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Determination of the Effects of Modified Atmosphere Packaging and Irradiation on Sensory Characteristics, Microbiology, ...


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DETERMINATION OF THE EFFECTS OF MODIFIED ATMOSHPERE PACKAGING AND IRRADIATION ON SENSORY CHARACTERISTICS, MICROBIOLOGY, TEXTURE AND COLO R OF FRESH-CUT CANTALOUPE USING MODELING FOR PACKAGE DESIGN By BRYAN BRUCE BOYNTON A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2004

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Copyright 2004 by Bryan Bruce Boynton

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To my parents & grandparents.

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iv ACKNOWLEDGMENTS I thank the Food Science and Human Nutr ition Department and my committee, especially Dr. Sims and Dr. Welt. I would al so like to thank all of my friends, family, and lab mates, especially Rena and Asli, who have helped me through the years. I also thank the gang at F.A.S.T. for accommodating all my irradiation needs in a very friendly manner and Wendy Dunlap at Cryovac for all packaging supplies.

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v TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES...........................................................................................................viii LIST OF FIGURES.............................................................................................................x ABSTRACT.....................................................................................................................xi ii CHAPTER 1 INTRODUCTION........................................................................................................1 2 LITERATURE REVIEW.............................................................................................6 Cantaloupe....................................................................................................................6 Respiration.................................................................................................................... 7 Fresh-cut.....................................................................................................................1 0 Flavor......................................................................................................................... .13 Modified Atmosphere Packaging...............................................................................13 Modeling.....................................................................................................................19 Michaelis-Menten.......................................................................................................22 Irradiation...................................................................................................................2 5 3 EFFECTS OF IRRADIATION ON FRESH-CUT CANTALOUPE STORED IN AN OPEN SYSTEM.............................................................................................30 Introduction.................................................................................................................30 Materials and Methods...............................................................................................32 Fruit Sample........................................................................................................32 Processing............................................................................................................32 Dosimetery..........................................................................................................34 Gas Analysis........................................................................................................35 Microbial Analysis..............................................................................................35 Color Analysis.....................................................................................................35 Texture.................................................................................................................36 Statistical Analysis..............................................................................................36 Results and Discussion...............................................................................................37 Respiration...........................................................................................................37

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vi Trial 1...........................................................................................................37 Trials 2 and 3................................................................................................38 Microbiology.......................................................................................................39 Texture.................................................................................................................44 Color....................................................................................................................45 Conclusions.........................................................................................................48 4 RESPIRATION OF IRRADIATED FRESH-CUT CANTALOUPE AND MODELLING OF RESPIRATION FOR MODIFIED ATMOSPHERE PACKAGING.............................................................................................................49 Introduction.................................................................................................................49 Materials and Methods...............................................................................................50 Fruit Sample........................................................................................................50 Processing............................................................................................................50 Dosimetery..........................................................................................................52 Gas Analysis........................................................................................................52 Modeling..............................................................................................................52 Film Permeability................................................................................................54 Modified Atmosphere Package Design...............................................................56 Results and Discussion...............................................................................................60 Modeling..............................................................................................................60 Film Permeability................................................................................................69 Conclusion..................................................................................................................71 5 DESIGN OF MODIFIED ATMOSPH ERE PACKAGE FOR IRRADIATED FRESH-CUT CANTALOUPE AND EVALUATION WITH DESCRIPTIVE ANALYSIS SENSORY PANEL...............................................................................72 Introduction.................................................................................................................72 Materials and Methods...............................................................................................73 Fruit Sample........................................................................................................73 Processing............................................................................................................73 Dosimetery..........................................................................................................75 Gas Analysis........................................................................................................76 Microbial Analysis..............................................................................................76 Sensory................................................................................................................76 Color Analysis.....................................................................................................78 Texture.................................................................................................................78 Statistical Analysis..............................................................................................78 Results and Discussion...............................................................................................79 MAP Design........................................................................................................79 Microbiology.......................................................................................................87 Texture.................................................................................................................89 Color....................................................................................................................90

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vii Sensory................................................................................................................91 Trial 1...........................................................................................................91 Trial 2...........................................................................................................98 Conclusion................................................................................................................102 6 CONCLUSIONS......................................................................................................103 REFERENCES................................................................................................................105 BIOGRAPHICAL SKETCH...........................................................................................113

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viii LIST OF TABLES Table page 2.1 Respiration rate ranges of canta loupe at various temperatures..................................9 3.1 Texture (max force kg) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 3)..............................................................................................44 3.2 Texture (max force kg) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 3)..............................................................................................45 3.3 Color of irradiated a nd non-irradiated fresh-cu t cantaloupe stored at 3 C (Trial 2)............................................................................................................46 3.4 Hue and chroma of irradiated and nonirradiated fresh-cut cantaloupe stored at 3 C (Trial 2)........................................................................................................47 3.5 Color of irradiated and non-irradi ated fresh-cut cantaloupe stored at 3 C (Trial 3)........................................................................................................47 3.6 Hue and chroma of irradiated and nonirradiated fresh-cut cantaloupe stored at 3 C (Trial 3)........................................................................................................48 4.1 Coefficients of Eqn. (4.1) and (4.2) describing the changes in oxygen and carbon dioxide concentrations, respectiv ely, over time for irradiated and non-irradiated fresh-cut cantaloupe stored in a closed system at 3 C.....................62 4.2 Coefficients of Michalis-Menten mode l Eqn (4.5) and (4.6) for changes in oxygen and carbon dioxide concentrati ons, respectively, over time for irradiated and non-irradiated fresh-cut can taloupe stored in a closed system at 3 C.......................................................................................................................63 4.3 Coefficients of the polynomial model Eqns. (4.10) and (4.11) for changes in oxygen and carbon dioxide concentrations, re spectively, over time for irradiated and non-irradiated fresh-cut cantaloupe stored in a closed system at 3 C..............66 4.4 Average oxygen (OTR) and carbon dioxide (CO2TR) transmission rates at various temperatures for films tested.......................................................................70 4.5 Arrhenius relationship values Ea and ko for two films tested..................................70

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ix 5.1 Headspace composition of modified atmos phere packages of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C...................................................85 5.2 Total plate count (TPC) a nd yeast and mold count (Y +M) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C in modified atmosphere packages (Trial 1).....................................................................................................88 5.3 Total plate count (TPC) a nd yeast and mold count (Y +M) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C in modified atmosphere packages (Trial 2).....................................................................................................89 5.4 Texture (kg) of irradiated and non-ir radiated fresh-cut cantaloupe during storage at 3 C in modified atmosphere packages....................................................90 5.5 Color (L*, a*, b*) of irradiated and n on-irradiated fresh-cut cantaloupe during storage at 3 C in modified atmosphere packages, by treatment (Trial 1)...............91 5.6 Color (L*, a*, b*) of irradiated and n on-irradiated fresh-cut cantaloupe during storage at 3 C in modified atmosphere packages, by storage.................................92 5.7 Color (L*, a*, b*) of irradiated and n on-irradiated fresh-cut cantaloupe during storage at 3 C in modified atmosphere packages, by treatment (Trial 2)...............92 5.8 Sensory results (Trial 1), by treatmen t and over storage of irradiated and nonirradiated fresh-cut cantaloupe (0 to 15 scale), stored at 3 C.................................94 5.9 Sensory results (Trial 2), by treatmen t and over storage of irradiated and nonirradiated fresh-cut cantaloupe (0 to 15 scale), stored at 3 C.................................95

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x LIST OF FIGURES Figure page 2.1 Recommended oxygen and carbon dioxide ra nges for the storage of some harvested vegetable comm odities (Saltveit, 2003)...................................................18 2.2 Recommended oxygen and carbon dioxide ranges for the storage of few harvested vegetable commodities showing differences within individual commodities (Saltveit, 2003)...................................................................................19 2.3 The radura symbol, which is required by U.S. law to be in plain sight on all packages of irradiated foods.....................................................................................26 3.1 Schematic of cantaloupe being irradiated in Ziploc bags on trays of ice.................33 3.2 Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 1)...........................................................................38 3.3 Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 2)...........................................................................39 3.4 Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 3)...........................................................................40 3.5 Total plate count (TPC) of irradiated and non-irradiat ed fresh-cut cantaloupe stored at 3 C (Trial 2)..............................................................................................40 3.6 Yeast and Molds counts of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 2)..............................................................................................41 3.7 Total plate count (TPC) of irradiated and non-irradiat ed fresh-cut cantaloupe stored at 3 C (Trial 3)..............................................................................................42 3.8 Yeast and Molds counts of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 3)..............................................................................................42 4.1 The input screen for all data necessa ry for the prediction program with variables described and units defined.......................................................................59 4.2 Percent oxygen and carbon dioxide in h eadspace during closed system storage of irradiated and non-irradiat ed fresh-cut cantaloupe at 3 C..................................62

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xi 4.3 Michaelis-Menten equation fit to observed respiration data vs. percent oxygen for non-irradiated fresh-cut cantaloupe stored in a closed system at 3 C...............64 4.4 Michaelis-Menten equation fit to observ ed respiration data vs. percent carbon dioxide for non-irradiated fr esh-cut cantaloupe stored in a closed system at 3 C...........................................................................................................................65 4.5 Second order polynomial equation fit for observed respiration data vs. percent oxygen within the critical range for non-irra diated fresh-cut cantaloupe stored in a closed system at 3 C.............................................................................................67 4.6 Polynomial equation fit to observed resp iration data vs. percent carbon dioxide for within the critical range for non-irra diated fresh-cut cant aloupe stored in a closed system at 3 C...............................................................................................68 4.7 Arrhenius relationship between the natu ral log of the oxygen transmission rate (O2TR) in ml/m2/ day and temperature for two films tested....................................70 4.8 Arrhenius relationship between the natura l log of the carbon dioxide transmission rate (CO2TR) in ml/m2/ day and temperature for two films tested..........................71 5.1 Predicted oxygen and carbon dioxide part ial pressures for 0.4 kGy samples in designed modified atmosphere packag e with initial gas flush of 4% O2 plus 10% CO2 for Trial 1 stored at 3 C...................................................................................80 5.2 Predicted oxygen and carbon dioxide part ial pressures for 0.4 kGy samples in designed modified atmosphere packag e with initial gas flush of 4% O2 plus 10% CO2 for Trial 2 stored at 3 C..........................................................................81 5.3 Actual oxygen partial pressures for all samples in designed modified atmosphere packages for Trial 1 stored at 3 C...........................................................................82 5.4 Actual carbon dioxide partial pressure s for all samples in designed modified atmosphere packages for Trial 1 stored at 3 C.......................................................82 5.5 Actual oxygen partial pressures for all samples in designed modified atmosphere packages for Trial 2 stored at 3 C...........................................................................83 5.6 Actual carbon dioxide partial pressure s for all samples in designed modified atmosphere packages for Trial 2 stored at 3 C.......................................................83 5.7 Trial 1 Predicted and observed oxygen and carbon dioxide levels inside designed modified atmosphere package containing irradi ated fresh-cut cantaloupe stored at 3 C..........................................................................................86

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xii 5.8 Trial 2 predicted and observed oxygen and carbon dioxide levels inside designed modified atmosphere package containing irradi ated fresh-cut cantaloupe stored at 3 C..........................................................................................87 5.9 Off flavor rating of treatmen ts at each storage (3 C)..............................................97 5.10 Acceptability rating of treatments at each storage date (3 C).................................97 5.11 Sweetness rating of treatment s at each storage (3 C).............................................99 5.12 Cantaloupe flavor intensity (CFI) rati ng of treatments at each storage date (3 C)......................................................................................................................100 5.13 Off flavor rating of treatments at each storage date (3 C)....................................101 5.14 Acceptability rating of treatments at each storage date (3 C)...............................101

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xiii Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy DETERMINATION OF THE EFFECTS OF MODIFIED ATMOSHPERE PACKAGING AND IRRADIATION ON SENSORY CHARACTERISTICS, MICROBIOLOGY, TEXTURE AND COLO R OF FRESH-CUT CANTALOUPE USING MODELING FOR PACKAGE DESIGN By Bryan Bruce Boynton December 2004 Chair: Charles Sims Cochair: Bruce Welt Major Department: Food Science and Human Nutrition Objectives of this project were to dete rmine effects of irradiation and modified atmosphere packaging on fresh-cut cantaloupe ( Cucumis melo Linnaeus reticulatus). Fresh-cut cantaloupe was exposed to doses ( 0.1-1.5 kGy) of electron beam irradiation and stored in open systems at 3 C. Microbial counts were c onsistently reduced in sympathy with irradiation dose. Respir ation rates were slightly higher in the irradiated samples compared to non-irradiated control within the first 24 hours and converged thereafter. Respiration rates of all samples remained similar until 7-10 days of storage when controls increased significantly. Highe r irradiation levels delaye d the onset of increased respiration. Samples irradiat ed at 0.3, 0.6, and 0.9 kGy were significantly less firm than non-irradiated samples only within 2 hrs of treatment during 13 days of storage.

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xiv Fresh-cut cantaloupe were irradiated at 0, 0.2, 0.4, and 0.6 kGy and stored in hermetically sealed containers at 3 C. Oxygen and carbon dioxide levels were measured over time. Attempts to fit respiration data to many common functi ons were unsuccessful, including the Michaelis-Menten enzyme equation, which is of ten used for this purpose. Therefore, polynomial equations were used. Arrhenius equations were used to describe temperature sensitivity of transmission ra tes for oxygen and carbon dioxide for two films commonly used in the fresh-cut industry. A computer program was written with Visual Basic for Applications using Microsoft Excel, which was used as an aid to design a modified atmosphere package based on predicted respiration and gas permea tion rates. This package was used in a subsequent study to determine combined effect s of irradiation and modified atmosphere on quality and sensory changes during storage. Irradiated samples (0.5 and 1.0 kGy) had a lowe r and more stable ra te of respiration than non-irradiated samples over the duration of the study. Color and texture remained stable for the duration of each study as measured by instrument and sensory panel. Sensory evaluation rated the 1.0 kGy sample hi ghest in sweetness and cantaloupe flavor intensity and lowest in off flavor after 17( 3) days storage. The program and model predicted respiration rates well. Low dose electron beam irradiation of fresh-cut cantaloupe with modified atmosphere packag ing offers promise as a method of extending shelf-life.

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1 CHAPTER 1 INTRODUCTION Melon is the fourth largest produced fr uit, by weight production, in the world (18,000,000 tons) behind orange, banana and grape. In 1999, the United States of America (USA) was third in melon production with 1,320,850 tons, behind China at 5,806,384 tons and Turkey at 1,800,000 tons (A guayo and others, 2004). The word “cantaloupe” is often used, especially in th e USA, to describe the netted melon or muskmelon ( Cucumis melo var. reticulatus ). A true cantaloupe is a non-netted fruit popular in Cantaluppi, Italy, a nd rarely grown in the USA (S hellie and Lester, 1999). In 1997, Florida cantaloupe acreage made up about one percent of the USA cantaloupe acreage. Fresh-cut products, also know n as lightly processed or minimally processed (Watada and others, 1996), offer convenience and reduced waste. Demand for fresh cut fruits and vegetables has been increasing grea tly in the USA for the past 10 years and is still considered in its infancy (Suslow and Cantwell, 2001). Fresh cut products have been available for many years, but in the past decade the types and quantity have expanded greatly. The sales of fresh-cut fruit have grown linearly approximately $1 billion per year (Anonymous, 1999a), due largely to incr eased regional producti on and distribution. Around 10% of all fresh fruits and vegetables sold in the USA in 1998 were fresh-cut sales at $8.8 billion, and sa les in 2004 should reach $15 billion (Anonymous, 1999b). The food service industry has been the primary purch aser of fresh-cut produc ts in the past, but warehouse stores, restaurants, and supermar kets have become major purchasers with

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2 increasing sales. The International Freshcut Produce Associati on (IFPA) purposefully chose the term fresh-cut to include the word fresh. In order for something to be labeled fresh-cut, it must meet the FDA’s current defi nition of the term fresh, which requires that produce be alive, actively respiring and ca rrying out the metabolic and biochemical activities of life. The IFPA supports the use of the term “f resh-cut” for labeling products treated by processes that do not cau se respiration to cease (Gorny, 2000). The goal of fresh-cut products is to deliver convenience and high quality. Therefore, fresh-cut products must not only be aesthetically pleasing, but also comply with food safety requirements. Consumers expect fresh-cut products to be without defects, of optimum maturity, fresh appear ance, and have high sensory and nutrient quality (Watada and Qi, 1999). Fresh-cuts are usually more perishable than uncut whole fruit, due to extreme physical stresses from processes such as peeling, cutting, slicing, shredding, trimming, coring, and removal of protective epidermal cells (Watada and others, 1996). High quality of raw product is necessary to achieve high quality fresh-cut product. Final product can only be as good as the incoming raw product. Quality of fresh-cut produce is direct ly related to wounding associated with processing. Physical wounding and damage also induce additional deleterious physiological changes within pr oduce (Brecht, 1995; Saltveit, 1997). Symptoms can be visual, such as deterioration from flaccidity w ith water loss, changes in color, especially browning at the surfaces, and microbial c ontamination (Brecht, 1995; King and Bolin, 1989; Varaquaux and Wiley, 1994). Wounding also leads to alterations in flavor and production of aroma volatile (Moretti and others, 2002).

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3 One of the first responses to wounding is a transient increase in ethylene production and an enhanced rate of respiration. Increase d respiration can lead to excessive losses of water and nutrients (Brecht, 1995). Generally, tissues with high respiration rates and/or low energy reserves have shorter postharvest lives (Eskin, 1990). Ethylene can also stimulate other physiological processes, cau sing accelerated membrane deterioration, loss of vitamin C and chlorophyll, abscission, t oughening, and undesirable flavor changes in many horticultural products (Kader, 1985). Wo unding also allows for easier attack and survival of plant pathogenic microorga nisms and food poisoning microorganisms. Radiation research directed towards the pr eservation of foods began in 1945 (Karel, 1975). “Irradiation” or “food irradiation” genera lly refers to the use of gamma rays from radionuclides such as 60Co or 137Cs, or high-energy electrons and X-rays produced by machine sources to treat foods. Electron beams (e-beams) can be emitted from the cathode of an evacuated tube subjected to an electrical potential or produced in linear accelerators (Karel, 1975). The energy of the electron beams is limited to 10 MeV for use in food treatment (Rosenthal, 1992). Using good manufacturing practices, irradiated foods have been established to be safe, w holesome and without residues (Farkas, 1998). Two major benefits of irradiation are that a pr oduct can be treated in its final package as a terminal treatment (Farkas, 1998), and the te mperature of the produc t is not significantly affected. In a paper by Minea and others (1996), st rawberries, cherries, apricots, and apples were irradiated with an elect ron accelerator at doses of 0.1 3 kGy at dose rates from 100 to 1500 Gy/min. Results showed very e ffective microbial dest ruction and a great influence on the decrease of enzymatic activitie s. Shelf life extension of at least 4-7

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4 days was achieved with sensory properties not significantly aff ected. There were no significant changes in the physical and ch emical properties of irradiated fruit. Respiration involves the consumption of oxygen and production of carbon dioxide, water and chemical energy in the form of AT P. Aerobic respiration can be slowed by limiting available oxygen. However, oxygen must be maintained above a minimum threshold to prevent anaerobic respiration (Knee, 1980). Additiona lly, increased carbon dioxide concentration has been shown to slow down ripening and respiration rates (Mathooko, 1996). Therefore, an optimal atmo sphere may be created via modified atmosphere packaging (MAP), where resp iration and ethylene production may be reduced as well as many other degrading processes. A MAP can be developed by matching the proper package and film with an appropriate amount of fruit with a given respiration rate. Modified atmosphere packages can be designed using predictive equations based on known respiration data. Respiration rate for most produce depends on the oxygen and carbon dioxide levels that surround the produce. An ideal package will maintain the desired levels of decreased oxygen and increased carbon dioxide based on the transmission rates of the package and the re spiration rate of the produce at the desired storage temperature. Packages can be flushed with the desired steady-state gas composition in order to more quickly achieve equilibrium conditions. The sooner the produce is brought to optimal atmospheric c onditions the more eff ective the package. A combination of MAP and ir radiation may have a synerg istic effect on the shelf life of produce. This was demonstrated by Prakash and others (2000) using cut romaine lettuce. Irradiation increased the shelf life of the MAP fresh-cut lettuce as compared to

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5 the non-irradiated MAP fresh-cut lettuce by re ducing the initial microbial load 1.5 log CFU/g and maintaining a 4 log CFU/g difference on the 18th day of storage. The purpose of this research had three main objectives. The first was to determine the effects of irradiation on fr esh-cut cantaloupe with regard to respiration rate, color, microbiology and texture during storage. Th e second was to use respiration data of irradiated and non-irradiated fresh-cut can taloupe to model oxygen and carbon dioxide concentrations over time in a MAP. The fina l objective was to use the model to design a MAP and test its effectiveness in maintaini ng fresh-cut cantaloupe quality using a trained descriptive analysis panel and determine th e designed MAP effects on product color, microbiology and texture.

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6 CHAPTER 2 LITERATURE REVIEW Cantaloupe Cantaloupe ( Cucumis melo ) is a member of the Cucu rbitaceae family. Cucurbits, of which squash, cucumbers and watermelon are all a part, originated in different locations. The cantaloupe is believed to have originated in Africa. Within the Cantaloupensis group, muskmelon fruit are classified into two major categories in the USA, the eastern and western type cantaloupe. The eastern cantaloupe is distinct by its sutured and netted surface and it has a spherical or elongated oval shape. Easterns also have relatively large moist se ed cavities and soft to medium flesh with strong aroma. Easterns characte ristically store poorly with a relatively short storage life. They have been adapted to grow in many clim ates and are not intended for long transport. The western type cantaloupe is commonly grow n in the arid southwestern USA and other countries with similar climate and tends to have a longer shelf-life than easterns (Lamikanra and others, 2003; Rubatzky and Yamaguchi, 1997). Westerns are usually without sutures, extensively netted, with a rugged thick fl esh suitable for long distance shipping. Their seed cavity is small and dry. "Super Market," "Summet," "Magnum 45," "Primo," "Mission," "Ambrosia," "Athena," "Cordele," and "Eclipse" are the Eastern Choice type cantaloupes that will grow produc tively in Florida (Mossler and Nesheim, 2001; Hochmuth and others, 2000). The average harvested yields per acre of cantaloupe crops in Florida have been 150 cwt over the la st few years (Hochmuth and others, 2000). Acreage intended for harvest in the USA for 2004 was forecast at 33,300 acres, up 13

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7 percent from 2003 (USDA Economi cs, Statistics and Market Information System, 2004). Cantaloupe is used more in the fresh-cut i ndustry than any other fruit (Lamikanra and Richard, 2002). Cantaloupe is prone to chilling injury wh en stored at temperatures less than 2 C for several days. Chilling injury sensitivity decreases as melon maturity and ripeness increase. Another source of postharvest lo ss can be disease, which can depend on season, region and handling practices. Commonly, decay or surface lesions result from fungal pathogens Alternaria, Penicillium, Cladosporium, Geotrichum Rhizopus, and to a lesser extent Mucor Cantaloupes are predominantly graded on external appearances and measured soluble solids. U.S. grades are Fancy, No. 1, Commercial and No. 2. Federal Grade Standards specify a minimum of 11% so luble solids for U.S. Fancy ("Very good internal quality") and 9% sol uble solids for U.S. 1 ("Good in ternal quality") (Suslow and others, 2001). As cantaloupe matures on the vine, the fru it begins to separate at the abscission layer where the stem (peduncle) attaches at the fruit. The maturity level is determined by the degree of separation and called “slip.” Therefore, if the abscission layer is detached, then the maturity level is called s lip, if it is detached, then it is called slip, etc. A good indicator of full ripeness and harvest time is pa rtial to complete separation. In the USA, to full slip is the maturity level for commercial practice of harvesting cantaloupe (Beaulieu and others, 2004). Respiration The word respiration is de rived from the Latin word respirare which literally means to breathe (Noggle and Fritz, 1983). It was first discovered that humans consume

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8 oxygen and produce carbon dioxide. At the e nd of the eighteenth century, Dutch plant physiologist Ingen-Housz discovere d that not only animals but also plants respire. It was well established by the middle of the nineteenth century that all growing cells of higher plants respire at all times, in the light as well as the dark, using oxygen, oxidizing carbonaceous substances, and produc ing carbon dioxide and water. Glucose is the respiratory substrate most commonly consumed in cellular respiration. The overall reac tion is usually written as C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O +Heat (2.1) However, this reaction omits the fact that oxygen does not react directly with sugar in respiration. Wate r molecules are joined with inte rmediate products during glucose degradation, one water molecule for each ca rbon in the sugar molecule. The hydrogen atoms in intermediate products are joined with oxygen to form water. A more complete reaction is written as C6H12O6 + 6 H2O + 6 O2 -> 6 CO2 + 12 H2O (2.2) Respiratory substrates co mmonly consumed are carbohydrates, lipids and organic acids. The overall sequence of events is re ferred to as respiratory metabolism. An abbreviated outline of respiratory metabolism is the process of glucose, in the cytosol, becoming pyruvic acid through glycolysis, goin g to the tricarboxylic acid cycle in the mitochondria and finally the electron transpor t system. Oxygen is also needed as a substrate in the respirator y reaction. The gas must travel from the surrounding environment through intercellu lar spaces, cell wall, cytoplasm and other membranes of plant cells. The rate of diffusion w ill have an effect on respiration rate.

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9 The rate of respiration for fresh-cut produce is measured by the amount of oxygen consumed or carbon dioxide produced per weight of produce for a period of time at a certain temperature. Table 2.1 lists the re spiration rates of cantaloupe at various temperatures (Kader, 1992). Table 2.1. Respiration rate ranges of cantaloupe at various temperatures. Temperature C mg CO2 kg-1 h-1 0 5 to 6 4 to 5 9 to 10 10 14 to 16 15 to 16 34 to 39 20 to 21 45 to 65 25 to 27 62 to 71 Ranges exist in respiration rate due to cultivar, growing season and conditions, harvest maturity and technique, and many other factors. Many methods are available for measuring respiration rate. The most common are the closed or static system, the flowing or flushed system and the permeable system (Fonseca and others, 2002). In the closed syst em method, a respiring sample is closed in an airtight container with known vol ume and initial oxygen and carbon dioxide concentrations. Gas samples are taken ove r time and respiration rate is based on concentration change (Eqns. 2.3 and 2.4). ) t t ( M 100 V ) y y ( Ri f outflow O low inf O O2 2 2 (2.3) ) t t ( M 100 V ) y y ( Ri f low inf CO outflow CO CO2 2 2 (2.4) The flow through system passes gas of know n concentrations over the sample in a barrier container. The respiration rate is de termined by the differences in the inflow and outflow gases (Eqns. 2.5 and 2.6).

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10 M 100 F ) y y ( Rout O in O O2 2 2 (2.5) M 100 F ) y y ( Rin O out CO CO2 2 2 (2.6) The permeable system uses a package of known gas transmi ssion rates and size filled with sample. Using the permeabil ity and the steady-state concentrations, respiration rate can be determined (Eqns. 2.7 and 2.8). ) y y ( M L 100 A P R2 2 2 2O eO O O (2.7) ) y y ( M L 100 A P R2 2 2 2eCO CO CO CO (2.8) 2ORand 2CORare respiration rate, oxygen uptak e and carbon dioxide evolution, respectively, y is volumetric concentration, V is volume, M is mass, t is time, f is final, i is initial, F is flow rate, A is area of package, P is permeability, L is thickness and e is external. Each system has its limitations and problem s, but an accurate range should be able to be achieved. Fresh-cut The fresh-cut industry continues to grow with technology increasing shelf life and duration of quality. Shelf life of fresh-cut fr uits and vegetables ranges from 7 20 days when held at optimal temperatures (Watad a and Qi, 1999). Fresh-cut cantaloupe had a reduction of “typical” fla vor during the first 4 days when stored at 4 C in rigid barrier containers (O’Connor-Shaw and others, 1994). At 7 days, bi tterness levels were lower and the fruit was firmer. At day 11, fruit was paler than originally and white colonies of

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11 microbes were observed. In a study by Ayhan and others (1998), the shelf life of freshcut honeydew and cantaloupe was determined. F our treatments were tested: I Fruit was cut without washing, II Fruit was washed with water before cutting, III Whole fruit was dipped in 200 ppm hypochlorite solution and cut fr uit was dipped in 50 ppm hypochlorite solution twice, IV Whole fruit was dipped in 2000 ppm hypochlor ite solution and cut fruit was dipped in 50 ppm hypochlorite solution twice. All samples were stored in full barrier laminated nylon film at 2.2 C. A 2 log (CFU/g) reduction of surface aerobic plate count for cantaloupe was observed in tr eatment III compared to treatment I and a 3.3 log reduction occurred between treatment IV and treatment I. The total psychotropic count of the processed cantal oupe was similar with a 3.3 l og reduction for both treatment III and IV compared to treatment I at day 0 with a continued 3 log reduction through day 20. Sensory characteristics (odor, taste, ove rall flavor, texture, appearance and overall acceptance) were evaluated during the 20 day storage of cantaloupe. Treatments III and IV were rated significantly hi gher in all characte ristics except odor on day 15, although they were rated higher, just not significantly No difference occurred between treatment III and IV for all sensory characte ristics through the entire study. The efficacy of decontamination treatments using water, sodium hypochlorite, hydrogen peroxide, commercial detergent formulations containing dodecylbenzene sulfonic acid and phosphoric acid, or trisodi um phosphate on fresh-cut cantaloupe was determined (Sapers and others, 2001). Micr obial population reductions were less than 1 log when plugs were washed with water, 1 to 2 logs with washing and sanitizing agents applied individually, and 3 l ogs with hydrogen peroxide. Th e most effective treatment, yielding a shelf life of greater than 2 w eeks, was hydrogen peroxide applied at 50 C.

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12 Calcium chloride dips are another trea tment commonly used in the fresh produce industry as a firming agent, the joining of cell wall and middle lamella improved structural integrity (Morris, 1980) and exte nded shelf life. Fresh-cut cantaloupe was dipped in 2.5% solutions of e ither calcium chloride at ~25 C or calcium lactate at ~25 and 60 C (Luna-Guzman and Barrett, 2000). Calcium chloride and calcium lactate provided significantly firmer samples than wa ter dipped at all dates tested during the 12 day storage. The maintenance of firmness te nded to be higher in the calcium lactate treatments. The sensory panel also rated th e calcium dipped samples significantly higher in firmness. The panel rated the calcium ch loride samples higher in bitterness, but not the calcium lactate samples. All other attrib utes were not significantly different among samples analyzed. No differences in tota l plate count were observed between any treatments. Many variables must be taken into acc ount when processing fresh produce to be stored for later consumption. The sharpness of the blade of the knife used can have an effect on the shelf life and quality of freshcut cantaloupe (Portella and Cantwell, 2001). Fresh-cut cantaloupe was prepared using a stainl ess steel borer with sharp or blunt blades and stored for 12 days in air at 5 C. Pieces cut with the sharp borer maintained marketable visual quality for at least 6 da ys and those cut with the blunt borer were considered unacceptable with su rface translucency and color changes. Decay, firmness, sugar content and aroma did not differ due to sharpness of borer. Blunt cut pieces had higher ethanol concentrations, off-odor scores electrolyte leakage and darker orange color with L* and chroma values decreasing significantly during st orage. Respiration

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13 rates were not affected for those samples stored at 5 C, but the blunt pieces stored at 10 C had a significant in crease after day 6. Flavor Volatile aroma constituents were assessed immediately after processing and after storage for 24 hrs, 3 days and 7 days at 4 C in fresh-cut cantaloupe (Lamikanra and Richard, 2002). Aliphatic and aromatic este rs were the predomin ant compounds isolated from the fruit immediately after cutting. Me thylbutyl acetate and hexyl acetate were the most prominent compounds, which are typically present in large quantities in cantaloupe (Nussbaumer and Hostettler, 1996; Moshonas and others, 1993). After storage for 24 hrs, a considerable decrease in the concentration of esters occurred and synthesis of terpenoid compounds B-ionone and geranylacetone was detected After the initi al decrease, the volatile aroma compounds remained fairly stab le over the 7 day stor age. The amount of terpenoid compounds decreased after the first day, but remained stable from day 3 to 7. The reduction of esters, which could be pr ecursors for synthesis of secondary volatile aroma compounds, may be directly related to a decrease of fresh like attributes in freshcut cantaloupe during storage. Modified Atmosphere Packaging Modified atmosphere packaging (MAP) refers to any container used to control the concentration of specific gases in order to achi eve levels desirable to content. The goals for MAP of fresh-cut produce are to maintain a lower oxygen and higher carbon dioxide level than that of the surroundings. Reducing respiration rate and extending shelf life are the returns for the added cost of using MAP films.

PAGE 28

14 The design of a MAP appears to be ra ther simple on the surface, but many considerations must be accounted for. The te mperature the produce is going to be held at is important since metabolic activity is very dependent on temperature. Most packages will go from the packinghouse, to a truck, to the point of sale, all with different temperatures. The change in respiration rate due to an increase in temperature is usually greater than the change in permeability of the package (Exama and others, 1993). The package may not be able to get back to equilibrium even once the lower temperature is achieved again, sin ce the product may have used more oxygen than planned and gone into anaerobic respiration. Respiration rates of horticu ltural commodities is also dependent on the amount of available oxygen and carbon dioxide present in the surrounding e nvironment (Beaudry, 2000; Watkins, 2000). Determination of the optimal surrounding atmosphere for freshcut produce is difficult due to the numerous possible combinations of oxygen and carbon dioxide concentrations. The changes in sensor y properties of fresh-cu t cantaloupe held at different controlled atmosphe res were determined (O’Conno r-Shaw and others, 1996). A large experimental design was used with 36 gas combinations and four air treatments. All possible combinations of 3.5, 6, 10.5, 13, 15.5, and 17 percent oxygen with 0, 6, 9.5, 15, 19.5, and 26 percent carbon di oxide were evaluated at 4.5 C. At 14 day intervals, a trained sensory panel assessed the stored fru it. Three treatments remained acceptable up to 28 days: 6% carbon dioxide and 6% oxyge n, 9.5% carbon dioxide and 3.5% oxygen, and 15% carbon dioxide and 6% oxygen. Great est reductions of quality were in samples held in 0, 19.5 or 26% carbon dioxide. Many other combinations of oxygen and carbon dioxide would have to be tested to finalize an optimal atmosphere.

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15 Internal gas mixtures of m odified atmosphere package may be attained naturally, by letting the respiration of the produce d ecrease oxygen and increase carbon dioxide to the desired levels (termed “p assive MAP”), or the packag e may be flushed with the desired gas mixture (active MAP). In a study by Bai and others (2001), fresh-cut cantaloupe was placed in film s ealed containers, stored at 5 C and allowed to attain an internal gas atmosphere na turally (nMAP) or flushed with 4 kPa oxygen and 10 kPa carbon dioxide (fMAP) and another group was maintained near atmospheric levels by perforating the film (PFP). The oxygen and carbon dioxide levels in the PFP remained similar to the ambient air until day 9 and then only changed by 1 to 2 kPa during the next 3 days. Using a flow through system to simulate the atmosphere within the PFP, the oxygen uptake was stable until day 5 at which po int it increased more than sixfold during the next 7 days. Neither oxygen or carbon dioxide reached an equilibrium in the nMAP, with the oxygen concentration decreasing to 8 kPa and the carbon dioxide increasing to 12 kPa during the 12 day storage. Respirati on rate remained stable through day 9 and then increased twofold by day 12. In the fMAP, the gas mixture remained essentially unchanged at 4 kPa oxygen and 10 kPa carbon dioxide Respiration rate was also stable in the fMAP for the duration of 12 days. Th e ethylene accumulation of the fMAP was of that of the nMAP. Visual quality and aroma were rated acceptable for 12 days for the nMAP and fMAP, whereas the PFP was only acceptable for an average of 6 days. Translucency was significant 2 da ys earlier in the nMAP and was two to fivefold higher between 9 and 12 days compared to the fM AP. Total microbial population was 1 log lower in both nMAP and fMAP compared to PFP. Yeast and mold populations were around 2 logs lower for both nMAP and fMAP Therefore, rapidly flushed active MAP

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16 (4 kPa oxygen and 10 kPa carbon dioxide) main tained better quality had better color retention and reduced translu cency, respiration rate, and microbial population compared to an air control (perforated film) and passive MAP (naturally obtained equilibrium). Respiration rate of fresh-cut apple slices was reduced by increasing carbon dioxide partial pressures from 0 to 30 kPa at 0.5, 1 and 10 kPa oxygen during storage (Gunes and others, 2001a). Carbon dioxide production was not affected during the first week of storage. By week 2 and 3, respiration rate decreased as carbon dioxide partial pressure increased and oxygen partial pressure decrease d. Elevated levels of carbon dioxide reduced respiration rate by inhibiting succi nate dehydrogenase and other enzymes of the TCA cycle with an indirect effect on oxida tive phosphorylation and a direct effect on mitochondrial activity (Mathooko, 1996). The elevated carbon dioxide also reduced browning to a limited extent. The question of whether an optimal cont rolled atmosphere for fresh-cut produce can really be found was reviewed extensivel y in a paper by Saltveit, (2003). A truly optimal atmosphere may be impossible to find due to the natural variability in the raw material and its dynamic response to pro cessing and storage conditions. The best approximations for an optimal modified atmosphere are derived from empirical observations from experimentation including a variety of temperature, relative humidity, oxygen, carbon dioxide, ethylene and duration c onditions during storage. Since these variables are usually held constant for the dura tion of the static experiment, the variability and dynamic response of the commodity to changes in storage environment may be overlooked. Many other variables may affect the environment such as microbial load, light, orientation of the product in the gravitational field a nd the concentration of other

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17 gases. The optimal modified atmosphere fo r some quality parameters can be mutually exclusive during storage. Mold control, reduction of ethylene ef fects and reduction of chlorophyll loss are benefits of high carbon dioxide leve ls. Increased anaerobic respiration and phenolic metabolism may also result from high carbon dioxide levels. Although low oxygen levels may reduce respir ation and ethylene synthesis, it also increases the chance of anaer obic respiration, off flavor production and growth of anaerobic microorganisms. The optimal storage atmosphere must be defined by the company responsible for the sale of the commodity. The goal is to pr oduce the best quality product, which allows for subjective and objective measures. Peopl e perceive cantaloupe in different ways, therefore there are likel y to be differences in descript ion about a “perfect” cantaloupe. Some may prefer a darker orange color and so fter texture and others may prefer a lighter orange color and firmer texture. Different cultivars, seasons and market segments make a strict universal description of quality very difficult to construe. Some quality aspects may be sacrificed for others along with thos e which jeopardize shelf life. Which market segment does a company package for and wh at quality parameters are the most important? These are the questions that mu st be answered in package design and are most likely answered by cost analysis and return on investment. A mathematical model that incorporates the dynamic response of th e produce to the storag e environment may be necessary for the optimal modified atmosphere design of a package. The following Figures (2.1 and 2.2) show ranges of recommended oxygen and carbon dioxide levels for storage of produce (S altveit, 2003). These ranges can be used

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18 as guidelines for designing a modified atmos phere package. The recommended range for fresh-cut cantaloupe is 3 5% oxygen and 5 15% carbon dioxide (Gorny, 2001). Figure 2.1. Recommended oxygen and carbon di oxide ranges for the storage of some harvested vegetable comm odities (Saltveit, 2003).

