tanger ines, as no decay symptoms associated with the laser etched area were observed. In fact, laser labeling appeared to prevent mold decay. Analysis of the data allows us to estimate an optimum exposure time that produces readable labels with minimal water loss (Figure 2-11). For tangerines, a label using 45-65 s exposure -5 0 5 10 15 20 12345% DecayTime after labeling (weeks) control 35 s 45s 85s 120sGeneral decay Label associated decay

PAGE 36

36 times is optimal. It is important that labels are protected with a wax coat to control water loss, or significant label collapse may occur. Figure 2 11. Combined data from Figure 2 3 and 2 4 showing water loss and label exposure tim e and t he oval area includes all readable labels 0.5 0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 0 500 1000 1500 2000 2500 3000 3500 15 0 15 30 45 60 75 90 105 120 135 150 Evaporation rate (mmol/m 2 sec) Surface area (m 2 ) Energy ( s )

PAGE 37

37 CHAPTER 3 LASER ETCHING: A NOVEL TECHNOLOGY TO LAB EL FLORIDA GRAPEFRUIT 3 1 Introduction Laser labeling has become an alternative me ans of fruit labeling in many areas of the world (e.g., New Zealand, Australia, Pacific Rim countries), approved in others (e.g., South Africa, Mexico, Canada, Argentina, Chile, EU), and currently in final approval stages by the Food and Drug Administratio n. The technique consists of etching the required information on the produce surface using a low energy carbon dioxide laser beam (10,600 nm) (Drouillard and Rowland, 1997). Etched markings are formed in dot matrix style letters and numbers, each dot cre ated by a pin hole depression. The advantages of laser labeling have been described previously (Etxeberria et al., 2006), yet some reservations linger about potential adverse effects during storage. The pinhole depressions applied after washing and waxing disrupt the natural cuticular barrier and the protective commercial wax cover, seemingly creating open cavities that would allow for increased water loss and facilitate entrance of decay organisms. In previous anatomical studies using tomato ( Lycopersi cum esculentum ) and avocado (Persea Americana ) (Etxeberria et al., 2006), it was demonstrated that cells under the affected area of a laser pinhole developed a protective layer mostly of lignin and phenolics when stored for 4 d at 10 C and 95% relative humidity (RH). This rapid healing response, accompanied by phenolic deposition, has been observed in Valencia oranges ( Citrus sinensis ) (Brown et al., 1979). When Ruby Red grapefruit ( Citrus paradisi ) were damaged by friction with sandpaper, penetratio n by Penicillium digitatum was inhibited where cells at the surface produced lignin before fungal entry (Brown et al., 1979). In a related study, Yuk et al. (2007) challenged tomato fruit with Salmonella immediately after labeling and observed no migration into the tissue by the organism, suggesting that some protection is supplied by the labeling process itself.

PAGE 38

38 Little information is available on the impact of this new technology on the overall quality of labeled produce, especially its effect on water los s and decay during prolonged storage. In Florida, grapefruit represents 43% of the citrus fresh market (Florida Citrus Mutual, 2008), a condition that requires extended storage especially when transported to international destinations. The present study determined the effects of laser labeling o n water loss and decay susceptibility during prolonged storage. 3 2 Materials and Methods 3 2 1 Plant Material Ruby Red grapefruit was procured from Haines City CGA (Citrus Growers Association) Packinghouse, Haines City, F L. The fruit had been washed and waxed with carnuba containing 15 ppm thiabendazole (TBZ) following established commercial practices. 3 2 2 Fruit Labeling Fruit was labeled as described by Etxeberria et al. (2006) using a low energy carbon dioxide laser labe ling machine (Model XY Mark 10, Sunkist Growers Inc., Fontana, CA) located at the University of Floridas Citrus Research and Education Center, Lake Alfred, FL. Individual fruit were placed against a polyvinyl chloride (PVC) rectangular frame stabilized 10 cm from the lasers output. The energy level used was the recommended 0.000752 W/dot per 35s exposure with a 25% duty cycle range. Differences in applied energy are expressed by variations in the exposure time to the laser, and varied according to i ndividual experiments as described below. 3 2 3 Selection of Optimal Exposure Time A label code containing one letter and one number (M1) was etched on fruit surfaces using different exposure times ranging from 30 s to 140 s. To enhance resolution, labels were rubbed gently with a cotton tipped swab dipped in a dark, fruit -based col orant Images of the

PAGE 39

39 dyed label were captured using a Canon Powershot S31S digital camera (Cannon, Lake Success, New York) mounted on a Wild Heerbrugg 165083 stereoscope (Leica Microsystems GmbH, Wetzlar, Germany). Surface area affected by the label was measured using image processing software developed by Dr. Arnold Schumann (Citrus Research and Education Center, University of Florida/IFAS, Lake Alfred, FL). Total area was calculated based on number of pixels within the area covered by the laser depress ions with 1 pixel corresponding to 50 m2. Five replicates per energy level were used. 3 2 4 Determination of Water Loss Water loss from the fruit surface was measured using a modified leaf porometer ( Decagon Devices, Pullman, WA ). To estimate water loss as a function of energy level, an etched rectangular matrix pattern of 7 X 8 dots was used for each of four pre -selected exposure times, low (30 s), commercial standard (45 s), medium (80 s) and high (120 s). The modified leaf porometer was placed on the t op of the treated area immediately after etching until a stable reading was obtained. Water vapor diffusion from grapefruit was calculated using equation 3 1 based on Ficks law where water vapor flux density or evaporation rate (F) is the product of vapor conductance (gv) and the difference between vapor concentration at the evaporating surface (Cvs) and water vapor concentration in atmosphere (Cva). Values are expressed as millimoles per square meter per second. The modified leaf porometer estimates the value for water vapor conductance (gv) which can be computed in the equation below to obtain Evaporation rate. F = gv (Cvs Cva) (3 1) Vapor concentration was calculated using equation 3 2, where ea is the vapor pressure (kPa) which is a function of temperature, and pa is the atmospheric pressure (kPa).

PAGE 40

40 = 2 (3 2) 3 2 5 Effect of Different Waxes on Water Loss from Labeled Areas Nine different commercial waxes were tested for their effect on moisture loss reduction from a labeled area Waxes were obtained directly from the manufacturers. Fruit were labeled using a single exposure time (45 s) then waxed using a sponge paint brush. Evaporation rate measurements of the labeled and unlabeled (control) surfaces were perfor med before and after waxing. Each measurement was replicated 30 times. Table 3 1 Nine commercial waxes tested for water loss reduction from laser labeled areas Names of waxes Names of Manufacturers Deco shellac Deco, Monrovia, CA Carnuba 505 Deco, Monrovia, CA Carnuba + TBZ Deco, Monrovia, CA Carnuba 231 Deco, Monrovia, CA Carnuba blend Deco, Monrovia, CA Citrus wax shellac HDH Agriproducts, Tavares, FL HDH Carnuba HDH Agriproducts, Tavares, FL Pace Carnuba Pace International, Visalia, CA Organic Carnuba Pace International, Visalia, CA A separate experiment was conducted to evaluate water loss from waxed and unwaxed etched areas during storage. Etched rectangles were waxed and fruit kept at 10 C and 95% RH for 7 d. Daily measurements of evaporation rates of the waxed label, unwaxed label and control (no label on fruit) were carried out. For each treatment, 30 separate measurements were made. 3 2 6 Peel Stability The label Florida citrus was etched on the fruit using four exposure times ( 35 s 45 s 85 s 120 s), and fruit was kept at 10 C and 65% or 95% RH for 4 weeks. Five replicates (1 replicate = 1 box = 35 fruit) per exposure time and control (non labeled fruit) were used. Weekly