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19 Figure 2.2. Recommended oxygen and carbon di oxide ranges for the storage of few harvested vegetable commodities showing differences within individual commodities (Saltveit, 2003). Figure 2.2 shows differences in recomme nded oxygen and carbon dioxide levels for storage within individual commodities. Differences within commodities tightens the range of atmospheres, enhancing the degr ee of difficulty in designing an optimal atmosphere for MAP. Modeling Predictive modeling in modified atmosphe re packages of fresh-cut produce is centered around the permeance of the film a nd the respiration rate of the product. Determination of the amount of oxygen di ffusing through a modified atmosphere package can be determined using Fick’s fi rst law of diffusion (Zhu and others, 2002): ) in pO out pO ( A X P J2 2 O O2 2 (2.9)

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20 where 2OJis the rate of diffusion of oxygen through the film in unit time (ml (STP)/hr), 2OP is oxygen permeability coefficient of the film (ml (STP)/m hr kPa), A is the total film surface area (m2), and X is the thickness of the film (m), pO2in is the oxygen partial pressure (kPa) inside the package and pO2out is the oxygen partial pressure (kPa) outside the package. A similar equation can be used for the rate of diffusion for carbon dioxide: ) out pCO in pCO ( A X P J2 2 CO CO2 2 (2.10) where 2COJ is the rate of diffusion of carbon di oxide through the film in unit time (ml (STP)/hr), 2COPis carbon dioxide permeability coeffici ent of the film (ml (STP)/m hr kPa), A is the total film surface area (m2), and X is the thickness of the film (m). pCO2in is the carbon dioxide partial pressure (kPa) inside the package and pCO2out is the carbon dioxide partial pressure (kPa ) outside the package. Acco rding to these equations, the 2OJ and 2COJ would both be positive under normal atmospheric conditions, around 21% oxygen and 0% carbon dioxide. Therefore, thes e equations are for typical conditions and attention must be paid if th e surrounding environment or fl ush gas causes a negative to result in the (pO2out – pO2in) or (pCO2in – pCO2out) part of the equation. Respiration rate of the product must be written in equation form to use for modeling. Most empirical models are for a specific temperature with the controllable variables being the oxygen a nd carbon dioxide concentrations. Many different models are presented in the literature: linear (Henig and Gilbert, 1975; Fishman and others, 1996; Lakalul and others, 1999), polynomial (Ya ng and Chinnan, 1988; Gong and Corey, 1994), exponential (Cameron and others, 1989 ; Edmond and others, 1993), and many Michaelis-Menten type equations (Lee a nd others, 1991; Haggar and others, 1992;

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21 Talasila and others, 1994). A typical respirat ion rate equation will have the units ml or mg of oxygen or carbon dioxide per kg of pr oduce per unit of time. Therefore, the oxygen consumption rate of produce in a p ackage can be expressed by Eqn. (2.11). 2 2O OR W Q (2.11) Where 2OQ is the oxygen consumption rate with units ml (STP)/ h and W is the weight of the produce in the sa me mass unit used in the respiration equation. Similarly, the carbon dioxide production rate of produce in a packag e can be expressed by Eqn. (2.12). 2 2CO COR W Q (2.12) Where2COQis the carbon dioxide production rate with units ml (STP)/h and W is the weight of the produce in the same mass un it used in the respir ation equation. To predict the gas compositions in side a package a stepwise integration can be performed with Eqns. (2.13 and 2.14) (Hayakawa and others, 1975; Zhu and others, 2002). t V ) t ( Pt ) Q J ( ) t ( pO ) t t ( pO2 2O O 2 2 (2.13) t V ) t ( Pt ) J Q ( ) t ( pCO ) t t ( pCO2 2CO CO 2 2 (2.14) The Pt term is expressed in Eqn. (2.15). The total pressure inside a package may not be constant due to th e respiratory quotient (RQ; carbon dioxide produced / oxygen consumed) not being unity and with most polym er films the ratio of the carbon dioxide to oxygen transmission rates is at least 2 or 3 to 1. Since nitrogen is neither used nor produced it can be assumed that the number of moles is constant and the total internal pressure at t can be calculated with the following equation (Moyls and others, 1992):

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22 303 101 t N % o N % t ) Pt (2 2 (2.15) where %N2o is the percent of nitrogen in the su rrounding atmosphere outside of the bag and %N2t is the percent of nitrogen inside the bag at time t. Using Eqns. (2.13 and 2.14), the internal gas composition at any time during the storage can be determined. An optimal pack age can be designed by adjusting the weight of the produce, choosing the best available film and amount of surface area, determining and flushing with the best gas composition and the amount of free volume as well as the optimal storage temperature. Michaelis-Menten The concept of enzyme kinetics being used for predictive modeling of the respiration rate of produce was introduced by Yang and Chinnan (1988). Lee and others (1991) suggested that a Michae lis-Menten type equation might work since re spiration is controlled by enzymatic reactions cataly zed by allosteric enzymes and governed by feedback inhibition (Solomos, 1983). They also speculated that since the MichaelisMenten equation is used to describe the resp iration rate of microorganisms and that fresh produce respiration and microorganism respirati on are similar, that it could be used for produce. In an atmosphere void of carbon dioxide, the respiration rate dependent on oxygen concentration can be dete rmined with Eqn. (2.16). ] O [ Km ] O [ Vm R2 2 (2.16) Vm is the maximum respiration rate with units mL/kg hr or mg/kg hr, [O2] is the oxygen concentration in percen tage, Km is the Michaelis-M enten constant in percent oxygen.

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23 The equation for the respiration rate with an uncompetitive inhibition mechanism due to carbon dioxide is expressed in Eqn. (2.17). ] O )[ Ki ] CO [ 1 ( Km ] O [ Vm R2 2 2 (2.17) Vm, Km and [O2] are the same as above and [CO2] is the carbon dioxide concentration in percentage and Ki is the inhibition constant in percent carbon dioxide. Functionality of (Eqn. 2.17) is dependent on sufficient oxygen concentration for aerobic respiration (Lee and others, 1991). To test the validity of these equations for use as a respiration model, published data was evaluated by Lee and others (1991). Eqn. (2.16) was linearized to become Eqn. (2.18). V m ] O [ V m Km r ] O [2 2 (2.18) The data were fit and a Haynes plot was preferred over the Lineweaver-Burk plot due to a more even distribution of error. Most of the data showed high linearity with coefficients of determination (R2) above 0.95. With the exclusion of one set of published data, the Michealis-Menten equation was conclu ded to express dependence of respiration rate on oxygen quite well. Eqn. (2.17) was linearized as Eqn. (2.19) to examine the effects of carbon dioxide on respiration rate. ] CO [ Vm Ki 1 ] O [ 1 Vm Km Vm 1 r 12 2 (2.19) Published data show high linearity for Eqn. (2.19) as well, with all coefficients of determination above 0.92. This equation was determined to be va lid up to the carbon

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24 dioxide tolerance limit of the produce. High levels of carbon dioxide may cause an increase in anaerobic respiration. The resp iratory quotient may change during anaerobic respiration along with the normal controlling effect on respiration rate of the oxygen and carbon dioxide concentrations. Lee and others (1991) also tested the Michaelis-Menten model with fresh-cut broccoli. The model was confirmed as successf ul based on the high linearity of the data on a Hanes plot and a small standard deviat ion of the respirati on rate. A modified atmosphere package was designed and test ed. The gas composition in the package agreed very well with predicted oxygen and carbon dioxide concentrations. The model proved to only work well when the oxygen le vel was high enough for aer obic respiration. Hagger and others (1992) developed an enzy me kinetics based respiration model, along with the closed system method for gene rating respiration rates of fresh produce as a function of oxygen and carbon dioxide concentra tions. Four temperat ures were tested and model parameters for Eqn. (2.17) were es timated with coefficients of determination all above 0.98. Respiration rates could be predicted at any con centration of oxygen and carbon dioxide. The model was tested with a permeable package and the values obtained at 13 C. The experimental and predicted gas c oncentrations were in good agreement. Equilibrium was not reached inside the packag e due to the high respiration rate of cut broccoli and the low oxygen and carbon dioxide permeabilities of the LDPE film used. Anaerobic respiration took over as the oxygen concentration approached zero. Jacxsens and others (2000) attempted to design MAPs for fresh-cut vegetables subjected to temperature changes. Respir ation rate was descri bed by four MichaelisMenten type equations. The equations were uninhibited, in the absence of CO2, and the

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25 three possible types of inhibition were competitive, uncompetitive, and noncompetitive. All four equations gave similar results in their experimentation considering CO2 levels never exceeded 10-15%. Only the in hibiting effect of a decreased O2 level on respiration rate was taken into consideration. High R2 values for the Michaelis-Menten coefficients Vmax and Km were determined although overestimation of O2 levels inside equilibrium modified atmosphere packages was common among fresh-cut produce tested. Irradiation A brief description of the history of f ood irradiation in the USA was summarized from Rosenthal (1992). In the early 1920’s, irradiation was used to kill the human parasite Trichinella spiralis in pork. In the 1940’s, larg e quantities of radioisotopes became readily available at low cost due to th e advent of many nuclear reactors. Van de Graaff generators and linear accelerators, wh ich produce high-energy electron beams also became available at the same time. The study of food irradiation began at Massachusetts Institute of Technology under the guidance of Prof. B. E. Proctor and spread to laboratories around the world after World War II. Most studies in the United States were aimed at sterilizing food. It was determined that doses up to 50 kGy were needed to eliminate heat resistant spores such as Chlostridium botulinum. However, this high dose caused unacceptable change in flavor and colo r, and the difficulty of finding participants for testing the wholesomeness of irradiated foods led to the decline in interest in irradiation technology. The inte rest in low-dose irradiation of food was rekindled in the late 1960’s with increased concern of synthetic additives, chemical residues and the prevention of food poisonings. This led to the U.S. Food and Drug Administration (FDA) ruling that ionizing ra diation should be treated as a food additive not a food process. This changed in 1986 when the F DA approved the use of ionizing radiation to

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26 inhibit the growth and maturation of fresh f oods and to disinfect food of arthropod pests at doses not to exceed 1 kGy (Rosenthal 1992; Code of Federal Regulations, 2004). The U.S. Code of Federal Regulations outlines the uses of ionizing radiation for the treatment of foods (Code of Federal Regulations, 2004). En ergy sources are limited to gamma rays from sealed units of radionuclid es Cobalt-60 and Cesium-137, electrons and x-rays generated from machine sources at energies not to exceed 10 and 5 million electron volts, respectively. According to U.S. law, foods treated with irradiation shall bear the logo (Figure 2.3) ; know as the radura, along w ith the following statement “Treated with radiation” or “Treated by irradiation” in a ddition to information required by other regulations. Figure 2.3. The radura symbol, which is required by U.S. law to be in plain sight on all packages of irradiated foods.

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27 Climacteric fruit ripening ma y be stimulated or delaye d by low-dose irradiation. Skin browning or scalding, internal browning and increased sensitivity to chilling injury are possible post irradiation problems. Pectin s, cellulose, hemicellulose and starch may be depolymerized in response to irradiation, which may cau se softening. There is a paucity of knowledge of the biochemical mechanisms underlying the delay in senescence of climacteric fruits by irradiation. Many hormonal and cellular ch anges occur during the ripening process and an accurate relationship with irradiation has not been established (Thomas 1985; Rosenthal 1992). Minea and others (1996) irradiated strawberries, che rries, sour cherries, apricots, nectarines and apples with an electron beam using a linear electron accelerator at doses between 0.1 and 3 kGy. A shelf-life extens ion was achieved for all irradiated fruit ranging from 4-8 days. No significant cha nges in soluble solids content (Brix), total sugars, reducing sugars, pH value and conduc tivity were observed in irradiated fruit compared to non-irradiated. An average 10% loss of vitamin C occurred in irradiated samples. The most efficient doses with respect to shelf-life extension were determined to be: 2-3 kGy for strawberries, 1 kGy for cherri es, 0.5-1 kGy for sour cherries, 0.5-0.7 kGy for apricots, 1-2 kGy for nectar ines and 0.5 kGy for apples. Irradiation wa s reported to have no effect on organoleptic properties fo r all fruits tested, a lthough on most storage dates irradiated fruits rated 23 increments higher in acceptability than non-irradiated on a 1-5 scale. Lu and others (In Press) irradiated freshcut celery at 0.5, 1.0 or 1.5 kGy using a gamma source. Microbial populations decrease d with an increase of dose with a 2 log reduction in bacteria and a 1 log reduction in fungi at 1.0kGy. Bacteria of the E. coli

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28 group were reduced to < 30 mpn (maximum probable number / 100 g) in the 1.0 kGy sample compared to 436 mpn in the non-irra diated controls. Re spiration rate and polyphenol oxidase activity were significantly reduced in the 1.0 and 1.5 kGy samples on day 3, 6, and 9. The sensory quality of irra diated celery was better than that of the nonirradiated celery, and the 1.0 kGy sample was the best among irradiated samples. Chervin and others (1992) examined the reduction of wound-i nduced respiration by irradiation in fresh-cut and intact carrots stored at 20 C. The uptake of oxygen in grated carrots was twice that of the intact organs. The respiration rate of intact carrots treated with gamma rays (2 kGy) was observed to be higher than non-irradiated samples at time 0, but after 12 hours the difference disapp eared. The non-irradiat ed grated carrots respiration rate increased mo re rapidly and peaked higher than the irradiated grated carrots. The consequences of irradiation on the composition of modified atmospheres in plastic bags were also eval uated. Differences occurred in the evolution of gaseous atmospheres in control and irradiated grated carrots. The concentr ation of carbon dioxide reached 17% after 17 days in non-irradiated samples, but they did not reach 10% in treated samples at 10 C. The values of the RQ remained stable and close to one throughout the experiment for all samples. Radiation induced texture ch anges in produce can be a major limiting factor. Many plant tissues have a th reshold level of irradi ation dose at which point softening becomes a problem (Massey and Bourke, 1967). Softeni ng in tissues may be due to breakdown of cell wall constituents such as pectin, cellulose and hemicellulose, and alteration of semipermeable membranes resulting in structur al weakening and loss of turgor (Kertesz and others, 1964). A threshold of 0.34 kGy was found for fresh-cut apple slices (Gunes

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29 and others, 2001b). Firmness decreased with in creased irradiation dos e above 0.34 kGy. Dose rate was determined to affect textural response of slices on day 0 with 2 kGy/h resulting in less loss of firmness than 0.4 kGy/h. The effect of dose rate was not significant after 3 and 6 days of storage at 5 C. Firmness slightly increased over time in samples irradiated at 1 kGy.

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30 CHAPTER 3 EFFECTS OF IRRADIATION ON FRESH-CUT CANTALOUPE STORED IN AN OPEN SYSTEM Introduction Fresh-cut produce continues to incr ease in demand with cantaloupe (Cucimus melo L reticulatus) among the most important in terms of volume produced and value (Suslow and others, 2001). The goal of fresh-cut pr oducts is to deliver convenience and high quality. Therefore, fresh-cut products must not only be aesthetically pleasing, but also comply with food safety requirements. C onsumers expect fresh-cut products to be without defects, of optimum maturity, fresh appearance, and have high sensory and nutrient quality (Watada and Qi, 1999). Fres h-cuts are usually more perishable and unstable than the original products, due to ex treme physical stresses from processes such as peeling, cutting, slicing, shredding, tr imming, coring, and removal of protective epidermal cells (Watada and others, 1996). A 10 day shelf life of fresh-cut melons is desirable in the distribution chai n, but marketing in retail stores usually does not exceed 3 day (Bai and others, 2001). Extension of shelf life while maintaining salable quality would be advantageous to producers and consumers. Quality of fresh-cut produce is directly related to wounding associated with processing. Physical wounding and damage also induces additional deleterious physiological changes within produce (Br echt and others, 2004; Saltveit, 1997). Symptoms can be visual, such as deteriorati on from flaccidity with water loss, changes in color, especially browning at the surfaces, and microbial contamination (Brecht, 1995;

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31 King and Bolin, 1989; Varaquaux and Wiley, 1994). Wounding also leads to reduction in flavor and aroma volatile production (Moretti and others, 2002). One of the first responses to wounding is a transient increase in ethylene production and an enhanced rate of respiration. Increa sed respiration can lead to excessive losses of nutrients (Brecht, 1995). Ethylene can also stimulate other physio logical processes, causing accelerated membrane deterioration, loss of vitamin C and chlorophyll, abscission, toughening, and unde sirable flavor changes in many horticultural products (Kader, 1985). Wounding also allows for easier attack and survival of plant pathogenic microorganisms and food poisoning microorganisms. Radiation research directed towards the pr eservation of foods began in 1945 (Karel, 1975). Food irradiation generally refers to the use of gamma rays from radionuclides such as 60Co or 137Cs, or high-energy electr ons and X-rays produ ced by machine sources to treat foods. Using good manufacturing pr actices, irradiated foods have been established to be safe, wholesome and w ithout residues (Farkas, 1998). Two major benefits of irradiation are that a product can be treated in its final package as a terminal treatment (Farkas, 1998), and the temperature of the product is not significantly affected. In a paper by Minea and others (1996), strawberries, cherries apricots, and apples were irradiated with an electron accelerator at dos es ranging from 0.1 to 3 kGy at dose rates from 100 to 1500 Gy/min. Results showed irradiation was very effective by way of microbial destruction and had a great influence in decreasing enzymatic activities. Shelf life extension of at least 4 to 7 days was achieved with organoleptic properties not significantly affected. There were no signi ficant changes in the physical and chemical properties of the irradiated fruit.

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32 To be labeled fresh-cut, fruit tissue must be living and theref ore respiring (Gorny, 2000). Respiration involves the cons umption of oxygen and production of carbon dioxide and water. Inhibition of respir ation and ethylene production, which slows deteriorative changes of senescence, gene rally extends shelf life (O’Connor-Shaw and others, 1996). Therefore, decreasing respirat ion rate without comp lete inhibition would be beneficial to produce to be labeled and sold as fresh-cut. The purpose of this research was to dete rmine the effects of different doses of electron beam irradiation on fresh-cut can taloupe considering respiration rates, microbiology, texture and color. Materials and Methods Fruit Sample Cantaloupes (Cucimus melo Linnaeus, cv. Athena) were purchased from a retail market in Gainesville, FL (Trial 1 and Tria l 2) or obtained from a regional supermarket distribution center (Trial 3). Cantaloupes were transferred to the University of Florida Food Science and Human Nutrition building via automobile and were stored at 25 C for 1 day and then placed in a 3 C storage room overnight befo re processing. Cantaloupes were picked at three quarter to full slip (commercial maturity, when a clear separation from the vine occurs with light pressure) and ready to eat. Processing Cantaloupes were rinsed in 100 ppm chlori nated water and allowed to dry for 1 hour before cutting. All knives, cutting boards and bowls were soaked with 100 ppm chlorinated water. For each experiment, can taloupes (12) were halved, de-seeded, and then halved again, resulting in four equal parts. Each quarter was sliced on a HP commercial deli slicer (Model 1712 E, Hobart Corporation, Troy, Ohio) with the blade set

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33 at 2.5 cm thick. Slices were then peeled and cut into approximately 2.5 cm pieces with a sharp knife. All pieces were placed in an aluminum bowl, which was surrounded with ice. Pieces were thoroughly mi xed to assure random sampling. Pieces (~300g) were placed in quart Zipl oc (S.C. Johnson & Son, Inc., Racine, WI) Freezer bags and sealed after e xpulsion of most of the air. Bags were placed in ice in a portable cooler and transported to the electron beam irradiation facility, which was a 90 mega amp, 95% scan (Florida Accelerator Services and Technology, Gainesville, FL). Plastic trays were previously frozen with 1.5 cm of ice in them. Bags (4) were taped to Figure 3.1. Schematic of cantaloupe being i rradiated in Ziploc bags on trays of ice. each tray with cantaloupe arranged in a single fl at layer in order for all pieces to receive equal dosage (Figure 3.1). Dosimeters were also attached to verify that target doses had been reached. The irradiator conveyor was se t at a speed of 10 feet per minute (fpm; 305 cm per minute) and 0.25 kGy per pass. To achieve 0.5 kGy, the sample was passed through twice, while for 0.75 kGy three times and so on. Bags were removed from the Tray of IceMelon in Zip-Lock Bags Direction of Motion Electron Beam(Scan is perpendicular to page)

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34 ice trays and placed back in the ice cooler af ter the desired number of passes. Samples were irradiated at 0, 0.25, 0.5, 0.75, 1.0, 1.25 or 1.5 kGy for Trial 1. The pieces (~300g) from each bag were then placed in 1-quart Ball Mason Jars (Alltrista Corporation, Indiana polis, IN). Jars and lids were sanitized with a Better Built Turbomatic washer and dryer. Lids were drilled with a 3/8” (0.95 cm) hole directly in the middle. Parafilm (American National Can, Menasha, WI) was wrapped around the top of the jar before attaching the lid to assure a gas-tight seal. Jars containing fresh-cut cantaloupe were stored at 3 C for the duration of the expe riment. Further testing was performed on 1, 3, 5, 7, 9, 12, 14, 16 and 18 d. Trial 2 was carried out exactly as above ex cept the irradiator was set at 0.1 kGy per pass. Samples were irradiated at 0, 0.1, 0.2, 0.3, 0.4, 0.5 or 0.7 kGy. Further testing was done on 1, 4, 6, 8, 11, 13, 17, and 20 d. Trial 3 was carried out exactly as above ex cept the irradiator was set at 0.3 kGy per pass. Samples were irradiated at 0, 0.3, 0. 6, or 0.9 kGy. Further testing was done on 0, 2, 4, 7, 10, 13, and 16 d. Dosimetery Radiographic dosimeters were placed under bags of cantaloupe, flat on the trays and on top of bags. Gafchromic MD-55 from International Specialty Products (Wayne, NJ, USA) were cut into 1x1 cm squares, placed in small envelopes and taped into place. The dosimeter film was exposed for 24 hrs and then read on a spectrophotometer at a wavelength of 510 nm. The per pass aver age was determined by averaging the dose received on top of the bag with that below the bag.

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35 Gas Analysis Headspace analysis was done by sampling gas composition of jars for contents of O2 and CO2 using an O2 and CO2 analyzer (Checkmate 9900, PBI-Dansensor, Ringsted, Denmark). Lids were sealed for 2 hrs be fore sampling with rubber serum stoppers and reopened immediately after ga s withdrawal. The sampling needle was pushed through the rubber serum stopper and allowed to take several readings and stabilize. Samples were taken at 3 C. Microbial Analysis Cantaloupe pieces (~20 g) were aseptically removed from the jars and placed in sterile stomacher bags. Samples were dilu ted 1:10 with phosphate buffer and stomached for 30 seconds. Further 1:10 dilutions were ca rried out by adding 1 ml of sample to 9 ml of phosphate buffer (1:800, pH 7.2) in dilution tubes and vortexing for 30 seconds. Aerobic Plate Count and Yeast and Mold Plate Count Petrifilm kits (3M Corporation, St Paul, MN) were used as describe d by instructions for all dilutions tested. Petrifilms were incubated at 25 C for 4 days until quantified. Color Analysis Cantaloupe pieces were aseptically rem oved from jars and placed on Styrofoam plates. In Trial 2, the samples were pl aced in the Color Machine Vision System consisting of light box and a CCD color camer a connected to a computer with a frame grabber along with an orange reference plate with L*, a* and b* values of 24.2, 19.7, and 5.4, respectively. The L* refers to brightne ss from 0 = black to 100 = white. The a* is from negative (green) to positive (red) a nd b* is from negative (blue) to positive (yellow). Images were taken of three side s of the sample and saved on the computer. The black frame of the reference plate was removed using Corel for Paint. The image

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36 was then analyzed using the software Color Expert Color Analysis of the system. All images were calibrated with the reference plat e. Hue, which is the quality of color and described by the words red, yellow, green, bl ue, etc., was calculat ed with the equation hue = arctan (b/a). Chroma, the quality which describes the extent to which a color differs from gray of the same value or light ness, was calculated with the equation chroma = (a2 + b2)1/2 (Billmeyer and Saltzman, 1966). In Trial 3, the color of the pieces was m easured using a hand held Minolta Chroma Meter CR-2006 (Minolta Camera Co., Osaka, Japan). The colorimeter was calibrated before each use with a standard white plat e D65 (Y = 94.4, x = 0.3158 and y = 0.3334). One side of each cube was placed flush against the light source and the L*, a*, b* values were measured. Texture The texture of the cantaloupe was meas ured by an Instron Universal Testing Instrument, model 4411 (Canton, MA). The six pieces that were analyzed for color were used for texture. The cantaloupe pieces were placed under a pl unger, establishing zero force contact, with a plunger diameter of 5.0 mm and compressed 3 mm with a 50 kg load cell. The plunger was driven into the piece with a crosshead speed of 30 mm/min. The maximum compression force was measured in kg. Statistical Analysis Data was analyzed using analysis of variance in The SAS System version 8e. The empirical model was determined best fit (low est p-value) after numerous combinations of variables were tested.

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37 Results and Discussion Respiration Trial 1 Respiration rates for the fresh-cut cantaloupe of Trial 1 stored at 3 C are shown in Figure 3.2. The respiratory quotient (RQ), defined as th e ratio of the volume of CO2 released to the volume of O2 consumed was found to be approximately “unity” for all dates tested. On Day 1, ther e was a significant difference in all irradiated samples in comparison to the control. All respiration rates (CO2 production) dropped to less than 3.3 ml per kg per hour on Day 3. An effect of ir radiation was clearly seen on Day 3 with the higher the irradiation dose the higher the respiration rate. In creased respiration by fruits and vegetables, which may continue for days after exposure, is one of the most readily discerned direct effects of i rradiation (Romani, 1966). A si milar effect of respiratory activity stimulation by irradia tion was observed on different apple cultivars (Massey and others; 1964; Gunes and others 2000). The respiration rate of the control was significantly greater (p<0.05) th an all other treatments after Day 7. The next sample to increase in respiration rate was the lowest ir radiation dose, 0.25 kGy. Again, the next sample to increase was the next least irradiated sample of 0.50 kGy. All samples irradiated above 0.50 kGy behaved very similarly throughout storage. The lower respiration rates of irradiated samples ha s been linked to the reduction of metabolic activity, with the higher the dose, the larger the reducti on (Benoit and others, 2000; Ajlouni and others, 1993). Incr ease in respiration rate after 7 to 9 days of storage at 5 C for fresh-cut non-irradiated cantaloupe was observed by Aguayo and others (2004). This data is also in agreement with results from Luna-Guzman and Barret (2000), Bai and

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38 others (2001), and Madrid and Cantwell (1993). Possible reasons reported were microbial growth and/or general deteri oration of tissue due to senescence. 0 2 4 6 8 10 12 14 03691215 Daysml CO2/kg-h Control 0.25 kGy 0.5 kGy 0.75 kGy 1.0 kGy 1.25 kGy 1.5 kGy Figure 3.2. Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 1). Trials 2 and 3 Respiration rates of fresh-cut cant aloupe for Trial 2, stored at 3 C are shown in Figure 3.3. The (RQ) was found to be appr oximately “unity” for all dates tested. Untreated controls had the lowest respira tion rates on Day 1 compared to irradiated samples, however, the difference was not st atistically significant. Decreases in respiration rates after Day 1 were expected due to recovery from initial cutting for sample preparation. Respiration rate s were similar for all samples through Day 8. Statistically significant differences (p<0. 05) were observed starting on Day 11, at which point, controls were significantly higher than irra diated samples. Similar results were found with cut iceberg lettuce, where irradiated samples (0.2 and 0.45 kGy) had higher respiration rates on Day 1 and lower on Day 13 (Hagenmaier and Baker, 1997).

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39 Respiration rates observed for Trial 3 (Figure 3.4) were very similar to the Trial 2 results. Headspace analysis was first done at a true time 0. The open system was plugged with the rubber stopper immediately upon placing the cantaloupe in the jars. The initial wound response is more appare nt with higher respiration rates observed compared to Day 1 values of other Trials The respiration rates of the controls significantly increased after day 7 and the irra diated samples did not rise until after day 11. The same effect was seen in which the higher the dose of irradiation the lower the respiration rate for longer over storage time. 0 5 10 15 20 25 30 35 40 45 036912151821 Daysml CO2/kg-h Control 0.1 kGy 0.2 kGy 0.3 kGy 0.4 kGy 0.5 kGy 0.7 kGy Figure 3.3. Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 2). Microbiology Microbiological results for Trial 2 are shown in Figure 3.5. Irradiation was responsible for a 1.5 log reducti on in total plate count (TPC) at 0.7 kGy on Day 1. This reduction steadily increased with time, reaching a maximum of 3 logs. Microbial counts of irradiated samples increased at a lower rate than non-irra diated controls, consistent

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40 0 5 10 15 20 25 30 35 40 45 03691215 Daysml CO2/kg-h Control 0.3 kGy 0.6 kGy 0.9 kGy Figure 3.4. Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 3). 0 1 2 3 4 5 6 7 8 9 036912 DaysLog CFU/g Control 0.1 kGy 0.2 kGy 0.3 kGy 0.4 kGy 0.5 kGy 0.7 kGy Figure 3.5. Total plate count (TPC) of irradiated and non-i rradiated fresh-cut cantaloupe stored at 3 C (Trial 2). with the possibility of non-lethal injury to irradiated bacteria as suggested by Welt and others (2001). The TPC for controls and 0.7 kGy samples increased 3.7 and 1.5 logs,

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41 respectively, by Day 11. All sample s had TPC levels greater than 108 at Day 13 except samples treated with 0.4, 0.5, or 0.7 kGy. At Day 17, only samples treated with 0.5 or 0.7 kGy had TPC counts below 108. The control was significa ntly higher (p<0.05) than all irradiated samples at days 1, 4, and 13. Irradiation had less affect on the yeast and mold counts, shown in Figure 3.6, with no significant differences among treatments at any 0 1 2 3 4 5 6 7 8 0369121518 DaysLog CFU/g Control 0.1 kGy 0.2 kGy 0.3 kGy 0.4 kGy 0.5 kGy 0.7 kGy Figure 3.6. Yeast and Molds counts of irradi ated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 2). storage times. The yeast and mold counts of all samples increased approximately 4 logs by Day 17. The TPC counts in Trial 3 were sim ilar to those in Trial 2 (Figure 3.7). The initial 1.5 log reduction of the 0.9 kGy sample only increased to 2.5 logs rather than 3 logs as did the 0.7 kGy sample in the previ ous study. At all dates, the control was significantly higher than all irra diation levels. In Trial 3, the yeast and mold counts were also similar to those of Trial 2 with a 4 log increase in all samples by day 13 (Figure 3.8).

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42 0 2 4 6 8 10 12 036912 DaysLog CFU/g Control 0.3 kGy 0.6 kGy 0.9 kGy Figure 3.7. Total plate count (TPC) of irradiated and non-i rradiated fresh-cut cantaloupe stored at 3 C (Trial 3). 0 1 2 3 4 5 6 7 036912 DaysLog CFU/g Control 0.3 kGy 0.6 kGy 0.9 kGy Figure 3.8. Yeast and Molds counts of irradi ated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 3). At Days 11 and 13 all respiration rates of irradiated samples were significantly lower than controls. Surprisingly, an analysis of covarian ce failed to uncover a

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43 correlation between microbial populations and ob served respiration rates. This suggests that the magnitude of differences in microbi al populations did not significantly alter respiration rate results. A dditionally, microbial p opulations on Day 13 for the 0.2 and 0.3 kGy treatments appeared to be higher than those for the control on Day 11, yet observed respiration rates for irradiated samples were significantly lower th an those observed for controls. Similar results were found in grated carrots irradiated at 2 kGy and stored at 10 C in plastic bags. The residual concentra tions of oxygen were 2-fold higher in the irradiated samples than in non-irradiated af ter 7 days of storage. Oxygen consumption was unaffected by microbial contamination (5 to 7 logs cfu/g). The correlation coefficient between the percent residual oxyge n and microbial counts was lower than the significant limit of r = 0.553 at the 0.05 leve l (Diem and Seldrup, 1982), indicating the two variables were independent (Chervin and others, 1992). Based on respiration rates, microbiol ogical bloom and informal sensory evaluations, irradiated samples appeared to maintain preferred quality for 3 to 5 days longer than non-irradiated c ontrols. Respiration rates of the controls increased significantly after Day 8 whereas irradiated samples showed a similar trend only after Day 13. Equation 3.1 is an empirical model, based on the data of Trial 2, which can be used to estimate respiration rate of fresh-cut can taloupe as a function of time and irradiation dose. RCO2 = 8.819 – 1.856(t) + 6.053(D) 0.919(t)(D) + 0.135(t)2 (3.1) where t is the storage time in days, D is irra diation dose level (at t = 0) in kGy, and RCO2 is the respiration rate (CO2 production) in ml/kg-hr.

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44 Variables included in Eqn. 3.1 were determ ined to be statistically significant (pvalues < 0.0001). The model provided an overall coefficient of determination R2 of 0.84. This empirical model was based solely on data obtained in this study and is intended to provide a convenient summary of data derived in this work. Texture The texture of the cantaloupe for Trial 3 is listed in Table 3.1. The texture of the non irradiated controls was significantly hi gher than irradiated samples on Day 0; thereafter there were no differences in firm ness between irradiated and non-irradiated cantaloupe pieces.. This data is similar to diced tomatoes (Prakash and others, 2002), apple slices (Gunes and othe rs, 2001b) and strawberries (Yu and others, 1996) where firmness decreased with increased irradiat ion. Fruit softening by irradiation was associated with increased water-soluble pe ctin and decreased oxalate-soluble pectin content. Similar effects were also observed considering the increase of firmness after Day 0 of irradiated cantaloupe pieces. Table 3.1. Texture (max for ce kg) of irradiated and non-i rradiated fresh-cut cantaloupe stored at 3 C (Trial 3). Values in columns with different letters are significantly different (p<0.05). Texture Day 0Day 2Day 4Day 7Day 10Day 13 Control 0.829a0.614a0.660a0.699a0.553a0.496a 0.3 kGy 0.625b0.735a0.638a0.533b0.611a0.577a 0.6 kGy 0.589b0.658a0.601a0.679a0.650a0.571a 0.9 kGy 0.607b0.750a0.701a0.685a0.667a0.508a The texture of the cantaloupe compared by time within treatments is shown in Table 3.2. The most noticeabl e and significant decline in firmness was in the controls. The 0.6 kGy sample remained significantly i ndifferent throughout st orage. Boyle and others (1957) reported th at threshold ranges of irradiati on dose on firmness of apples and carrots depending on cultivar, rang ing from ~0.04 to 1.0 kGy.

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45 Table 3.2. Texture (max for ce kg) of irradiated and non-i rradiated fresh-cut cantaloupe stored at 3 C (Trial 3). Values in columns with different letters are significantly different (p<0.05). Control0.3 kGy0.6 kGy0.9 kGy Day 0 0.829a0.625ab0.589a0.607bc Day 2 0.614bcd0.735a0.658a0.750a Day 4 0.660bc0.638ab0.601a0.701ab Day 7 0.699b0.533b0.679a0.685ab Day 10 0.553cd0.611ab0.650a0.667ab Day 13 0.496d0.577ab0.571a0.508c Color The color of all samples remained stable throughout the storage duration for Trial 2 (Table 3.3 and 3.4). The L*, a*, b*, hue, and chroma values varied more from piece to piece and melon to melon than between treatmen ts. No trends in significant differences were found within treatments. Results of the color for Trial 3 were similar to the previous study except after day 7 the contro ls were significantly lower in L*, a*, b* (Table 3.5) and hue and chroma (Table 3. 6). Hue was significantly different on Day 13 only. Chroma was significantly lowest on Day 10 and 13 in the non-irradiated controls. The loss of color may be attributed to the oxidation of B-carotene. No discoloration developed on cantaloupe pieces in any treatmen t. This absence of browning is the result of a lack of polyphenol oxidase (PPO) en zyme and/or oxidizable phenols in the cantaloupe (Lamikanra and Watson, 2000). Othe rs have reported that hue, chroma and L* values of non-irradiated fresh-cut cantaloupe significantly changed during 25 days of storage at 4 C (Lamikanra and Watson, 2000). While irradiation had no effect on color in Trial 2, irradiation of fres h-cut cantaloupe in Trial 3 helped maintain color after 8 days of storage. Maintenance of color is very important in the fresh-cut produce industry, where visual appearance on the shelf may be a key factor for extended shelf life purchases.

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46 Differences in L*, a*, and b* values between Trial 2 and Trial 3 may be a result of two reasons. First, the cantal oupes were of different variet ies and seasons. The second reason for differences is the method of obtai ning color values. The method of Trial 2 involves the use of a digital im age that averaged the entire surface of the piece of melon. In Trial 3, the hand held colorimeter only captured a small circle (8 mm2) of the middle of the surface of the melon piece. Therefore, the broad spectrum of colors averaged over the entire surface of cantaloupe (Trial 2) differs from the single point repeatedly measured with the hand held colorimeter (Trial 3). Table 3.3. Color of irradiat ed and non-irradiated fresh-cu t cantaloupe stored at 3 C (Trial 2). Values in columns with different letters are significantly different (p<0.05). Day 1Day 4Day 6Day 8Day 11Day 13 Control 70.8a67.9a66.8ab68.0a65.1a65.2a 0.1 kGy 71.4a68.7a68.6ab70.3a70.7a69.0a 0.2 kGy 67.5ab67.8a62.1b66.7a68.5a70.6a 0.3 kGy 64.1b71.4a71.6a71.4a72.2a62.8a 0.4 kGy 71.4a68.4a67.7ab67.7a68.1a70.8a 0.5 kGy 67.0ab67.1a68.3ab66.7a70.8a62.3a 0.7 kGy 70.2a69.0a67.3ab64.4a67.0a68.3a Day 1Day 4Day 6Day 8Day 11Day 13 Control 28.5a36.6a27.6a20.7b24.0a30.7a 0.1 kGy 29.7a34.0a26.5a23.1ab16.7a22.3a 0.2 kGy 26.5a33.6a36.0a33.5ab25.8a20.0a 0.3 kGy 38.3a28.5a20.2a21.8b18.1a38.1a 0.4 kGy 27.2a34.5a32.7a28.6ab28.4a23.7a 0.5 kGy 28.4a35.6a26.4a31.4ab21.1a41.1a 0.7 kGy 26.3a33.3a32.6a41.6a33.7a26.1a Day 1Day 4Day 6Day 8Day 11Day 13 Control 63.5a63.3a59.3ab58.7a55.3b57.5c 0.1 kGy 56.9c64.5a60.5ab61.7a60.4ab60.0abc 0.2 kGy 62.4ab62.5a57.3b61.3a61.1ab61.5ab 0.3 kGy 62.1ab64.7a62.4a63.8a63.0a57.9bc 0.4 kGy 61.2ab64.0a62.8a61.3a61.2ab63.4a 0.5 kGy 61.6ab63.1a62.4a61.5a62.8a58.6bc 0.7 kGy 58.6bc64.9a61.6ab61.6a61.6a60.2abc L a b

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47 Table 3.4. Hue and chroma of irradiated and non-irradiat ed fresh-cut cantaloupe stored at 3 C (Trial 2). Values in columns with different letters are significantly different (p<0.05). Table 3.5. Color of irradiat ed and non-irradiated fresh-cu t cantaloupe stored at 3 C (Trial 3). Values in columns with different letters are significantly different (p<0.05). Day 1Day 4Day 6Day 8Day 11Day 13 Control 66.1a60.0a65.2ab70.6a66.6a61.9a 0.1 kGy 62.5a62.3a66.4ab69.6a74.6a69.8a 0.2 kGy 67.0a61.7a57.8b61.5a67.4a72.0a 0.3 kGy 58.4a66.2a72.1a71.2a73.9a56.8a 0.4 kGy 66.0a61.8a62.5ab65.0a65.2a69.6a 0.5 kGy 65.3a60.6a67.0ab63.0a71.4a54.9a 0.7 kGy 65.8a62.9a62.1ab55.9a61.3a66.6a Day 1Day 4Day 6Day 8Day 11Day 13 Control 69.9a73.2a65.4b62.3c60.2b65.1a 0.1 kGy 64.3a72.9a66.1ab65.9bc62.7ab64.0a 0.2 kGy 67.8a71.0a67.7ab69.9ab66.3ab64.7a 0.3 kGy 73.0a70.7a65.6b67.4bc65.5ab69.3a 0.4 kGy 67.0a72.7a70.9a67.6b67.5ab67.7a 0.5 kGy 67.8a72.5a67.7ab69.0b66.2ab71.6a 0.7 kGy 64.2a73.0a69.7ab74.3a70.2a65.6a Chroma Hue Day 0Day 2Day 4Day 7Day 10Day 13 Control 63.7a63.7a65.5a57.0a46.6b42.9b 0.3 kGy 64.0a64.5a58.3ab55.7a61.5a62.4a 0.6 kGy 62.7a63.8a63.6a60.8a62.2a53.7a 0.9 kGy 62.6a62.3a54.5b62.6a59.7a54.6a Day 0Day 2Day 4Day 7Day 10Day 13 Control 12.6a11.3a11.9a11.2a7.1b5.1b 0.3 kGy 11.0a12.4a11.7a10.1a11.9a11.3a 0.6 kGy 11.7a13.0a12.3a11.8a11.8a10.0a 0.9 kGy 12.0a11.7a10.3a12.2a10.2a10.3a Day 0Day 2Day 4Day 7Day 10Day 13 Control 33.6a33.8a34.0a31.6a22.8b18.2b 0.3 kGy 31.1a35.0a33.3a30.4a34.8a33.1a 0.6 kGy 32.9a35.9a35.2a31.2a34.9a29.3a 0.9 kGy 32.9a33.8a30.3a35.3a31.8a29.7a L a b

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48 Table 3.6. Hue and chroma of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C (Trial 3). Values in columns with different letters are significantly different (p<0.05). Samples removed from jars for color work were used for informal sensory evaluation after being digitally photographed. Four panelists tasted the samples and suggested that there were no substantial differences between the treatments for 8 days. After Day 8, samples treated with higher ir radiation dose levels generally had better flavor and texture. Conclusions Low dose electron beam irradi ation of fresh-cut cantal oupe offers promise as a method of maintaining preferre d-quality of this product durin g shelf life. Knowledge of the effects of irradiation on product respirati on rates, as summarized in Eqn. 3.1, should provide a means to develop modified atmos phere packaging that could further enhance the ability of irradiation to exte nd fresh-cut cantaloupe shelf-life. Day 0Day 2Day 4Day 7Day 10Day 13 Control 69.4a71.6a70.7a70.5a73.1a74.5a 0.3 kGy 70.5a70.6a70.7a71.7a71.2a71.2b 0.6 kGy 70.4a70.0a70.7a68.7a71.4a71.2b 0.9 kGy 70.0a70.9a71.4a70.9a72.3a70.0b Day 0Day 2Day 4Day 7Day 10Day 13 Control 33.5a35.7a36.0a33.8a23.9b18.9b 0.3 kGy 30.5a37.1a35.3a32.1a36.8a35.0a 0.6 kGy 32.4a38.2a37.2a33.4a36.8a31.0a 0.9 kGy 32.6a35.7a32.0a37.4a33.4a31.4a Hue Chroma

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49 CHAPTER 4 RESPIRATION OF IRRADIATED FRES H-CUT CANTALOUPE AND MODELLING OF RESPIRATION FOR MODIFIED ATMOSPHERE PACKAGING Introduction An effective way to extend the shelf life of fresh produce is to use a modified atmosphere package (MAP). The package s hould maintain an optimal atmosphere that will reduce respiration and slow physiological and microbiological changes that decrease shelf life. The respiration rate of horticultural commodities is dependent on the amount of available oxygen and carbon dioxide pr esent in the surrounding environment (Beaudry, 2000; Watkins, 2000). Determina tion of the optimal surrounding atmosphere for fresh-cut produce that minimizes respir ation without initia ting anaerobiosis or injuring the plant tissue is di fficult due to the numerous possible combinations of oxygen and carbon dioxide concentrations. Determination of respiration rate at different O2 and CO2 concentrations is an important factor in the design of a MAP fo r fresh produce. Generating all the possible combinations of O2 and CO2 concentrations using a flow through or flush system in order to determine unique respiration rates would be very time consuming. The closed system has been used to generate more ra pid results and cover a range of O2 and CO2 concentrations (Haggar and others, 1992; Henig and Gilb ert, 1975; Yang and Chinnan, 1988; Gong and Corey, 1994; Cameron and others, 1989). Determination of the amount of O2 and CO2 diffusing in and out of a MAP can be determined using Fick’s first law of diffu sion (Zhu and others, 2002). The inflow and

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50 outflow of each gas is controlled by the temperature, internal and external gas concentration and transmissi on rate of the film. Predictive modeling in MAPs of fres h-cut produce is centered around the respiration rate of the product and the permea tion of gases through the film. The amount of fruit, size of permeable packaging, te mperature and starting atmosphere can be adjusted for an optimal package with know n respiration rate and gas transmission equations. The objective of this research was to determ ine the respiration rate of irradiated and non-irradiated fresh-cut cantaloupe in order to develop pr edictive equations that could be used to design a MAP with a desirable steady state atmosphere. Materials and Methods Fruit Sample Cantaloupes (Cucumis melo Linnaeus, cv. Athena) were purchased from a local grocery store in Gainesville, FL and transfer red to the University of Florida Food Science and Human Nutrition building via auto mobile and were stored in a 3 C storage room overnight before processing. Cantaloupes we re picked at three quarter to full slip (commercial maturity, when a clear separation from the vine occurs with light pressure) and ready to eat. Processing Cantaloupes were rinsed in 100 ppm chlo rinated water and allowed to dry 1 hour before cutting. All knives, cutting boards and bowls were soaked with 100 ppm chlorinated water. Fifteen cantaloupes were halved, deseeded, and then halved again resulting in 4 equal parts. Each quarter was sliced on a HP commercial deli slicer (Model 1712E, Hobart Corporation, Troy, Ohio ) with the blade set at 2.5 cm thick.

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51 Slices were then peeled and cut into approximate ly 2.5 cm pieces with a knife. All pieces were placed in an aluminum bowl, whic h was surrounded with ice. Pieces were thoroughly mixed to assure random sampling. Pieces (~300g) were placed in quart Zi ploc (S.C. Johnson & Son, Inc., Racine, WI) Freezer bags and sealed after expulsion of most of the air. Bags were placed in ice in a portable cooler and transported to the el ectron beam irradiation facility, which was a 90 mega amp, 95% scan (Florida Accelerator Services and Technology, Gainesville, FL). Plastic trays were previously frozen with 1.5 cm of ice in them. Four bags were taped to each tray with cantaloupe arranged in a single fl at layer in order for all pieces to receive equal dosage. Dosimeters were also attached to verify that target doses had been reached. The irradiator conveyor was set at a speed of 10 feet per minute (fpm; 305 cm per minute) and 0.1 kGy per pass. To achieve 0. 2 kGy, the sample was passed through twice, 0.4 kGy four times and so on. Bags were removed from the ice trays and placed back in the ice cooler after the desired number of passes. Samples were irradiated at 0, 0.2, 0.4 or 0.6 kGy. The pieces (~300g) from each bag were th en placed in 1-quart Ball Mason Jars (Alltrista Corporation, Indianapolis, IN). Three jars of each irradiation dose and three controls, which where processed exactly th e same without receivi ng irradiation were tested. Jars and lids were sanitized with a Better Built Turbomatic washer and dryer. Lids were drilled with a 3/8” (0.95 cm) hole directly in the middle. Parafilm (American National Can, Menasha, WI) was wrapped aroun d the top of the jar before attaching the lid to assure a gas-tight seal Jars containing fresh-cut cantaloupe were stored at 3 C for the duration of the experiment. Rubber stoppers were placed in the hole in the lid to

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52 create a closed system immedi ately upon closing the jar. Ga s samples were taken every 4 to 12 hours throughout the 14 day storage duration. Dosimetery Radiographic dosimeters were placed under bags of cantaloupe, flat on the trays and on top of bags. Gafchromic MD-55 from International Specialty Products (Wayne, NJ, USA) were cut into 1x1 cm squares, placed in small envelopes and taped into place. The dosimeter film was exposed for 24 hrs and then read on a spectrophotometer at a wavelength of 510 nm. The per pass aver age was determined by averaging the dose received on top of the bag with that below the bag. Gas Analysis Headspace analysis was done by sampling ga s composition of jars for contents of O2 and CO2 using an O2 and CO2 analyzer (Checkmate 9900, PBI-Dansensor, Ringsted, Denmark). The sampling needle was pushed through the rubber stopper and allowed to take several readings and stabilize. Sample s were taken in the cold room without moving the jars. Modeling The O2 and CO2 concentrations were fit to equations (4.1) and (4.2) using KalediaGraph 3.5 (Synergy Software, Reading, PA). The following equations were used in a paper by Hagger and others (1992) to design an enzyme kinetics based respiration model. 1C 1 1 2) B t (A t 21 ] O [ (4.1) 2C 2 2 2) B t (A t ] CO [ (4.2)

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53 The equations were solved for coefficients A, B and C across time (t) in hours and [O2] and [CO2] in percent. At each sampling time, the respiration rates were calculated by substituting the first derivatives of Eqns. (4.1) and (4.2) into Eqns. (4.5) and (4.6), respectively. Eqns. (4.3) and (4.4) are the first derivatives of E qns. (4.1) and (4.2). 1 1C 1 1 ) C 1 ( 1 1 1 1 2) B t A ( ) B t A ( t C A ] d[O (4.3) 2 2C 2 2 ) C 1 ( 2 2 2 2 2) B t A ( ) B t A ( t C A ] d[CO (4.4) ) T W R 100 V P M ( d t ] O [ d r2 2O 2 O (4.5) ) T W R 100 V P M ( d t ] CO [ d r2 2CO 2 CO (4.6) 2Oris the respiration rate in term s of oxygen consumption (mg/kg h), 2COr is the respiration rate in terms of carbon dioxide production, 2OM and 2COMare the molecular weights of oxygen and carbon dioxide (kg/mole), respectively, P is the pressure inside the jar (Pa), V is the free volume (ml), R is the universal gas law consta nt (8.314 J/mol K), W is the weight of the cantal oupe (kg), and T is the temper ature (in degrees Kelvin). The respiration rates were fit with the O2 and CO2 concentrations in the MichaelisMenten enzyme model Eqn. (4.7). ] O )[ K / ] CO [ 1 ( K ] O [ V r2 i 2 m 2 m (4.7) Km is the Michaelis-Menten constant (% O2), Vm is the maximum respiration rate (mg/kg h) and Ki is the inhibition constant (% CO2). Respirations rates from Eqns. (4.5) and (4 .6) were also fit to several exponential growth curve functions with Eqns. (4.8) and (4.9) fitting with the highest R-value.

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54 ]) O [ 2 b exp( 1 b r2 O2 (4.8) ]) CO [ 2 b exp( 1 b r2 CO2 (4.9) Variables b1 and b2 were solved using KalediaGraph 3.5. Respirations rates from Eqns. (4.5) and (4.6) were also fit to several polynomial functions with Eqns. (4.10) and (4 .11) having the highest R-value. ) ] O [ 2 M ( ]) O [ 1 M ( 0 M r2 2 2 O2 (4.10) ) ] CO [ 2 M ( ]) CO [ 1 M ( 0 M r2 2 2 CO2 (4.11) Variables M0, M1 and M2 were solved usi ng KalediaGraph 3.5. All equations were also fit to the respiration data in exclusive ranges of [O2] and [CO2] specific to desirable modified atmosphere packaging conditions for fresh-cut cantaloupe: 10 to 3 percent for [O2] and 18 to 5 percent for [CO2]. Film Permeability Based on the respiration rates of th e fresh-cut cantaloupe at the desired temperature, two multilayer coextruded bags were provided by Cryovac Sealed Air Corporation (Duncan, SC). A ll properties reported by the ma nufacturer were determined at 22.8 C. Further testing was needed to determine oxygen and carbon dioxide transmission rates at 3 C. The two bags were the PD-961EZ Bag and the PD-900 Bag. Oxygen transmission rates (OTR) were m easured using a Mocon two-cell Oxtran 2/20 (Mocon Controls Inc, Minneapolis MN). Sample film pieces (100 cm2) were cut using a stainless steel template. The cut pie ces were placed on both testing cells of the Oxtran 2/20 with vacuum grease smoothly appl ied to the outer edge where the seal is created. The film samples were conditioned for one hour to remove traces of oxygen by flushing them with the test gas mixture, 96% nitrogen plus 4% hydrogen. In the testing

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55 chamber, the film creates a barrier betw een a steady flow (20 ml/min) of 100% oxygen and a steady flow (20 ml/min) of the test ga s mixture. The test gas mixture flows to a coulometric oxygen sensor, which detects the oxygen that permeated through the sample film by producing an electri cal current directly proportiona l to the flux of oxygen across the film. The Mocon unit switches testi ng chambers when the amount of oxygen detected stops changing. Gas transmission ra tes were determined at 10, 15, 24, 30, and 35 C and 50% relative humidity. Four 100 cm2 sections were tested for each film. Carbon dioxide transmission rates were de termined using the same Mocon Oxtran 2/20 unit with a few modifications. Pure carbon dioxide was connected to the oxygen inlet of the Oxtran 2/20. The oxygen sensor was bypassed, and 10 ml samples were taken from the outflow of test gas. Carbon dioxi des levels in the carrier gas after permeation through the film were determined using a Fisher Gas Partitioner model 1200 gas chromatograph (GC; Fisher Scientific, P ittsburgh, PA) with a thermal conductivity detector that was equipped with a 1,966 x 3.12 mm 80/100 mesh Porapak column at 60 The detector and injector temperatures were set 90 C. Eqn. (4.12) was used to convert the %CO2 reading from the GC into a transmission rate. A 1 day min 1440 FR 100 R CO TR CO2 2 (4.12) Where CO2TR is the carbon dioxide transmission rate in ml/m2/day, CO2R is the carbon dioxide reading from the GC in %, FR is the flow rate of the outflow gas in ml/min, and A is area of the film in m2.

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56 The Arrhenius method used for OTR determination was used for carbon dioxide transmission rates, except for the use of th e gas chromatograph. Gas transmission rates were determined at 10, 15, 24, 30, and 35 C and 50% relative humidity. The natural log of the OTRs and th e carbon dioxide transmission rates were plotted on the y-axis with 1/T (Kelvin) on th e x-axis. Linear regression was done with Microsoft Excel 2000 yielding Eqn. (4.13), whic h in Arrhenius form is Eqn. (4.14) and rearranged as Eqn. (4.15) y = mx +b (4.13) RT Ea ) ko ln( ) k ln( (4.14) } RT Ea exp{ ko k (4.15) k is the permeability of the film in ml/m2/day, ko is the permeability coefficient, Ea is the activation energy for th e transport of oxygen or carbon dioxide through the film in kJ/mol, R is the universal gas constant and T is the absolute temperature in degrees Kelvin. Transmission rates can be determined at any temperature using any of the Eqns. (4.13) – (4.15). Modified Atmosphere Package Design A program to predict the changes over time in [O2] and [CO2] of the headspace, surrounding a known weight of fresh-cut canta loupe in a MAP was written in Microsoft Excel 2000 using Visual Basic for Applic ations. The following code was used. Option Explicit Dim PO2 As Double Dim PCO2 As Double

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57 Dim A As Double Dim pO2out As Double Dim pCO2out As Double Dim pO2in As Double Dim pCO2in As Double Dim pN2out As Double Dim pN2in As Double Dim W As Double Dim RO2 As Double Dim RCO2 As Double Dim V As Double Dim Pt As Double Dim t As Double Dim QO2 As Double Dim JO2 As Double Dim QCO2 As Double Dim JCO2 As Double Dim PN2 As Double Dim JN2 As Double Dim M1O2 As Double Dim M2O2 As Double Dim M3O2 As Double Dim M1CO2 As Double Dim M2CO2 As Double Dim M3CO2 As Double Public Sub GetInput() PO2 = Range("IN!C1").Value PCO2 = Range("IN!C10").Value PN2 = Range("IN!C15").Value A = Range("IN!C2").Value pO2out = Range("IN!C3").Value pO2in = Range("IN!C4").Value pCO2out = Range("IN!C11").Value pCO2in = Range("IN!C12").Value pN2out = Range("IN!C13").Value pN2in = Range("IN!C14").Value W = Range("IN!C5").Value 'RO2 = Range("IN!C6").Value V = Range("IN!C7").Value Pt = Range("IN!C8").Value 't = Range("IN!C1").Value M1O2 = Range("IN!C16").Value M2O2 = Range("IN!C17").Value

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58 M3O2 = Range("IN!C18").Value M1CO2 = Range("IN!C19").Value M2CO2 = Range("IN!C20").Value M3CO2 = Range("IN!C21").Value End Sub Public Sub Main() Call GetInput Call SimLoop End Sub Public Sub SimLoop() t = 1 Do While t < 5000 RO2 = M1O2 + (M2O2 pO2in) + (M3O2 pO2in ^ 2) RCO2 = M1CO2 + (M2CO2 pC O2in) + (M3CO2 pCO2in ^ 2) QO2 = RO2 W QCO2 = RCO2 W JO2 = PO2 A (pO2out pO2in) 0.01 JCO2 = PCO2 A (pCO2in pCO2out) 0.01 JN2 = PN2 A (pN2out pN2in) 0.01 pO2in = pO2in + ((JO2 QO2) (100 / V) 0.1) 't=.1 hardcode pCO2in = pCO2in + ((QCO2 JCO2) (100 / V) 0.1) 't=.1 hardcode V = ((-QO2 + QCO2 JCO2 + JO2 + JN2) 0.1) + V Worksheets("Out").Ce lls(t + 1, 1).Value = t Worksheets("O ut").Cells(t + 1, 2).Value = pO2in Worksheets("O ut").Cells(t + 1, 3).Value = pCO2in Worksheets("Out").Ce lls(t + 1, 4).Value = V Worksheets("Out").Ce lls(t + 1, 5).Value = RO2

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59 Worksheets("Out").Ce lls(t + 1, 6).Value = RCO2 t = t + 1 Loop End Sub Figure 4.1. The input screen for all data necessary for the prediction program with variables described and units defined The model determines the predicted ga s composition inside the bag every 6 minutes. The amount of oxygen consumed a nd carbon dioxide evolved are determined by the respiration rate of the produce at the initial gas levels for time 1. The amount of oxygen and carbon dioxide that passes through the package is ba sed on the area of transmissible film and the concentration of gases inside and outside the package. The

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60 new internal gas composition and volume are th en calculated. The program then loops and recalculates based on new gas com position. The program displays the gas concentrations inside the bag and the free volume in graph form The respiration rates at each time are also listed in table form. Figur e (4.1) is the input screen for the program. Results and Discussion Modeling Headspace concentrations of O2 and CO2 over time in the closed jars acted as Control0 5 10 15 20 25 0100200300400 Time (h)% in headspace O2 CO2 expected with the O2 dropping close to 5% and CO2 rising to almost 20% during 14 days of storage. Figure (4.2) shows the averag es of the three jars of each treatment. Coefficients A, B and C of Eqns. (4.1) a nd (4.2) were solved across time t with high correlation for all treatments (Table 4.1).

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61 0.2 kGy0 5 10 15 20 25 0100200300400 Time (h)% in headspace O2 CO2 0.4 kGy0 5 10 15 20 25 0100200300400 Time (h)% in headspace O2 CO2

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62 0.6 kGy0 5 10 15 20 25 0100200300400 Time (h)% in headspace O2 CO2 Figure 4.2. Percent oxygen and carbon di oxide in headspace during closed system storage of irradiated and non-irra diated fresh-cut cantaloupe at 3 C. Table 4.1. Coefficients of Eqn. (4.1) and (4.2) describing the changes in oxygen and carbon dioxide concentrations, respectivel y, over time for irradiated and nonirradiated fresh-cut can taloupe stored in a closed system at 3 C. Control0.2 kGy0.4 kGy0.6 kGy A 0.4130.2610.1440.222 B 3.4034.6963.6134.827 C 0.6350.6720.7680.717 R 0.9960.9990.9990.999 Control0.2 kGy0.4 kGy0.6 kGy A 0.7520.4660.3290.9615 B 0.0012140.4860.2293.03E-06 C 0.5330.5860.6020.494 R 0.9930.9970.9980.98 O2CO2 Oxygen consumption and carbon dioxide e volution at each sampling time were solved by inserting the results of Eqns. (4.3) and (4.4) into Eqns. (4.5) and (4.6). The

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63 Table 4.2. Coefficients of Michalis-Mente n model Eqn (4.5) and (4.6) for changes in oxygen and carbon dioxide concentrati ons, respectively, over time for irradiated and non-irradiated freshcut cantaloupe stored in a closed system at 3 C. Control0.2 kGy0.4 kGy0.6 kGy Vm 26.1465.4180.857.9 Km -226.1-3209.9-917.9-348.58 Ki 0.290.0020.080.21 R 0.9930.9720.9740.985 Control0.2 kGy0.4 kGy0.6 kGy Vm 1.481.461.691.74 Km -2.92-3.39-3.76-3.3 Ki 8.20E+091.90E+061.60E+221.60E+11 R 0.9440.9630.9240.958 O2CO2 respiration rates from Eqns. (4.5) and (4.6) wher e then used to solve the parameters of the Michaelis-Menten Eqn. (4.7), which are listed in Table (4.2). The R values are high suggesting the data fit well. The model looks good until the gas composition inside a permeable package is predicted. Figure (4.3 ) and (4.4) shows the curve of the respiration rates across time and the models’ predicted resp iration rates across time for the control, with irradiated samples behaving similarly. The critical area of this curve for O2 consumption is between 3 and 10% and for CO2 evolution it is between 5 and 18%. The lower the O2 concentration, the poorer the Michaelis-Menten equation fit. This could be due to the fact that the Michaelis-Menten model is only valid for aer obic respiration (Lee and othe rs, 1991). Peppelenbos and Leven (1996) determined a significant decrease in O2 consumption in apples and asparagus at CO2 levels of 10% and above. Therefor e in the critical MAP range, this model will not suffice. An active MAP shoul d start and remain at gas compositions within critical ranges for the produce.

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64 0 5 10 15 20 25 0510152025 Observed DataResp. Rate (mg O2/kg h)% O2 --= r = Vm[O2] / Km+(1+[CO2]/Ki)[O2] Error Value 2205.4 117.9 Vm 16440 -910.13 Km 1.2413 0.06713 Ki NA 5.4373 Chisq NA 0.99358 R Figure 4.3. Michaelis-Menten equation fit to observed respiration data vs. percent oxygen for non-irradiated fresh-cut cantaloup e stored in a closed system at 3 C. The parameters of Eqn. (4.7) were then solved for the critical ranges using the respiration rates at only times when [O2] was between 3 and 10% and [CO2] was between 5 and 18%. The results were very similar when using all times, therefore this was ineffective as well. The exponential growth curv es of Eqns. (4.8) and (4.9) were solved using all respiration data in Figure (4.2). The results were very similar to the solutions for Eqn.

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65 0 2 4 6 8 10 12 05101520 Observed DataResp. Rate (mg CO2/kg h)% CO2 --= r = Vm[O2] / Km+(1+[CO2]/Ki)[O2] Error Value 0.19934 1.476 Vm 0.89274 -2.9239 Km 9.2819e+17 8.2242e+09 Ki NA 13.03 Chisq NA 0.94419 R Figure 4.4. Michaelis-Menten eq uation fit to observed respir ation data vs. percent carbon dioxide for non-irradiated fr esh-cut cantaloupe stored in a closed system at 3 C. (4.7). The R values were very high (~0.99) yet in the critical areas for MAP, the predicted respiration rates would be erroneous Once again, fitting the critical areas only to the curve was ineffective, therefore con tinuing the search for the equation yielding proper prediction confidence. The data was then fit to polynomial curves of Eqns. (4.10) and (4.11) with good results. Fitting the critical areas separately yielded excellent results for all treatments as

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66 seen by the controls in Figures (4.5) and (4.6 ). The parameter values are listed in Table (4.3). Table 4.3. Coefficients of the polynomial m odel Eqns. (4.10) and (4.11) for changes in oxygen and carbon dioxide concentrati ons, respectively, over time for irradiated and non-irradiated fresh-cut can taloupe stored in a closed system at 3 C. Control0.2 kGy0.4 kGy0.6 kGy M0 1.2571.17261.4281.5276 M1 -0.114-0.2485-0.3592-0.37 M2 0.0130.0270.0440.034 R 0.9940.9990.9990.999 Control0.2 kGy0.4 kGy0.6 kGy M0 3.5795.738.4569.757 M1 -0.33-0.52-0.649-1.0329 M2 0.0090.0140.0150.032 R 0.9940.9990.9980.985 O2CO2 The respiration rate can be determined at any O2 plus CO2 combination within the ranges solved for by the polynomial equations. This was considered acceptable since the MAP design in the next chapter was planned to use a gas flush with the desired steady state package atmosphere. It is uncertain why the Michaelis-Menten e quation did not fit the data better in the critical areas. Most published research using the Michaelis-Menten equation for modeling produce respiration invol ved intact fruits and vege tables or produce lightly processed to a lesser extent than the fruit in this work. Th e pieces of fresh-cut cantaloupe in this experiment were wounded on all sides. The fruit was peeled, seeded by cutting the most inner cavity layer out and then cubed, which leaves no side uncut. This wounding causes an increase in respiration at time 0 comp ared to the intact fruit. The pieces also are exposed to gases on all sides with an in creased surface area. The solubility and

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67 1 1.1 1.2 1.3 1.4 1.5 567891011 Observed DataResp.Rate (mg O2/kg h)% O2 ---= r = M0 + M1*x + M2*x2 1.2573 M0 -0.11414 M1 0.012984 M2 0.99391 R Figure 4.5. Second order polynomial equati on fit for observed respiration data vs. percent oxygen within th e critical range for non-irradiated fresh-cut cantaloupe stored in a closed system at 3 C. diffusion rates of O2 and CO2 would also have been affect ed. The initial wound response along with exposure to gases on all sides with differing diffusion and solubility rates may not allow the Michaelis-Menten model to be the best choice. Most work done with the Michaelis-Mente n equation has been performed at higher temperatures than the work done for this paper. Also, the most common fresh-cut produce modeled is broccoli (Fonseca and ot hers, 2002). Therefore, published data shows the depletion of oxygen and increase in ca rbon dioxide at a fast er rate, especially

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68 0.5 0.6 0.7 0.8 0.9 1 1.1 101214161820 Observed DataResp. Rate (mg CO2/kg h)% CO2 ---= r = M0 + M1*x + M2*x2 3.5787 M0 -0.33022 M1 0.0089975 M2 0.99407 R Figure 4.6. Polynomial equation fit to obs erved respiration data vs. percent carbon dioxide for within the cr itical range for non-irradiat ed fresh-cut cantaloupe stored in a closed system at 3 C. later in storage when broccoli enters a clim acteric phase of incr easing respiration. Although cantaloupe is also a clim acteric crop, the fruit used in this work were already ripe and presumably postclimacter ic at the start of the experi ments. Cold storage and the naturally low respiratio n rate of cantaloupe may cause it to be an unsuitable candidate for Michaelis-Menten modeling. Many limitations exist in prediction modeling of fresh-cut produce. The results of experimentation can be specific to the environmental conditions as well as the variability

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69 in the commodity. The closed system expe riment above started and continued through O2 and CO2 combinations that would not be pres ent in an active MAP. Most closed system models predict respiration rates of pr oduces at internal atmosphere different than those used in the creation of the model. For example, the internal starting gas composition for the MAPs of the next experiment are 4% oxygen and 10% carbon dioxide. Therefore, as seen in Figure (4 .2), the percent oxygen at the time when the carbon dioxide is 10% is not near 4, and similarly the carbon dioxide percent is very high when oxygen is low. The above prediction equa tions give respiration rates from different observed data. Inhibitory and/or promotiona l effects of the other gas concentration, for example oxygen when determining carbon di oxide evolution, may be overlooked. Although significant results may be obtained from closed system modeling, further testing should be carried out with package design. Film Permeability The oxygen and carbon dioxide tr ansmission rates of the films for the temperatures tested are listed in Table (4.4 ). The Arrhenius relationshi ps between transmission rates and temperature are shown in Figure (4.7) and (4.8). The OTRs for PD-900 and PD961EZ at 3 C were determined by extrapolation of the Arrhenius curve to be 657.31 and 1529.56 ml/m2/day. The carbon dioxide transmissi on rates for PD-900 and PD-961EZ at 3 C were similarly determined to be 3434.03 and 8035.77 ml/m2/day. The Arrhenius relationship values Ea and ko are listed in Table (4.5). The activation energy determined for bot h films was slightly higher in oxygen permeability compared to carbon dioxide permeability. Therefore, the oxygen concentrations inside the packages will be more easily influenced by temperature

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70 fluctuations during storage compared to the carbon dioxide concentrations (Van de Velde and others, 2002). Table 4.4. Average oxygen (OTR) and carbon dioxide (CO2TR) transmission rates at various temperatures for films tested. Temp degree C OTR CO2TR OTR CO2TR 10 10362393703314844 15 13983159779318524 24 22905121988420166 30 320070951287426300 35 421694151807536806 PD 900 ml/m2/day PD 961 EZ ml/m2/day Figure 4.7. Arrhenius relationship between the natural log of the oxygen transmission rate (O2TR) in ml/m2/ day and temperature for two films tested. Table 4.5. Arrhenius relationship va lues Ea and ko for two films tested. Film ko ml/m 2/day Ea kJ/mol PD 900 40.5 3.06E+10 PD 961 EZ 39.5 4.63E+10 PD 900 31.9 9.26E+09 PD 961 EZ 35.3 1.63E+10 OTR CO 2 TR y = -4754.3x + 24.559 R2 = 0.9971 y = -4871.5x + 24.144 R2 = 0.9959 6.8 7.3 7.8 8.3 8.8 9.3 9.8 0.00320.003250.00330.003350.00340.003450.00350.00355 1/T(k)ln(O2TR) PD 961 EZ PD 900

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71 Figure 4.8. Arrhenius relationship between the natural log of the carbon dioxide transmission rate (CO2TR) in ml/m2/ day and temperature for two films tested. Conclusion The Michaelis-Menten enzyme kinetics equation was not a suitable model for fresh-cut cantaloupe. A polynomial mode l fit the oxygen consumption and carbon dioxide evolution data very well and, most importantly, the fit was good in the critical oxygen and carbon dioxide concentration ranges desirable for fresh-cut cantaloupe for MAP. An Arrhenius equation accurately predicted the oxygen and carbon dioxide transmission rates of packaging polymers over a range of temperatures. With known prediction equations for respiration rate of produce and transmission rates of packaging films, an optimal MAP can be easily designed. y = -3842.4x + 22.949 R2 = 0.9672 y = -4251.7x + 23.512 R2 = 0.9781 8 8.5 9 9.5 10 10.5 11 0.00320.003250.00330.003350.00340.003450.0035 1/T (K)ln(CO2TR) PD 961 EZ PD 900

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72 CHAPTER 5 DESIGN OF MODIFIED ATMOSPHERE PACKAGE FOR IRRADIATED FRESHCUT CANTALOUPE AND EVALUATION WITH DESCRIPTIVE ANALYSIS SENSORY PANEL Introduction Respiration involves the consumption of oxygen and production of carbon dioxide and water. Aerobic respira tion can be slowed by limiting available oxygen. However, oxygen must be maintained above a minimum th reshold to prevent an aerobic respiration (Knee, 1980). Additionally, increased carbon dioxide concentration has been shown to slow down ripening and respiration rates (Mat hooko, 1996). Therefore, an optimal micro atmosphere may be created via modified atmosphere packaging (MAP), where respiration and ethylene produc tion may be reduced as well as many other degradative processes. A MAP can be developed by matc hing the proper film w ith the weight and respiration rate of the respiring contents. Modified atmosphere packages can be de signed using predictive equations based on known respiration data. The respiration rate of most produce is dependent on the oxygen and carbon dioxide levels that surround the produce. An ideal package will maintain the desired levels of decrease d oxygen and increased carbon dioxide based on the transmission rates of the package and the re spiration rate of the produce at the desired storage temperature. Packages can be flushed with the desired steady-state gas composition in order to avoid the duration of relying on the dynamic process. The quicker the produce is at the optimal atmo sphere the more effective the package.