PAGE 41

41 examination of the label appearance and surrounding area was performed. Peel stability was determi ned on the basis of a visual rating scale according to the shrinkage of the skin around label as follows: 0 (no shrinkage); 1 (very low); 2 (low); 3 (medium); 4 (high); 5 (very high) (Figure 3 1). Figure 3 1 Shrinkage rating scale for laser -labeled Ruby Red grapefruit peel. Scale ranges from 0 (no shrinkage) to 5 (total label collapse). Fruit were labeled at 45 s with the label Florida Citrus 3 2 7 Decay Study Fruit treated as indicated above and stored at 95% RH were examined weekly for decay symptoms for 5 weeks. Decay was categorized individually, but reported as total decay. 3 2 8 Mold Inoculation Study Fruit labeled Florida Citrus were subjected to four treatments: 1) Inoculation of fruit prior to labeling; 2) Inoculation after labeling; 3) Inoculation on waxed label; 4) Waxing of inoculated label. Inoculum was prepared as described in chapter 2. Inoc ulated fruit were stored at 10 C and 95% RH for 3 weeks and examined for decay weekly. Thirty replicates of one fruit each were used for all four treatments. Labeling was performed using one exposure time (45s). In a separate experiment, 250 L of the P. digitatum spore suspension was spread on agar plates, allowed to dry and incubated at 23 C. In a separate experiment, spores were allowed to

PAGE 42

42 germinate for 72 h and plates were then labeled as indicated above. Lase r labels were observed under microscope immediatel y and 48 h after labeling. 3.3 Results 3.3.1 Optimization of Exposure Time for Grapefruit Labeling A previous study demonstrated that the dot matrix style forming the alphanumerical characters of laser labels constitute superfic ial ruptures (pinholes) of the epidermal layer exposing the contrasting underlying tissue (Etxeberria et al., 2006). On citrus fruit, however, because the colored epidermis (flavedo) is thicke r than the depth of th e pinholes, vegetable dye was applied to provide contrast. The visual effect of increa sing laser labeling exposure time on grapefruit peel is shown in Figure 3-2. At the lowest possible exposure ti me of 30 s, the label was faint and hardly visible, whereas at th e highest exposure time the pinhole depressions merged into solid lines. Figure 3-2. A group photograph of labels etched on Ruby Red grapefruit using different exposure times/energy levels. The 45 s pict ure represents the energy level generally recommended for commercial use. Contrast of etched label was enhanced using fruit based color

PAGE 43

43 Using image process ing software, affected surface area was calculated as a factor of increasing exposure time. In general, area covered by the etched marking increased with higher exposure times (Figure 33). As expected, the rate of peel surface area disruption declined a t higher exposure times as pinholes began to merge. Figure 3 3 Relationship between exposure time (30 to 140 s) and laser -labeled surface area (covered by 100 dots) of Ruby Red grapefruit. Each poin t represents the average of five replicates labeled at ambient temperature. Vertical lines represent the standard error 3 3 2 Measurements of Water Loss Water loss from etched surfaces was measured as a function of exposure time and pinhole size (Figure 3 4). For this experiment, four exposure times were selected representing low (35 s), commercially recommended (45 s), medium (85 s) and high (120 s). Water loss measurements were made immediately after labeling. As shown in Figure 3 4, there was a rapid i ncrease in the rate of water loss between 45 and 85 s. Afterwards, increase in the rate of water loss was negligible. y = 1472.3ln(x) 4958.3 R = 0.9069 0 500 1000 1500 2000 2500 3000 0 50 100 150 Surface area (m 2 /100 dots) Exposure time (s)

PAGE 44

44 Figure 3 4 Water loss from laser labeled Ruby Red grapefruit peel using four di fferent exposure times. Water loss from the etched surface was measured at ambient temperature immediately after laser labeling 30 fruit per exposure time. Letters atop bars indicate statistical groupings. Bars with different letters are significantly dif ferent (P=0.05) 3 3 3 Effect of Waxes on Water Loss Retardation in Labeled Area The effect of waxing on reducing water loss from etched fruit surfaces was investigated using different waxes. All nine waxes t ested reduced water loss by 25% to 94% with four coatings showing over 90% reduction (Figure 3 5). Citrus wax shellac resulted in the highest reduction of water loss (94%; Figure 3 5) whereas shellac resulted in moderate water loss reduction as previously described by Hagenmaier and Shaw (1991). Figure 3 5 Percentage decrease in the rate of water loss from laser labeled Ruby Red grapefruit peel by different commercial waxes compared to unwaxed label. Bars with different letter s are significantly different by t Tests (LSD= 14.7, P=0.05) b b a a 0 2 4 6 8 10 35 45 85 120 Evaporation rate (mmol.m 2 .sec 1 ) Exposure time (s) LSD1.19 0 20 40 60 80 100 120 Decrease in evaporation rate (%) Type of wax a a a a b b c cd d

PAGE 45

45 Water loss from unwaxed labeled areas declined with time in storage (Figure 3-6). There was a steady decline in the rate of water loss up to 72 h after labeling which continued more gradually thereafter. Water lo ss from unwaxed labeled areas never reached control levels (Figure 3-6) as they did with tangerines ( Citrus reticulata ) 4 d after labeling (Sood et al., 2008). During the first 24 h, the rate of water loss fr om waxed etched areas was approximately 40% higher than control. Afterwards, water loss fr om control and waxed labeled surface remained nearly identical. Figure 3-6. Water loss from unwaxed label, waxed (carnuba) label and control Ruby Red grapefruit (no label) during 7 d storage at 10 C (50.0 F). Initial measurements were taken on 30 fruit immediately after labeling at ambient temperature. Vertical lines represent standard error of the averages. 3.3.4 Peel Stability The potential effect of water loss from the et ched area on the label stability during storage was investigated at two levels of RH. To determine the physical effect on label stability, a visual scale was created (see Materials and Methods; Fi gure 3-1). As expected, degree of label distortion increased with time and was inversely proportional to ambient RH (Figures 3-7 and 30 2 4 6 8 10 024487296120144Evaporation rate (mmol.m -2.sec -1)Time after labeling (h) unwaxed label waxed label control

PAGE 46

46 8). After 4 weeks in storage, approximately 40% of etched labels in fruit stored at 95% RH showed some degree of shrinkage, although most were classified as very low (Figure 3 7). On the contrary, storage at 65% RH resulted in substantial label shrinkage with approximately 98% of the fruit affected (Figure 3 8). This is in sharp contrast to tangerines which showed minimal shrinkage when s tored at similar RH (Sood et al., 2008). Table 3 2 Peel stability of laser labeled Ruby Red grapefruit using 45 s and stored at 10 oC and 95% RH Percentage of total fruit Time after labeling (weeks) 1 (very low) 2(low) 3(medium) 4(high) 5(very high) 1 15.38 1.14 0 0 0 2 28.55 2.28 0 0 0 3 28.54 5.13 0 0 0 4 27.39 10.26 1.14 0 0 Figure 3 7 Peel shrinkage of etched Ruby Red grapefruit during storage at 10 C (50.0 F) and 95% relative humidity. Shrinkage severity was determined on 175 unwaxed fruit per exposure time using a visual scale of 0 (very low or no shrinkage) to 5 (very high or to tal label collapse) depicted in Figure 3 1. 0 10 20 30 40 50 60 70 1 2 3 4 % of total fruit Time after labeling (week) 1 (very low) 2 (low) 3 (medium) 4 (high) 5 (very high)

PAGE 47

47 Table 3 3 Peel stability of laser labeled Ruby Red grapefruit using 45 s and stored at 10oC and 65% RH Percentage of total fruit Time after labeling (weeks) 1 (very low) 2(low) 3(medium) 4(high) 5(very high) 1 19.96 13.68 3.99 0 0 2 58.24 25.1 5.13 0 0 3 50.24 24.54 13.68 2.28 0 4 55.4 23.4 11.4 4.56 1.14 Figure 3 8 Peel shrinkage of etched Ruby Red grapefruit during storage at 10 C (50.0 F) and 65% relative humidity. Shrinkage severity was determined on 175 unwaxed fruit per exposure time using a visual scale of 0 (very low or no shrinkage) to 5 (very high or tot al label collapse) depicted in Figure 3 1. 3 3 5 Decay Study Fruit decay was followed for 5 weeks in packed grapefruit stored at 10 C and 95% RH. Close attention was placed to the sites of decay with special emphasis on the labeled area. Although different ki nds of decay were noted, we report total decay for simplification. In the present study, fruit decay in fruits labeled with all four exposure times was similar to control non labeled fruit (Figure 3 9). All decay present during the 5 -week storage period was 0 10 20 30 40 50 60 70 1 2 3 4 % of total fruit Time after labeling (week) 1 (very low) 2 (low) 3 (medium) 4 (high) 5 (very high)

PAGE 48

48 independent from the labeled areas, the most common being stem end rot. These results are analogous to those of Yuk et al. (2007) who demonstrated a lack of Salmonella migration and survival in tomato laser labels. Table 3 4 Decay of non laser labeled and laser labeled Ruby Red grapefruit using four different exposure time Total Decay (%) Time after labeling (weeks) Control 35 s 45 s 85 s 120 s 1 0 0 0 1.14 0 2 0.57 0 0 1.14 0 3 1.71 0 0.57 1.14 0.57 4 1.71 0.57 0.57 1.71 1.41 5 1.71 0.57 0.57 1.71 1.41 Figure 3 9 Total decay of labeled Ruby Red grapefruit in storage. Fruit were labeled using 4 exposure times (35 s, 45 s 85 s and 120 s) at ambient temperature and stored at 10 C (50.0 F) and 95% relative humidity. There was no decay associated with the laser label. Each point represents the average of five boxes, each box containing 50 fruit. Vertical lines represent standard error of the averages In citrus fruits, green mold caused by P. digitatum is the most common postharvest decay. Surprisingly, fruit inoculated prior to or after labeling with a P. digitatum spore suspension showed no symptoms of mold growth even after 3 weeks in storage. On the contrary, the control fruit which was wounded and inoculated with the same spore suspension decayed within a week. a a a a a 0 1 2 3 4 5 1 2 3 4 5 Total decay (%) Time after labeling (weeks) 35 s 45s 85s 120s control

PAGE 49

49 In a separate experiment, laser la beling appeared to destroy mold spores layered on dextrose agar plates, as no germination occurred on the la beled pinholes while the area around sustained a dense network of fungal hyph ae (Figure 3-10A). When spores were allowed to germinate and were then subjected to laser labeling, vegetativ e hyphae was eliminated from the labeled areas (Figure 3-10B). Figure 3-10. Fungal hyphae grown for 72 h on potato dextrose agar. A) after a lawn of spores was laser labeled at 45 s, B) laser labeling of 72 h grown hyphae 3.4 Discussion Laser labeling of fruits and vegetables is ba sed on etching the required information on the produce surface with permanent dot matrix alphanume rical characters or symbols. In doing so, the physical disruption of the na tural epidermal and cuticular pr otection may introduce artifacts with potential detrimental consequences. For example, epidermal waxes, which play a vital role in retaining moisture in the fruit and vegetabl es (Riederer and Schreibe r, 2001), are disrupted by the laser generated pinholes potentially renderi ng the produce surface susc eptible to water loss and secondary invasion by decay organisms. The relationship between pinhole size and wa ter loss was investigated as a means to establish optimal label boundaries in terms of maximal readability with minimal water loss. Our results showed that increasing labeling time beyond 45 s substantially increased water loss (Figure 3-4) proportional to pore size (Figure 3-3), yet readability was optimal between 55 to 85

PAGE 50

50 s. Therefore, optimizing readability at the lowest range of water loss between the range 45 to 55 s can be achieved without risking additional detrimental effects due to water loss. During commercial operations at the packinghouse, waxing of citrus fruits precedes fruit labeling, packing, storage, and long-distance transport. Whereas sticker labels do not suffer physical deterioration in storage, the loss of water from the etched labels (Figure 3 6) may alter the physical appear ance of the fruits surface, thereby distorting the label (Figures 31, 37, 38) and making it less effective and appealing. As reported, RH has a direct effect on the rate of moisture loss from produce surfaces (Forbes and Watson, 1992). The data indic ated that a considerable portion of the fruit showed some level of shrinkage making the label unreadable, especially fruit stored at 65% RH for 4 weeks. Even the lowest shrinkage (or shriveling) obtained at 95% RH can be sufficient to make the fruit less appealing. It is likely that at some point in the commercial chain of events, fruit may encounter lower than 65% RH. Although the natural healing process of the label pinholes reduced water loss to control levels after 4 d (Figure 3 6; Etxeberria et al., 2006), addition of a secondary wax coat immediately after labeling reduced water loss to control levels (Figure 3 6) which delayed or preve nted unnecessary shrinkage. In a s much as a second wax application is not commercially feasible at the moment, metho ds should be developed to address this problem in the future to avoid loss of visual appeal and functionality. Citrus fruits are relatively non perishable, and can normally be stored for long periods (Kader, 2002). Grapefruit can be stored at 10 to 15 C and 90% to 95% RH for 5 to 8 weeks (Grierson, 1974). In general, citrus fruits are vulnerable to various decay organisms during storage, especially Penicillium sp. (Kinay et al., 2001). Penicillium sp. growth necessitates rupture of the produce surfaces (Eckert and Brown, 1986) a condit ion seemingly created by the

PAGE 51

51 laser pinholes. Our data from fruit held at 10 C and 95% RH for 5 weeks showed no decay symptoms associated with the etched area. Brown et al. (1979) found that accumulation of lignin occurred rapidly in injuries at 30 C and RH over 90%, likely creating rapid protection. Although our experiments were conducted at 10 C, either formation of lignin or loss of humidity from the pinhole area appeared sufficient to deter decay. This is probable because P. digitatum is a wound pa rasite and does not actively invade intact plant tissue. There were some decayed fruit in the etched fruit samples; however, it was no different than that of non -etched fruit control samples. The lack of decay associated with etched areas was further substantiated by exposing the fruit to four possible conditions : 1) Inoculation of fruit prior to labeling; 2) Inoculation after labeling; 3) Inoculation on waxed label; 4) Waxing of inoculated label. Whether coated with a high concentration of P. digitatum spores before laser labeling or a layer of spores coated over the freshly etched surface, no fruit decay took place from the labeled area during 4 weeks in storage. The lack of decay by mold was unexpected given that, in one instance, fruit were essentia lly inoculated with P. digitatum spores immediately after laser labeling These data, and especially those of Figure 310 showing lack of spore germination on etched areas and the elimination of veg etative hyphal growth by laser labeling demonstrate that the laser labeled areas do not have increased susceptibility to decay organisms in grapefruit. There was an appreciable difference in the postharvest behavior of laser labeled fruit between grapefruit and tangerines, especially on the efficacy of differe nt waxes in preventing water loss and in label shrinkage (Sood et al., 2008). Differences in wax efficiency are difficult to reconcile considering that surface area affected by different labeling times was nearly identical in both types of citrus and cove rage by waxes is expected to be alike. However, previous work by the authors showed that any treatment of fruit peel affects the cuticle, and therefore, could

PAGE 52

52 have an effect on the way that additional coatings are laid down. Re arrangement of the epicuticular waxes, even in different areas on the same fruit, will determine the coverage of waxes applied to the peel (data not shown). Also the differences in peel topography between the tangerine and the grapefruit may be an added factor in the uniformity of t he applied coating. The larger number of grapefruit affected by label shrinkage, however, is likely due to the higher percentage of water loss through the labeled areas as compared to non labeled areas. Although restricted to one commodity, this study shows that laser labeling of grapefruit is a viable option to identify produce with a permanent tag. When compared to sticker labeled fruit, a laser labeled commodity is relatively tamper free and the fruit quality remains high as the invasion of the epidermi s does not incite decay, provide an avenue for food pathogens and water loss is easily controlled.