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73 A combination of MAP and ir radiation may have a synerg istic effect on the shelf life of produce. This was demonstrated by Prakash and others (2000) with cut romaine lettuce. Irradiation increased the shelf life of the MAP fresh-cut lettuce compared to the non-irradiated MAP fresh-cut lettuce by reduc ing the initial microb ial load by 1.5 log CFU/g and maintaining a 4 l og CFU/g difference on the 18th day of storage. The first objective of this research wa s to design a MAP for irradiated and nonirradiated fresh-cut cantaloupe based on polynomial respiration rate prediction equations and known transmission rates of packaging film s. The second objective was to determine the validity of the prediction model and the effectiveness of the package with a trained sensory panel and evaluation of color, texture and microbiology. Materials and Methods Fruit Sample Cantaloupes (Cucumis melo Linnaeus, cv. Magellan and Acclaim) were purchased from a local grocery store in Gainesville, FL on March 14 (Trial 1) and March 30, 2004 (Trial 2). Prior to purchase, the cantal oupes purchased on March 14 and March 30 were shipped from Del Monte (Costa Rica) and Del Sol (Costa Rica), respectively, in a 2% oxygen bag and maintained at 3 C. Cantaloupes were transfe rred to the University of Florida Food Science and Human Nutrition buil ding via automobile and were stored at 25 C for 1 day and then placed in a 3 C storage room overnight before processing. Cantaloupes were picked at thr ee quarter to full slip (comme rcial maturity, when a clear separation from the vine occurs with light pressure) and ready to eat. Processing Cantaloupes were rinsed in 100 ppm chlori nated water and allowed to dry 1 hour before cutting. All knives, cutting boards and bowls were soaked with 100 ppm

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74 chlorinated water. Twenty four cantaloupe s were halved, deseeded, and then halved again resulting in 4 equal parts. Each part was then halved again resulting in 8 canoe shaped pieces. Slices were then peeled a nd cut into approximately 2.5 cm pieces with a knife. All pieces were placed in an alumin um bowl, which was surrounded with ice. Pieces were thoroughly mixed to assure random sampling. Pieces in Trial 1 (~625g) and Trial 2 (~520 g) were placed in Cryovac Sealed Air Corporation (Duncan, South Carolina) polypr opylene trays. Trays were placed in Cryovac Sealed Air Corporation PD-900 MAP bags cut to 32 x 28 cm. The MAP bags were placed on a PAC Table Top Vac/Gas Sealer Model No. PVTSG-24 (Packaging Aids Corporation, San Raphael, CA). The equipmen t settings were Vacuum 4, Flush Gas 9, Seal Time 11, and Cool Time 5. Th e flush gas was 3.97% oxygen, 10.0% carbon dioxide, and balanced with nitrogen (BOC Gas, Riverton, NJ). The PAC Table Top Vac/Gas Sealer pulls a vacuum and refills the pouch full with the flush gas, then seals and cools before releasing. Bags were placed in ice in portable coolers and transported to the electron beam irradiati on facility (Florida Accelerator Services and Technology, Gainesville, FL). Plastic trays were previously frozen with 1.5 cm of ice in them. Four bags were taped to each tray with cantaloupe ar ranged in a single flat layer in order for all pieces to receive equal dosage. Dosimeters we re also attached to verify target dose had been reached. The irradiator was set at 10 fpm and 0.5 kGy per pass. To achieve 1.0 kGy, the sample was passed through twice. Bags were removed from ice trays and placed back in the ice cooler after desired number of passes. Samples were irradiated at 0, 0.5, or 1.0 kGy.

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75 Packages were transferred back to the FSHN building and stored at 3 C for the duration of the experiment. Further testing wa s done on 1, 4, 6, 8, 11, 14, 18, and 20 d for Trial 1 and on 1, 4, 6, 11, 15, 18, and 20 d for Trial 2. A closed system experiment was also r un with the same fruit to produce a rapid method for respiration rate prediction equati on determination. Pieces (~300g) were also placed in quart Ziploc (S.C. Johnson & Son, Inc., Racine, WI) Freezer bags and sealed after expulsion of most air. The bags were handled in th e same way as the modified atmosphere packages above and ir radiated at 0.5, or 1.0 kGy. The pieces (~300g) of each bag were then placed in a 1-quart Ball Mason Jars (Alltrista Corporation, Indiana polis, Indiana). Jars and lids were sanitized with a Better Built Turbomatic washer and dryer. Lids were drilled with a 3/8” hole directly in the middle. Parafilm (American National Can, Menasha, WI) was wrapped around the top of the jar before applying the lid to assure a gas tight seal. Jars were stored at 3 C for the duration of the experiment. Rubber stoppers were placed in the hole in the lid to create a closed system immediately upon closing the jar. Gas samples were taken every 4 to 12 hours throughout a 14 day storage duration. Dosimetery Radiographic dosimeters were placed under bags of cantaloupe, flat on the trays and on top of bags. Gafchromic MD-55 from International Specialty Products (Wayne, NJ, USA) were cut into 1x1 cm squares, placed in small envelopes and taped into place. The dosimeter film was allowed to expose for 24 hrs and then read on a spectrophotometer at a wavele ngth of 510 nm. The per pass average was determined by averaging the dose received on top of the bag with that below the bag.

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76 Gas Analysis Headspace analysis was done by sampling ga s composition of bags or jars for contents of O2 and CO2 using an O2 and CO2 analyzer (Checkmate 9900, PBI-Dansensor, Ringsted, Denmark). Septums of 1.3 cm diameter were placed on all bags. Rubber serum stoppers were placed in the hole in the jar lids. The Checkmate sampling needle was inserted through the se ptum or stopper. The O2 and CO2 percentages were recorded when readings stabilized. All gas sample s were taken in the cold storage room. Microbial Analysis Cantaloupe (~20 g) were aseptically rem oved from the packages and placed in sterile stomacher bags. Samples were dilute d 1:10 with phosphate buffer (1:800, pH 7.2) and stomached for 30 seconds. Further 1:10 dilu tions were carried out by adding 1 ml to 9 ml of phosphate buffer in dilution tubes a nd vortexing for 30 seconds. Aerobic Plate Count and Yeast and Mold Plate Count Petrif ilm (3M Corporation, St Paul, MN) were used as described by instructi ons for all dilutions tested. Petrifilms were incubated at 25 C for 4 days then quantified. Sensory Sensory analysis using desc riptive analysis wa s conducted by sixteen panelists (8 male, 8 female, 21-45 years of age) who were students and staff of the University of Florida, Food Science and Human Nutrition Department. The pane lists were trained during four, 1 hour sessions to recognize fresh and stored cantaloupe attrib utes, a week before the first evaluation. Cantaloupes stor ed for different times, some vacuum sealed, some exposed to air, some irradiated and fr esh cantaloupes were give n to panelists during the first training session. The panelists were asked to write down all terms they felt described the different samples. All pane lists announced their descriptor terms and

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77 discussed them. All terms were compiled and given to the panelists on the second training date. Samples were analyzed agai n and through elimination and agreement, the most important terms were finalized: appearan ce termsorange and moist; texture termsfirmness, mealy, juicy and cr ispness; and flavor termssweetness, cantaloupe flavor intensity, off-flavor, pumpkin and overall acceptability. In the third session, the panelists were gi ven a practice ballot and rated the training samples. Each attribute was rated using a 15 cm line scale with an chors at 13 mm from each end, anchored with the terms high and lo w. Panelists were instructed to mark anywhere on the line to rate the intensity. Pa nelists discussed their re sults and agreed that the ballot covered all necessary terms. The panel also decided where typical or common fresh-cut cantaloupe should be rated. In the fourth session, panelists were gi ven a practice ballot and rated cantaloupe irradiated that day, as well as stored fresh a nd irradiated samples. Panelists rated samples consistently with one another. At each test date, panelists evaluated thr ee samples (control, 0.5 kGy and 1.0 kGy). Samples were coded with a three digit random number and served in small plastic cups (2-3 pieces of cantaloupe). The panelists we re provided with water and unsalted crackers in a private booth equipped w ith a monitor, mouse and key board. The panelists marked on the open line on the screen to indicate intens ity ratings for each attribute. Compusense five release C5R4.6 (Guelph, Ontario, Canada ) was used to design and run all sensory tests. All orders of presentation were pres ented once, then at random. The samples were evaluated again for replication in the same manner after a short break by the panelist.

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78 Color Analysis Six cantaloupe pieces from each treatmen t were removed and placed on Styrofoam plates. The color of the pieces was measur ed using a hand held Minolta Chroma Meter CR-2006 (Minolta Camera Co., Osaka, Japan). The colorimeter was calibrated before each use with a standard white plate (D 65 Y = 94.4, x = 0.3158 and y = 0.3334). One side of each cube was placed flush against th e light source and the L*, a*, b* values were measured. The L* refers to brightness from 0 = black to 100 = white. The a* is from negative (green) to positive (red) and b* is fr om negative (blue) to positive (yellow). Hue, the quality of color, which we describe by the words red, yellow, green, blue, etc., was calculated with the equation hue = arctan (b/a). Chroma, the quality describing the extent to which a color differs from gray of the same value or lightness, was calculated with equation chroma = (a2 + b2)1/2 (Billmeyer and Saltzman, 1966). Texture The texture of the cantaloupe was meas ured by an Instron Universal Testing Instrument, model 4411 (Canton, Massachusetts). The six pie ces that were analyzed for color were used for texture. The canta loupe pieces were placed under a plunger, establishing zero force contact, with a diamet er of 5.0 mm and compressed 3 mm with a 50 kg load cell. The plunger was driven in to the piece with a cr osshead speed of 30 mm/min. The maximum compression force was measured in kg. Statistical Analysis Non-sensory data was analyzed using an alysis of variance in The SAS System version 9e. The sensory data we re analyzed two ways. In th e first analysis, the data from each storage time were analyzed separately by an alysis of variance using SAS version 9e.

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79 The model consisted of panelist effect, treatme nt effect, panelist*treatment interaction, and replication effect. In the second analysis, all data were anal yzed as split plot design using analysis of variance, with panelists as bl ocks, treatment as subplot, and storage time as whole plot. Means were separated by Duncan’s Multiple Range Test when a significant F value was obtained (p=0.05). All other data (color, texture and micro) we re subjected to analysis of variance as a completely randomized design, with the model consisting of treatment effect and storage time effect. Results and Discussion MAP Design The first step in the design of the modifi ed atmosphere package was the choice of the Cryovac PD-900 film over the PD-961 EZ film. Quick analysis reve aled that a large amount of fresh-cut cantaloupe would be requi red to reach an equilibrium (maintenance of desired internal atmosphere) of gases based on the low respiration rate of the fruit and the higher transmission rate of the PD-961EZ film. The internal atmosphere beginning c onditions were chosen to be 4% O2 and 10% CO2. These values of oxygen and carbon di oxide are both in the middle of the recommended ranges for storing fresh-cut ca ntaloupe (Gorny, 2001). This allowed for maximum unpredicted deviation in either dir ection, especially important for preventing the growth of anaerobic organisms. Ideally the internal atmosphere of the package would stay very close to the flush gas composition. With known respiration rates of the ir radiated and non-irradiated fruit and transmission rates of the film, the adjustable parameters were the amount of fresh-cut cantaloupe and the surface area of film. A weight of 500 to 650 g of fresh-cut cantaloupe

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80 was considered reasonable for the Cryovac tray s provided. Based on the dimensions of the tray, reasonable bag sizes were determined Adjusting these two variables, a bag size with total area of 0.135 m2 (0.32 m x 0.211 m x 2 sides) a nd a fruit weight of 625 g gave satisfactory prediction results. One bag design was chosen for all treatments for consistency in experimentation, with O2 and CO2 concentrations varying no more than 2% in predicted headspa ce compositions. Figure 5.1 shows the predicted gas compositions over 500 hours or ~21 days for can taloupe irradiated at 0.4 kGy. The O2 concentration steadily increased to just less than 5.9% and the CO2 concentration rose to just below 10.6% in the first 300 hours and leveled off for the duration. 0 2 4 6 8 10 12 0100200300400500600 HoursPartial Pressure O2 CO2 Figure 5.1. Predicted oxygen and carbon dioxide partial pressures for 0.4 kGy samples in designed modified atmosphere packag e with initial gas flush of 4% O2 plus 10% CO2 for Trial 1 stored at 3 C.

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81 For the second trial, a bag si ze with total area of 0.13 m2 (0.203 m x 0.32 m x 2 sides) was used with a fruit weight of 520 g, which also gave satisfactory prediction results. Figure 5.2 shows the predicted headspace compositions over 500 hours or ~21 days for cantaloupe irradiat ed at 0.4 kGy. The O2 concentration steadily increased to just above 5% and the CO2 concentration rose to just above 10% and remained constant for the duration. 0 2 4 6 8 10 12 0100200300400500600 HoursPartial Pressure O2 CO2 Figure 5.2. Predicted oxygen and carbon dioxide partial pressures for 0.4 kGy samples in designed modified atmosphere packag e with initial gas flush of 4% O2 plus 10% CO2 for Trial 2 stored at 3 C. Figures 5.3-5.6 show the %O2 and %CO2 across time for both trials. Lines in between points are presumed patterns of gas be havior and not actual data. On Day 1 of Trial 1, the %O2 was approximately 5.7% for all tr eatments. Although a strong vacuum

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82 was pulled on the bags and filled with 4% O2 plus 10% CO2 gas mixture, a small amount of ambient air remained in the pockets and cavities created by the stacked fruit. The composition of the air that rema ined was approximately 21% O2 and 0.0% CO2, which caused the initial internal atmosphere to be higher than 4% O2, which is seen in both trials. This also leads to the expectation of the %CO2 in the fill gas to be slightly diluted. This was seen in Trial 2 but not Trial 1. 0 1 2 3 4 5 6 7 05101520 Days% O2 Control 0.5 kGy 1.0 kGy Figure 5.3. Actual oxygen partial pressu res for all samples in designed modified atmosphere packages for Trial 1 stored at 3 C. 0 2 4 6 8 10 12 14 16 05101520 Days% CO2 Control 0.5 kGy 1.0 kGy Figure 5.4. Actual carbon dioxi de partial pressures for all samples in designed modified atmosphere packages for Trial 1 stored at 3 C.

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83 0 2 4 6 8 10 12 05101520 Days% O2 Control 0.5 kGy 1.0 kGy Figure 5.5. Actual oxygen partial pressu res for all samples in designed modified atmosphere packages for Trial 2 stored at 3 C. 0 2 4 6 8 10 12 05101520 Days% CO2 Control 0.5 kGy 1.0 kGy Figure 5.6. Actual carbon dioxi de partial pressures for all samples in designed modified atmosphere packages for Trial 2 stored at 3 C. In Trial 1, the %O2 remained steady in the control through Day 6 and for the 0.5 kGy and 1.0 kGy through Day 8. The %CO2 slowly declined through Day 8 for all treatments. The control %O2 decreased from Day 6 to 11 and then climbed back up to ~6%. The control %O2 was significantly the lowest on Day 8 and 11 (Table 5.1). The

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84 %CO2 in the controls increased between Da y 8 and Day 14 and was significantly the highest on Day 11 and 14. These results are ve ry similar to the open system results of Chapter 1. A significant increase in respir ation rate was seen in the non-irradiated controls before the irradiated samples. The 1.0 kGy sample changed the least of all samples maintaining the lowest respiration rate The lower respiration rates of irradiated samples are linked to the reduction of meta bolic activity, with the higher the dose the larger the reduction (Benoit and others, 2000; Aljouni and others, 1993). Increase in respiration rate after 79 days of storage at 5 C of fresh-cut cantaloupe was observed by Aguayo and others (2004). Th is data is also in agreem ent with results from LunaGuzman and Barret (2000), Bai and others (2001), and Madrid and Cantwell (1993). Possible reasons reported were microbial growth and/or gene ral deteriora tion of tissue due to senescence. In Trial 2, all treatments %O2 behaved very similarly through Day 11 (Table 5.1). The %O2 in the control dropped while the %O2 in the irradiated samples increased after Day 8. The %CO2 remained similar through Day 11 although significantly different on Day 1 through Day 6, it is presumed to be due to a replication eff ect at each time. The effect of treatment was clearly seen af ter Day 11, when the consumption of O2 and evolution of CO2 was significantly much higher in th e controls. Similar results were found with cut iceberg lettuce, where irradiat ed samples (0.2 and 0.45 kGy) had higher respiration rates on Day 1 and lower on Day 13 (Hagenmaier and Baker, 1997). Figures 5.7 and 5.8 compare predicted vs. act ual internal atmospheres of packages. In Trial 1, the oxygen prediction and experime ntal data are in good agreement with very

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85 similar values for 8 days. The carbon dioxide predicted slowly rose to just under 11% and the actual level droppe d to just under 8%. Table 5.1. Headspace composition of modified atmosphere packages of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C. Means within a column sharing the same letter are not significantly different (p<0.05). Trial 1 %O2Day 1Day 4Day 6Day 8Day 11Day 14Day 18Day 20 Control 5.7a5.5a5.4a3.9b0.1b0.7b4.4a6.1a 0.5kGy 5.8a5.6a5.7a5.7a3.9a1.1b3.8a5.2a b 1.0kGy 5.7a5.4a5.5a5.7a4.9a2.1a3.2a4.2b %CO2Day 1Day 4Day 6Day 8Day 11Day 14Day 18Day 20 Control 10a8.6b8.2a7.6a12a14a14a13a 0.5kGy 10a8.9b8a7.7a9.1b13b13a13a 1.0kGy 10a9.3a8.1a7.7a8.4c11c13a13a Trial 2 %O2Day 1Day 4Day 6Day 11Day 15Day 18Day 20 Control 5.5a6.2a6.9a9.1a4.5b1.3b1.4b 0.5kGy 5.3a5.9a6.7a9.4a11a11a9a 1.0kGy 5.4a6a6.3a8.9a10a11a9.6a %CO2Day 1Day 4Day 6Day 11Day 15Day 18Day 20 Control 8.2b6.8b6.1c4.8a8.3a11a10a 0.5kGy 8.4a7a6.3b4.8a4.3b5.2b6.5b 1.0kGy 8.5a7.2a6.5a5a4.3b4.6b5.7b There are many reasons why the model may slightly differ from the experimental results. First, the data collected for the model was from fresh-cut cantaloupe irradiated in Ziploc bags with ambient air and then transf erred to jars of ambi ent air, whereas the experimental data is from fr esh-cut cantaloupe irradiated an d stored in a bag with 4% oxygen and 10% carbon dioxide.

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86 0 2 4 6 8 10 0510 DaysGas Concentration (%) Oxygen 0.4 kGy (predicted) Oxygen 0.5 kGy (experimental) Carbon dioxide 0.4 kGy (predicted) Carbon dioxide 0.5 kGy (experimental) Figure 5.7. Trial 1 Predicted and observe d oxygen and carbon dioxide levels inside designed modified atmosphere packag e containing irradiated fresh-cut cantaloupe stored at 3 C. Therefore, the closed system generated a unique set of gas con centrations starting with high oxygen and low carbon dioxide a nd progressing to low oxygen and high carbon dioxide. The modified atmosphere packag es maintained a low oxygen and high carbon dioxide headspace that was not observed in the closed system. This must be taken into consideration when designing a package based on closed system experiments. As seen from the data above, a package can be designe d to maintain gas concentrations within critical ranges from closed system data. Second, closed system data was from samples irradiated at 0.4 and 0.6 kG y, and irradiation of these packages was 0.5 kGy. A limitation of irradiation was exposed here. Th e exact dosage of elect ron beam irradiation is difficult to achieve. Many variables come in to play when trying to treat a product with a low dose. All settings in an irradiation facility may be the same as the day before, but a different dose may occur when running a very similar experiment. Not only does the actual irradiation emitted change, but the product composition, temperature, thickness

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87 and etc., affects the average dose received as well. The intended average dose for the cantaloupe irradiated in this experiment was 0.4 and 0.8 kGy, in order to compare predicted respiration rates from the closed system data with experimental. Fortunately, the average dose did not exceed 1.0 kGy, th e legal limit allowed by the FDA for fresh produce. 0 2 4 6 8 10 051015 DaysGas Concentration (%) Oxygen 0.6 kGy (predicted) Oxygen 0.5 kGy (experimental) Carbon dioxide 0.6 kGy (predicted) Carbon dioxide 0.5 kGy (experimental) Figure 5.8. Trial 2 predicted and observe d oxygen and carbon dioxide levels inside designed modified atmosphere packag e containing irradiated fresh-cut cantaloupe stored at 3 C. Microbiology The TPC counts were significantly highe r in the controls through Day 11 and remained the highest through the duration in Tr ial 1 (Table 5.2). The largest treatment difference was a 2 log reduction on Day 6 betw een the control and 1.0 kGy treatment. The greatest increase in a treatment over time was the control from Day 1 to Day 6 with a ~2.3 log jump. The results are similar to Chapter 3. The microb iology counts were not significantly different at Day 14 and 18, yet at Day 8, 11, 14 and 18, there were significant differences in %O2. It may be assumed that the reduction in respiration rate is

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88 not solely due to reduction in microorganism s. In a paper by Bai and others (2001), fresh-cut cantaloupe was stored in MAPs flushed with 4% O2 plus 10% CO2 at 5 C. The total plate count started just above 3 logs CFU/g and increas ed to ~9 logs CFU/g in 12 days. The respiration rate remained steady for the duration of the study, suggesting no effect of microorganisms. There were no si gnificant differences between treatments in yeast and mold counts at all stor age dates tested (Table 5.2). Table 5.2. Total plate count (TPC) and yeas t and mold count (Y+M ) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C in modified atmosphere packages (Trial 1). CFU/g = colony form ing units per gram. Means within a column sharing the same letter are not significantly different (p<0.05). Trial 1 CFU/g Day 1Day 6Day 11Day 14Day 18 Control 8.40E+04a1.59E+07a1.21E+09a1.18E+09a1.60E+09a TPC0.5 kGy 1.57E+04b1.67E+06b1.49E+08b1.00E+09a1.05E+09a 1.0 kGy 1.18E+04b1.58E+05b5.52E+07b5.20E+08a1.40E+09a CFU/g Day 1Day 6Day 11Day 14Day 18 Control 4.53E+03a9.13E+04a2.11E+06a1.35E+05a4.90E+05a Y+M0.5 kGy 6.30E+02a4.80E+04a1.58E+05a2.88E+05a6.50E+05a 1.0 kGy 1.37E+03a3.75E+03a1.48E+05a1.98E+05a5.05E+06a In Trial 2, the TPC counts were ~1.5 logs lower than the counts from Trial 1 on Day 1 (Table 5.3). There were significant di fferences with the control being the highest at all storage dates. The largest increase in counts in the control was between Day 6 and Day 11, almost 3 logs. This increase did not take place in the 0.5 kGy sample until between Day 15 and 20 and between Day 11 and 15 for the 1.0 kGy. The %O2 increased and the %CO2 decreased between Day 6 and 11 in all samples. There seemed to be no relationship between respira tion and microorganism count. There were no significant differences between treatments for yeast and mold counts at all storage dates. Results were similar to those reported by Ahn and others (2005) for minimally processed salted Chinese cabbage treated with MAP and irradiation during refrigerated

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89 storage. Total aerobic bacteria count reductions of 0.7 and 1. 5 logs were observed at time 0 in packages flushed with 25% CO2 plus 75% N2 and irradiated at 0.5 kGy and 1.0 kGy, respectively. Initial populations of total ae robic bacteria in salted Chinese cabbage were significantly reduced by gamma irradiat ion at 0.5 and 1.0 kGy (p < 0.05). Table 5.3. Total plate count (TPC) and yeas t and mold count (Y+M ) of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 C in modified atmosphere packages (Trial 2). CFU/ g = colony forming units per gram. Means within a column sharing the same letter are not significantly different (p<0.05). Trial 2 CFU/g Day 1Day 6Day 11Day 15Day 20 Control 3.08E+03a2.20E+04a1.03E+07a9.31E+08a1.15E+09a TPC0.5 kGy 7.50E+02b7.00E+02b1.58E+04b5.28E+04b1.63E+08b 1.0 kGy 2.83E+02c2.30E+02b6.00E+03b3.23E+06b2.72E+08b CFU/g Day 1Day 6Day 11Day 15Day 20 Control 1.00E+01a1.00E+01a2.90E+03a7.90E+04a2.43E+05a Y+M0.5 kGy 1.00E+01a1.00E+01a1.03E+03a3.86E+04a5.83E+05a 1.0 kGy 1.00E+01a1.00E+01a1.00E+02a1.35E+04a4.49E+05a The quality of fresh-cut can taloupe cubes in a study by Bai and others (2001) remained acceptable even though bacterial count s increased above 8 logs CFU/g. Yeast and mold were also less numerous in these tr ial as with others fr esh-cut produce studies (Nguyen-The and Cartin, 1994). Two benefits of elevated carbon dioxide are its fungistatic and bacteristatic ch aracteristics against many spoila ge organisms that are able to multiply at refrigerator temperatures, and the ability to prolong the lag phase of spoilage organisms (Enfors and Molin, 1978). Texture The significant differences observed in the texture of the fresh-cut cantaloupe in Trial 1 were likely the result of variation from piece to piece rather than effect of treatment or storage (Table 5.4). Considerable variability from melon to melon was noted while processing. The mel ons in Trial 2 were much more consistent in texture. No

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90 significant differences between treatments we re observed at any storage dates. The texture readings in Trial 2 remained steady ac ross time with no interaction effect between treatment and storage. No consistent differe nces in texture were reported in Chinese cabbage irradiated at 0.5 or 1. 0 kGy and stored in MAP at 4 C (Ahn and others, 2005). Table 5.4. Texture (kg) of irradiated and non-irradiated fresh-cut cantaloupe during storage at 3 C in modified atmosphere packages. Means within a column sharing the same letter are not significantly different (p<0.05). Trial 1 max kg Day 1Day 6Day 11Day 14Day 18 Control 1.214a0.919a0.863b1.16a0.891a 0.5kGy 0.903b0.688a1.199a0.793b1.012a 1.0kGy 0.93b0.824a1.068ab1.092a0.869a Trial 2 max kg Day 1Day 6Day 11Day 15Day 20 Control 1.116a1.069a0.997a1.078a1.08a 0.5kGy 1.167a1.216a1.033a1.024a1.136a 1.0kGy 1.056a1.068a0.989a1.073a1.084a Color The L*, a* and b* values observed over time are listed in Table 5.5. In Trial 1, there were significant differences in L* values only at Day 1. The a* and b* values did not differ significantly throughout the duration of the storage. The differences in color were attributed more to piece to piece varia tion than effect of treatment. No specific trends were seen across time within treatme nts (Table 5.6). The color of fresh-cut cantaloupe irradiated or not remained stable fo r 18 days. These results are very similar to those found by Lamikanra and others (2000), wh ere no significant ch anges occurred in lightness (L*), hue and chroma of fresh-cut cantaloupe stored at 4 C for 7 days. In contrast, in another study (Lamikanra and Wa tson, 2000), storage of fresh-cut cantaloupe at 4 C for 25 days resulted in considerable changes in hue, chroma and L* values. Lamikanra and Watson (2000) observed bleaching of cantaloupe, which was attributed to

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91 oxidation of B-carotene. This may not have been a problem in this research due to the low oxygen atmosphere maintained by the MAP. Table 5.5. Color (L*, a*, b*) of irradiated and non-irradiated fr esh-cut cantaloupe during storage at 3 C in modified atmosphere packages, by treatment (Trial 1). Means within a column sharing the same letter are not significantly different (p<0.05). L Day 1Day 6Day 11Day 14Day 18 Control 68.76a59.33a61.94a65.56a64.98a 0.5kGy 64.38ab59.23a66.41a65.38a63.75a 1.0kGy 62.49b58.99a63.38a63.89a61.82a a Day 1Day 6Day 11Day 14Day 18 Control 11.59a11.74a12.08a11.77a12.69a 0.5kGy 11.93a11.46a12.48a12.35a12.49a 1.0kGy 12.01a11.62a12.12a12.56a12.69a b Day 1Day 6Day 11Day 14Day 18 Control 33.16a31.09a31.03a31.58a32.06a 0.5kGy 31.73a29.52a32.41a33.35a31.45a 1.0kGy 31.40a30.28a32.63a32.64a31.18a In Trial 2, significant differences between treatments in L* values were observed on Day 6 (Table 5.7). The a* values differed significantly only on Day 20. The b* values differed significantly on Day 6 and 20. As in Trial 1, no trends were observed with respect to the effect of treatment. An e ffect of storage was seen in Trial 2, with the control and 1.0 kGy samples having the signifi cantly lowest L*, a* and b* values on Day 20. The 0.5 kGy samples remained very stable over time. Sensory Trial 1 The trained panelists rated the appear ance attribute orange, of the control significantly lower than that of the irradiat ed samples when averaged across all storage times (Table 5.8). Orange was significantly different between Day 1 and Day 18 within

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92 Table 5.6. Color (L*, a*, b*) of irradiated and non-irradiated fr esh-cut cantaloupe during storage at 3 C in modified atmosphere packages, by storage. Means within a column sharing the same letter are not significantly different (p<0.05). Trial 1 Trial 2 Control Control L a b L a b Day 1 68.76 a 11.59 b 33.16 a Day 1 65.34 bc 11.13 a 30.97 a Day 6 59.33 c 11.74 b 31.09 b Day 6 68.23 a 11.36 a 31.73 a Day 11 61.94 c 12.08 ab 31.03 b Day 11 68.63 a 10.61 ab 31.11 a Day 14 65.56 b 11.77 b 31.58 b Day 15 66.90 ab 10.88 a 30.60 a Day 18 64.98 b 12.69 a 32.06 ab Day 20 63.53 c 9.99 b 27.63 b 0.5kGy 0.5kGy L a b L a b Day 1 64.38 a 11.93 a 31.73 a Day 1 65.93 a 11.31 a 30.40 ab Day 6 59.23 b 11.46 a 29.52 b Day 6 64.66 a 11.33 a 29.68 ab Day 11 66.41 a 12.48 a 32.41 a Day 11 65.98 a 10.99 a 30.58 ab Day 14 65.38 a 12.56 a 33.35 a Day 15 65.23 a 10.93 a 29.28 b Day 18 63.75 a 12.69 a 31.45 ab Day 20 66.40 a 11.03 a 31.03 a 1.0kGy 1.0kGy L a b L a b Day 1 62.49 ab 12.01 ab 31.40 ab Day 1 68.77 a 10.40 bc 30.27 a Day 6 58.99 b 11.62 b 30.28 b Day 6 65.68 ab 10.54 b 30.55 a Day 11 63.38 a 12.12 ab 32.63 a Day 11 68.09 a 10.83 ab 30.08 a Day 14 63.89 a 12.56 a 32.64 a Day 15 64.78 bc 11.53 ab 30.68 a Day 18 61.82 ab 12.69 a 31.18 ab Day 20 61.97 c 9.64 c 26.45 b Table 5.7. Color (L*, a*, b*) of irradiated and non-irradiated fr esh-cut cantaloupe during storage at 3 C in modified atmosphere packages, by treatment (Trial 2). Means within a column sharing the same letter are not significantly different (p<0.05). L Day 1Day 6Day 11Day 15Day 20 Control 65.34a68.23a68.63a66.90a63.53a 0.5kGy 65.93a64.66b65.98a65.23a66.40a 1.0kGy 68.77a65.68ab68.09a64.78a61.97a a Day 1Day 6Day 11Day 15Day 20 Control 11.13a11.36a10.61a10.88a9.99ab 0.5kGy 11.31a11.33a10.99a10.93a11.03a 1.0kGy 10.40a10.54a10.83a11.53a9.64b b Day 1Day 6Day 11Day 15Day 20 Control 30.97a31.73a31.11a30.60a27.63ab 0.5kGy 30.40a29.68b30.58a29.28a31.03a 1.0kGy 30.27a30.55ab30.08a30.68a26.45b

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93 all treatments with a slight increase over ti me. Day 6 is the only day that colorimeter readings for a* and b* were bot h higher in the control. The other appearance attribute, moist was rated lowest in the control over all storage times. Within all treatments, moist, increased over time and wa s rated significantly different only between Day 14 and Day 18. There was no storage*treatment interaction for the appearance attributes. The texture attribute firmness was rated significantly higher in the control than both irradiated samples. There was no storage* treatment interaction effect or trend in firmness over time with the only differen ce between Day 1 and Day 11. Crispness was rated the lowest in the 1.0 kGy sample. Fi rmness and crispness being significantly lower in the 1.0 kGy treatment is consistent with the literature where higher doses of irradiation are more likely to induce so ftening of tissue (Massey a nd Bourke, 1967; Kertesz and others 1964; Gunes and others, 2001b). As pr eviously stated, considerable variability from melon to melon in texture was noted while processing. No differences between treatments were observed in mealy over all time nor did it change dur ing storage. Juicy was significantly highest in the 1.0 kGy treatment, but no differences were observed during storage with no interaction effect. A storage*treatment interaction effect was observed in crispness and mealy, although no clear trends were observed by treatment over time. The sweetness attribute was rated significantl y lowest in the control compared to both irradiated samples. A significant d ecrease in sweetness was observed on Day 18. No storage*treatment interaction effect wa s observed in sweetness. Differences in sweetness may be attributed to lower cons umption rates of carbohydrates (glucose, fructose and sucrose) due to lower respiration rates in irradiated tissue. Similar results

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94 Table 5.8. Sensory results (Trial 1), by treatment and over storage of irradiated and non-irradiated fresh-cut cantaloupe (0 t o 15 scale), stored at 3 C. CFI* = Cant aloupe Flavor Intensity. Means within a column sharing the sa me letter are not significantly different (p<0.05). ns = non signi ficant, = significant (p<0.05) Treatment OrangeMoistFirmnessMealyJuicyCrispnessSweetnes s CFI*Off FlavorPumpkinAccept. Control 7.09b7.59b8a0.84a7.31b8.06a6.53b6.8b2.65a0.67a6.61b 0.5 kGy 7.73a8.1a7.47b0.82a7.73ab8.02a7.01a7.75a1.8b0.43a7.37a 1.0 kGy 7.63a8.13a7.15b0.71a8.02a7.03b7.21a8.01a1.72b0.43a7.53a Storage OrangeMoistFirmnessMealyJuicyCrispnessSweetnes s CFI*Off FlavorPumpkinAccept. Day 1 7.24b7.61b7.87a0.91a7.6a8.06a6.87a7.75ab1.41bc0.68a7.88a Day 6 7.4ab7.61b7.68ab0.51a7.63a8.15a7.44a8.49a0.71c0.38a8.63a Day 11 7.55ab7.95b7.17b0.59a7.63a7.31b7.01a7.52ab1.38bc0.29a7.45ab Day 14 7.57ab8.22ab7.43ab0.69a7.69a7.21b7a7.35b2.61b0.51a6.21b Day 18 7.86a8.71a7.46ab1.57a8.05a7.69ab5.72b5.53c6.03a0.75a4.2c Interact nsnsns*ns*nsns*ns*

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95Table 5.9. Sensory results (Trial 2), by treatment and over storage of irradiated and non-irradiated fresh-cut cantaloupe (0 t o 15 scale), stored at 3 C. CFI* = Cant aloupe Flavor Intensity. Means within a column sharing the sa me letter are not significantly different (p<0.05). ns = non signi ficant, = significant (p<0.05) Treatment OrangeMoistFirmnessMealyJuicyCrispnessSweetnes s CFI*Off FlavorPumpkinAccept. Control 6.84a7.32a7.93a0.49a6.93ab7.96a6.45a7.34a1.76a0.26a7.2b 0.5 kGy 6.45b6.98b7.98a0.41a6.77b8.02a6.48a7.4a1.01b0.32a7.57ab 1.0 kGy 6.7a7.23ab7.68a0.44a7.21a7.71a6.71a7.63a0.91b0.23a7.89a Storage OrangeMoistFirmnessMealyJuicyCrispnessSweetnes s CFI*Off FlavorPumpkinAccept. Day 1 7.02a7.36a7.78ab0.32b7.09a7.71ab6.9a8.41a0.95b0.33a7.88ab Day 6 6.39a7.22a8.38a0.33b6.77a8.47a6.38a7.59ab0.69b0.25a7.83ab Day 11 6.74a7.35a8.07ab0.65a7.39a7.93ab6.45a7.64ab0.95b0.26a8.22a Day 15 6.58a6.97a7.55ab0.35b6.87a7.5b6.18a6.54b0.94b0.25a7.13bc Day 20 6.62a6.96a7.44b0.6a6.73a7.82ab6.87a7.05b2.82a0.26a6.59c Interact *nsnsns*ns***ns*

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96 were found with fresh-cut irradi ated carrots compared to non irradiated, whereby controls consumed twice the amount of overa ll carbohydrates within 96 hours at 20 C (Chervin and others, 1992). Cantaloupe flavor intensity (CFI) was ra ted significantly lower in the control compared to both irradiated samples. W ithin all treatments, a decline over time was observed with significant differences on bot h Day 14 and 18. No storage*treatment interaction effect was observed in cantaloupe flavor intensity. Off flavor was rated significantly highest in the control compared to both irradiated samples. Within all treatments, an increase over time was observed with significant differences on Days 6, 14 and 18. A storage* treatment interaction effect was observed in off flavor such that the o ff flavor was significantly lowe r on Day 14 in both irradiated samples that in the control (Figure 5.9). An increase in off flavor of the control was seen from Day 6 through Day 11. Not only did irra diation not impart a ny off flavors, it delayed off flavor formation. In both irra diated samples off fl avor only significantly increased on Day 18. No differences were observed in the pumpkin attribute. The control was rated significantly the least acceptable between treatments. Acceptability declined significantly fo r all treatments during storage with a storage*treatment interaction effect such that the acceptability of the control was significantly lower on Day 11 and Day 14 for both irradiated samples (Figure 5.10). Fresh-cut produce generally loses freshness, flavor and salability while stored in refrigerated conditions due to physiological and biochemi cal changes (Watada and Qi, 1999). The control decreased in sweetness, ca ntaloupe flavor intens ity and increased in

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97 off flavor more rapidly than the irradiated samples. The sustained higher microbiological counts and increase in respira tion rate of the controls may be the main causes for a a a a a a a a b a a a a b a 0 1 2 3 4 5 6 7 8 16111418 Time (days)Rating Control 0.5 kGy 1.0 kGy Figure 5.9. Off flavor rating of treatments at each storage (3 C). Means sharing the same letter within a storage time are not significantly different (p<0.05). a b b a ab a a a a b a a a a a 0 1 2 3 4 5 6 7 8 9 10 16111418 Time (days)Rating Control 0.5 kGy 1.0 kGy Figure 5.10. Acceptability ra ting of treatments at each storage date (3 C). Means sharing the same letter within a storag e time are not significantly different (p<0.05).