PAGE 53

53 CHAPTER 4 EFFECTS OF LASER LAB ELING ON THE POSTHAR VEST STORAGE BEHAVIO UR OF TOMATO AND PEPPER FR UIT 4 1 Introduction Produce consumption is considered as the prime s ource of food borne illnesses in the US (Center for Disease Control and Prevention, 2006). The difficulty to trace the past outbreaks such as Salmonella in tomatoes, E.coli O157:H7 in apples etc. has made the labeling of produce a necessity. Labeling helps track and trace the product to its original source (i.e. grower and packer) Thus far, the most widely used labeling system for produce is Price Look Up (P.L.U.) stickers/adhesive labels. These stickers offer several advantages such as making the checkout process easier, helps distinguishing between similar products and tracing back to the original sources. However the non permanency of these stickers urged industry and scientists to develop a more efficient and permanent labeling method called as laser la beling. Laser labeling, as mentioned in previous chapters, involves the use of low energy CO2 to etch information directly onto the fruit surface by creating pinhole depressions. These etched openings can promote undesirable water loss and serve as an entr y site for pathogen invasion. However, anatomical and morphological studies of laser etched depressions in tomato and avocado showed the accumulation of additional waxes and phenolic compounds around exposed cell walls and underneath tissues, thereby propo sing the self healing mechanism of laser etched areas (Etxeberria et al., 2006). Initial studies to investigate the postharvest effect of the laser labeling were conducted on citrus fruit such as tangerine and grapefruit. The results helped in identifying the optimum laser energies for commercial use in both the fruits. Additionally, it was shown that laser labeling does not promote decay and only allows minimal water loss in citrus fruits. The appearance of the label does change with the time unless wax coated. The present study deals with fruit with

PAGE 54

54 edible peel such as tomato and pepper. Because of the variation in the morphology of the fruits with nonedible peel fruit like citrus, laser labeling was anticipated to behave differently. Tomato ( Lycopersi con esculentum ) is one of the most widely consumed vegetable crops worldwide ( Chapagain and Wiesman, 2004) .Botanically, a tomato fruit is a berry consists of seed enclosed in fleshy pericarp developed from ovary. Pericarp is further divided into exocarp o r fruit skin, parenchymatous mesocarp and a single celled layer of endocarp. The fruit skin or exocarp composed of the outer epidermal layer and two to four layers of thick walled hypodermal cells with collenchymatous thickenings. Epidermal layer of a tom ato fruit is covered with thin waxy cuticle. Green pepper ( Capsicum annum ) is a berry fruit with capsule shaped hollow structure. The berry is formed by a thick juicy pericarp and a placenta binding the seeds. The pericarp is further composed of an epicarp or external layer, mesocarp or fleshy intermediate zone and a membranous endocarp. This study was focused on the effects of laser labeling on water loss and other postharvest concerns (e.g., decay, label shrinkage) in thin skinned peel -edible produce such as tomato and green peppers and to contrast the results with those obtained for citrus fruit. 4 2 Materials and Methods 4 2 1 Plant Material Tomato fruit variety BHN602 was purchased from Taylor and Fulton Packinghouse, Palmetto, Floridaon 10 June, 2008. Tomato f ruit was procured at mature green stage. On the other hand, pepper fruit was purchased from and J&J Ag Products, Inc. Packinghouse, Clewiston, Florida on 5 th July, 2008. Both the fruits had been washed and coated with mineral oil based waxes following established commercial practices.

PAGE 55

55 4 2 2 Fruit Labeling Fruit was labeled as described in chapter 3. Applied energy or exposure time varied depending on the type of experiments conducted. 4 2 3 Selection of Optimal Exposure Time A label code containing one letter and one number (O1) was etched on fruit surfaces using different exposure times ranging from 30 s to 120 s. A dark, fruit based colorant was rubbed gently over the labels with a cotton-tipped swab to enhance resolution. Total area covered by the lase r depressions was calculated by following the procedure described in chapter 3. Five replicates per energy level were used. 4 2 4 Determination of Water Loss Water loss was measured as described in chapter 3 except the exposure times used. Tomato and pepper fru it were labeled using four pre -selected exposure times, low (35 s), standard (55 s), medium (75 s) and high (100 s). 4 2 5 Peel Stability The label Florida tomato was etched on tomato fruit using an optimum exposure time and fruit was kept at 12.5C and 65% or 95% RH for 3 weeks. Five replicates (1 replicate = 1 box = 50 fruit) per exposure time and control (non labeled fruit) were used. Similarly, pepper fruit was etched with the label Florida pepper and stored at 7oC and 65% or 95% RH for 3 weeks. Five replicates (1 replicate = 1 box = 30 fruit) per exposure time and control (non labeled fruit) were used. Fruit was examined for label appearance and surrounding area for 3 weeks. Peel stability of both the fruit types was determined on the basis of a visual rating scale according to the shrinkage of the skin around label as follows: 0 (no shrinkage); 1 (very low); 2 (low); 3 (medium); 4 (high); 5 (very high) (Figure 4 1) and (Figure 42).

PAGE 56

5 6 A separate experiment was conducted to evaluate peel stability of wa xed and unwaxed etched areas in tomato fruit during storage. Daily visual observations of the unwaxed and waxed laser labels on tomato fruit was done for 7 days 4 2 6 Decay Study Fruit treated as indicated above and stored at 95% RH were examined for decay sym ptoms nearly every alternate day for 3 weeks. Results were reported as total decay. Figure 4 1 Shrinkage rating scale for laser -labeled tomato peel. Scale ranges from 0 (no shrinkage) to 5 (total label c ollapse). Fruit were labeled at 55 s with the label Florida tomato Figure 4 2 Shrinkage rating scale for laser -labeled pepper peel. Scale ranges from 0 (no shrinkage) to 5 (total label collapse). Fruit were labeled at 55 s with the label Florida pepper

PAGE 57

57 4 2 7 Inoculation Study Pathogen inoculation study on fruit labeled Florida tomato and Florida pepper was conducted as described in chapter 3. Tomato and pepper fruit were inoculated with Geotrichu m candidum Link The inoculum was prepared using the same method as with the Penicillium digitatum Inoculated tomato and pepper fruit were stored for 3 weeks at 95% RH and at 12.5 oC and 7 oC, respectively. Weekly examination of the inoculated fruit was c arried out. Labeling was performed using one exposure time (55s). 4 3 Results 4 3 1 Optimum Exposure Time for Labeling Previous anatomical and morphological studies demonstrated that the dot matrix style forming the alphanumerical characters of laser labels repres ent surface ruptures (pinholes) of the epidermal layer exposing the contrasting underlying tissue (Etxeberria et al., 2006). The visual effect of increasing laser labeling exposure time on tomato and pepper peel is shown in Figure 4 3 and Figure 4 4. As i n previous tests on tangerine and grapefruit, the lowest possible exposure time of 30 s generate d faint, very superficial and slightly visible label, whereas the highest exposure time caused the merging of the pinhole depressions into solid lines. These r esults were similar to as seen in citrus fruit (Sood et al, 2007). However, because of the difference in skin morphology, the labels on tomato and pepper were clearer and more visible than on citrus. The affected surface area as a function of increasing e xposure time was calculated using the same image processing software developed by Dr. Arnold Schumann. As previously demonstrated in citrus fruit, (Chapter 1 an d 2), area covered by etched markings increased in response to higher exposure times (Figure 4 5 and Figure 4 6). As expected, the rate of peel

PAGE 58

58 surface area disruption in both the fruit types did not increase significantly at higher exposure times due to merging of the pinholes. Figure 4 3 A group photograph of l aser labels on tomato fruit using different exposure times/energy levels. Contrast of etched label was enhanced using fruit based color. Figure 4 4 A group photograph of labels etched on pepper fruit using different exposure times/energy levels. Contrast of etched label was enhanced using fruit based color

PAGE 59

59 Figure 4 5 Relationship between exposure time (30 to 120 s) and laser -labele d surface area (covered by 100 dots) of tomato fruit. Each point represents the average of five replicates labeled at ambient temperature. Vertical lines represent the standard error Figure 4 6 Relationship between exposure time (30 to 120 s) and laser -labeled surface area (covered by 100 dots) of pepper fruit. Each point represents the average of five replicates labeled at ambient temperature. Vertical lines represent the standard error 4 3 2 Measur ements of Water Loss Water loss from laser labeled surfaces was measured as a factor of exposure time and pinhole size (Figure 4 7 and Figure 4 8). For this experiment, four different exposure times, 35 s, 55 s, 75 s and 100 s were selected. Water los s measurements were made immediately y = 0.1174x 2 + 37.354x 1010.1 R = 0.8819 0 500 1000 1500 2000 2500 0 15 30 45 60 75 90 105 120 Surface Area (m 2 \ 100dots) Exposure time (s) y = 3.0718x 1.4518 R = 0.9142 0 500 1000 1500 2000 2500 3000 3500 4000 0 15 30 45 60 75 90 105 120 135 Surface Area (m 2 \ 100dots) Exposure time (s)

PAGE 60

60 after labeling. As shown in Figure 47, the rate of water loss from tomato fruit followed a nearly linear pattern while pepper fruit (Figure 4 8), showed a rapid increase in the rate of water loss between 35 and 55 s. Afterwards, there was a negligible increase in the rate of water loss. The results for both the fruits were represented using the same scal e so as to provide for a better comparison. Figure 4 7 Water loss from laser labeled tomato fruit peel using four different exposure t imes. Water loss from the labeled surface was measured at ambient temperature immediately after laser labeling 20 fruit per exposure time. Letters atop bars indicate statistical groupings Bars with different letters are significantly different (P=0.05). Figure 4 8 Water loss from laser labeled pepper fruit peel using four different exposure t imes. Water loss from the laser labeled surf ace was measured at ambient temperature immediately after laser labeling 20 fruit per exposure time. Letters atop bars indicate statistical groupings. Bars with different letters are significantly different (P=0.05) c b b a 0 2 4 6 8 10 12 14 16 18 20 35 55 75 100 Evaporation rate (mmol/m 2 sec) Exposure time (s) c b ba a 0 2 4 6 8 10 12 14 16 18 20 35 55 75 100 Evaporation rate (mmol \ m 2 sec) Exposure time (s)

PAGE 61

61 4 3 3 Peel Stability The potential effe ct of water loss from the etched area on the label stability during storage was investigated at two levels of RH. To determine the physical effect on label stability a visual scale was created (see Materials and Methods; Figure 4 1and Figure 4 2). As expected, degree of label distortion increased with time and was inversely proportional to ambient RH (Figures 4 7 and Figure 4 8). After just a week in storage, approximately 50% of laser labels in fruit at 95% RH showed some degree of shrinkage, although most we re classified as very low (Figure 4 9 and Figure 4 11). On the contrary, storage at 65% RH resulted in substantial and rapid label shrinkage with approximately 98% of the fruit affected (Figure 4 10 and Figure 4 12). The results presented do not include t he decayed fruit which were discarded during the evaluation. There was a sharp contrast in the label stability of tomato and pepper fruit when compared to citrus. Owing to the epidermal permeability of tomato and pepper fruit, there was a quick and very high level of shrinkage of the laser labels and surrounding ar e as as compared to citrus fruit. Table 4 1 Peel stability of laser labeled tomato fruit stored at 12.5oC and 65% RH Percentage of total fruit Time after labeling (days ) 1 (very low) 2(low) 3(medium) 4(high) 5(very high) 2 94 6 0 0 0 6 79.2 8.8 4.8 0 0 8 66 21.6 10.8 1.2 0 10 16 23 59.6 27.6 19.2 27.2 54.4 57.2 10 11.6 10.4 3.6 3.6 5.2 0 0 0 Table 4 2 Peel stability of laser labeled tomato fruit stored at 12.5oC and 95% RH Percentage of total fruit Time after labeling (days) 1 (very low) 2(low) 3(medium) 4(high) 5(very high) 2 74.8 7.2 0 0 0 6 85.6 10 3.6 4.4 0 8 82.4 13.2 4.4 0 0 10 16 23 77.2 64.8 46.8 14 17.6 26.8 6.8 1 0.4 8.4 0 1.2 0 0 0 0

PAGE 62

62 Figure 4 9 Peel shrinkage o f laser labeled tomato fruit during storage at 12.5C (55 F) and 95% relative humidity. Shrinkage severity was determined on 250 unwaxed fruit per exposure time using a visual scale of 0 (very low or no shrinkage) to 5 (very high or total label collapse) depicted in Figure 4 1. Figure 4 10. Peel shrinkage of laser labeled tomato fruit during storage at 12.5 C (55 F) and 65% relative humidity. Shrinkag e severity was determined on 250 unwaxed fruit per exposure time using a visual scale of 0 (very low or no shrinkage) to 5 (very high or total label collapse) depicted in Figure 4 1. 0 10 20 30 40 50 60 70 80 90 100 2 6 8 10 16 23 % of total fruit Time after labeling (days) 1 (very low) 2 (low) 3 (medium) 4 (high) 5 (very high) 0 10 20 30 40 50 60 70 80 90 100 2 6 8 10 16 23 % of total fruit Time after labeling (days) 1 (very low) 2 (low) 3 (medium) 4 (high) 5 (very high)

PAGE 63

63 Table 4 3 Peel stability of laser labeled pepper fruit stored at 7.5oC and 65% RH Percentage of total fruit Time after labeling (days) 1 (very low) 2(low) 3(medium) 4(high) 5(very high) 4 3.32 19.4 62.4 1.98 0 7 0 0 49.8 44.2 2.4 11 0 0 35 48.4 5.8 1 4 1 8 2 1 0 0 0 0 0 0 0 0 0 19 .6 19. 8 2.6 34.6 36.6 18.4 Table 4 4 Peel stability of laser labeled pepper fruit stored at 7.5oC and 95% RH Percentage of total fruit Time after labeling (days) 1 (very low) 2(low) 3(medium) 4(high) 5(very high) 4 15.8 54.6 23.8 0 0 7 0 14.2 72.8 5.2 0 11 0 3.2 46.8 35.6 1.2 14 18 21 0 0 0 1.2 1.2 0 34.4 15.8 7.2 41 37.6 34.4 6.4 11.8 18.4 Figure 4 11. Peel shrinkage of laser labele d pepper fruit during storage at 7C (45 F) and 95% relative humidity. Shrinkage severity was determined on 150 unwaxed fruit per exposure time using a visual scale of 0 (very low or no shrinkage) to 5 (very high or total label collapse) depic ted in Figure 4 2 0 10 20 30 40 50 60 70 80 90 100 4 7 11 14 18 21 % of total fruit Time after labeling (days) 1 (very low) 2 (low) 3 (medium) 4 (high) 5 (very high)