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98 these sensory differences. Lactobacilli spp. are most likely the microorganism responsible (Salama and others, 1995). Lactobacilli spp. ferment glucose, fructose and sucrose during growth while producing lactic ac id. Fruit flavor deterioration may be due to increased lipase producti on by lactic acid bacteria (Lamikanra and others, 2000; Chandler and Ranganathon, 1975; Meyers and others, 1996). The higher respiration rate leads to increased respiratory metabolism and senescence. Trial 2 The 0.5 kGy sample was slightly lower in the orange attribute compared to the other treatments. No effect of storage was seen in orange color, but there was a storage*treatment interaction e ffect (Table 5.9) that result ed in the control and 0.5 kGy samples being rated significantly lower on Da y 20 than on all other days, while the 1.0 kGy sample was rated significantly higher than all other days of all treatments. This large difference may be from the panelists reaction to seeing a clear difference for the first time and overrating the 1.0 kGy sample No apparent differences explain the interaction effect. The moist attribute did not decrease during storag e in Trial 2, with slight differences in tr eatment and no storage*treat ment interaction effect. No differences in firmness due to treatment were observed. Within all treatments, a decline over time was observed with a significa nt difference between Day 6 and Day 20. No storage*treatment interaction effect was observed in firmness. No differences in crispness due to treatment were observed, and there were no clear tre nds during storage. The fruit used in Trial 2 were more consiste nt with regards to te xture at time 0 and remained stable over the duration of the storage.

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99 No differences in mealy due to treatme nt were observed, and increased only slightly on Day 11 and Day 20. No storage*tr eatment interaction effect was observed for mealy. Juicy was the only texture attribute with significant differences in treatments over all storage times, with the 0.5 kGy sample the lowest and the 1.0 kGy the highest. No effect of storage was seen but there was a storage*treatment interaction effect. This interaction showed no consistent trends in the juicy attribute. There were no differences in sweetness due to treatment or storage. However, a storage*treatment interac tion effect was observed fo r sweetness. Sweetness was determined to be significantly highest in the 1.0 kGy sample on both Day 11 and Day 20 (Figure 5.11). Differences in sweetness may be attributed to lower consumption rates of carbohydrates (glucose, fructose and sucrose) du e to lower respiration rates in irradiated tissue as observed in Trial 1 and others (Chervin and others, 1992). a a b a b a a b a b a a a a a 0 1 2 3 4 5 6 7 8 9 16111520 Time (days)Rating Control 0.5 kGy 1.0 kGy Figure 5.11. Sweetness rating of treatments at each storage (3 C). Means sharing the same letter within a storage time are not significantly different (p<0.05).

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100 No differences in cantaloupe flavor in tensity (CFI) between treatments were observed when averaged across all storage time s, but there were significant differences during storage over all treatments with a stor age*treatment interaction effect. The 1.0 kGy treatment had higher CFI on Day 20 (Figure 5.12). b a ab a a b a b ab a a a a b a 0 1 2 3 4 5 6 7 8 9 10 16111520 Time (days)Rating Control 0.5 kGy 1.0 kGy Figure 5.12. Cantaloupe flavor intensity (CFI) rating of treatments at each storage date (3 C). Means sharing the same letter with in a storage time are not significantly different (p<0.05). A significant interaction be tween treatment and storage was also found for off flavor (Figure 5.13). On Day 15 and 20, the control was significantly the highest in off flavor. At Day 20, the 0.5 kGy treatment also had a higher off flavor rating than the 1.0 kGy treatment. No notable differences in the pum pkin attribute were observed. The 1.0 kGy sample was rated significantly higher in acceptability than the control when averaged across all storage times (Table 5.9). Acceptability tended to decrease during storage and there was a storage*treatmen t interaction. The interaction shows that

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101 there were significant differences in accepta bility only on Day 20, when the control had the lowest acceptability and the 1.0 kG y treatment the highest (Figure 5.14). a a ab a c a ab b b b a b a b a 0 1 2 3 4 5 6 16111520 Time (days)Rating Control 0.5 kGy 1.0 kGy Figure 5.13. Off flavor rating of treatments at each storage da te (3 C). Means sharing the same letter within a storage time are not significantly different (p<0.05). c a ab a a b a b a a a a a a a 0 1 2 3 4 5 6 7 8 9 10 16111520 Time (days)Rating Control 0.5 kGy 1.0 kGy Figure 5.14. Acceptability ra ting of treatments at each storage date (3 C). Means sharing the same letter within a storag e time are not significantly different (p<0.05).

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102 Conclusion With known prediction equations for respir ation rate of fresh-cut cantaloupe and gas transmission rate properties of packag ing films, an optimal MAP was designed. Total plate count was signifi cantly reduced in irradiated samples through Day 11 in Trial 1 and through Day 20 in Trial 2. No trends in color or texture were observed with respect to the effect of treatment in either Trial. Irradiated samples had a lower and more stable rate of respiration ove r the duration of the study than non-irradiated samples. Sensory evaluation rated the 1.0 kGy sample highest in sweetness and cantaloupe flavor intensity and lowest in off flavor after 14 days of storage in Trial 1 an d after 20 days of storage in Trial 2. Low dose electron beam irradiati on of fresh-cut cantal oupe with MAP offers promise as a method of extending shelf-life.

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103 CHAPTER 6 CONCLUSIONS Low dose electron beam irradi ation of fresh-cut cantal oupe stored in modified atmosphere packages (MAP) offers promise as a method of increa sing quality and shelf life. Knowledge of the effect s of irradiation on product respir ation rates, as summarized in Eqn. (3.1) or in other forms such as polynomial or Michaelis-Menten fits, should provide a means to develop MAP that could fu rther enhance the ability of irradiation to extend fresh-cut cant aloupe shelf-life. The Michaelis-Menten enzyme kinetics e quation may not be a suitable model for all fresh-cut produce, especially those with lo w respiration rates. A polynomial model fit the oxygen consumption and carbon dioxide evolu tion data for fresh-cut cantaloupe very well and most importantly in the critical ra nges for MAP. An Arrhenius equation can be used to express the oxygen and carbon dioxide transmission rates of packaging polymers over a range of temperatures. Determination of prediction equations for respiration rate of produce over a range of oxygen and carbon di oxide concentrations and transmission rates of packaging films allows for an optimal MAP to be easily designed. With known prediction equations for respir ation rate of fresh-cut cantaloupe and transmission rates of packaging films, an optimal MAP was designed. Internal gas composition of packages were determined similar to predictions. Total plate count was significantly reduced in irradi ated samples through Day 11 in Trial 1 and through Day 20 in Trial 2. No trends in color or texture were observed with resp ect to the effect of treatment in either trial. Irradiated samp les had a lower and more stable rate of

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104 respiration over the duration of the study than non-irradiated samples. Sensory evaluation rated the 1.0 kGy sample highest in sweetness and cantaloupe flavor intensity and lowest in off flavor after 14 days of storage in Trial 1 an d after 20 days of storage in Trial 2. Low dose electron beam irradiati on of fresh-cut cantal oupe with MAP offers promise as a method of extending shelf-life. The suppression of re spiration rate rise, decrease of microbial load, extension of shelf-life with no adverse effects on sensory characteristics, and the ability to treat in th e final package make ir radiation an excellent tool for the fresh-cut cantaloupe market.

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113 BIOGRAPHICAL SKETCH I was born and raised in West Palm Beach Florida. I obtained my undergraduate degree in food science and huma n nutrition with a business minor. I then completed my master’s in food science working with ma ngo and carambola treated with high pressure processing. During my pursuit of a doctoral degree in food science, I obtained a master’s in decision information science. All degrees were completed at the University of Florida in Gainesville, Florida.


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Permanent Link: http://ufdc.ufl.edu/UFE0008326/00001

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Title: Determination of the Effects of Modified Atmosphere Packaging and Irradiation on Sensory Characteristics, Microbiology, Texture and Color of Fresh-Cut Cantaloupe Using Modeling for Package Design
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Copyright Date: 2008

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Source Institution: University of Florida
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Permanent Link: http://ufdc.ufl.edu/UFE0008326/00001

Material Information

Title: Determination of the Effects of Modified Atmosphere Packaging and Irradiation on Sensory Characteristics, Microbiology, Texture and Color of Fresh-Cut Cantaloupe Using Modeling for Package Design
Physical Description: Mixed Material
Copyright Date: 2008

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Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0008326:00001


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DETERMINATION OF THE EFFECTS OF MODIFIED ATMOSHPERE
PACKAGING AND IRRADIATION ON SENSORY CHARACTERISTICS,
MICROBIOLOGY, TEXTURE AND COLOR OF FRESH-CUT CANTALOUPE
USING MODELING FOR PACKAGE DESIGN















By

BRYAN BRUCE BOYNTON


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


2004

































Copyright 2004

by

Bryan Bruce Boynton


































To my parents & grandparents.















ACKNOWLEDGMENTS

I thank the Food Science and Human Nutrition Department and my committee,

especially Dr. Sims and Dr. Welt. I would also like to thank all of my friends, family,

and lab mates, especially Rena and Asli, who have helped me through the years. I also

thank the gang at F.A.S.T. for accommodating all my irradiation needs in a very friendly

manner and Wendy Dunlap at Cryovac for all packaging supplies.
















TABLE OF CONTENTS

page

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

LIST OF TABLES ....................................................... .. ........ .............. viii

LIST OF FIGU RE S ...................... ...... ...................... ........... .........x

A B S T R A C T ......... .................................. ...................................................x iii

CHAPTER

1 IN TR O D U C TIO N ......................................................................... .... .. ........

2 LITER A TU R E R EV IEW ............................................................... ...................... 6

C a n ta lo u p e ................................................................................. 6
R e sp iratio n ................................................................................ 7
F re sh -c u t ........................................................................................................ 1 0
F la v o r ................................................................................................1 3
Modified Atmosphere Packaging .................................. ............................... 13
M o d e lin g ................................................................................................................ 1 9
Michaelis-Menten .................. ........... ......... 22
Irra d iatio n .............................................................................2 5

3 EFFECTS OF IRRADIATION ON FRESH-CUT CANTALOUPE STORED
IN AN OPEN SYSTEM ................................. .......................... ............30

In tro d u ctio n .......................................................................................3 0
M materials an d M eth od s .......................................................................................... 32
F ru it S am p le ................................................................3 2
P ro c e ssin g ....................................................................................3 2
D o sim etery ................................................................3 4
G as A n aly sis .................................................... 3 5
M icrobial A naly sis ...........................................................35
C olor A analysis ..................................... ....................... 35
T e x tu re ............................................................................................................ 3 6
Statistical A naly sis ............................................................36
R esu lts an d D iscu ssion .......................................................................................... 3 7
R expiration ................................................................................................. ....... 37


v









T ria l 1 ....................................................... 3 7
T rials 2 an d 3 ............................................................ 3 8
M ic ro b io lo g y ................................................................................................. 3 9
Texture ............... ......... ........................................................ ......44
C olor .......... ......... ................................................................................ 45
C o n c lu sio n s ................................................................................................... 4 8

4 RESPIRATION OF IRRADIATED FRESH-CUT CANTALOUPE AND
MODELLING OF RESPIRATION FOR MODIFIED ATMOSPHERE
P A C K A G IN G ....................................................................................................... 4 9

In tro d u ctio n .......................................................................................4 9
M materials an d M eth od s ......................................................................................... 50
F ru it S am p le ................................................................5 0
P processing ............................................................................................. ....... 50
D o sim etery ................................................................52
G as A nalysis................................................... 52
M odeling..................................................52
F ilm P erm ability ............................................................54
Modified Atmosphere Package Design .......................................................56
R esu lts an d D iscu ssion ......................................................................................... 6 0
M odeling..................................................60
F ilm P erm ability ............................................................69
C conclusion ...................................................................................................... ....... 7 1

5 DESIGN OF MODIFIED ATMOSPHERE PACKAGE FOR IRRADIATED
FRESH-CUT CANTALOUPE AND EVALUATION WITH DESCRIPTIVE
ANALYSIS SEN SORY PANEL ....................................................... 72

In tro d u ctio n ..........................................................................................7 2
M materials an d M eth od s ......................................................................................... 73
F ru it S am p le ................................................................7 3
Processing ................. ............................. 73
D o sim etery ................................................................7 5
G a s A n a ly sis .................................................................................................. 7 6
M icrobial A naly sis ...........................................................76
S e n so ry ................................................................7 6
Color Analysis ..................................... ........ ............. ...... 78
T e x tu re ........................................................................................................... 7 8
Statistical A naly sis ............................................................78
R esu lts an d D iscu ssion ......................................................................................... 7 9
M A P D design ................................................................... ............ 79
M ic ro b io lo g y ................................................................................................. 8 7
T e x tu re ........................................................................................................... 8 9
C o lo r ........................................................................................9 0









Sensory ....................................................... 91
T ria l 1 ....................................................... 9 1
T ria l 2 ....................................................... 9 8
C o n c lu sio n ........................................................................................................... 1 0 2

6 CON CLU SION S ................................................................................................. 103

REFEREN CES ........................................................................................................... 105

BIO GR A PH ICA L SK ETCH ...................................................................................... 113















LIST OF TABLES


Table page

2.1 Respiration rate ranges of cantaloupe at various temperatures................................9

3.1 Texture (max force kg) of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 3)..................... ........................ ....... 44

3.2 Texture (max force kg) of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 3)..................... ........................ ....... 45

3.3 Color of irradiated and non-irradiated fresh-cut cantaloupe stored at
3 C (T rial 2) .........................................................................4 6

3.4 Hue and chroma of irradiated and non-irradiated fresh-cut cantaloupe stored
at 3 C (T rial 2) .......................................................................47

3.5 Color of irradiated and non-irradiated fresh-cut cantaloupe stored
at 3 C (T rial 3). .................................................... ................. 47

3.6 Hue and chroma of irradiated and non-irradiated fresh-cut cantaloupe stored
at 3 C (T rial 3) .......................................................................4 8

4.1 Coefficients of Eqn. (4.1) and (4.2) describing the changes in oxygen and
carbon dioxide concentrations, respectively, over time for irradiated and
non-irradiated fresh-cut cantaloupe stored in a closed system at 3 C.....................62

4.2 Coefficients of Michalis-Menten model Eqn (4.5) and (4.6) for changes in
oxygen and carbon dioxide concentrations, respectively, over time for
irradiated and non-irradiated fresh-cut cantaloupe stored in a closed system
at 3 OC ............................................................................... 6 3

4.3 Coefficients of the polynomial model Eqns. (4.10) and (4.11) for changes in
oxygen and carbon dioxide concentrations, respectively, over time for irradiated
and non-irradiated fresh-cut cantaloupe stored in a closed system at 3 OC..............66

4.4 Average oxygen (OTR) and carbon dioxide (CO2TR) transmission rates at
various temperatures for films tested. ........................................... ............... 70

4.5 Arrhenius relationship values Ea and ko for two films tested...............................70









5.1 Headspace composition of modified atmosphere packages of irradiated and
non-irradiated fresh-cut cantaloupe stored at 3 C............................. ............... 85

5.2 Total plate count (TPC) and yeast and mold count (Y+M) of irradiated and
non-irradiated fresh-cut cantaloupe stored at 3 OC in modified atmosphere
packages (Trial 1).................... .. ................. ................ .. 88

5.3 Total plate count (TPC) and yeast and mold count (Y+M) of irradiated and
non-irradiated fresh-cut cantaloupe stored at 3 OC in modified atmosphere
packages (Trial 2)................................... ...................................... 89

5.4 Texture (kg) of irradiated and non-irradiated fresh-cut cantaloupe during
storage at 3 C in modified atmosphere packages ................................................90

5.5 Color (L*, a*, b*) of irradiated and non-irradiated fresh-cut cantaloupe during
storage at 3 C in modified atmosphere packages, by treatment (Trial 1)...............91

5.6 Color (L*, a*, b*) of irradiated and non-irradiated fresh-cut cantaloupe during
storage at 3 C in modified atmosphere packages, by storage..............................92

5.7 Color (L*, a*, b*) of irradiated and non-irradiated fresh-cut cantaloupe during
storage at 3 C in modified atmosphere packages, by treatment (Trial 2)...............92

5.8 Sensory results (Trial 1), by treatment and over storage of irradiated and non-
irradiated fresh-cut cantaloupe (0 to 15 scale), stored at 3 OC ..............................94

5.9 Sensory results (Trial 2), by treatment and over storage of irradiated and non-
irradiated fresh-cut cantaloupe (0 to 15 scale), stored at 3 OC ..............................95















LIST OF FIGURES


Figure pge

2.1 Recommended oxygen and carbon dioxide ranges for the storage of some
harvested vegetable commodities (Saltveit, 2003)........................................18

2.2 Recommended oxygen and carbon dioxide ranges for the storage of few
harvested vegetable commodities showing differences within individual
com m odities (Saltveit, 2003). ............................................................................19

2.3 The radura symbol, which is required by U.S. law to be in plain sight on all
packages of irradiated foods ..................................................................................26

3.1 Schematic of cantaloupe being irradiated in Ziploc bags on trays of ice ................33

3.2 Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut
cantaloupe stored at 3 OC (Trial 1). ............................................... ............... 38

3.3 Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut
cantaloupe stored at 3 OC (Trial 2). ............................................... ............... 39

3.4 Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut
cantaloupe stored at 3 OC (Trial 3). ............................................... ............... 40

3.5 Total plate count (TPC) of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 2)..................... ........................ ....... 40

3.6 Yeast and Molds counts of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 2)..................... ........................ ....... 41

3.7 Total plate count (TPC) of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 3)..................... ........................ ....... 42

3.8 Yeast and Molds counts of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 3)..................... ........................ ....... 42

4.1 The input screen for all data necessary for the prediction program with
variables described and units defined................................. ......................... 59

4.2 Percent oxygen and carbon dioxide in headspace during closed system storage
of irradiated and non-irradiated fresh-cut cantaloupe at 3 C............. ..................62









4.3 Michaelis-Menten equation fit to observed respiration data vs. percent oxygen
for non-irradiated fresh-cut cantaloupe stored in a closed system at 3 C...............64

4.4 Michaelis-Menten equation fit to observed respiration data vs. percent carbon
dioxide for non-irradiated fresh-cut cantaloupe stored in a closed system at
3 C ................................................................................... . 6 5

4.5 Second order polynomial equation fit for observed respiration data vs. percent
oxygen within the critical range for non-irradiated fresh-cut cantaloupe stored in
a closed system at 3 OC ...................... .. .................. .. ...... .. ............... 67

4.6 Polynomial equation fit to observed respiration data vs. percent carbon dioxide
for within the critical range for non-irradiated fresh-cut cantaloupe stored in a
closed system at 3 C ..................... .................. ................... ......... 68

4.7 Arrhenius relationship between the natural log of the oxygen transmission rate
(O2TR) in ml/m2/ day and temperature for two films tested.................................70

4.8 Arrhenius relationship between the natural log of the carbon dioxide transmission
rate (CO2TR) in ml/m2/ day and temperature for two films tested ........................71

5.1 Predicted oxygen and carbon dioxide partial pressures for 0.4 kGy samples in
designed modified atmosphere package with initial gas flush of 4% 02 plus 10%
C O 2 for Trial 1 stored at 3 C ...................................... ............... ............... 80

5.2 Predicted oxygen and carbon dioxide partial pressures for 0.4 kGy samples in
designed modified atmosphere package with initial gas flush of 4% 02 plus
10% CO2 for Trial 2 stored at 3 C. .............................. .... ............................. 81

5.3 Actual oxygen partial pressures for all samples in designed modified atmosphere
packages for Trial 1 stored at 3 C.......................................................... ........... 82

5.4 Actual carbon dioxide partial pressures for all samples in designed modified
atmosphere packages for Trial 1 stored at 3 C. ............................................... 82

5.5 Actual oxygen partial pressures for all samples in designed modified atmosphere
packages for Trial 2 stored at 3 C................................................................. 83

5.6 Actual carbon dioxide partial pressures for all samples in designed modified
atmosphere packages for Trial 2 stored at 3 C. ............................................... 83

5.7 Trial 1 Predicted and observed oxygen and carbon dioxide levels inside
designed modified atmosphere package containing irradiated fresh-cut
cantaloupe stored at 3 C ............................................... ............................... 86









5.8 Trial 2 predicted and observed oxygen and carbon dioxide levels inside
designed modified atmosphere package containing irradiated fresh-cut
cantaloupe stored at 3 C ............................................... ............................... 87

5.9 Off flavor rating of treatments at each storage (3 C)............................................97

5.10 Acceptability rating of treatments at each storage date (3 C).............................97

5.11 Sweetness rating of treatments at each storage (3 C). .........................................99

5.12 Cantaloupe flavor intensity (CFI) rating of treatments at each storage date
(3 C)........................ ................................. 100

5.13 Off flavor rating of treatments at each storage date (3 C) ..............................101

5.14 Acceptability rating of treatments at each storage date (3 C).............................101















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

DETERMINATION OF THE EFFECTS OF MODIFIED ATMOSHPERE
PACKAGING AND IRRADIATION ON SENSORY CHARACTERISTICS,
MICROBIOLOGY, TEXTURE AND COLOR OF FRESH-CUT CANTALOUPE
USING MODELING FOR PACKAGE DESIGN

By

Bryan Bruce Boynton

December 2004

Chair: Charles Sims
Cochair: Bruce Welt
Major Department: Food Science and Human Nutrition

Objectives of this project were to determine effects of irradiation and modified

atmosphere packaging on fresh-cut cantaloupe (Cucumis melo Linnaeus reticulatus).

Fresh-cut cantaloupe was exposed to doses (0.1-1.5 kGy) of electron beam irradiation and

stored in open systems at 30C. Microbial counts were consistently reduced in sympathy

with irradiation dose. Respiration rates were slightly higher in the irradiated samples

compared to non-irradiated control within the first 24 hours and converged thereafter.

Respiration rates of all samples remained similar until 7-10 days of storage when controls

increased significantly. Higher irradiation levels delayed the onset of increased

respiration. Samples irradiated at 0.3, 0.6, and 0.9 kGy were significantly less firm than

non-irradiated samples only within 2 hrs of treatment during 13 days of storage.









Fresh-cut cantaloupe were irradiated at 0, 0.2, 0.4, and 0.6 kGy and stored in

hermetically sealed containers at 30C. Oxygen and carbon dioxide levels were measured

over time. Attempts to fit respiration data to many common functions were unsuccessful,

including the Michaelis-Menten enzyme equation, which is often used for this purpose.

Therefore, polynomial equations were used. Arrhenius equations were used to describe

temperature sensitivity of transmission rates for oxygen and carbon dioxide for two films

commonly used in the fresh-cut industry.

A computer program was written with Visual Basic for Applications using

Microsoft Excel, which was used as an aid to design a modified atmosphere package

based on predicted respiration and gas permeation rates. This package was used in a

subsequent study to determine combined effects of irradiation and modified atmosphere

on quality and sensory changes during storage.

Irradiated samples (0.5 and 1.0 kGy) had a lower and more stable rate of respiration

than non-irradiated samples over the duration of the study. Color and texture remained

stable for the duration of each study as measured by instrument and sensory panel.

Sensory evaluation rated the 1.0 kGy sample highest in sweetness and cantaloupe flavor

intensity and lowest in off flavor after 17(3) days storage. The program and model

predicted respiration rates well. Low dose electron beam irradiation of fresh-cut

cantaloupe with modified atmosphere packaging offers promise as a method of extending

shelf-life.














CHAPTER 1
INTRODUCTION

Melon is the fourth largest produced fruit, by weight production, in the world

(18,000,000 tons) behind orange, banana and grape. In 1999, the United States of

America (USA) was third in melon production with 1,320,850 tons, behind China at

5,806,384 tons and Turkey at 1,800,000 tons (Aguayo and others, 2004). The word

"cantaloupe" is often used, especially in the USA, to describe the netted melon or

muskmelon (Cucumis melo, var. reticulatus). A true cantaloupe is a non-netted fruit

popular in Cantaluppi, Italy, and rarely grown in the USA (Shellie and Lester, 1999). In

1997, Florida cantaloupe acreage made up about one percent of the USA cantaloupe

acreage.

Fresh-cut products, also known as lightly processed or minimally processed

(Watada and others, 1996), offer convenience and reduced waste. Demand for fresh cut

fruits and vegetables has been increasing greatly in the USA for the past 10 years and is

still considered in its infancy (Suslow and Cantwell, 2001). Fresh cut products have been

available for many years, but in the past decade the types and quantity have expanded

greatly. The sales of fresh-cut fruit have grown linearly approximately $1 billion per

year (Anonymous, 1999a), due largely to increased regional production and distribution.

Around 10% of all fresh fruits and vegetables sold in the USA in 1998 were fresh-cut

sales at $8.8 billion, and sales in 2004 should reach $15 billion (Anonymous, 1999b). The

food service industry has been the primary purchaser of fresh-cut products in the past, but

warehouse stores, restaurants, and supermarkets have become major purchasers with









increasing sales. The International Fresh-cut Produce Association (IFPA) purposefully

chose the term fresh-cut to include the word fresh. In order for something to be labeled

fresh-cut, it must meet the FDA's current definition of the term fresh, which requires that

produce be alive, actively respiring and carrying out the metabolic and biochemical

activities of life. The IFPA supports the use of the term "fresh-cut" for labeling products

treated by processes that do not cause respiration to cease (Gorny, 2000).

The goal of fresh-cut products is to deliver convenience and high quality.

Therefore, fresh-cut products must not only be aesthetically pleasing, but also comply

with food safety requirements. Consumers expect fresh-cut products to be without

defects, of optimum maturity, fresh appearance, and have high sensory and nutrient

quality (Watada and Qi, 1999). Fresh-cuts are usually more perishable than uncut whole

fruit, due to extreme physical stresses from processes such as peeling, cutting, slicing,

shredding, trimming, coring, and removal of protective epidermal cells (Watada and

others, 1996). High quality of raw product is necessary to achieve high quality fresh-cut

product. Final product can only be as good as the incoming raw product.

Quality of fresh-cut produce is directly related to wounding associated with

processing. Physical wounding and damage also induce additional deleterious

physiological changes within produce (Brecht, 1995; Saltveit, 1997). Symptoms can be

visual, such as deterioration from flaccidity with water loss, changes in color, especially

browning at the surfaces, and microbial contamination (Brecht, 1995; King and Bolin,

1989; Varaquaux and Wiley, 1994). Wounding also leads to alterations in flavor and

production of aroma volatile (Moretti and others, 2002).









One of the first responses to wounding is a transient increase in ethylene production

and an enhanced rate of respiration. Increased respiration can lead to excessive losses of

water and nutrients (Brecht, 1995). Generally, tissues with high respiration rates and/or

low energy reserves have shorter postharvest lives (Eskin, 1990). Ethylene can also

stimulate other physiological processes, causing accelerated membrane deterioration, loss

of vitamin C and chlorophyll, abscission, toughening, and undesirable flavor changes in

many horticultural products (Kader, 1985). Wounding also allows for easier attack and

survival of plant pathogenic microorganisms and food poisoning microorganisms.

Radiation research directed towards the preservation of foods began in 1945 (Karel,

1975). "Irradiation" or "food irradiation" generally refers to the use of gamma rays from

radionuclides such as 60Co or 137Cs, or high-energy electrons and X-rays produced by

machine sources to treat foods. Electron beams (e-beams) can be emitted from the

cathode of an evacuated tube subjected to an electrical potential or produced in linear

accelerators (Karel, 1975). The energy of the electron beams is limited to 10 MeV for

use in food treatment (Rosenthal, 1992). Using good manufacturing practices, irradiated

foods have been established to be safe, wholesome and without residues (Farkas, 1998).

Two major benefits of irradiation are that a product can be treated in its final package as a

terminal treatment (Farkas, 1998), and the temperature of the product is not significantly

affected.

In a paper by Minea and others (1996), strawberries, cherries, apricots, and apples

were irradiated with an electron accelerator at doses of 0.1 3 kGy at dose rates from 100

to 1500 Gy/min. Results showed very effective microbial destruction and a great

influence on the decrease of enzymatic activities. Shelf life extension of at least 4-7









days was achieved with sensory properties not significantly affected. There were no

significant changes in the physical and chemical properties of irradiated fruit.

Respiration involves the consumption of oxygen and production of carbon dioxide,

water and chemical energy in the form of ATP. Aerobic respiration can be slowed by

limiting available oxygen. However, oxygen must be maintained above a minimum

threshold to prevent anaerobic respiration (Knee, 1980). Additionally, increased carbon

dioxide concentration has been shown to slow down ripening and respiration rates

(Mathooko, 1996). Therefore, an optimal atmosphere may be created via modified

atmosphere packaging (MAP), where respiration and ethylene production may be

reduced as well as many other degrading processes. A MAP can be developed by

matching the proper package and film with an appropriate amount of fruit with a given

respiration rate.

Modified atmosphere packages can be designed using predictive equations based

on known respiration data. Respiration rate for most produce depends on the oxygen and

carbon dioxide levels that surround the produce. An ideal package will maintain the

desired levels of decreased oxygen and increased carbon dioxide based on the

transmission rates of the package and the respiration rate of the produce at the desired

storage temperature. Packages can be flushed with the desired steady-state gas

composition in order to more quickly achieve equilibrium conditions. The sooner the

produce is brought to optimal atmospheric conditions the more effective the package.

A combination of MAP and irradiation may have a synergistic effect on the shelf

life of produce. This was demonstrated by Prakash and others (2000) using cut romaine

lettuce. Irradiation increased the shelf life of the MAP fresh-cut lettuce as compared to









the non-irradiated MAP fresh-cut lettuce by reducing the initial microbial load 1.5 log

CFU/g and maintaining a 4 log CFU/g difference on the 18th day of storage.

The purpose of this research had three main objectives. The first was to determine

the effects of irradiation on fresh-cut cantaloupe with regard to respiration rate, color,

microbiology and texture during storage. The second was to use respiration data of

irradiated and non-irradiated fresh-cut cantaloupe to model oxygen and carbon dioxide

concentrations over time in a MAP. The final objective was to use the model to design a

MAP and test its effectiveness in maintaining fresh-cut cantaloupe quality using a trained

descriptive analysis panel and determine the designed MAP effects on product color,

microbiology and texture.














CHAPTER 2
LITERATURE REVIEW

Cantaloupe

Cantaloupe (Cucumis melo) is a member of the Cucurbitaceae family. Cucurbits,

of which squash, cucumbers and watermelon are all a part, originated in different

locations. The cantaloupe is believed to have originated in Africa.

Within the Cantaloupensis group, muskmelon fruit are classified into two major

categories in the USA, the eastern and western type cantaloupe. The eastern cantaloupe

is distinct by its sutured and netted surface and it has a spherical or elongated oval shape.

Easterns also have relatively large moist seed cavities and soft to medium flesh with

strong aroma. Easterns characteristically store poorly with a relatively short storage life.

They have been adapted to grow in many climates and are not intended for long transport.

The western type cantaloupe is commonly grown in the arid southwestern USA and other

countries with similar climate and tends to have a longer shelf-life than eastern

(Lamikanra and others, 2003; Rubatzky and Yamaguchi, 1997). Westerns are usually

without sutures, extensively netted, with a rugged thick flesh suitable for long distance

shipping. Their seed cavity is small and dry. "Super Market," "Summet," "Magnum 45,"

"Primo," "Mission," "Ambrosia," "Athena," "Cordele," and "Eclipse" are the Eastern

Choice type cantaloupes that will grow productively in Florida (Mossler and Nesheim,

2001; Hochmuth and others, 2000). The average harvested yields per acre of cantaloupe

crops in Florida have been 150 cwt over the last few years (Hochmuth and others, 2000).

Acreage intended for harvest in the USA for 2004 was forecast at 33,300 acres, up 13









percent from 2003 (USDA Economics, Statistics and Market Information System, 2004).

Cantaloupe is used more in the fresh-cut industry than any other fruit (Lamikanra and

Richard, 2002).

Cantaloupe is prone to chilling injury when stored at temperatures less than 2 C

for several days. Chilling injury sensitivity decreases as melon maturity and ripeness

increase. Another source of postharvest loss can be disease, which can depend on season,

region and handling practices. Commonly, decay or surface lesions result from fungal

pathogens Alternaria, Penicillium, Cladosporium, Geotrichum Rhizopus, and to a lesser

extent Mucor. Cantaloupes are predominantly graded on external appearances and

measured soluble solids. U.S. grades are Fancy, No. 1, Commercial and No. 2. Federal

Grade Standards specify a minimum of 11% soluble solids for U.S. Fancy ("Very good

internal quality") and 9% soluble solids for U.S. 1 ("Good internal quality") (Suslow and

others, 2001).

As cantaloupe matures on the vine, the fruit begins to separate at the abscission

layer where the stem pedunclee) attaches at the fruit. The maturity level is determined by

the degree of separation and called "slip." Therefore, if the abscission layer is /2

detached, then the maturity level is called 12 slip, if it is 3% detached, then it is called 34

slip, etc. A good indicator of full ripeness and harvest time is partial to complete

separation. In the USA, 34 to full slip is the maturity level for commercial practice of

harvesting cantaloupe (Beaulieu and others, 2004).

Respiration

The word respiration is derived from the Latin word respirare which literally

means to breathe (Noggle and Fritz, 1983). It was first discovered that humans consume









oxygen and produce carbon dioxide. At the end of the eighteenth century, Dutch plant

physiologist Ingen-Housz discovered that not only animals but also plants respire. It was

well established by the middle of the nineteenth century that all growing cells of higher

plants respire at all times, in the light as well as the dark, using oxygen, oxidizing

carbonaceous substances, and producing carbon dioxide and water.

Glucose is the respiratory substrate most commonly consumed in cellular

respiration. The overall reaction is usually written as

C6H1206 + 6 02 -> 6 CO2 + 6 H20 +Heat (2.1)

However, this reaction omits the fact that oxygen does not react directly with sugar

in respiration. Water molecules are joined with intermediate products during glucose

degradation, one water molecule for each carbon in the sugar molecule. The hydrogen

atoms in intermediate products are joined with oxygen to form water. A more complete

reaction is written as

C6H1206 + 6 H20 + 6 02 -> 6 C02 + 12 H20 (2.2)

Respiratory substrates commonly consumed are carbohydrates, lipids and organic

acids. The overall sequence of events is referred to as respiratory metabolism. An

abbreviated outline of respiratory metabolism is the process of glucose, in the cytosol,

becoming pyruvic acid through glycolysis, going to the tricarboxylic acid cycle in the

mitochondria and finally the electron transport system. Oxygen is also needed as a

substrate in the respiratory reaction. The gas must travel from the surrounding

environment through intercellular spaces, cell wall, cytoplasm and other membranes of

plant cells. The rate of diffusion will have an effect on respiration rate.