PAGE 64

64 Figure 4 12. Peel shrinkage of laser labele d pepper fruit during storage at 7C (45 F) and 65% relative humidity. Shrinkage severity was determined on 150 unwaxed fruit per exposure time using a visual scale of 0 (very low or no shrinkage) to 5 (very high or total label collapse) depicted in Figur e 4 2. Figure 4 13. Unwaxed and waxed laser labeled tomato fruit during storage. 0 10 20 30 40 50 60 70 80 90 100 4 7 11 14 18 21 % of total fruit Time after labeling (days) 1 (very low) 2 (low) 3 (medium) 4 (high) 5 (very high)

PAGE 65

65 When stored for 7 days at 12.5 oC and 95% RH conditions, waxed laser labels maintained the peel integrity as opposed to unwa xed labels which showed considerable shrinkage around the labeled area (Figure 4 13). 4 3 4 Decay Study Fruit decay was monitored for 3 weeks in packed tomato and pepper stored at their respective optimum temperature and 95% RH. Close attention was placed to the sites of decay with special emphasis on the labeled area. Although different kinds of decay were observed, for simplification, only total decay is reported. Decay in fruits labeled with all four exposure times was similar to control non labeled fruit (F igure 4 1 4 and F igure 4 15). Most of the decay during the 3 -week storage period was independent from the labeled areas, the most common being soft rot ( Erwinia carotovora) in both tomato and pepper and sour rot ( Geotrichum candidum ) i n tomato. Unlike citrus, laser labeled tomato and pepper fruit occasionally showed some decay about 2 3 % of the total decay on and around the label. However, there may be varied reasons for this observation. The hig h moisture content of the etched surface may provide entr y sites for pathogens as compared to citrus. Despite of having few fruits with decay on label, the overall decay study results are in conformity to those of Yuk et al. (2007) who demonstrated a lack of Salmonella migration and survival in tomato laser lab els. Table 4 5 Decay of non laser labeled and laser labeled tomato fruit using four different exposure time Total Decay (%) Time after labeling (days) Control 35 s 55 s 75 s 100 s 2 0 0 0.4 0 0 6 0 1.2 0.8 0 0 8 0 1.2 0.8 0 0 10 0 1.2 0.8 0.4 0 16 0.8 4.8 14.8 12.8 18.4 23 1.6 17.2 36.4 41.2 34.4

PAGE 66

66 Figure 4 14. Total decay of labeled tomato fruit in storage. Fruit were labeled using 4 exposure times (35 s, 55 s 75 s and 100 s) at ambient temperature and stored at 12.5C (55 F) and 95% relative humidity. Each point represents the average of five boxes, each box containing 50 fruit Table 4 6 Decay of non laser labeled and laser labeled pepper fruit using four different exposure time Total Decay (%) Time after labeling (days) Control 35 s 55 s 75 s 100 s 2 1.3 0 1.3 0 0 4 3.9 5.3 3.9 0.6 6 7 13.2 7.3 5.9 2.6 9.3 11 16.5 17.3 11.2 10.6 12.6 14 21.8 19.9 15.2 15.9 21.2 18 57.8 30.5 31.8 40.5 31.2 21 62.4 47.8 58.4 62.5 72.5 Figure 4 15. Total decay of labeled pepper fruit in storage. Fruit were labeled using 4 exposure times (35 s, 55 s 75 s and 100 s) at ambient temperature and stored at 7C (45 F) and 95% relative humidity. E ach point represents the average of five boxes, each box containing 30 fruit 20 10 0 10 20 30 40 50 2 6 8 10 16 23 Total decay ( %) Time after labeling (days) control 35 s 55s 75s 100s 20 10 0 10 20 30 40 50 60 70 80 2 4 7 11 14 18 21 Total decay (%) Time after labeling(days) control 35 s 55s 75s 100s

PAGE 67

67 4 4 Discussion Etching the required information in form of permanent dot matrix style alphanumerical characters or letters causes the opening up of outer protective cuticular barrier. These pinhole depressions created can serve as a potential site for water loss and pat hogen invasion. However, it appears that the low energy CO2 beam momentarily vaporizes the natural and commercial wax accumulating in exposed cell walls, thus creating a repellent shield (Etxeberria et al, 2006). The relationship between pinhole size and water loss was investigated to establish optimal label range in terms of maximal readability with minimal water loss. Unlike citrus, tomato and pepper peel pro vides a good contrast for laser labels. Therefore, no additional dyeing of the label s is required. Tomatoes were laser labeled when mature green. The laser labels were faint in the beginning due to the lack of contrast provided by green tomato peel. However, they became clear and developed visual appeal with the time as the tomato ripened. The results showed that increasing exposure time beyond 45 s substantially increased water loss proportional to perforation size in both tomato (Figure 4 3 and Figure 4 4) and pepper (Figure 4 5 and Figure 4 6), while readability was optimal between 45 to 85 s. Therefore, optimizing readability at the lowest range of water loss between the range 45 to 55 s can be achieved without substantial amount of water loss. Resistance to water movement is mainly offered by the natural cuticular layer (Ben Yehoshu a, 1969; Burg and Burg, 1965; Horrocks, 1964). Water permeabilities from cuticle vary with plant species and organ (Becker et al, 1986). During packinghouse operations, commercial waxes are applied to most horticultural commodities to alleviate undesirable water loss and improve visual appeal. Furthermore, storage at high RH conditions (90 95%) helps in retaining moisture in the tissue. Water loss from the etched areas alters the appearance of the label. The present study results also showed fruit peel shri nkage on and around the label. The distortion of

PAGE 68

68 the labels occurred rapidly in tomato and pepper as compared to citrus fruit. This faster and large num ber of label shrinkage in laser labeled tomato and pepper peel could be likely due to higher amount of w ater loss through the labeled areas. Tomato is a climacteric fruit and mostly harvested in the mature green stage. Tomato fruit is quite perishable in nature, and storage at optimum temperature and relative humidity is very essential to maintain its qual ity postharvest. The mature green or partially ripe fruit can be stored best at 12.7 to 15.5 oC for 2 4 weeks in contrast to ripe fruit which is best at 7.2 to 10 oC for nearly 2 weeks. On the other hand, Pepper is best stored at 7.5 oC for maximum shelf l ife of 3 5 weeks (Kader, 2002). In general, these fruits are vulnerable to various decay organisms during storage, especially Erwinia sp and Geotrichum sp Most pathogen requires the rupture of the produce surfaces for penetration and growth. Laser gene rated pinhole depressions seemingly provide the avenue for the pathogen invasion, although as noticed previously, citrus fruit held at 10 C and 95% RH for 5 weeks showed no decay symptoms associated with the laser labeled area. Stored laser labeled tomato es and peppers were stored for maximum of 3 weeks to monitor decay. In the present study, we observed appreciable differences in the postharvest behavior of laser labeled between tomato and pepper fruit especially on the extent of decay associated with th e label. Nearly 45 70% of tomato fruit showed decay symptoms as oppose to pepper with 25 40% decay. These decay symptoms were not associated with the etching markings. Additionally, these results were different than the citrus decay study results as the pe rcentage of decayed tomato and pepper fruit obtained was higher than that of citrus In very few instances, laser labeled tomato and pepper developed bacterial rot symptoms on the labels. These results were in contrast to citrus fruit where there was no decay observed on and around the label. Further, some inoculated fruits also developed bacterial ooze on the label during the storage. Despite of having

PAGE 69

69 some decay fruits (23% of the total rots) with decay symptoms on the label; the overall decay was not statistically associated with the etched areas. The disassociation between decay and labeled area was further confirmed by exposing the fruit to their most common postharvest organism. The fruit was also subjected to the worst conditions where inoculation was per formed immediately after laser labeling As expected, there was no decay in either of the situations. As evident from these results and the ones presented in previous chapters, this novel technology could be a viable alternative to label produce. Be sides being permanent, it does not support pathogen invasion, incite decay and water loss, thereby keeping the fruit quality maintained.

PAGE 70

70 CHAPTER 5 CONCLUSIONS The study reported here was aimed at determining the effects of laser labeling, an emerging technology, on the overall storage quality of selected fruits and vegetables. The effects of this technique on the storage quality vary with the crop type. According to the results, the optimum laser energy for the entire selected commodities ranged between 40 55 s. It was also noticed that etched markings on tangerine and grapefruit require dyeing by a food based color as the citrus peel does not provides a better contrast for the labels. Water loss measured from the laser labels was proportional to the exposure t ime of laser beam in all the selected crops. However, the rate of water loss was highest in laser labeled pepper fruit among all. Citrus, a relatively non perishable crop when laser labeled and stored at optimum temperature (10 oC) and relative humidity ( 95%) conditions for 4 weeks, exhibited negligible water loss throughout the storage period. Additionally, the rate of water loss from waxed labels was no different than the control (non laser labeled) in citrus fruit after 4 7 days of storage. The laser labels were waxed using different kinds of commercial coatings. The data showed that wax application on the labels subsequently diminishes the rate of water loss from 35% to 94 % in citrus fruit. Among all the waxes used, citrus wax shellac resulted in the highest reduction of water loss Further it was noticed that the water loss preserves the label appearance in all selected commodities. A considerable portion of fruit with unwaxed labels showed some level of shrinkage rendering the label unreadable. T he shrinkage was proportional to relative humidity and time of storage. The label distortion or shrinkage was more at low RH (65%) than the higher RH (95%) conditions. Tomato and pepper fruit showed severe and quicker label shrinkage than citrus at both th e low and higher humidity conditions. However this label

PAGE 71

71 distortion was negligible when wax is applied immediately after labeling as waxing helps in sealing of the pinhole depressions for further water loss. Fruit held at 95% relative humidity, storage conditions conducive for decay and their respective optimum temperature, showed nearly no decay symptoms associated with the etched areas. Although some decaye d fruit were found in the laser labeled fruit samples in all the selected crops however, were no di ffer ent than the control (non laser labeled) fruit sample s. In very few instances, laser labeled tomato and pepper developed decay symptoms on the labels. Despite having some fruits with decay symptoms on the labels (2 3% of the total decay), the overall decay was not statistically associated with the etched markings. The lack of decay associated with inoculated etched areas also confirmed that laser labeling does not facilitate decay. Whether coated with pathogen spo res before laser labeling or a layer of spores spread over the freshly etched areas, no fruit decay from the labeled area was noticed in all the four selected commodities. This further corroborates the previous findings of Yuk et al (2007) who challenged tomato fruit with Salmone lla and found t hat laser labeling does not cause sufficient damage to allow Salmonella infiltration. It can be assumed that, with time, the accumulation of lignin and wax deposits in and around etched areas also provides a repellant shield and prevents the penetration of decay organism through etched openings. Various studies have shown previously that the deposition of lignin and other cell wall components in the wound tissue provides resistance to the diseases. The fungal development was found to be arrested by phenolic compounds and callose deposits in the cell walls of young tomato fruit inoculated with Botrytis cinerea (Glazener, 1982). There was indeed an appreciable difference in the postharvest behavior of laser labeled fruit namely citrus, tomato and pepper. For e xample the optimum exposure time of laser beam

PAGE 72

72 for tomato and pepper is shorter than citrus fruit The optimum range of exposure times with minimum water loss while maintaining the readability of labels was 45 55s in citrus fruit whereas 35 45s in tomato and pepper fruit. Additionally, the extent of laser label shrinkage was higher in tomato and pepper as compared to citrus. All these differences are mainly attributed to the peel morphology of the above selected crops. As depicted the thin skinned fruits such as tomato and pepper suffer substantial amount of water loss at etched areas than the thick peeled citrus fruit, as the thickness of the cuticle is directly related to the protection against undesirable moisture loss, but this loss can be greatly dimi nished by applying wax coatings on the label. Taking into account all these above mentioned results, this study suggests that laser labeling could be a viable alternative to the current labeling system; provide individual traceability without enhancing saf ety concerns. It was demonstrated that the fruit quality of the laser labeled fruit remains high as the invasion of epidermis does not promote decay, provide avenue for pathogens and water loss is easily controlled.

PAGE 73

73 LIST OF REFERENCES Arpaia, M.L. and Ka der, A.A., 2006. Recommendations for maintaining postharvest quality. http://postharvest.ucdavis.edu/Produce/ProduceFacts/Fruit/mandarin.shtml. Bartz, J.A. and Brecht, J.K., 2002. Postharvest physiology and pathology of vegetables Marcel Dekker, New York. Baudoin, A. and Eckert, J.W., 1985. Development of Resistance against Geotrichum -Candidum in Lemon Peel Injuries. Phytopathology 75:174179. Biale, J.B. and Young, R.E. 1981. Respiration and ripening in fruits: retrospect and prospect., London. Blakeman, J.P. 1985. Ecological succession of leaf surface microorganisms in relation to biological control. Bollen, A.K., Riden, C.P., and Opara, L.U., 2006. Traceability in postharvest quality management. International Journal of Postharvest Technology and Innovat ion. 1:93105. Brown, G.E., 1973. Development of Green Mold in Degreened Oranges. Phytopathology 63:11041107. Brown, G.E., Ismail, M.A., and Barmore, C.R., 1979. Lignification of injuries to citrus fruit and susceptibility to green mold, p. 124 126, Proc. Fla. State Hort. Soc. Burg, S.P. and Burg, E.A., 1965. Gas Exchange in Fruits. Physiol. Plant. 18:870 Cao, G.H., Sofic, E., and Prior, R.L., 1996. Antioxidant capacity of tea and common vegetables. J. Agric. Food Chem. 44:34263431. Centers for Disease Co ntrol and Prevention.2006. Preliminary FoodNet data on the incidence of infection with pathogens transmitted commonly through food: 10 sites, United States, 2005. MMWR Morbid. Mortal. Wkly. Rpt. 55:392395. Center for Food Safety and Applied Nutrition.1998. Guide to minimize microbial food safety hazards for fresh fruits and vegetables. IX. Traceback. Guidance for food industry. U.S. Dept. Health and Human Serv., Food and Drug Administration. Oct.1998. Washin gton, D.C. Chakraverty, A., Mujumdar, A.S., Raghaven, G.V.S., and Ramaswamy, H.S., 2003. Handbook of Postharvest Technology: Cereals, Fruits, Vegetables, Tea, and Spices CRC Press. Chapagain, B.P. and Wiesman, Z., 2004. Effect of potassium magnesium chlo ride in the fertigation solution as partial source of potassium on growth, yield and quality of greenhouse tomato. Sci. Hortic. 99:279288.