The rate of respiration for fresh-cut produce is measured by the amount of oxygen

consumed or carbon dioxide produced per weight of produce for a period of time at a

certain temperature. Table 2.1 lists the respiration rates of cantaloupe at various

temperatures (Kader, 1992).

Table 2.1. Res iration rate ranges of cantaloupe at various temperatures.
Temperature C mg CO2 kg1 h
0 5 to6
4 to 5 9 to 10
10 14 to 16
15 to 16 34 to 39
20 to 21 45 to 65
25 to 27 62 to 71

Ranges exist in respiration rate due to cultivar, growing season and conditions,

harvest maturity and technique, and many other factors.

Many methods are available for measuring respiration rate. The most common are

the closed or static system, the flowing or flushed system and the permeable system

(Fonseca and others, 2002). In the closed system method, a respiring sample is closed in

an airtight container with known volume and initial oxygen and carbon dioxide

concentrations. Gas samples are taken over time and respiration rate is based on

concentration change (Eqns. 2.3 and 2.4).

(y 2 nflow Y20outflow) xV
Ro (2.3)
2 100 x M x (t, t,)


(y co2outflow CO2 inflow ) X V
Rco = (2.4)
100xMx(tf -t)

The flow through system passes gas of known concentrations over the sample in a

barrier container. The respiration rate is determined by the differences in the inflow and

outflow gases (Eqns. 2.5 and 2.6).










(Yom Yo2out) x F (2.5)
R* =------ (2.5)
S10xM

(ycoout -Yo21n)xF
Rc (y (2.6)
100 x M

The permeable system uses a package of known gas transmission rates and size

filled with sample. Using the permeability and the steady-state concentrations,

respiration rate can be determined (Eqns. 2.7 and 2.8).

Po xA
Ro x(y ec -Yo ) (2.7)
100xLxM

P, xA
Rco, = 10 x (Yc2- Yeco,) (2.8)
100 xLxM

Ro, and Rc2 are respiration rate, oxygen uptake and carbon dioxide evolution,

respectively, y is volumetric concentration, V is volume, M is mass, t is time, fis final, i

is initial, F is flow rate, A is area of package, P is permeability, L is thickness and e is

external.

Each system has its limitations and problems, but an accurate range should be able

to be achieved.

Fresh-cut

The fresh-cut industry continues to grow with technology increasing shelf life and

duration of quality. Shelf life of fresh-cut fruits and vegetables ranges from 7 20 days

when held at optimal temperatures (Watada and Qi, 1999). Fresh-cut cantaloupe had a

reduction of "typical" flavor during the first 4 days when stored at 4 OC in rigid barrier

containers (O'Connor-Shaw and others, 1994). At 7 days, bitterness levels were lower

and the fruit was firmer. At day 11, fruit was paler than originally and white colonies of









microbes were observed. In a study by Ayhan and others (1998), the shelf life of fresh-

cut honeydew and cantaloupe was determined. Four treatments were tested: I Fruit was

cut without washing, II Fruit was washed with water before cutting, III Whole fruit was

dipped in 200 ppm hypochlorite solution and cut fruit was dipped in 50 ppm hypochlorite

solution twice, IV Whole fruit was dipped in 2000 ppm hypochlorite solution and cut

fruit was dipped in 50 ppm hypochlorite solution twice. All samples were stored in full

barrier laminated nylon film at 2.2 C. A 2 log (CFU/g) reduction of surface aerobic

plate count for cantaloupe was observed in treatment III compared to treatment I and a

3.3 log reduction occurred between treatment IV and treatment I. The total psychotropic

count of the processed cantaloupe was similar with a 3.3 log reduction for both treatment

III and IV compared to treatment I at day 0 with a continued 3 log reduction through day

20. Sensory characteristics (odor, taste, overall flavor, texture, appearance and overall

acceptance) were evaluated during the 20 day storage of cantaloupe. Treatments III and

IV were rated significantly higher in all characteristics except odor on day 15, although

they were rated higher, just not significantly. No difference occurred between treatment

III and IV for all sensory characteristics through the entire study.

The efficacy of decontamination treatments using water, sodium hypochlorite,

hydrogen peroxide, commercial detergent formulations containing dodecylbenzene

sulfonic acid and phosphoric acid, or trisodium phosphate on fresh-cut cantaloupe was

determined (Sapers and others, 2001). Microbial population reductions were less than 1

log when plugs were washed with water, 1 to 2 logs with washing and sanitizing agents

applied individually, and 3 logs with hydrogen peroxide. The most effective treatment,

yielding a shelf life of greater than 2 weeks, was hydrogen peroxide applied at 50 OC.









Calcium chloride dips are another treatment commonly used in the fresh produce

industry as a firming agent, the joining of cell wall and middle lamella improved

structural integrity (Morris, 1980) and extended shelf life. Fresh-cut cantaloupe was

dipped in 2.5% solutions of either calcium chloride at -25 C or calcium lactate at -25

and 60 C (Luna-Guzman and Barrett, 2000). Calcium chloride and calcium lactate

provided significantly firmer samples than water dipped at all dates tested during the 12

day storage. The maintenance of firmness tended to be higher in the calcium lactate

treatments. The sensory panel also rated the calcium dipped samples significantly higher

in firmness. The panel rated the calcium chloride samples higher in bitterness, but not

the calcium lactate samples. All other attributes were not significantly different among

samples analyzed. No differences in total plate count were observed between any

treatments.

Many variables must be taken into account when processing fresh produce to be

stored for later consumption. The sharpness of the blade of the knife used can have an

effect on the shelf life and quality of fresh-cut cantaloupe (Portella and Cantwell, 2001).

Fresh-cut cantaloupe was prepared using a stainless steel borer with sharp or blunt blades

and stored for 12 days in air at 5 OC. Pieces cut with the sharp borer maintained

marketable visual quality for at least 6 days and those cut with the blunt borer were

considered unacceptable with surface translucency and color changes. Decay, firmness,

sugar content and aroma did not differ due to sharpness of borer. Blunt cut pieces had

higher ethanol concentrations, off-odor scores, electrolyte leakage and darker orange

color with L* and chroma values decreasing significantly during storage. Respiration









rates were not affected for those samples stored at 5 OC, but the blunt pieces stored at 10

C had a significant increase after day 6.

Flavor

Volatile aroma constituents were assessed immediately after processing and after

storage for 24 hrs, 3 days and 7 days at 4 OC in fresh-cut cantaloupe (Lamikanra and

Richard, 2002). Aliphatic and aromatic esters were the predominant compounds isolated

from the fruit immediately after cutting. Methylbutyl acetate and hexyl acetate were the

most prominent compounds, which are typically present in large quantities in cantaloupe

(Nussbaumer and Hostettler, 1996; Moshonas and others, 1993). After storage for 24 hrs,

a considerable decrease in the concentration of esters occurred and synthesis of terpenoid

compounds B-ionone and geranylacetone was detected. After the initial decrease, the

volatile aroma compounds remained fairly stable over the 7 day storage. The amount of

terpenoid compounds decreased after the first day, but remained stable from day 3 to 7.

The reduction of esters, which could be precursors for synthesis of secondary volatile

aroma compounds, may be directly related to a decrease of fresh like attributes in fresh-

cut cantaloupe during storage.

Modified Atmosphere Packaging

Modified atmosphere packaging (MAP) refers to any container used to control the

concentration of specific gases in order to achieve levels desirable to content. The goals

for MAP of fresh-cut produce are to maintain a lower oxygen and higher carbon dioxide

level than that of the surroundings. Reducing respiration rate and extending shelf life are

the returns for the added cost of using MAP films.









The design of a MAP appears to be rather simple on the surface, but many

considerations must be accounted for. The temperature the produce is going to be held at

is important since metabolic activity is very dependent on temperature. Most packages

will go from the packinghouse, to a truck, to the point of sale, all with different

temperatures. The change in respiration rate due to an increase in temperature is usually

greater than the change in permeability of the package (Exama and others, 1993). The

package may not be able to get back to equilibrium even once the lower temperature is

achieved again, since the product may have used more oxygen than planned and gone

into anaerobic respiration.

Respiration rates of horticultural commodities is also dependent on the amount of

available oxygen and carbon dioxide present in the surrounding environment (Beaudry,

2000; Watkins, 2000). Determination of the optimal surrounding atmosphere for fresh-

cut produce is difficult due to the numerous possible combinations of oxygen and carbon

dioxide concentrations. The changes in sensory properties of fresh-cut cantaloupe held at

different controlled atmospheres were determined (O'Connor-Shaw and others, 1996). A

large experimental design was used with 36 gas combinations and four air treatments.

All possible combinations of 3.5, 6, 10.5, 13, 15.5, and 17 percent oxygen with 0, 6, 9.5,

15, 19.5, and 26 percent carbon dioxide were evaluated at 4.5 C. At 14 day intervals, a

trained sensory panel assessed the stored fruit. Three treatments remained acceptable up

to 28 days: 6% carbon dioxide and 6% oxygen, 9.5% carbon dioxide and 3.5% oxygen,

and 15% carbon dioxide and 6% oxygen. Greatest reductions of quality were in samples

held in 0, 19.5 or 26% carbon dioxide. Many other combinations of oxygen and carbon

dioxide would have to be tested to finalize an optimal atmosphere.









Internal gas mixtures of modified atmosphere package may be attained naturally,

by letting the respiration of the produce decrease oxygen and increase carbon dioxide to

the desired levels (termed "passive MAP"), or the package may be flushed with the

desired gas mixture (active MAP). In a study by Bai and others (2001), fresh-cut

cantaloupe was placed in film sealed containers, stored at 5 OC and allowed to attain an

internal gas atmosphere naturally (nMAP) or flushed with 4 kPa oxygen and 10 kPa

carbon dioxide (fMAP) and another group was maintained near atmospheric levels by

perforating the film (PFP). The oxygen and carbon dioxide levels in the PFP remained

similar to the ambient air until day 9 and then only changed by 1 to 2 kPa during the next

3 days. Using a flow through system to simulate the atmosphere within the PFP, the

oxygen uptake was stable until day 5 at which point it increased more than sixfold during

the next 7 days. Neither oxygen or carbon dioxide reached an equilibrium in the nMAP,

with the oxygen concentration decreasing to 8 kPa and the carbon dioxide increasing to

12 kPa during the 12 day storage. Respiration rate remained stable through day 9 and

then increased twofold by day 12. In the fMAP, the gas mixture remained essentially

unchanged at 4 kPa oxygen and 10 kPa carbon dioxide. Respiration rate was also stable

in the fMAP for the duration of 12 days. The ethylene accumulation of the fMAP was 14

of that of the nMAP. Visual quality and aroma were rated acceptable for 12 days for the

nMAP and fMAP, whereas the PFP was only acceptable for an average of 6 days.

Translucency was significant 2 days earlier in the nMAP and was two to fivefold higher

between 9 and 12 days compared to the fMAP. Total microbial population was 1 log

lower in both nMAP and fMAP compared to PFP. Yeast and mold populations were

around 2 logs lower for both nMAP and fMAP. Therefore, rapidly flushed active MAP









(4 kPa oxygen and 10 kPa carbon dioxide) maintained better quality, had better color

retention and reduced translucency, respiration rate, and microbial population compared

to an air control (perforated film) and passive MAP (naturally obtained equilibrium).

Respiration rate of fresh-cut apple slices was reduced by increasing carbon dioxide

partial pressures from 0 to 30 kPa at 0.5, 1 and 10 kPa oxygen during storage (Gunes and

others, 2001a). Carbon dioxide production was not affected during the first week of

storage. By week 2 and 3, respiration rate decreased as carbon dioxide partial pressure

increased and oxygen partial pressure decreased. Elevated levels of carbon dioxide

reduced respiration rate by inhibiting succinate dehydrogenase and other enzymes of the

TCA cycle with an indirect effect on oxidative phosphorylation and a direct effect on

mitochondrial activity (Mathooko, 1996). The elevated carbon dioxide also reduced

browning to a limited extent.

The question of whether an optimal controlled atmosphere for fresh-cut produce

can really be found was reviewed extensively in a paper by Saltveit, (2003). A truly

optimal atmosphere may be impossible to find due to the natural variability in the raw

material and its dynamic response to processing and storage conditions. The best

approximations for an optimal modified atmosphere are derived from empirical

observations from experimentation including a variety of temperature, relative humidity,

oxygen, carbon dioxide, ethylene and duration conditions during storage. Since these

variables are usually held constant for the duration of the static experiment, the variability

and dynamic response of the commodity to changes in storage environment may be

overlooked. Many other variables may affect the environment such as microbial load,

light, orientation of the product in the gravitational field and the concentration of other









gases. The optimal modified atmosphere for some quality parameters can be mutually

exclusive during storage. Mold control, reduction of ethylene effects and reduction of

chlorophyll loss are benefits of high carbon dioxide levels. Increased anaerobic

respiration and phenolic metabolism may also result from high carbon dioxide levels.

Although low oxygen levels may reduce respiration and ethylene synthesis, it also

increases the chance of anaerobic respiration, off flavor production and growth of

anaerobic microorganisms.

The optimal storage atmosphere must be defined by the company responsible for

the sale of the commodity. The goal is to produce the best quality product, which allows

for subjective and objective measures. People perceive cantaloupe in different ways,

therefore there are likely to be differences in description about a "perfect" cantaloupe.

Some may prefer a darker orange color and softer texture and others may prefer a lighter

orange color and firmer texture. Different cultivars, seasons and market segments make a

strict universal description of quality very difficult to construe. Some quality aspects

may be sacrificed for others along with those which jeopardize shelf life. Which market

segment does a company package for and what quality parameters are the most

important? These are the questions that must be answered in package design and are

most likely answered by cost analysis and return on investment. A mathematical model

that incorporates the dynamic response of the produce to the storage environment may be

necessary for the optimal modified atmosphere design of a package.

The following Figures (2.1 and 2.2) show ranges of recommended oxygen and

carbon dioxide levels for storage of produce (Saltveit, 2003). These ranges can be used







18


as guidelines for designing a modified atmosphere package. The recommended range for

fresh-cut cantaloupe is 3 5% oxygen and 5 15% carbon dioxide (Gorny, 2001).



21


-1 --------- -------------- ---------- 4 ------ ...
20s~ |-1--P---- -- *----- --"^----l--- '-4- --.t- --.f-- '...---l.---l



q m
A .4 .... ... ..............
1 4 .... -....... -.............................. ............................. I ....... ..







S .... .... ................................. ................
| 4 .........'."- ......................... .. .

.. B... .. i,'t .. ......... ........ ......... .......... .......
01 i .1f4- L eik, i i i i

0 2 4 6 8 10 12 14 16 18 20 21
Oxygen concentration (%)

Figure 2.1. Recommended oxygen and carbon dioxide ranges for the storage of some
harvested vegetable commodities (Saltveit, 2003).











S------- ----------------- ------- --------------------


-4-


^ -------- ------------ ---------- --------




0
Tdmab
----- ----- ----------- -------------------------- ------- --- ---





F g r 2 .* *-im....... .. .. .. .... ... ................. ......




Oxygen concentration (%)

Figure 2.2. Recommended oxygen and carbon dioxide ranges for the storage of few
harvested vegetable commodities showing differences within individual
commodities (Saltveit, 2003).

Figure 2.2 shows differences in recommended oxygen and carbon dioxide levels

for storage within individual commodities. Differences within commodities tightens the

range of atmospheres, enhancing the degree of difficulty in designing an optimal

atmosphere for MAP.

Modeling

Predictive modeling in modified atmosphere packages of fresh-cut produce is

centered around the permeance of the film and the respiration rate of the product.

Determination of the amount of oxygen diffusing through a modified atmosphere

package can be determined using Fick's first law of diffusion (Zhu and others, 2002):

Po
J 2 = o A(pO,2ut pOin) (2.9)
X









where Jo2 is the rate of diffusion of oxygen through the film in unit time (ml (STP)/hr),

P0 is oxygen permeability coefficient of the film (ml (STP)/m hr kPa), A is the total film

surface area (m2), and X is the thickness of the film (m), pO2in is the oxygen partial

pressure (kPa) inside the package and pO2out is the oxygen partial pressure (kPa) outside

the package. A similar equation can be used for the rate of diffusion for carbon dioxide:


J CO, = *A(pCOin pCO2out) (2.10)
X

where J o is the rate of diffusion of carbon dioxide through the film in unit time (ml

(STP)/hr), Po0 is carbon dioxide permeability coefficient of the film (ml (STP)/m hr

kPa), A is the total film surface area (m2), and X is the thickness of the film (m). pCO2in

is the carbon dioxide partial pressure (kPa) inside the package and pCO2out is the carbon

dioxide partial pressure (kPa) outside the package. According to these equations, the Jo2

and JoC would both be positive under normal atmospheric conditions, around 21%

oxygen and 0% carbon dioxide. Therefore, these equations are for typical conditions and

attention must be paid if the surrounding environment or flush gas causes a negative to

result in the (pO2out pO2in) or (pCO2in pCO2out) part of the equation.

Respiration rate of the product must be written in equation form to use for

modeling. Most empirical models are for a specific temperature with the controllable

variables being the oxygen and carbon dioxide concentrations. Many different models

are presented in the literature: linear (Henig and Gilbert, 1975; Fishman and others, 1996;

Lakalul and others, 1999), polynomial (Yang and Chinnan, 1988; Gong and Corey,

1994), exponential (Cameron and others, 1989; Edmond and others, 1993), and many

Michaelis-Menten type equations (Lee and others, 1991; Haggar and others, 1992;









Talasila and others, 1994). A typical respiration rate equation will have the units ml or

mg of oxygen or carbon dioxide per kg of produce per unit of time. Therefore, the

oxygen consumption rate of produce in a package can be expressed by Eqn. (2.11).

Qo2 =W*Ro (2.11)

Where Qo0 is the oxygen consumption rate with units ml (STP)/h and W is the

weight of the produce in the same mass unit used in the respiration equation. Similarly,

the carbon dioxide production rate of produce in a package can be expressed by Eqn.

(2.12).

Qc2 = W*Rco, (2.12)

Where Qco2 is the carbon dioxide production rate with units ml (STP)/h and W is

the weight of the produce in the same mass unit used in the respiration equation. To

predict the gas compositions inside a package a stepwise integration can be performed

with Eqns. (2.13 and 2.14) (Hayakawa and others, 1975; Zhu and others, 2002).

pO2 (t + At) pOt)(J Q) Pt(t)At (2.13)
V


pCO2(t + At)= pCO2 (t) + (Q C2 Jit) At (2.14)
V

The Pt term is expressed in Eqn. (2.15). The total pressure inside a package may

not be constant due to the respiratory quotient (RQ; carbon dioxide produced / oxygen

consumed) not being unity and with most polymer films the ratio of the carbon dioxide to

oxygen transmission rates is at least 2 or 3 to 1. Since nitrogen is neither used nor

produced it can be assumed that the number of moles is constant and the total internal

pressure at t can be calculated with the following equation (Moyls and others, 1992):










(Pt)t = N2 *101.303 (2.15)
%N2t

where %N20o is the percent of nitrogen in the surrounding atmosphere outside of the bag

and %N2t is the percent of nitrogen inside the bag at time t.

Using Eqns. (2.13 and 2.14), the internal gas composition at any time during the

storage can be determined. An optimal package can be designed by adjusting the weight

of the produce, choosing the best available film and amount of surface area, determining

and flushing with the best gas composition and the amount of free volume as well as the

optimal storage temperature.

Michaelis-Menten

The concept of enzyme kinetics being used for predictive modeling of the

respiration rate of produce was introduced by Yang and Chinnan (1988). Lee and others

(1991) suggested that a Michaelis-Menten type equation might work since respiration is

controlled by enzymatic reactions catalyzed by allosteric enzymes and governed by

feedback inhibition (Solomos, 1983). They also speculated that since the Michaelis-

Menten equation is used to describe the respiration rate of microorganisms and that fresh

produce respiration and microorganism respiration are similar, that it could be used for

produce. In an atmosphere void of carbon dioxide, the respiration rate dependent on

oxygen concentration can be determined with Eqn. (2.16).

R Vm[2 (2.16)
Km+[O2]

Vm is the maximum respiration rate with units mL/kg hr or mg/kg hr, [02] is the

oxygen concentration in percentage, Km is the Michaelis-Menten constant in percent

oxygen.









The equation for the respiration rate with an uncompetitive inhibition mechanism

due to carbon dioxide is expressed in Eqn. (2.17).


R = Vm[O2 (2.17)
Km + (1+ C )[02]
Ki

Vm, Km and [02] are the same as above and [CO2] is the carbon dioxide

concentration in percentage and Ki is the inhibition constant in percent carbon dioxide.

Functionality of (Eqn. 2.17) is dependent on sufficient oxygen concentration for aerobic

respiration (Lee and others, 1991).

To test the validity of these equations for use as a respiration model, published data

was evaluated by Lee and others (1991). Eqn. (2.16) was linearized to become Eqn.

(2.18).

[O2] Km [02]
+ (2.18)
r Vm Vm

The data were fit and a Haynes plot was preferred over the Lineweaver-Burk plot

due to a more even distribution of error. Most of the data showed high linearity with

coefficients of determination (R2) above 0.95. With the exclusion of one set of published

data, the Michealis-Menten equation was concluded to express dependence of respiration

rate on oxygen quite well.

Eqn. (2.17) was linearized as Eqn. (2.19) to examine the effects of carbon dioxide

on respiration rate.

1 1 Km 1 1
-= +-* + *[CO2] (2.19)
r Vm Vm [O2] Ki*Vm

Published data show high linearity for Eqn. (2.19) as well, with all coefficients of

determination above 0.92. This equation was determined to be valid up to the carbon









dioxide tolerance limit of the produce. High levels of carbon dioxide may cause an

increase in anaerobic respiration. The respiratory quotient may change during anaerobic

respiration along with the normal controlling effect on respiration rate of the oxygen and

carbon dioxide concentrations.

Lee and others (1991) also tested the Michaelis-Menten model with fresh-cut

broccoli. The model was confirmed as successful based on the high linearity of the data

on a Hanes plot and a small standard deviation of the respiration rate. A modified

atmosphere package was designed and tested. The gas composition in the package

agreed very well with predicted oxygen and carbon dioxide concentrations. The model

proved to only work well when the oxygen level was high enough for aerobic respiration.

Hagger and others (1992) developed an enzyme kinetics based respiration model,

along with the closed system method for generating respiration rates of fresh produce as a

function of oxygen and carbon dioxide concentrations. Four temperatures were tested

and model parameters for Eqn. (2.17) were estimated with coefficients of determination

all above 0.98. Respiration rates could be predicted at any concentration of oxygen and

carbon dioxide. The model was tested with a permeable package and the values obtained

at 13 C. The experimental and predicted gas concentrations were in good agreement.

Equilibrium was not reached inside the package due to the high respiration rate of cut

broccoli and the low oxygen and carbon dioxide permeabilities of the LDPE film used.

Anaerobic respiration took over as the oxygen concentration approached zero.

Jacxsens and others (2000) attempted to design MAPs for fresh-cut vegetables

subjected to temperature changes. Respiration rate was described by four Michaelis-

Menten type equations. The equations were uninhibited, in the absence of C02, and the









three possible types of inhibition were competitive, uncompetitive, and noncompetitive.

All four equations gave similar results in their experimentation considering CO2 levels

never exceeded 10-15%. Only the inhibiting effect of a decreased 02 level on respiration

rate was taken into consideration. High R2 values for the Michaelis-Menten coefficients

Vmax and Km were determined, although overestimation of 02 levels inside equilibrium

modified atmosphere packages was common among fresh-cut produce tested.

Irradiation

A brief description of the history of food irradiation in the USA was summarized

from Rosenthal (1992). In the early 1920's, irradiation was used to kill the human

parasite Trichinella spiralis in pork. In the 1940's, large quantities of radioisotopes

became readily available at low cost due to the advent of many nuclear reactors. Van de

Graaff generators and linear accelerators, which produce high-energy electron beams also

became available at the same time. The study of food irradiation began at Massachusetts

Institute of Technology under the guidance of Prof. B. E. Proctor and spread to

laboratories around the world after World War II. Most studies in the United States were

aimed at sterilizing food. It was determined that doses up to 50 kGy were needed to

eliminate heat resistant spores such as Chlostridium botulinum. However, this high dose

caused unacceptable change in flavor and color, and the difficulty of finding participants

for testing the wholesomeness of irradiated foods led to the decline in interest in

irradiation technology. The interest in low-dose irradiation of food was rekindled in the

late 1960's with increased concern of synthetic additives, chemical residues and the

prevention of food poisonings. This led to the U.S. Food and Drug Administration

(FDA) ruling that ionizing radiation should be treated as a food additive not a food

process. This changed in 1986 when the FDA approved the use of ionizing radiation to









inhibit the growth and maturation of fresh foods and to disinfect food of arthropod pests

at doses not to exceed 1 kGy (Rosenthal, 1992; Code of Federal Regulations, 2004).

The U.S. Code of Federal Regulations outlines the uses of ionizing radiation for the

treatment of foods (Code of Federal Regulations, 2004). Energy sources are limited to

gamma rays from sealed units of radionuclides Cobalt-60 and Cesium-137, electrons and

x-rays generated from machine sources at energies not to exceed 10 and 5 million

electron volts, respectively. According to U.S. law, foods treated with irradiation shall

bear the logo (Figure 2.3); know as the radura, along with the following statement

"Treated with radiation" or "Treated by irradiation" in addition to information required

by other regulations.


Figure 2.3. The radura symbol, which is required by U.S. law to be in plain sight on all
packages of irradiated foods.









Climacteric fruit ripening may be stimulated or delayed by low-dose irradiation.

Skin browning or scalding, internal browning and increased sensitivity to chilling injury

are possible post irradiation problems. Pectins, cellulose, hemicellulose and starch may

be depolymerized in response to irradiation, which may cause softening. There is a

paucity of knowledge of the biochemical mechanisms underlying the delay in senescence

of climacteric fruits by irradiation. Many hormonal and cellular changes occur during the

ripening process and an accurate relationship with irradiation has not been established

(Thomas 1985; Rosenthal 1992).

Minea and others (1996) irradiated strawberries, cherries, sour cherries, apricots,

nectarines and apples with an electron beam using a linear electron accelerator at doses

between 0.1 and 3 kGy. A shelf-life extension was achieved for all irradiated fruit

ranging from 4-8 days. No significant changes in soluble solids content (Brix), total

sugars, reducing sugars, pH value and conductivity were observed in irradiated fruit

compared to non-irradiated. An average 10% loss of vitamin C occurred in irradiated

samples. The most efficient doses with respect to shelf-life extension were determined to

be: 2-3 kGy for strawberries, 1 kGy for cherries, 0.5-1 kGy for sour cherries, 0.5-0.7 kGy

for apricots, 1-2 kGy for nectarines and 0.5 kGy for apples. Irradiation was reported to

have no effect on organoleptic properties for all fruits tested, although on most storage

dates irradiated fruits rated 2-3 increments higher in acceptability than non-irradiated on a

1-5 scale.

Lu and others (In Press) irradiated fresh-cut celery at 0.5, 1.0 or 1.5 kGy using a

gamma source. Microbial populations decreased with an increase of dose with a 2 log

reduction in bacteria and a 1 log reduction in fungi at 1.OkGy. Bacteria of the E. coli









group were reduced to < 30 mpn (maximum probable number / 100 g) in the 1.0 kGy

sample compared to 436 mpn in the non-irradiated controls. Respiration rate and

polyphenol oxidase activity were significantly reduced in the 1.0 and 1.5 kGy samples on

day 3, 6, and 9. The sensory quality of irradiated celery was better than that of the non-

irradiated celery, and the 1.0 kGy sample was the best among irradiated samples.

Chervin and others (1992) examined the reduction of wound-induced respiration by

irradiation in fresh-cut and intact carrots stored at 20 OC. The uptake of oxygen in grated

carrots was twice that of the intact organs. The respiration rate of intact carrots treated

with gamma rays (2 kGy) was observed to be higher than non-irradiated samples at time

0, but after 12 hours the difference disappeared. The non-irradiated grated carrots

respiration rate increased more rapidly and peaked higher than the irradiated grated

carrots. The consequences of irradiation on the composition of modified atmospheres in

plastic bags were also evaluated. Differences occurred in the evolution of gaseous

atmospheres in control and irradiated grated carrots. The concentration of carbon dioxide

reached 17% after 17 days in non-irradiated samples, but they did not reach 10% in

treated samples at 10 OC. The values of the RQ remained stable and close to one

throughout the experiment for all samples.

Radiation induced texture changes in produce can be a major limiting factor. Many

plant tissues have a threshold level of irradiation dose at which point softening becomes a

problem (Massey and Bourke, 1967). Softening in tissues may be due to breakdown of

cell wall constituents such as pectin, cellulose and hemicellulose, and alteration of

semipermeable membranes resulting in structural weakening and loss of turgor (Kertesz

and others, 1964). A threshold of 0.34 kGy was found for fresh-cut apple slices (Gunes






29


and others, 2001b). Firmness decreased with increased irradiation dose above 0.34 kGy.

Dose rate was determined to affect textural response of slices on day 0 with 2 kGy/h

resulting in less loss of firmness than 0.4 kGy/h. The effect of dose rate was not

significant after 3 and 6 days of storage at 5 OC. Firmness slightly increased over time in

samples irradiated at 1 kGy.














CHAPTER 3
EFFECTS OF IRRADIATION ON FRESH-CUT CANTALOUPE STORED IN AN
OPEN SYSTEM

Introduction

Fresh-cut produce continues to increase in demand with cantaloupe (Cucimus melo

L reticulatus) among the most important in terms of volume produced and value (Suslow

and others, 2001). The goal of fresh-cut products is to deliver convenience and high

quality. Therefore, fresh-cut products must not only be aesthetically pleasing, but also

comply with food safety requirements. Consumers expect fresh-cut products to be

without defects, of optimum maturity, fresh appearance, and have high sensory and

nutrient quality (Watada and Qi, 1999). Fresh-cuts are usually more perishable and

unstable than the original products, due to extreme physical stresses from processes such

as peeling, cutting, slicing, shredding, trimming, coring, and removal of protective

epidermal cells (Watada and others, 1996). A 10 day shelf life of fresh-cut melons is

desirable in the distribution chain, but marketing in retail stores usually does not exceed 3

day (Bai and others, 2001). Extension of shelf life while maintaining salable quality

would be advantageous to producers and consumers.

Quality of fresh-cut produce is directly related to wounding associated with

processing. Physical wounding and damage also induces additional deleterious

physiological changes within produce (Brecht and others, 2004; Saltveit, 1997).

Symptoms can be visual, such as deterioration from flaccidity with water loss, changes in

color, especially browning at the surfaces, and microbial contamination (Brecht, 1995;









King and Bolin, 1989; Varaquaux and Wiley, 1994). Wounding also leads to reduction

in flavor and aroma volatile production (Moretti and others, 2002).

One of the first responses to wounding is a transient increase in ethylene production

and an enhanced rate of respiration. Increased respiration can lead to excessive losses of

nutrients (Brecht, 1995). Ethylene can also stimulate other physiological processes,

causing accelerated membrane deterioration, loss of vitamin C and chlorophyll,

abscission, toughening, and undesirable flavor changes in many horticultural products

(Kader, 1985). Wounding also allows for easier attack and survival of plant pathogenic

microorganisms and food poisoning microorganisms.

Radiation research directed towards the preservation of foods began in 1945 (Karel,

1975). Food irradiation generally refers to the use of gamma rays from radionuclides

such as 60Co or 137Cs, or high-energy electrons and X-rays produced by machine sources

to treat foods. Using good manufacturing practices, irradiated foods have been

established to be safe, wholesome and without residues (Farkas, 1998). Two major

benefits of irradiation are that a product can be treated in its final package as a terminal

treatment (Farkas, 1998), and the temperature of the product is not significantly affected.

In a paper by Minea and others (1996), strawberries, cherries, apricots, and apples were

irradiated with an electron accelerator at doses ranging from 0.1 to 3 kGy at dose rates

from 100 to 1500 Gy/min. Results showed irradiation was very effective by way of

microbial destruction and had a great influence in decreasing enzymatic activities. Shelf

life extension of at least 4 to 7 days was achieved with organoleptic properties not

significantly affected. There were no significant changes in the physical and chemical

properties of the irradiated fruit.









To be labeled fresh-cut, fruit tissue must be living and therefore respiring (Gorny,

2000). Respiration involves the consumption of oxygen and production of carbon

dioxide and water. Inhibition of respiration and ethylene production, which slows

deteriorative changes of senescence, generally extends shelf life (O'Connor-Shaw and

others, 1996). Therefore, decreasing respiration rate without complete inhibition would

be beneficial to produce to be labeled and sold as fresh-cut.

The purpose of this research was to determine the effects of different doses of

electron beam irradiation on fresh-cut cantaloupe considering respiration rates,

microbiology, texture and color.

Materials and Methods

Fruit Sample

Cantaloupes (Cucimus melo Linnaeus, cv. Athena) were purchased from a retail

market in Gainesville, FL (Trial 1 and Trial 2) or obtained from a regional supermarket

distribution center (Trial 3). Cantaloupes were transferred to the University of Florida

Food Science and Human Nutrition building via automobile and were stored at 25 C for

1 day and then placed in a 3 C storage room overnight before processing. Cantaloupes

were picked at three quarter to full slip (commercial maturity, when a clear separation

from the vine occurs with light pressure) and ready to eat.

Processing

Cantaloupes were rinsed in 100 ppm chlorinated water and allowed to dry for 1

hour before cutting. All knives, cutting boards and bowls were soaked with 100 ppm

chlorinated water. For each experiment, cantaloupes (12) were halved, de-seeded, and

then halved again, resulting in four equal parts. Each quarter was sliced on a 1/2 HP

commercial deli slicer (Model 1712E, Hobart Corporation, Troy, Ohio) with the blade set









at 2.5 cm thick. Slices were then peeled and cut into approximately 2.5 cm pieces with a

sharp knife. All pieces were placed in an aluminum bowl, which was surrounded with

ice. Pieces were thoroughly mixed to assure random sampling.

Pieces (-300g) were placed in quart Ziploc (S.C. Johnson & Son, Inc., Racine, WI)

Freezer bags and sealed after expulsion of most of the air. Bags were placed in ice in a

portable cooler and transported to the electron beam irradiation facility, which was a 90

mega amp, 95% scan (Florida Accelerator Services and Technology, Gainesville, FL).

Plastic trays were previously frozen with 1.5 cm of ice in them. Bags (4) were taped to








Melon in Zip-Lock Bags




Tray of Ice



Direction of Motion
Electron Beam
(Scan is perpendicular to page)

Figure 3.1. Schematic of cantaloupe being irradiated in Ziploc bags on trays of ice.

each tray with cantaloupe arranged in a single flat layer in order for all pieces to receive

equal dosage (Figure 3.1). Dosimeters were also attached to verify that target doses had

been reached. The irradiator conveyor was set at a speed of 10 feet per minute (fpm; 305

cm per minute) and 0.25 kGy per pass. To achieve 0.5 kGy, the sample was passed

through twice, while for 0.75 kGy three times and so on. Bags were removed from the









ice trays and placed back in the ice cooler after the desired number of passes. Samples

were irradiated at 0, 0.25, 0.5, 0.75, 1.0, 1.25 or 1.5 kGy for Trial 1.

The pieces (-300g) from each bag were then placed in 1-quart Ball Mason Jars

(Alltrista Corporation, Indianapolis, IN). Jars and lids were sanitized with a Better Built

Turbomatic washer and dryer. Lids were drilled with a 3/8" (0.95 cm) hole directly in the

middle. Parafilm (American National Can, Menasha, WI) was wrapped around the top of

the jar before attaching the lid to assure a gas-tight seal. Jars containing fresh-cut

cantaloupe were stored at 3 OC for the duration of the experiment. Further testing was

performed on 1, 3, 5, 7, 9, 12, 14, 16 and 18 d.

Trial 2 was carried out exactly as above except the irradiator was set at 0.1 kGy per

pass. Samples were irradiated at 0, 0.1, 0.2, 0.3, 0.4, 0.5 or 0.7 kGy. Further testing was

done on 1, 4, 6, 8, 11, 13, 17, and 20 d.

Trial 3 was carried out exactly as above except the irradiator was set at 0.3 kGy per

pass. Samples were irradiated at 0, 0.3, 0.6, or 0.9 kGy. Further testing was done on 0,

2, 4, 7, 10, 13, and 16 d.

Dosimetery

Radiographic dosimeters were placed under bags of cantaloupe, flat on the trays

and on top of bags. Gafchromic MD-55 from International Specialty Products (Wayne,

NJ, USA) were cut into lxl cm squares, placed in small envelopes and taped into place.

The dosimeter film was exposed for 24 hrs and then read on a spectrophotometer at a

wavelength of 510 nm. The per pass average was determined by averaging the dose

received on top of the bag with that below the bag.









Gas Analysis

Headspace analysis was done by sampling gas composition of jars for contents of

02 and CO2 using an 02 and CO2 analyzer (Checkmate 9900, PBI-Dansensor, Ringsted,

Denmark). Lids were sealed for 2 hrs before sampling with rubber serum stoppers and

reopened immediately after gas withdrawal. The sampling needle was pushed through

the rubber serum stopper and allowed to take several readings and stabilize. Samples

were taken at 3 C.

Microbial Analysis

Cantaloupe pieces (-20 g) were aseptically removed from the jars and placed in

sterile stomacher bags. Samples were diluted 1:10 with phosphate buffer and stomached

for 30 seconds. Further 1:10 dilutions were carried out by adding 1 ml of sample to 9 ml

of phosphate buffer (1:800, pH 7.2) in dilution tubes and vortexing for 30 seconds.

Aerobic Plate Count and Yeast and Mold Plate Count Petrifilm kits (3M Corporation, St

Paul, MN) were used as described by instructions for all dilutions tested. Petrifilms were

incubated at 250C for 4 days until quantified.

Color Analysis

Cantaloupe pieces were aseptically removed from jars and placed on Styrofoam

plates. In Trial 2, the samples were placed in the Color Machine Vision System

consisting of light box and a CCD color camera connected to a computer with a frame

grabber along with an orange reference plate with L*, a* and b* values of 24.2, 19.7, and

5.4, respectively. The L* refers to brightness from 0 = black to 100 = white. The a* is

from negative (green) to positive (red) and b* is from negative (blue) to positive

(yellow). Images were taken of three sides of the sample and saved on the computer.

The black frame of the reference plate was removed using Corel for Paint. The image









was then analyzed using the software Color Expert Color Analysis of the system. All

images were calibrated with the reference plate. Hue, which is the quality of color and

described by the words red, yellow, green, blue, etc., was calculated with the equation

hue = arctan (b/a). Chroma, the quality which describes the extent to which a color

differs from gray of the same value or lightness, was calculated with the equation chroma

= (a2 + b2)1/2 (Billmeyer and Saltzman, 1966).

In Trial 3, the color of the pieces was measured using a hand held Minolta Chroma

Meter CR-2006 (Minolta Camera Co., Osaka, Japan). The colorimeter was calibrated

before each use with a standard white plate D65 (Y = 94.4, x = 0.3158 and y = 0.3334).

One side of each cube was placed flush against the light source and the L*, a*, b* values

were measured.

Texture

The texture of the cantaloupe was measured by an Instron Universal Testing

Instrument, model 4411 (Canton, MA). The six pieces that were analyzed for color were

used for texture. The cantaloupe pieces were placed under a plunger, establishing zero

force contact, with a plunger diameter of 5.0 mm and compressed 3 mm with a 50 kg

load cell. The plunger was driven into the piece with a crosshead speed of 30 mm/min.

The maximum compression force was measured in kg.

Statistical Analysis

Data was analyzed using analysis of variance in The SAS System version 8e. The

empirical model was determined best fit (lowest p-value) after numerous combinations of

variables were tested.









Results and Discussion

Respiration

Trial 1

Respiration rates for the fresh-cut cantaloupe of Trial 1 stored at 30C are shown in

Figure 3.2. The respiratory quotient (RQ), defined as the ratio of the volume of CO2

released to the volume of 02 consumed was found to be approximately "unity" for all

dates tested. On Day 1, there was a significant difference in all irradiated samples in

comparison to the control. All respiration rates (CO2 production) dropped to less than 3.3

ml per kg per hour on Day 3. An effect of irradiation was clearly seen on Day 3 with the

higher the irradiation dose the higher the respiration rate. Increased respiration by fruits

and vegetables, which may continue for days after exposure, is one of the most readily

discerned direct effects of irradiation (Romani, 1966). A similar effect of respiratory

activity stimulation by irradiation was observed on different apple cultivars (Massey and

others; 1964; Gunes and others, 2000). The respiration rate of the control was

significantly greater (p<0.05) than all other treatments after Day 7. The next sample to

increase in respiration rate was the lowest irradiation dose, 0.25 kGy. Again, the next

sample to increase was the next least irradiated sample of 0.50 kGy. All samples

irradiated above 0.50 kGy behaved very similarly throughout storage. The lower

respiration rates of irradiated samples has been linked to the reduction of metabolic

activity, with the higher the dose, the larger the reduction (Benoit and others, 2000;

Ajlouni and others, 1993). Increase in respiration rate after 7 to 9 days of storage at 5 C

for fresh-cut non-irradiated cantaloupe was observed by Aguayo and others (2004). This

data is also in agreement with results from Luna-Guzman and Barret (2000), Bai and









others (2001), and Madrid and Cantwell (1993). Possible reasons reported were

microbial growth and/or general deterioration of tissue due to senescence.



14


-2- Control
0 \ -.- 0.25 kGy
8 0.5 kGy

5 6 0.75 kGy
E \ i 1.0 kGy
4 \ ...*... 1.25 kGy
.. \ -4- 1.5 kGy
2 -

0
0 3 6 9 12 15
Days

Figure 3.2. Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut
cantaloupe stored at 3 OC (Trial 1).

Trials 2 and 3

Respiration rates of fresh-cut cantaloupe for Trial 2, stored at 3 OC are shown in

Figure 3.3. The (RQ) was found to be approximately "unity" for all dates tested.

Untreated controls had the lowest respiration rates on Day 1 compared to irradiated

samples, however, the difference was not statistically significant. Decreases in

respiration rates after Day 1 were expected due to recovery from initial cutting for sample

preparation. Respiration rates were similar for all samples through Day 8. Statistically

significant differences (p<0.05) were observed starting on Day 11, at which point,

controls were significantly higher than irradiated samples. Similar results were found

with cut iceberg lettuce, where irradiated samples (0.2 and 0.45 kGy) had higher

respiration rates on Day 1 and lower on Day 13 (Hagenmaier and Baker, 1997).









Respiration rates observed for Trial 3 (Figure 3.4) were very similar to the Trial 2

results. Headspace analysis was first done at a true time 0. The open system was

plugged with the rubber stopper immediately upon placing the cantaloupe in the jars.

The initial wound response is more apparent with higher respiration rates observed

compared to Day 1 values of other Trials. The respiration rates of the controls

significantly increased after day 7 and the irradiated samples did not rise until after day

11. The same effect was seen in which the higher the dose of irradiation the lower the

respiration rate for longer over storage time.


45
40
35
-35-- Control
.= 30 -- 0.1 kGy
25 0.2 kGy
20.3 kGy
C 20
-15 *- 0.4 kGy
/10 0.5 kGy
10 ---- 0.7 kGy

0
0 3 6 9 12 15 18 21
Days
Figure 3.3. Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut
cantaloupe stored at 3 OC (Trial 2).

Microbiology

Microbiological results for Trial 2 are shown in Figure 3.5. Irradiation was

responsible for a 1.5 log reduction in total plate count (TPC) at 0.7 kGy on Day 1. This

reduction steadily increased with time, reaching a maximum of 3 logs. Microbial counts

of irradiated samples increased at a lower rate than non-irradiated controls, consistent











45
40
35
IF30
S-*- Control
2.25 /
-. 0.3 kGy
020 1 0.6 kGy
E15 0.9 kGy
10
5
0
0 3 6 9 12 15
Days

Figure 3.4. Respiration rate (CO2 production) of irradiated and non-irradiated fresh-cut
cantaloupe stored at 3 OC (Trial 3).



9


7
Control
0)6 0--- 1 kGy
5 5 0.2 kGy
S3 .. --- 0.4 kGy

---.--- 0.5 kGy
2 -+- 0.7 kGy
1
0
0 3 6 9 12
Days

Figure 3.5. Total plate count (TPC) of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 2).

with the possibility of non-lethal injury to irradiated bacteria as suggested by Welt and

others (2001). The TPC for controls and 0.7 kGy samples increased 3.7 and 1.5 logs,









respectively, by Day 11. All samples had TPC levels greater than 108 at Day 13 except

samples treated with 0.4, 0.5, or 0.7 kGy. At Day 17, only samples treated with 0.5 or

0.7 kGy had TPC counts below 108. The control was significantly higher (p<0.05) than

all irradiated samples at days 1, 4, and 13. Irradiation had less affect on the yeast and

mold counts, shown in Figure 3.6, with no significant differences among treatments at

any


8

7

6 .,., -
-.. -*- Control
5 --- 0.1 kGy
S04. 0.2 kGy
o)0.3 kGy
S3 -*-0.4 kGy
2 ------ 0.5 kGy
-- 0.7 kGy

0
0 3 6 9 12 15 18
Days

Figure 3.6. Yeast and Molds counts of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 2).

storage times. The yeast and mold counts of all samples increased approximately 4 logs

by Day 17. The TPC counts in Trial 3 were similar to those in Trial 2 (Figure 3.7). The

initial 1.5 log reduction of the 0.9 kGy sample only increased to 2.5 logs rather than 3

logs as did the 0.7 kGy sample in the previous study. At all dates, the control was

significantly higher than all irradiation levels. In Trial 3, the yeast and mold counts

were also similar to those of Trial 2 with a 4 log increase in all samples by day 13 (Figure

3.8).
















--- Control
-- 0.3 kGy
0.6 kGy
0.9 kGy


Days

Figure 3.7. Total plate count (TPC) of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 3).


--- Control
-.-0.3 kGy
0.6 kGy
0.9 kGy


Days

Figure 3.8. Yeast and Molds counts of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 3).

At Days 11 and 13 all respiration rates of irradiated samples were significantly

lower than controls. Surprisingly, an analysis of covariance failed to uncover a









correlation between microbial populations and observed respiration rates. This suggests

that the magnitude of differences in microbial populations did not significantly alter

respiration rate results. Additionally, microbial populations on Day 13 for the 0.2 and 0.3

kGy treatments appeared to be higher than those for the control on Day 11, yet observed

respiration rates for irradiated samples were significantly lower than those observed for

controls. Similar results were found in grated carrots irradiated at 2 kGy and stored at 10

C in plastic bags. The residual concentrations of oxygen were 2-fold higher in the

irradiated samples than in non-irradiated after 7 days of storage. Oxygen consumption

was unaffected by microbial contamination (5 to 7 logs cfu/g). The correlation

coefficient between the percent residual oxygen and microbial counts was lower than the

significant limit ofr = 0.553 at the 0.05 level (Diem and Seldrup, 1982), indicating the

two variables were independent (Chervin and others, 1992).

Based on respiration rates, microbiological bloom and informal sensory

evaluations, irradiated samples appeared to maintain preferred quality for 3 to 5 days

longer than non-irradiated controls. Respiration rates of the controls increased

significantly after Day 8 whereas irradiated samples showed a similar trend only after

Day 13.

Equation 3.1 is an empirical model, based on the data of Trial 2, which can be used

to estimate respiration rate of fresh-cut cantaloupe as a function of time and irradiation

dose.

RCO2 = 8.819 1.856(t) + 6.053(D) 0.919(t)(D) + 0.135(t)2 (3.1)

where t is the storage time in days, D is irradiation dose level (at t = 0) in kGy, and RCO2

is the respiration rate (CO2 production) in ml/kg-hr.









Variables included in Eqn. 3.1 were determined to be statistically significant (p-

values < 0.0001). The model provided an overall coefficient of determination R2 of 0.84.

This empirical model was based solely on data obtained in this study and is intended to

provide a convenient summary of data derived in this work.

Texture

The texture of the cantaloupe for Trial 3 is listed in Table 3.1. The texture of the

non irradiated controls was significantly higher than irradiated samples on Day 0;

thereafter there were no differences in firmness between irradiated and non-irradiated

cantaloupe pieces.. This data is similar to diced tomatoes (Prakash and others, 2002),

apple slices (Gunes and others, 2001b) and strawberries (Yu and others, 1996) where

firmness decreased with increased irradiation. Fruit softening by irradiation was

associated with increased water-soluble pectin and decreased oxalate-soluble pectin

content. Similar effects were also observed considering the increase of firmness after

Day 0 of irradiated cantaloupe pieces.

Table 3.1. Texture (max force kg) of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 3). Values in columns with different letters are
significantly different (p<0.05).
Texture
Day 0 Day 2 Day 4 Day 7 Day 10 Day 13
Control 0.829 a 0.614 a 0.660 a 0.699 a 0.553 a 0.496 a
0.3 kGy 0.625 b 0.735 a 0.638 a 0.533 b 0.611 a 0.577 a
0.6 kGy 0.589 b 0.658 a 0.601 a 0.679 a 0.650 a 0.571 a
0.9 kGy 0.607 b 0.750 a 0.701 a 0.685 a 0.667 a 0.508 a

The texture of the cantaloupe compared by time within treatments is shown in

Table 3.2. The most noticeable and significant decline in firmness was in the controls.

The 0.6 kGy sample remained significantly indifferent throughout storage. Boyle and

others (1957) reported that threshold ranges of irradiation dose on firmness of apples and

carrots depending on cultivar, ranging from -0.04 to 1.0 kGy.









Table 3.2. Texture (max force kg) of irradiated and non-irradiated fresh-cut cantaloupe
stored at 3 C (Trial 3). Values in columns with different letters are
significantly different (p<0.05).
Control 0.3 kGy 0.6 kGy 0.9 kGy
Day 0 0.829 a 0.625 ab 0.589 a 0.607 bc
Day 2 0.614 bcd 0.735 a 0.658 a 0.750 a
Day 4 0.660 bc 0.638 ab 0.601 a 0.701 ab
Day 7 0.699 b 0.533 b 0.679 a 0.685 ab
Day 10 0.553 cd 0.611 ab 0.650 a 0.667 ab
Day 13 0.496 d 0.577 ab 0.571 a 0.508 c

Color

The color of all samples remained stable throughout the storage duration for Trial 2

(Table 3.3 and 3.4). The L*, a*, b*, hue, and chroma values varied more from piece to

piece and melon to melon than between treatments. No trends in significant differences

were found within treatments. Results of the color for Trial 3 were similar to the

previous study except after day 7 the controls were significantly lower in L*, a*, b*

(Table 3.5) and hue and chroma (Table 3.6). Hue was significantly different on Day 13

only. Chroma was significantly lowest on Day 10 and 13 in the non-irradiated controls.

The loss of color may be attributed to the oxidation of B-carotene. No discoloration

developed on cantaloupe pieces in any treatment. This absence of browning is the result

of a lack of polyphenol oxidase (PPO) enzyme and/or oxidizable phenols in the

cantaloupe (Lamikanra and Watson, 2000). Others have reported that hue, chroma and

L* values of non-irradiated fresh-cut cantaloupe significantly changed during 25 days of

storage at 4 C (Lamikanra and Watson, 2000). While irradiation had no effect on color

in Trial 2, irradiation of fresh-cut cantaloupe in Trial 3 helped maintain color after 8 days

of storage. Maintenance of color is very important in the fresh-cut produce industry,

where visual appearance on the shelf may be a key factor for extended shelf life

purchases.







46


Differences in L*, a*, and b* values between Trial 2 and Trial 3 may be a result of

two reasons. First, the cantaloupes were of different varieties and seasons. The second

reason for differences is the method of obtaining color values. The method of Trial 2

involves the use of a digital image that averaged the entire surface of the piece of melon.

In Trial 3, the hand held colorimeter only captured a small circle (8 mm2) of the middle

of the surface of the melon piece. Therefore, the broad spectrum of colors averaged over

the entire surface of cantaloupe (Trial 2) differs from the single point repeatedly

measured with the hand held colorimeter (Trial 3).

Table 3.3. Color of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 OC
(Trial 2). Values in columns with different letters are significantly different
(p<0.05).
L
Day 1 Day 4 Day 6 Day 8 Day 11 Day 13
Control 70.8 a 67.9 a 66.8 ab 68.0 a 65.1 a 65.2 a
0.1 kGy 71.4 a 68.7 a 68.6 ab 70.3 a 70.7 a 69.0 a
0.2 kGy 67.5 ab 67.8 a 62.1 b 66.7 a 68.5 a 70.6 a
0.3 kGy 64.1 b 71.4 a 71.6 a 71.4 a 72.2 a 62.8 a
0.4 kGy 71.4 a 68.4 a 67.7 ab 67.7 a 68.1 a 70.8 a
0.5 kGy 67.0 ab 67.1 a 68.3 ab 66.7 a 70.8 a 62.3 a
0.7 kGy 70.2 a 69.0 a 67.3 ab 64.4 a 67.0 a 68.3 a

a
Day 1 Day 4 Day 6 Day 8 Day 11 Day 13
Control 28.5 a 36.6 a 27.6 a 20.7 b 24.0 a 30.7 a
0.1 kGy 29.7 a 34.0 a 26.5 a 23.1 ab 16.7 a 22.3 a
0.2 kGy 26.5 a 33.6 a 36.0 a 33.5 ab 25.8 a 20.0 a
0.3 kGy 38.3 a 28.5 a 20.2 a 21.8 b 18.1 a 38.1 a
0.4 kGy 27.2 a 34.5 a 32.7 a 28.6 ab 28.4 a 23.7 a
0.5 kGy 28.4 a 35.6 a 26.4 a 31.4 ab 21.1 a 41.1 a
0.7 kGy 26.3 a 33.3 a 32.6 a 41.6 a 33.7 a 26.1 a

b
Day 1 Day 4 Day 6 Day 8 Day 11 Day 13
Control 63.5 a 63.3 a 59.3 ab 58.7 a 55.3 b 57.5 c
0.1 kGy 56.9 c 64.5 a 60.5 ab 61.7 a 60.4 ab 60.0 abc
0.2 kGy 62.4 ab 62.5 a 57.3 b 61.3 a 61.1 ab 61.5 ab
0.3 kGy 62.1 ab 64.7 a 62.4 a 63.8 a 63.0 a 57.9 bc
0.4 kGy 61.2 ab 64.0 a 62.8 a 61.3 a 61.2 ab 63.4 a
0.5 kGy 61.6 ab 63.1 a 62.4 a 61.5 a 62.8 a 58.6 bc
0.7 kGy 58.6 bc 64.9 a 61.6 ab 61.6 a 61.6 a 60.2 abc







47


Table 3.4. Hue and chroma of irradiated and non-irradiated fresh-cut cantaloupe stored
at 3 C (Trial 2). Values in columns with different letters are significantly
different (p<0.05).


Control
0.1 kGy
0.2 kGy
0.3 kGy
0.4 kGy
0.5 kGy
0.7 kGy




Control
0.1 kGy
0.2 kGy
0.3 kGy
0.4 kGy
0.5 kGy
0.7 kGy


Day 1
66.1 a
62.5 a
67.0 a
58.4 a
66.0 a
65.3 a
65.8 a


Day 1
69.9 a
64.3 a
67.8 a
73.0 a
67.0 a
67.8 a
64.2 a


Day 4
60.0 a
62.3 a
61.7 a
66.2 a
61.8 a
60.6 a
62.9 a


Day 4
73.2 a
72.9 a
71.0 a
70.7 a
72.7 a
72.5 a
73.0 a


Hue
Day 6
65.2 E
66.4 E
57.8 t
72.1 E
62.5 E
67.0 E
62.1 E


Chroma
Day 6
65.4 b
66.1 ab
67.7 ab
65.6 b
70.9 a
67.7 ab
69.7 ab


Day 8
70.6
69.6
61.5
71.2
65.0
63.0
55.9


Day 8
62.3
65.9
69.9
67.4
67.6
69.0
74.3


Day 11
66.6
74.6
67.4
73.9
65.2
71.4
61.3


Day 11
60.2
62.7
66.3
65.5
67.5
66.2
70.2


Day 13
61.9
69.8
72.0
56.8
69.6
54.9
66.6


Day 13
65.1
64.0
64.7
69.3
67.7
71.6
65.6


Table 3.5. Color of irradiated and non-irradiated fresh-cut cantaloupe stored at 3 OC
(Trial 3). Values in columns with different letters are significantly different
(p<0.05).


Control
0.3 kGy
0.6 kGy
0.9 kGy




Control
0.3 kGy
0.6 kGy
0.9 kGy




Control
0.3 kGy
0.6 kGy
0.9 kGy


Day 0
63.7 a
64.0 a
62.7 a
62.6 a


Day 0
12.6 a
11.0 a
11.7 a
12.0 a


Day 0
33.6 a
31.1 a
32.9 a
32.9 a


Day 2
63.7 a
64.5 a
63.8 a
62.3 a


Day 2
11.3 a
12.4 a
13.0 a
11.7 a


Day 2
33.8 a
35.0 a
35.9 a
33.8 a


L
Day 4
65.5
58.3
63.6
54.5

a
Day 4
11.9
11.7
12.3
10.3

b
Day 4
34.0
33.3
35.2
30.3


Day 7
57.0
55.7
60.8
62.6


Day 7
11.2
10.1
11.8
12.2


Day 7
31.6
30.4
31.2
35.3


Day 10
46.6
61.5
62.2
59.7


Day 10
7.1
11.9
11.8
10.2


Day 10
22.8
34.8
34.9
31.8


Day 13
42.9
62.4
53.7
54.6


Day 13
5.1
11.3
10.0
10.3


Day 13
18.2
33.1
29.3
29.7










Table 3.6. Hue and chroma of irradiated and non-irradiated fresh-cut cantaloupe stored at
3 C (Trial 3). Values in columns with different letters are significantly
different (p<0.05).
Hue
Day 0 Day 2 Day 4 Day 7 Day 10 Day 13
Control 69.4 a 71.6 a 70.7 a 70.5 a 73.1 a 74.5 a
0.3 kGy 70.5 a 70.6 a 70.7 a 71.7 a 71.2 a 71.2 b
0.6 kGy 70.4 a 70.0 a 70.7 a 68.7 a 71.4 a 71.2 b
0.9 kGy 70.0 a 70.9 a 71.4 a 70.9 a 72.3 a 70.0 b

Chroma
Day 0 Day 2 Day 4 Day 7 Day 10 Day 13
Control 33.5 a 35.7 a 36.0 a 33.8 a 23.9 b 18.9 b
0.3 kGy 30.5 a 37.1 a 35.3 a 32.1 a 36.8 a 35.0 a
0.6 kGy 32.4 a 38.2 a 37.2 a 33.4 a 36.8 a 31.0 a
0.9 kGy 32.6 a 35.7 a 32.0 a 37.4 a 33.4 a 31.4 a


Samples removed from jars for color work were used for informal sensory

evaluation after being digitally photographed. Four panelists tasted the samples and

suggested that there were no substantial differences between the treatments for 8 days.

After Day 8, samples treated with higher irradiation dose levels generally had better

flavor and texture.

Conclusions

Low dose electron beam irradiation of fresh-cut cantaloupe offers promise as a

method of maintaining preferred-quality of this product during shelf life. Knowledge of

the effects of irradiation on product respiration rates, as summarized in Eqn. 3.1, should

provide a means to develop modified atmosphere packaging that could further enhance

the ability of irradiation to extend fresh-cut cantaloupe shelf-life.














CHAPTER 4
RESPIRATION OF IRRADIATED FRESH-CUT CANTALOUPE AND MODELLING
OF RESPIRATION FOR MODIFIED ATMOSPHERE PACKAGING

Introduction

An effective way to extend the shelf life of fresh produce is to use a modified

atmosphere package (MAP). The package should maintain an optimal atmosphere that

will reduce respiration and slow physiological and microbiological changes that decrease

shelf life. The respiration rate of horticultural commodities is dependent on the amount

of available oxygen and carbon dioxide present in the surrounding environment

(Beaudry, 2000; Watkins, 2000). Determination of the optimal surrounding atmosphere

for fresh-cut produce that minimizes respiration without initiating anaerobiosis or

injuring the plant tissue is difficult due to the numerous possible combinations of oxygen

and carbon dioxide concentrations.

Determination of respiration rate at different 02 and CO2 concentrations is an

important factor in the design of a MAP for fresh produce. Generating all the possible

combinations of 02 and CO2 concentrations using a flow through or flush system in order

to determine unique respiration rates would be very time consuming. The closed system

has been used to generate more rapid results and cover a range of 02 and CO2

concentrations (Haggar and others, 1992; Henig and Gilbert, 1975; Yang and Chinnan,

1988; Gong and Corey, 1994; Cameron and others, 1989).

Determination of the amount of 02 and CO2 diffusing in and out of a MAP can be

determined using Fick's first law of diffusion (Zhu and others, 2002). The inflow and









outflow of each gas is controlled by the temperature, internal and external gas

concentration and transmission rate of the film.

Predictive modeling in MAPs of fresh-cut produce is centered around the

respiration rate of the product and the permeation of gases through the film. The amount

of fruit, size of permeable packaging, temperature and starting atmosphere can be

adjusted for an optimal package with known respiration rate and gas transmission

equations.

The objective of this research was to determine the respiration rate of irradiated and

non-irradiated fresh-cut cantaloupe in order to develop predictive equations that could be

used to design a MAP with a desirable steady state atmosphere.

Materials and Methods

Fruit Sample

Cantaloupes (Cucumis melo Linnaeus, cv. Athena) were purchased from a local

grocery store in Gainesville, FL and transferred to the University of Florida Food Science

and Human Nutrition building via automobile and were stored in a 3 C storage room

overnight before processing. Cantaloupes were picked at three quarter to full slip

(commercial maturity, when a clear separation from the vine occurs with light pressure)

and ready to eat.

Processing

Cantaloupes were rinsed in 100 ppm chlorinated water and allowed to dry 1 hour

before cutting. All knives, cutting boards and bowls were soaked with 100 ppm

chlorinated water. Fifteen cantaloupes were halved, deseeded, and then halved again

resulting in 4 equal parts. Each quarter was sliced on a 12 HP commercial deli slicer

(Model 1712E, Hobart Corporation, Troy, Ohio) with the blade set at 2.5 cm thick.









Slices were then peeled and cut into approximately 2.5 cm pieces with a knife. All pieces

were placed in an aluminum bowl, which was surrounded with ice. Pieces were

thoroughly mixed to assure random sampling.

Pieces (-300g) were placed in quart Ziploc (S.C. Johnson & Son, Inc., Racine,

WI) Freezer bags and sealed after expulsion of most of the air. Bags were placed in ice

in a portable cooler and transported to the electron beam irradiation facility, which was a

90 mega amp, 95% scan (Florida Accelerator Services and Technology, Gainesville, FL).

Plastic trays were previously frozen with 1.5 cm of ice in them. Four bags were taped to

each tray with cantaloupe arranged in a single flat layer in order for all pieces to receive

equal dosage. Dosimeters were also attached to verify that target doses had been reached.

The irradiator conveyor was set at a speed of 10 feet per minute (fpm; 305 cm per

minute) and 0.1 kGy per pass. To achieve 0.2 kGy, the sample was passed through twice,

0.4 kGy four times and so on. Bags were removed from the ice trays and placed back in

the ice cooler after the desired number of passes. Samples were irradiated at 0, 0.2, 0.4 or

0.6 kGy.

The pieces (-300g) from each bag were then placed in 1-quart Ball Mason Jars

(Alltrista Corporation, Indianapolis, IN). Three jars of each irradiation dose and three

controls, which where processed exactly the same without receiving irradiation were

tested. Jars and lids were sanitized with a Better Built Turbomatic washer and dryer.

Lids were drilled with a 3/8" (0.95 cm) hole directly in the middle. Parafilm (American

National Can, Menasha, WI) was wrapped around the top of the jar before attaching the

lid to assure a gas-tight seal. Jars containing fresh-cut cantaloupe were stored at 3 OC for

the duration of the experiment. Rubber stoppers were placed in the hole in the lid to









create a closed system immediately upon closing the jar. Gas samples were taken every 4

to 12 hours throughout the 14 day storage duration.

Dosimetery

Radiographic dosimeters were placed under bags of cantaloupe, flat on the trays

and on top of bags. Gafchromic MD-55 from International Specialty Products (Wayne,

NJ, USA) were cut into lxl cm squares, placed in small envelopes and taped into place.

The dosimeter film was exposed for 24 hrs and then read on a spectrophotometer at a

wavelength of 510 nm. The per pass average was determined by averaging the dose

received on top of the bag with that below the bag.

Gas Analysis

Headspace analysis was done by sampling gas composition of jars for contents of

02 and CO2 using an 02 and CO2 analyzer (Checkmate 9900, PBI-Dansensor, Ringsted,

Denmark). The sampling needle was pushed through the rubber stopper and allowed to

take several readings and stabilize. Samples were taken in the cold room without moving

the jars.

Modeling

The 02 and CO2 concentrations were fit to equations (4.1) and (4.2) using

KalediaGraph 3.5 (Synergy Software, Reading, PA). The following equations were used

in a paper by Hagger and others, (1992) to design an enzyme kinetics based respiration

model.


[O2]=21- (4.1)
(Alt +B,)c1

t
[CO2]= (4.2)
(A2t + B2)2









The equations were solved for coefficients A, B and C across time (t) in hours and

[02] and [CO2] in percent. At each sampling time, the respiration rates were calculated

by substituting the first derivatives of Eqns. (4.1) and (4.2) into Eqns. (4.5) and (4.6),

respectively. Eqns. (4.3) and (4.4) are the first derivatives of Eqns. (4.1) and (4.2).

d[O2]= A1Clt(Alt +B, )(1-cl) (Alt + B) C1 (4.3)

d[CO2] = -A2C2t(A2t +B2 )(-1-C2 +(A2t +B2) C2 (4.4)

d[O2] MPV
ro( ) (4.5)
S dt 100RWT

d[CO21] M,2 PV
rco ( ) (4.6)
dt 100RWT

ro is the respiration rate in terms of oxygen consumption (mg/kg h), rco0 is the

respiration rate in terms of carbon dioxide production, Mo2 and MC02 are the molecular

weights of oxygen and carbon dioxide (kg/mole), respectively, P is the pressure inside the

jar (Pa), V is the free volume (ml), R is the universal gas law constant (8.314 J/mol K), W

is the weight of the cantaloupe (kg), and T is the temperature (in degrees Kelvin).

The respiration rates were fit with the 02 and CO2 concentrations in the Michaelis-

Menten enzyme model Eqn. (4.7).

Vm[O2]
r = (4.7)
Km +(1+[CO2]/K,)[O2]

Km is the Michaelis-Menten constant (% 02), Vm is the maximum respiration rate

(mg/kg h) and Ki is the inhibition constant (% CO2).

Respirations rates from Eqns. (4.5) and (4.6) were also fit to several exponential

growth curve functions with Eqns. (4.8) and (4.9) fitting with the highest R-value.









r2 =bl exp(b2[O ]) (4.8)

rco2 = bl* exp(b2[CO2]) (4.9)

Variables bl and b2 were solved using KalediaGraph 3.5.

Respirations rates from Eqns. (4.5) and (4.6) were also fit to several polynomial

functions with Eqns. (4.10) and (4.11) having the highest R-value.

ro0 = MO + (M1[2 ]) + (M2[2 ]2) (4.10)

r2 = MO + (M1[CO ]) + (M2[CO2 ]2) (4.11)

Variables MO, Ml and M2 were solved using KalediaGraph 3.5. All equations

were also fit to the respiration data in exclusive ranges of [02] and [C02] specific to

desirable modified atmosphere packaging conditions for fresh-cut cantaloupe: 10 to 3

percent for [02] and 18 to 5 percent for [C02].

Film Permeability

Based on the respiration rates of the fresh-cut cantaloupe at the desired

temperature, two multilayer coextruded bags were provided by Cryovac Sealed Air

Corporation (Duncan, SC). All properties reported by the manufacturer were determined

at 22.8 C. Further testing was needed to determine oxygen and carbon dioxide

transmission rates at 3 C. The two bags were the PD-961EZ Bag and the PD-900 Bag.

Oxygen transmission rates (OTR) were measured using a Mocon two-cell Oxtran

2/20 (Mocon Controls Inc, Minneapolis, MN). Sample film pieces (100 cm2) were cut

using a stainless steel template. The cut pieces were placed on both testing cells of the

Oxtran 2/20 with vacuum grease smoothly applied to the outer edge where the seal is

created. The film samples were conditioned for one hour to remove traces of oxygen by

flushing them with the test gas mixture, 96% nitrogen plus 4% hydrogen. In the testing









chamber, the film creates a barrier between a steady flow (20 ml/min) of 100% oxygen

and a steady flow (20 ml/min) of the test gas mixture. The test gas mixture flows to a

coulometric oxygen sensor, which detects the oxygen that permeated through the sample

film by producing an electrical current directly proportional to the flux of oxygen across

the film. The Mocon unit switches testing chambers when the amount of oxygen

detected stops changing. Gas transmission rates were determined at 10, 15, 24, 30, and

350C and 50% relative humidity. Four 100 cm2 sections were tested for each film.

Carbon dioxide transmission rates were determined using the same Mocon Oxtran

2/20 unit with a few modifications. Pure carbon dioxide was connected to the oxygen

inlet of the Oxtran 2/20. The oxygen sensor was bypassed, and 10 ml samples were taken

from the outflow of test gas. Carbon dioxides levels in the carrier gas after permeation

through the film were determined using a Fisher Gas Partitioner model 1200 gas

chromatograph (GC; Fisher Scientific, Pittsburgh, PA) with a thermal conductivity

detector that was equipped with a 1,966 x 3.12 mm 80/100 mesh Porapak column at 60

The detector and injector temperatures were set 90 OC. Eqn. (4.12) was used to convert

the %C02 reading from the GC into a transmission rate.

CO2R 1440 min 1
CO2TR *FR* 1440 (4.12)
100 day A

Where CO2TR is the carbon dioxide transmission rate in ml/m2/day, CO2R is the

carbon dioxide reading from the GC in %, FR is the flow rate of the outflow gas in

ml/min, and A is area of the film in m2









The Arrhenius method used for OTR determination was used for carbon dioxide

transmission rates, except for the use of the gas chromatograph. Gas transmission rates

were determined at 10, 15, 24, 30, and 350C and 50% relative humidity.

The natural log of the OTRs and the carbon dioxide transmission rates were

plotted on the y-axis with 1/T (Kelvin) on the x-axis. Linear regression was done with

Microsoft Excel 2000 yielding Eqn. (4.13), which in Arrhenius form is Eqn. (4.14) and

rearranged as Eqn. (4.15)

y = mx +b (4.13)

Ea
In(k) = ln(ko) -- (4.14)
RT

Ea
k= ko*exp{- } (4.15)
RT

k is the permeability of the film in ml/m2/day, ko is the permeability coefficient, Ea

is the activation energy for the transport of oxygen or carbon dioxide through the film in

kJ/mol, R is the universal gas constant and T is the absolute temperature in degrees

Kelvin. Transmission rates can be determined at any temperature using any of the Eqns.

(4.13) -(4.15).

Modified Atmosphere Package Design

A program to predict the changes over time in [02] and [CO2] of the headspace,

surrounding a known weight of fresh-cut cantaloupe in a MAP was written in Microsoft

Excel 2000 using Visual Basic for Applications. The following code was used.