PAGE 74

74 Cohen, J.H., Kristal, A.R., and Stanford, J.L., 2000. Fruit and vegetable intakes and prostate cancer risk. J. Natl. Cancer Inst. 92:6168. Delong, M.J., Prochaska, H.J., and Talalay, P., 1986. Induction of NAD (P) H -quinone reductase in murine hepatoma cells by phenolic antioxidants, azo dyes, and other chemoprotectors a model system for the study of anticarcinogens. P roc. Natl. Acad. Sci. U. S. A. 83:787791. Drouillard, G. and Rowland, R.W., 1997. Method of laser marking of produce. In: U.S.Department of Commerce, P. a. T. O., Washington, D.C. (ed.). Eckert, J.W. and Brown, G.E., 1986. Postharvest citrus diseases and their control, p. 315360. In: Wardowski, W. F., Nagy, S., and Grierson, W. (eds.), Fresh citrus fruits. AVI Publishing, Westport, CT, USA. Etxeberria, E., Miller, W.M., and Achor, D., 2006. Anatomical and morphological characteristics of laser labeling d epressions for fruit labeling. Horttechnology 16:527532. Forbes, J.C. and Watson, R.D., 1992. p. 293. In: Forbes, J. C. and Watson, R. D. (eds.), Plants in agriculture. Cambridge University Press, Cambridge. Florida Citrus Mutual. 2008. Annual stati stical report for 2006 2007 Florida citrus harvesting season. http://www.flcitrusmutual.com/files/8d69285e 786f 47698.pdf Giovannoni, J.J., 2004. Genetic regulation of fruit deve lopment and ripening. Plant Cell 16:S170S180. Grierson, W., 1974. V.Chilling injury in tropical and subtropical fruit. Effect of harvest date, degreening, delay storage and peel color on chilling injury of grapefruit, p. 6673, Proc. Trop. Reg. Amer. Soc. Hort. Sci. Hagenmaier, R.D. and Shaw, P.E., 1991. Permeability of Shellac Coatings to Gases and Water Vapor. J. Agric. Food Chem. 39:825829. Hecht, J., 1994. Understanding lasers IEEE Press, New York. Horrocks, R.L., 1964. Wax + Water Vapour Permeab ility of Apple Cuticle. Nature 203:547&. Kader, A.A., 2002. Postharvest biology and technology :overview, p. 39 48. In: Kader, A. A. (ed.), Postharvest Technology of Horticultural Crops. Regents of the University of California, Division of Agricultural and Natural Resources, Oakland, CA. Kays, S.J., 1991. Postharvest physiology and handling of perishable plant products Van Nostrand Reinhold Inc. New York. Kays, S.J. and Paull, R.E., 2004. Postharvest Biology Exon Press, Athens, GA.

PAGE 75

75 Kidd, F. and West, C. 1925. The course of respiratory activity throughout the life of an apples. Great Britain department of science and Industry research, Food Investigation Board, London. Kinay, P., Yildiz, F., Sen, F., Yildiz, M., and Karacali, I., 2005. Integration of pre and postharvest treatments to minimize Penicillium decay of Satsuma mandarins. Postharvest Biol. Technol. 37:3136. Kinay, P., Yildiz, M., Yildiz, Y., Delen, N., and Tosun, N., 2001. Control of postharvest pencillium decay of citrus fruits with antagonisti c yeast and chemical fungicides, p. 383385. In: Arie, R. B. and Hadas, S. P. (eds.), Proc. 4th Int. Conference on Postharvest. Knee, M., 2002. Fruit Quality and Its Biological Basis Blackwell Publishing, UK. Knee, M., Sargent, J.A., and Osborne, D.J., 1 977. Cell Wall Metabolism in Developing Strawberry Fruits. J. Exp. Bot. 28:377396. Lam, L.K.T., Li, Y., and Hasegawa, S., 1989. Effects of citrus limonoids on glutathione s transferase activity in mice. J. Agric. Food Chem. 37:878880. Larson, R.A., 1988. The antioxidants of higher plants. Phytochemistry 27:969978. Mead, P.S., Slutsker, L., Dietz, V., McCaig, L.F., Bresee, J.S., Shapiro, C., Griffin, P.M., and Tauxe, R.V., 1999. Food-related illness and death in the UnitedStates. Emerg. Infect.Dis. 5:607625. Miller, E.G., Fanous, R., Riverahidalgo, F., Binnie, W.H., Hasegawa, S., and Lam, L.K.T., 1989. The effects of citrus limonoids on hamster buccal pouch carcinogenesis. Carcinogenesis 10:15351537. Newhall, W.F. and Grierson, W., 1955. A low -cost self polishing, fungicidal water wax for citrus fruit. Amer. Soc. Hort. Sci. Proc. 66:146154. Nues, M.C., 2007. Quality of fruits and vegetables. Wiley -Blackwell Publishers, Indianapolis, Ind. Pittenger, D.R., 2002. p. 5 28, California master garderner handbook. University of California, Agri and natural resources, Publication. Produce Electronic Identification Board. 1995. Guide to coding fresh produce. PEIB, Newark, Del. Radha, T. and Mathew, L., 2007. Fruit Crops New Delhi Publishing Agency, New Delhi. Rahman, M.S., 2007. Handbook of Food Preservation. Marcel Dekker Inc., New York. Riederer, M. and Schreiber, L., 2001. Protecting against water loss: analysis of the barrier properties of plant cuticles. J. Exp. Bot. 52:20232032.

PAGE 76

76 Rober tson, G.L., 2005. Food Packaging. Marcel Dekker,New York. Salunkhe, D.K. and Kadam, S.S., 1995. Handbook of Fruit Science and Technology: Production, Composition, Storage and Processing. Marcel Dekker, New York. Sood, P., Ference, C., Narciso, J., and Etxe berria, E., 2008. Effect of laser labeling on the quality of tangerines during storage. Proc. Fla. State Hort. Soc. Spurr, H.W., Jr., 1994. The microbial ecology of fruit and vegetable surfaces: Its relationship to postharvest biocontrol, p. 11 23, Bio logical control of postharvest diseases: Theory and practice. CRC Press, Inc.; CRC Press. Stange, R.R., Jr. and Eckert, J.W., 1994. Influence of postharvest handling and surfactants on control of green mold of lemons by curing. Phytopathology 84:612616. S udheer, K.P. and Indira, V., 2007. Postharvest technology of horticultural crops New India Publishing Agency, New Delhi. Thopmson, J.F., Mitchell, F.G., Rumsey, T.M., Kasmire, R.F., and Crisosto, C.H., 1998. The Commodity, p. 1 7, Commercial cooling of fr uits, vegetables, and flowers. ANR Publications, University of California. Varon, M.A. and Paddock, P.F., 1978. Apparatus for applying a label to an object. Patent no. 4,123,310. U.S Department of Commerce, Patent and Trademark Office, Washington, D.C. Ve getables, 2000 summary. U.S Department of Agriculture. National Agricultural Statistics Service (NASS). Verma, L.R. and Joshi, V.K., 2000. Postharvest technology of fruits and vegetables Indus Publicating Co., New Delhi. Walter, W.M., Randallschadel, B., and Schadel, W.E., 1990. Wound-Healing in Cucumber Fruit. J. Am. Soc. Hortic. Sci. 115:444452. Willis, R., McGlasson, B., Graham, D., and Joyce, D., 1998. Introduction, p. 1 14, Postharvest: An Introduction to the Physiology and Handling of Fruit, Vegeta bles and Ornamentals. UNSW Press Ltd., Sydney, Australia. Yehoshua, B. and Rodov, V., 2002. Transpiration and water stress. In: Bartz, J. A. and Brecht, J. K. (eds.), Postharvest physiology and pathology of vegetables. Marcel Dekker, New York. Yuk, H.G., Warren, B.R., and Schneider, K.R., 2007. Infiltration and survival of Salmonella spp. on tomato surfaces labeled using a low -energy carbon dioxide laser device. HortTechnology 17:6771. Zhang, Y.H., Kramer, T.R., Taylor, P.R., and Li, J.Y., 1995 Possible immunological involvement of antoxidants in cancer prevention. American Journal of Clinical Nutrition. 62:14771482

PAGE 77

77 BIOGRAPHICAL SKETCH Preeti Sood was born in India. She obtained her Bachelor of Science in a griculture from Punjab Agricultural University, Ludhiana, India in 2006. In May 2007, she started her masters program in h orticulture at the University of Florida and successfully completed her degree in 2009.