Option Explicit

Dim PO2 As Double
Dim PCO2 As Double









Dim A As Double
Dim pO2out As Double
Dim pCO2out As Double
Dim p02in As Double
Dim pCO2in As Double
Dim pN2out As Double
Dim pN2in As Double
Dim W As Double
Dim R02 As Double
Dim RCO2 As Double
Dim V As Double
Dim Pt As Double
Dim t As Double
Dim Q02 As Double
Dim J02 As Double
Dim QCO2 As Double
Dim JCO2 As Double
Dim PN2 As Double
Dim JN2 As Double
Dim M102 As Double
Dim M202 As Double
Dim M302 As Double
Dim M1CO2 As Double
Dim M2C02 As Double
Dim M3C02 As Double


Public Sub GetInputo

P02 = Range("IN!C1").Value
PCO2 = Range("IN!C10").Value
PN2 = Range("IN!C 15").Value
A= Range("IN!C2").Value
pO2out = Range("IN! C3").Value
p02in = Range("IN! C4").Value
pCO2out = Range("IN!C11 ").Value
pCO2in = Range("IN!C12").Value
pN2out= Range("IN!C 13").Value
pN2in = Range("IN! C14").Value
W = Range("IN!C5").Value
'R02 = Range("IN! C6").Value
V = Range("IN!C7").Value
Pt = Range("IN!C8").Value
't = Range("IN!C1").Value
M102 = Range("IN!C 16").Value
M202 = Range("IN! C 17").Value









M302 =
M1CO2
M2C02
M3C02


Range("IN!C18").Value
= Range("IN!C 19").Value
= Range("IN! C20").Value
= Range("IN! C21").Value


End Sub

Public Sub Maino

Call GetInput

Call SimLoop

End Sub


Public Sub SimLoopo

t= 1

Do While t < 5000


R02 = M102 + (M202 p02in) + (M302 p02in A 2)

RCO2 = M1CO2 + (M2C02 pCO2in) + (M3C02 pCO2in A 2)

Q02 = R02 W

QCO2= RC2 W

J02 = P02 A (pO2out p02in) 0.01

JCO2 = PCO2 A (pCO2in pCO2out) 0.01

JN2 = PN2 A (pN2out pN2in) 0.01

p02in = p02in + ((J02 Q02) (100 / V) 0.1) 't=.1 hardcode

pCO2in = pCO2in + ((QCO2 JCO2) (100 / V) 0.1) 't=.1 hardcode

V = ((-Q02 + QC02 JC02 + J02 + JN2) 0.1) + V


Worksheets("Out").Cells(t + 1, 1).Value
Worksheets("Out").Cells(t + 1, 2).Value
Worksheets("Out").Cells(t + 1, 3).Value
Worksheets("Out").Cells(t + 1, 4).Value
Worksheets("Out").Cells(t + 1, 5).Value


t
p02in
pCO2in
V
R02










Worksheets("Out").Cells(t + 1, 6).Value

t=t+l

Loop

End Sub


"~T~' A B_ C 0 E IF G FIr |
1 ......-.... .............. ........-.-.................-- p ^ .......... : .............. ---. -............-- -- ....... E .............. .. ...--- -. ;. _.... ...... ... ...- ... -
I Pilm 02 Pemn mIrnh kpa) PO2 27.375 PD961 IPD 900
2 !Area (m2) A 0.13 63.71 27.375
3 Paral press 02 out kppa) p02out 21
SPartial press 02 In kpal pO21n 5.4
SWeight R&g) W 0.52
e Respiration Rare imnlkg h) R02 model
7 Free Volume (ml) V 2500
8 Total Press (Ipa) Pt 100
9 Time (h) 02
10 Film C02 Perm (miUm h kpa) PC02 143.1 Control 0.2 0 0.6
iI Partial press C02 out (kpa pCo2ou 0.001 M0 1.257 1.1726 1A.42 1.5276
SPartial press C02 In (kpa) pCO2In 8.35 M1 40.114 40.2485 -0.3592 -0.37
13 Parial press% N2 0Ut (pa) pNZout 78.999 M2 0.013 0,027 0,044 0.034
14 Partal press N2 In (kpa) pN21n 86.24
iF Film N2 Perm mllnm h kpa) PN2 13.6875 C02
ie Polynomial Coelficients M102 1.5276 Control 0.2 0. 0.6
17 M202 -0.37 MO 3.579 5.73 S456 9.757
18 M302 0.034 M1 -0,33 -0.52 -0.564 -1,0320
19 MIC02 G.757 M2 0.009 0.014 0.015 0.032
20 M2CO2 -1.0329
21 M3C02 0.032

1%.W .. ..s... .. .O..... 1 -~ ....- = f p'I.



Figure 4.1. The input screen for all data necessary for the prediction program with
variables described and units defined

The model determines the predicted gas composition inside the bag every 6

minutes. The amount of oxygen consumed and carbon dioxide evolved are determined

by the respiration rate of the produce at the initial gas levels for time 1. The amount of

oxygen and carbon dioxide that passes through the package is based on the area of

transmissible film and the concentration of gases inside and outside the package. The


RCO2









new internal gas composition and volume are then calculated. The program then loops

and recalculates based on new gas composition. The program displays the gas

concentrations inside the bag and the free volume in graph form. The respiration rates at

each time are also listed in table form. Figure (4.1) is the input screen for the program.

Results and Discussion

Modeling

Headspace concentrations of 02 and CO2 over time in the closed jars acted as


Control


200

Time (h)


300


*02
C02


400


expected with the 02 dropping close to 5% and CO2 rising to almost 20% during 14 days

of storage. Figure (4.2) shows the averages of the three jars of each treatment.

Coefficients A, B and C of Eqns. (4.1) and (4.2) were solved across time t with high

correlation for all treatments (Table 4.1).


IL



FONES
Eu.










0.2 kGy


100 200 300


Time (h)





0.4 kGy


100 200 300


Time (h)


() .-'
U
u0 15
*o
CD
S10

5

0


*02
C02


400


. 10

5


0


n02
C02


400












0.6 kGy


(U
u 15
(Q
*" 10


0


0 100 200 300


*02

C02


400


Time (h)



Figure 4.2. Percent oxygen and carbon dioxide in headspace during closed system
storage of irradiated and non-irradiated fresh-cut cantaloupe at 3 OC.

Table 4.1. Coefficients of Eqn. (4.1) and (4.2) describing the changes in oxygen and
carbon dioxide concentrations, respectively, over time for irradiated and non-
irradiated fresh-cut cantaloupe stored in a closed system at 3 OC.


Control
1:1 4 1 :
t-: -40:
I I' -. : ,


0.2 kGy

-4 t-. iI,


0.4 kGy
0 1-4.4

I I +2-.:


0.6 kGy

4 :


R I' C I CI C I I

CO2


Control
-1 1 -T .2
1i ii 2 14


0.2 kGy
1:1 -4i:,
4.4.:6.:.


0.4 kGy

I I C, I I


0.6 kGy

1:1 4., 1 4


Oxygen consumption and carbon dioxide evolution at each sampling time were

solved by inserting the results of Eqns. (4.3) and (4.4) into Eqns. (4.5) and (4.6). The










Table 4.2. Coefficients of Michalis-Menten model Eqn (4.5) and (4.6) for changes in
oxygen and carbon dioxide concentrations, respectively, over time for
irradiated and non-irradiated fresh-cut cantaloupe stored in a closed
system at 3 C.
02
Control 0.2 kGy 0.4 kGy 0.6 kGy
Vm 26.1 465.4 180.8 57.9
Km -226.1 -3209.9 -917.9 -348.58
Ki 0.29 0.002 0.08 0.21

R 0.993 0.972 0.974 0.985

C02
Control 0.2 kGy 0.4 kGy 0.6 kGy
Vm 1.48 1.46 1.69 1.74
Km -2.92 -3.39 -3.76 -3.3
Ki 8.20E+09 1.90E+06 1.60E+22 1.60E+11

R 0.944 0.963 0.924 0.958

respiration rates from Eqns. (4.5) and (4.6) where then used to solve the parameters of the

Michaelis-Menten Eqn. (4.7), which are listed in Table (4.2). The R values are high

suggesting the data fit well. The model looks good until the gas composition inside a

permeable package is predicted. Figure (4.3) and (4.4) shows the curve of the respiration

rates across time and the models' predicted respiration rates across time for the control,

with irradiated samples behaving similarly.

The critical area of this curve for 02 consumption is between 3 and 10% and for

CO2 evolution it is between 5 and 18%. The lower the 02 concentration, the poorer the

Michaelis-Menten equation fit. This could be due to the fact that the Michaelis-Menten

model is only valid for aerobic respiration (Lee and others, 1991). Peppelenbos and

Leven (1996) determined a significant decrease in 02 consumption in apples and

asparagus at CO2 levels of 10% and above. Therefore in the critical MAP range, this

model will not suffice. An active MAP should start and remain at gas compositions

within critical ranges for the produce.















- Observed Data


-= r = Vm[02] / Km+(1 +[C02]/Ki)[02]
Value Error
Vm 117.9 2205.4
Km -910.13 16440
Ki 0.06713 1.2413
Chisq 5.4373 NA
R 0.99358 NA


%O
2

Figure 4.3. Michaelis-Menten equation fit to observed respiration data vs. percent
oxygen for non-irradiated fresh-cut cantaloupe stored in a closed system at 3
oC.

The parameters of Eqn. (4.7) were then solved for the critical ranges using the

respiration rates at only times when [02] was between 3 and 10% and [CO2] was between

5 and 18%. The results were very similar when using all times, therefore this was

ineffective as well.

The exponential growth curves of Eqns. (4.8) and (4.9) were solved using all

respiration data in Figure (4.2). The results were very similar to the solutions for Eqn.














- Observed Data


--- = r = Vm[02] / Km+(1+[C02]/Ki)[02]
Value Error
Vm 1.476 0.19934
Km -2.9239 0.89274
Ki 8.2242e+09 9.2819e+17
Chisq 13.03 NA
R 0.94419 NA


10
% CO
2


Figure 4.4. Michaelis-Menten equation fit to observed respiration data vs. percent carbon
dioxide for non-irradiated fresh-cut cantaloupe stored in a closed system at 3
oC.

(4.7). The R values were very high (-0.99), yet in the critical areas for MAP, the

predicted respiration rates would be erroneous. Once again, fitting the critical areas only

to the curve was ineffective, therefore continuing the search for the equation yielding

proper prediction confidence.

The data was then fit to polynomial curves of Eqns. (4.10) and (4.11) with good

results. Fitting the critical areas separately yielded excellent results for all treatments as










seen by the controls in Figures (4.5) and (4.6). The parameter values are listed in Table

(4.3).

Table 4.3. Coefficients of the polynomial model Eqns. (4.10) and (4.11) for changes in
oxygen and carbon dioxide concentrations, respectively, over time for
irradiated and non-irradiated fresh-cut cantaloupe stored in a closed system at
3 oC.
02
Control 0.2 kGy 0.4 kGy 0.6 kGy
MO 1.257 1.1726 1.428 1.5276
M1 -0.114 -0.2485 -0.3592 -0.37
M2 0.013 0.027 0.044 0.034

R 0.994 0.999 0.999 0.999

CO2
Control 0.2 kGy 0.4 kGy 0.6 kGy
MO 3.579 5.73 8.456 9.757
M1 -0.33 -0.52 -0.649 -1.0329
M2 0.009 0.014 0.015 0.032

R 0.994 0.999 0.998 0.985

The respiration rate can be determined at any 02 plus CO2 combination within the

ranges solved for by the polynomial equations. This was considered acceptable since the

MAP design in the next chapter was planned to use a gas flush with the desired steady

state package atmosphere.

It is uncertain why the Michaelis-Menten equation did not fit the data better in the

critical areas. Most published research using the Michaelis-Menten equation for

modeling produce respiration involved intact fruits and vegetables or produce lightly

processed to a lesser extent than the fruit in this work. The pieces of fresh-cut cantaloupe

in this experiment were wounded on all sides. The fruit was peeled, seeded by cutting the

most inner cavity layer out and then cubed, which leaves no side uncut. This wounding

causes an increase in respiration at time 0 compared to the intact fruit. The pieces also

are exposed to gases on all sides with an increased surface area. The solubility and







67


1.5


1.4


c-




E
O,

ry 1.2
CV)


- r= MO+ M1*x+ M2*x2
MO 1.2573
M1 -0.11414
M2 0.012984
R 0.99391


S Observed Data

1.1

11 ----------------------------------------------------



5 6 7 8 9 10 11
%O
2
Figure 4.5. Second order polynomial equation fit for observed respiration data vs.
percent oxygen within the critical range for non-irradiated fresh-cut
cantaloupe stored in a closed system at 3 OC.

diffusion rates of 02 and CO2 would also have been affected. The initial wound response

along with exposure to gases on all sides with differing diffusion and solubility rates may

not allow the Michaelis-Menten model to be the best choice.

Most work done with the Michaelis-Menten equation has been performed at higher

temperatures than the work done for this paper. Also, the most common fresh-cut

produce modeled is broccoli (Fonseca and others, 2002). Therefore, published data

shows the depletion of oxygen and increase in carbon dioxide at a faster rate, especially














--=r =MO + M1*x + M2*x2
MO 3.5787
M1 -0.33022
M2 0.0089975
R 0.99407


I- Observed Data


% CO
2


Figure 4.6. Polynomial equation fit to observed respiration data vs. percent carbon
dioxide for within the critical range for non-irradiated fresh-cut cantaloupe
stored in a closed system at 3 OC.

later in storage when broccoli enters a climacteric phase of increasing respiration.

Although cantaloupe is also a climacteric crop, the fruit used in this work were already

ripe and presumably postclimacteric at the start of the experiments. Cold storage and the

naturally low respiration rate of cantaloupe may cause it to be an unsuitable candidate for

Michaelis-Menten modeling.

Many limitations exist in prediction modeling of fresh-cut produce. The results of

experimentation can be specific to the environmental conditions as well as the variability









in the commodity. The closed system experiment above started and continued through

02 and CO2 combinations that would not be present in an active MAP. Most closed

system models predict respiration rates of produces at internal atmosphere different than

those used in the creation of the model. For example, the internal starting gas

composition for the MAPs of the next experiment are 4% oxygen and 10% carbon

dioxide. Therefore, as seen in Figure (4.2), the percent oxygen at the time when the

carbon dioxide is 10% is not near 4, and similarly the carbon dioxide percent is very high

when oxygen is low. The above prediction equations give respiration rates from different

observed data. Inhibitory and/or promotional effects of the other gas concentration, for

example oxygen when determining carbon dioxide evolution, may be overlooked.

Although significant results may be obtained from closed system modeling, further

testing should be carried out with package design.

Film Permeability

The oxygen and carbon dioxide transmission rates of the films for the temperatures

tested are listed in Table (4.4). The Arrhenius relationships between transmission rates

and temperature are shown in Figure (4.7) and (4.8). The OTRs for PD-900 and PD-

961EZ at 30C were determined by extrapolation of the Arrhenius curve to be 657.31 and

1529.56 ml/m2/day. The carbon dioxide transmission rates for PD-900 and PD-961EZ at

3C were similarly determined to be 3434.03 and 8035.77 ml/m2/day. The Arrhenius

relationship values Ea and ko are listed in Table (4.5).

The activation energy determined for both films was slightly higher in oxygen

permeability compared to carbon dioxide permeability. Therefore, the oxygen

concentrations inside the packages will be more easily influenced by temperature









fluctuations during storage compared to the carbon dioxide concentrations (Van de Velde

and others, 2002).

Table 4.4. Average oxygen (OTR) and carbon dioxide (CO2TR) transmission rates at
various temperatures for films tested.
Temp PD 961 EZ
degree C PD 900 mm ay ml/m2/dav


OTR
1036
1398
2290
3200
4216


CO2TR
2393
3159
5121
7095
9415


O
7(
71
9(
12
18


>TR CO2TR
033 14844
793 18524
884 20166
:874 26300
1075 36806


* PD961 EZ
* PD900


6.8 I -
0.0032 0.00325 0.0033 0.00335 0.0034 0.00345 0.0035 0.00355
1/T(k)


Figure 4.7. Arrhenius relationship between the natural log of the oxygen transmission
rate (O2TR) in ml/m2/ day and temperature for two films tested.

Table 4.5. Arrhenius relationship values Ea and ko for two films tested.


Film rl/rn/day


Ea
kJ/mol


OTR PD 900
PD 961 EZ

C2R PD 900
C2TR 961
PD 961 EZ


40.5 3.06E+10
39.5 4.63E+10


31.9
35.3


9.26E+09
1.63E+10


y = -4871.5x + 24.144
R2 = 0.9959





y = -4754.3x + 24559-
R2 = 0.9971











11
10.5 = -3842.4x + 22.949
10 R2 = 0.9672
,10
9.5 PD961 EZ
O 9.5- PD900
S 9 y = -4251.7x + 23.512 "
R2 = 0.9781
8.5

8
0.0032 0.00325 0.0033 0.00335 0.0034 0.00345 0.0035
1IT (K)

Figure 4.8. Arrhenius relationship between the natural log of the carbon dioxide
transmission rate (CO2TR) in ml/m2/ day and temperature for two films tested.

Conclusion

The Michaelis-Menten enzyme kinetics equation was not a suitable model for

fresh-cut cantaloupe. A polynomial model fit the oxygen consumption and carbon

dioxide evolution data very well and, most importantly, the fit was good in the critical

oxygen and carbon dioxide concentration ranges desirable for fresh-cut cantaloupe for

MAP. An Arrhenius equation accurately predicted the oxygen and carbon dioxide

transmission rates of packaging polymers over a range of temperatures. With known

prediction equations for respiration rate of produce and transmission rates of packaging

films, an optimal MAP can be easily designed.














CHAPTER 5
DESIGN OF MODIFIED ATMOSPHERE PACKAGE FOR IRRADIATED FRESH-
CUT CANTALOUPE AND EVALUATION WITH DESCRIPTIVE ANALYSIS
SENSORY PANEL

Introduction

Respiration involves the consumption of oxygen and production of carbon dioxide

and water. Aerobic respiration can be slowed by limiting available oxygen. However,

oxygen must be maintained above a minimum threshold to prevent anaerobic respiration

(Knee, 1980). Additionally, increased carbon dioxide concentration has been shown to

slow down ripening and respiration rates (Mathooko, 1996). Therefore, an optimal micro

atmosphere may be created via modified atmosphere packaging (MAP), where

respiration and ethylene production may be reduced as well as many other degradative

processes. A MAP can be developed by matching the proper film with the weight and

respiration rate of the respiring contents.

Modified atmosphere packages can be designed using predictive equations based

on known respiration data. The respiration rate of most produce is dependent on the

oxygen and carbon dioxide levels that surround the produce. An ideal package will

maintain the desired levels of decreased oxygen and increased carbon dioxide based on

the transmission rates of the package and the respiration rate of the produce at the desired

storage temperature. Packages can be flushed with the desired steady-state gas

composition in order to avoid the duration of relying on the dynamic process. The

quicker the produce is at the optimal atmosphere the more effective the package.









A combination of MAP and irradiation may have a synergistic effect on the shelf

life of produce. This was demonstrated by Prakash and others (2000) with cut romaine

lettuce. Irradiation increased the shelf life of the MAP fresh-cut lettuce compared to the

non-irradiated MAP fresh-cut lettuce by reducing the initial microbial load by 1.5 log

CFU/g and maintaining a 4 log CFU/g difference on the 18th day of storage.

The first objective of this research was to design a MAP for irradiated and non-

irradiated fresh-cut cantaloupe based on polynomial respiration rate prediction equations

and known transmission rates of packaging films. The second objective was to determine

the validity of the prediction model and the effectiveness of the package with a trained

sensory panel and evaluation of color, texture and microbiology.

Materials and Methods

Fruit Sample

Cantaloupes (Cucumis melo Linnaeus, cv. Magellan and Acclaim) were purchased

from a local grocery store in Gainesville, FL on March 14 (Trial 1) and March 30, 2004

(Trial 2). Prior to purchase, the cantaloupes purchased on March 14 and March 30 were

shipped from Del Monte (Costa Rica) and Del Sol (Costa Rica), respectively, in a 2%

oxygen bag and maintained at 3 OC. Cantaloupes were transferred to the University of

Florida Food Science and Human Nutrition building via automobile and were stored at 25

C for 1 day and then placed in a 3 C storage room overnight before processing.

Cantaloupes were picked at three quarter to full slip (commercial maturity, when a clear

separation from the vine occurs with light pressure) and ready to eat.

Processing

Cantaloupes were rinsed in 100 ppm chlorinated water and allowed to dry 1 hour

before cutting. All knives, cutting boards and bowls were soaked with 100 ppm









chlorinated water. Twenty four cantaloupes were halved, deseeded, and then halved

again resulting in 4 equal parts. Each part was then halved again resulting in 8 canoe

shaped pieces. Slices were then peeled and cut into approximately 2.5 cm pieces with a

knife. All pieces were placed in an aluminum bowl, which was surrounded with ice.

Pieces were thoroughly mixed to assure random sampling.

Pieces in Trial 1 (-625g) and Trial 2 (-520 g) were placed in Cryovac Sealed Air

Corporation (Duncan, South Carolina) polypropylene trays. Trays were placed in

Cryovac Sealed Air Corporation PD-900 MAP bags cut to 32 x 28 cm. The MAP bags

were placed on a PAC Table Top Vac/Gas Sealer Model No. PVTSG-24 (Packaging Aids

Corporation, San Raphael, CA). The equipment settings were Vacuum 4, Flush Gas 9,

Seal Time 11, and Cool Time 5. The flush gas was 3.97% oxygen, 10.0% carbon

dioxide, and balanced with nitrogen (BOC Gas, Riverton, NJ). The PAC Table Top

Vac/Gas Sealer pulls a vacuum and refills the pouch full with the flush gas, then seals

and cools before releasing. Bags were placed in ice in portable coolers and transported to

the electron beam irradiation facility (Florida Accelerator Services and Technology,

Gainesville, FL). Plastic trays were previously frozen with 1.5 cm of ice in them. Four

bags were taped to each tray with cantaloupe arranged in a single flat layer in order for all

pieces to receive equal dosage. Dosimeters were also attached to verify target dose had

been reached. The irradiator was set at 10 fpm and 0.5 kGy per pass. To achieve 1.0

kGy, the sample was passed through twice. Bags were removed from ice trays and

placed back in the ice cooler after desired number of passes. Samples were irradiated at

0, 0.5, or 1.0 kGy.









Packages were transferred back to the FSHN building and stored at 3 OC for the

duration of the experiment. Further testing was done on 1, 4, 6, 8, 11, 14, 18, and 20 d

for Trial 1 and on 1, 4, 6, 11, 15, 18, and 20 d for Trial 2.

A closed system experiment was also run with the same fruit to produce a rapid

method for respiration rate prediction equation determination. Pieces (-300g) were also

placed in quart Ziploc (S.C. Johnson & Son, Inc., Racine, WI) Freezer bags and sealed

after expulsion of most air. The bags were handled in the same way as the modified

atmosphere packages above and irradiated at 0.5, or 1.0 kGy.

The pieces (-300g) of each bag were then placed in a 1-quart Ball Mason Jars

(Alltrista Corporation, Indianapolis, Indiana). Jars and lids were sanitized with a Better

Built Turbomatic washer and dryer. Lids were drilled with a 3/8" hole directly in the

middle. Parafilm (American National Can, Menasha, WI) was wrapped around the top of

the jar before applying the lid to assure a gas tight seal. Jars were stored at 3 OC for the

duration of the experiment. Rubber stoppers were placed in the hole in the lid to create a

closed system immediately upon closing the jar. Gas samples were taken every 4 to 12

hours throughout a 14 day storage duration.

Dosimetery

Radiographic dosimeters were placed under bags of cantaloupe, flat on the trays

and on top of bags. Gafchromic MD-55 from International Specialty Products (Wayne,

NJ, USA) were cut into lxl cm squares, placed in small envelopes and taped into place.

The dosimeter film was allowed to expose for 24 hrs and then read on a

spectrophotometer at a wavelength of 510 nm. The per pass average was determined by

averaging the dose received on top of the bag with that below the bag.









Gas Analysis

Headspace analysis was done by sampling gas composition of bags or jars for

contents of 02 and CO2 using an 02 and CO2 analyzer (Checkmate 9900, PBI-Dansensor,

Ringsted, Denmark). Septums of 1.3 cm diameter were placed on all bags. Rubber

serum stoppers were placed in the hole in the jar lids. The Checkmate sampling needle

was inserted through the septum or stopper. The 02 and CO2 percentages were recorded

when readings stabilized. All gas samples were taken in the cold storage room.

Microbial Analysis

Cantaloupe (-20 g) were aseptically removed from the packages and placed in

sterile stomacher bags. Samples were diluted 1:10 with phosphate buffer (1:800, pH 7.2)

and stomached for 30 seconds. Further 1:10 dilutions were carried out by adding 1 ml to

9 ml of phosphate buffer in dilution tubes and vortexing for 30 seconds. Aerobic Plate

Count and Yeast and Mold Plate Count Petrifilm (3M Corporation, St Paul, MN) were

used as described by instructions for all dilutions tested. Petrifilms were incubated at 25

C for 4 days then quantified.

Sensory

Sensory analysis using descriptive analysis was conducted by sixteen panelists (8

male, 8 female, 21-45 years of age) who were students and staff of the University of

Florida, Food Science and Human Nutrition Department. The panelists were trained

during four, 1 hour sessions to recognize fresh and stored cantaloupe attributes, a week

before the first evaluation. Cantaloupes stored for different times, some vacuum sealed,

some exposed to air, some irradiated and fresh cantaloupes were given to panelists during

the first training session. The panelists were asked to write down all terms they felt

described the different samples. All panelists announced their descriptor terms and









discussed them. All terms were compiled and given to the panelists on the second

training date. Samples were analyzed again and through elimination and agreement, the

most important terms were finalized: appearance terms- orange and moist; texture terms-

firmness, mealy, juicy and crispness; and flavor terms- sweetness, cantaloupe flavor

intensity, off-flavor, pumpkin and overall acceptability.

In the third session, the panelists were given a practice ballot and rated the training

samples. Each attribute was rated using a 15 cm line scale with anchors at 13 mm from

each end, anchored with the terms high and low. Panelists were instructed to mark

anywhere on the line to rate the intensity. Panelists discussed their results and agreed that

the ballot covered all necessary terms. The panel also decided where typical or common

fresh-cut cantaloupe should be rated.

In the fourth session, panelists were given a practice ballot and rated cantaloupe

irradiated that day, as well as stored fresh and irradiated samples. Panelists rated samples

consistently with one another.

At each test date, panelists evaluated three samples (control, 0.5 kGy and 1.0 kGy).

Samples were coded with a three digit random number and served in small plastic cups

(2-3 pieces of cantaloupe). The panelists were provided with water and unsalted crackers

in a private booth equipped with a monitor, mouse and keyboard. The panelists marked

on the open line on the screen to indicate intensity ratings for each attribute. Compusense

five release C5R4.6 (Guelph, Ontario, Canada) was used to design and run all sensory

tests. All orders of presentation were presented once, then at random. The samples were

evaluated again for replication in the same manner after a short break by the panelist.









Color Analysis

Six cantaloupe pieces from each treatment were removed and placed on Styrofoam

plates. The color of the pieces was measured using a hand held Minolta Chroma Meter

CR-2006 (Minolta Camera Co., Osaka, Japan). The colorimeter was calibrated before

each use with a standard white plate (D65 Y = 94.4, x = 0.3158 and y = 0.3334). One

side of each cube was placed flush against the light source and the L*, a*, b* values were

measured. The L* refers to brightness from 0 = black to 100 = white. The a* is from

negative (green) to positive (red) and b* is from negative (blue) to positive (yellow).

Hue, the quality of color, which we describe by the words red, yellow, green, blue, etc.,

was calculated with the equation hue = arctan (b/a). Chroma, the quality describing the

extent to which a color differs from gray of the same value or lightness, was calculated

with equation chroma = (a2 + b2)1/2 (Billmeyer and Saltzman, 1966).

Texture

The texture of the cantaloupe was measured by an Instron Universal Testing

Instrument, model 4411 (Canton, Massachusetts). The six pieces that were analyzed for

color were used for texture. The cantaloupe pieces were placed under a plunger,

establishing zero force contact, with a diameter of 5.0 mm and compressed 3 mm with a

50 kg load cell. The plunger was driven into the piece with a crosshead speed of 30

mm/min. The maximum compression force was measured in kg.

Statistical Analysis

Non-sensory data was analyzed using analysis of variance in The SAS System

version 9e. The sensory data were analyzed two ways. In the first analysis, the data from

each storage time were analyzed separately by analysis of variance using SAS version 9e.









The model consisted of panelist effect, treatment effect, panelist*treatment interaction,

and replication effect.

In the second analysis, all data were analyzed as split plot design using analysis of

variance, with panelists as blocks, treatment as subplot, and storage time as whole plot.

Means were separated by Duncan's Multiple Range Test when a significant F value was

obtained (p=0.05). All other data (color, texture and micro) were subjected to analysis of

variance as a completely randomized design, with the model consisting of treatment

effect and storage time effect.

Results and Discussion

MAP Design

The first step in the design of the modified atmosphere package was the choice of

the Cryovac PD-900 film over the PD-961 EZ film. Quick analysis revealed that a large

amount of fresh-cut cantaloupe would be required to reach an equilibrium (maintenance

of desired internal atmosphere) of gases based on the low respiration rate of the fruit and

the higher transmission rate of the PD-961EZ film.

The internal atmosphere beginning conditions were chosen to be 4% 02 and 10%

CO2. These values of oxygen and carbon dioxide are both in the middle of the

recommended ranges for storing fresh-cut cantaloupe (Gorny, 2001). This allowed for

maximum unpredicted deviation in either direction, especially important for preventing

the growth of anaerobic organisms. Ideally, the internal atmosphere of the package

would stay very close to the flush gas composition.

With known respiration rates of the irradiated and non-irradiated fruit and

transmission rates of the film, the adjustable parameters were the amount of fresh-cut

cantaloupe and the surface area of film. A weight of 500 to 650 g of fresh-cut cantaloupe









was considered reasonable for the Cryovac trays provided. Based on the dimensions of

the tray, reasonable bag sizes were determined. Adjusting these two variables, a bag size

with total area of 0.135 m2 (0.32 mx 0.211 mx 2 sides) and a fruit weight of 625 g gave

satisfactory prediction results. One bag design was chosen for all treatments for

consistency in experimentation, with 02 and CO2 concentrations varying no more than +

2% in predicted headspace compositions. Figure 5.1 shows the predicted gas

compositions over 500 hours or -21 days for cantaloupe irradiated at 0.4 kGy. The 02

concentration steadily increased to just less than 5.9% and the CO2 concentration rose to

just below 10.6% in the first 300 hours and leveled off for the duration.


12


10





U, 02
a) 6
-02


a. 4


2


0
0 100 200 300 400 500 600
Hours

Figure 5.1. Predicted oxygen and carbon dioxide partial pressures for 0.4 kGy samples in
designed modified atmosphere package with initial gas flush of 4% 02 plus
10% CO2 for Trial 1 stored at 3 OC.









For the second trial, a bag size with total area of 0.13 m2 (0.203 m x 0.32 m x 2

sides) was used with a fruit weight of 520 g, which also gave satisfactory prediction

results. Figure 5.2 shows the predicted headspace compositions over 500 hours or -21

days for cantaloupe irradiated at 0.4 kGy. The 02 concentration steadily increased to just

above 5% and the CO2 concentration rose to just above 10% and remained constant for

the duration.


12


10


8

U 02
~.C 6 02

4 --O


2


0
0 100 200 300 400 500 600
Hours

Figure 5.2. Predicted oxygen and carbon dioxide partial pressures for 0.4 kGy samples in
designed modified atmosphere package with initial gas flush of 4% 02 plus
10% CO2 for Trial 2 stored at 3 OC.

Figures 5.3-5.6 show the %02 and %C02 across time for both trials. Lines in

between points are presumed patterns of gas behavior and not actual data. On Day 1 of

Trial 1, the %02 was approximately 5.7% for all treatments. Although a strong vacuum






82


was pulled on the bags and filled with 4% 02 plus 10% CO2 gas mixture, a small amount

of ambient air remained in the pockets and cavities created by the stacked fruit. The

composition of the air that remained was approximately 21% 02 and 0.0% C02, which

caused the initial internal atmosphere to be higher than 4% 02, which is seen in both

trials. This also leads to the expectation of the %C02 in the fill gas to be slightly diluted.

This was seen in Trial 2 but not Trial 1.

7


5
.4 s Control
4 + 0.5 kGy
3
2 1.0 kGy

1
0
0 5 10 15 20
Days
Figure 5.3. Actual oxygen partial pressures for all samples in designed modified
atmosphere packages for Trial 1 stored at 3 OC.


16
14
12
S 10 -.-- Control
O 8 0.5 kGy
6 1.0 kGy
4
2
0
0 5 10 15 20
Days

Figure 5.4. Actual carbon dioxide partial pressures for all samples in designed modified
atmosphere packages for Trial 1 stored at 3 OC.










12

10

8

6
4

2

0


SControl
--0.5 kGy
1.0 kGy


Days


Figure 5.5. Actual oxygen partial pressures for all samples in designed modified
atmosphere packages for Trial 2 stored at 3 OC.


12

10

S / -*-Control
o 6 0.5 kGy
., 1.0 kGy


0 5 10 15 20
Days


Figure 5.6. Actual carbon dioxide partial pressures for all samples in designed modified
atmosphere packages for Trial 2 stored at 3 OC.

In Trial 1, the %02 remained steady in the control through Day 6 and for the 0.5

kGy and 1.0 kGy through Day 8. The %CO2 slowly declined through Day 8 for all

treatments. The control %02 decreased from Day 6 to 11 and then climbed back up to

-6%. The control %02 was significantly the lowest on Day 8 and 11 (Table 5.1). The









%CO2 in the controls increased between Day 8 and Day 14 and was significantly the

highest on Day 11 and 14. These results are very similar to the open system results of

Chapter 1. A significant increase in respiration rate was seen in the non-irradiated

controls before the irradiated samples. The 1.0 kGy sample changed the least of all

samples maintaining the lowest respiration rate. The lower respiration rates of irradiated

samples are linked to the reduction of metabolic activity, with the higher the dose the

larger the reduction (Benoit and others, 2000; Aljouni and others, 1993). Increase in

respiration rate after 7-9 days of storage at 5 OC of fresh-cut cantaloupe was observed by

Aguayo and others (2004). This data is also in agreement with results from Luna-

Guzman and Barret (2000), Bai and others (2001), and Madrid and Cantwell (1993).

Possible reasons reported were microbial growth and/or general deterioration of tissue

due to senescence.

In Trial 2, all treatments %02 behaved very similarly through Day 11 (Table 5.1).

The %02 in the control dropped while the %02 in the irradiated samples increased after

Day 8. The %C02 remained similar through Day 11 although significantly different on

Day 1 through Day 6, it is presumed to be due to a replication effect at each time. The

effect of treatment was clearly seen after Day 11, when the consumption of 02 and

evolution of CO2 was significantly much higher in the controls. Similar results were

found with cut iceberg lettuce, where irradiated samples (0.2 and 0.45 kGy) had higher

respiration rates on Day 1 and lower on Day 13 (Hagenmaier and Baker, 1997).

Figures 5.7 and 5.8 compare predicted vs. actual internal atmospheres of packages.

In Trial 1, the oxygen prediction and experimental data are in good agreement with very









similar values for 8 days. The carbon dioxide predicted slowly rose to just under 11%

and the actual level dropped to just under 8%.

Table 5.1. Headspace composition of modified atmosphere packages of irradiated and
non-irradiated fresh-cut cantaloupe stored at 3 OC. Means within a column
sharing the same letter are not significantly different (p<0.05).
Trial 1


Control
0.5kGy
1.OkGy




Control
0.5kGy
1.OkGy


Trial 2


Control
0.5kGy
1.OkGy




Control
0.5kGy
1.OkGy


Day 1
5.7
5.8
5.7


Day 1
10
10
10


Day 1
5.5
5.3
5.4


Day 1
8.2 1
8.4
8.5


Day 4
5.5 a
5.6 a
5.4 a



Day 4
8.6 b
8.9 b
9.3 a


Day 4
6.2 a
5.9 a
6a



Day 4
6.8 b
7a
7.2 a


%02
Day 6
5.4 a
5.7 a
5.5 a

%C02
Day 6
8.2 a
8a
8.1 a


%02
Day 6
6.9 a
6.7 a
6.3 a

%C02
Day 6
6.1 c
6.3 b
6.5 a


Day 8
3.9 b
5.7 a
5.7 a



Day 8
7.6 a
7.7 a
7.7 a


Day 11
9.1 a
9.4 a
8.9 a



Day 11
4.8 a
4.8 a
5 a


Day 11
0.1 b
3.9 a
4.9 a



Day 11
12 a
9.1 b
8.4 c


Day 15
4.5 b
11 a
10 a



Day 15
8.3 a
4.3 b
4.3 b


Day 14
0.7 b
1.1 b
2.1 a



Day 14
14 a
13 b
11 c


Day 18
1.3 b
11 a
11 a



Day 18
11 a
5.2 b
4.6 b


Day 18
4.4 a
3.8 a
3.2 a



Day 18
14 a
13 a
13 a


Day 20
6.1 a
5.2 ab
4.2 b



Day 20
13 a
13 a
13 a


Day 20
1.4 b
9a
9.6 a



Day 20
10 a
6.5 b
5.7 b


There are many reasons why the model may slightly differ from the experimental

results. First, the data collected for the model was from fresh-cut cantaloupe irradiated in

Ziploc bags with ambient air and then transferred to jars of ambient air, whereas the

experimental data is from fresh-cut cantaloupe irradiated and stored in a bag with 4%


oxygen and 10% carbon dioxide.











10
,- ---Oxygen 0.4 kGy
c __ (predicted)
IU Oxygen 0.5 kGy
S 6 (experimental)
W Carbon dioxide 0.4
c 4 kGy (predicted)
0 Carbon dioxide 0.5
) 2 kGy (experimental)

0
0 5 10
Days


Figure 5.7. Trial 1 Predicted and observed oxygen and carbon dioxide levels inside
designed modified atmosphere package containing irradiated fresh-cut
cantaloupe stored at 3 OC.

Therefore, the closed system generated a unique set of gas concentrations starting

with high oxygen and low carbon dioxide and progressing to low oxygen and high carbon

dioxide. The modified atmosphere packages maintained a low oxygen and high carbon

dioxide headspace that was not observed in the closed system. This must be taken into

consideration when designing a package based on closed system experiments. As seen

from the data above, a package can be designed to maintain gas concentrations within

critical ranges from closed system data. Second, closed system data was from samples

irradiated at 0.4 and 0.6 kGy, and irradiation of these packages was 0.5 kGy. A

limitation of irradiation was exposed here. The exact dosage of electron beam irradiation

is difficult to achieve. Many variables come into play when trying to treat a product with

a low dose. All settings in an irradiation facility may be the same as the day before, but a

different dose may occur when running a very similar experiment. Not only does the

actual irradiation emitted change, but the product composition, temperature, thickness