EFFECT OF PREFREEZING TREATMENTS ON QUALITY OF MANGO (Manguifera Indica L.) DURING FROZEN STORAGE by ANGELA RINCON (Under the direction of William L. Kerr) ABSTRACT At the moment there is a high demand for high-quality fruit ingredients to be used in many food formulations such as pastry and confectionery products, ice cream, frozen desserts and sweets, fruit salads, cheese and yoghurt. The overall objective was to improve quality of frozen mango using two types of food cryoprotection: one was the reduction of water content of the fruit (osmotic dehydration) and the other was the formulation of mango pulp with carbohydrates of different molecular weight to increase frozen stability. Osmotic dehydration was able to modify quality parameters of slices before and after frozen storage. Values for some parameters such as vitamin C, lightness (L*), chroma (C*), and firmness for non osmotically dehydrated slices were significantly higher than osmotically dehydrated slices. However, treatments carried out with osmotic solutions (especially those with high concentrations of sucrose) improved significantly the quality of mango slices after frozen storage. Higher moisture losses and solid gain values were reported for slices from the highest osmotic solution concentration. Thus, slices dipped in 30oBrix were better protected against freezing damage. Effects of sucrose concentration on the slices and ripening stage on frozen-thawed mango flavor perception were determined. Six flavor descriptors (color, flavor, sweetness, sourness, firmness and juiciness) were evaluated by a sensory trained panel. All descriptors were affected by sugar content and ripening stage. To study the effect of mango fruit composition on frozen stability, five pulp samples were prepared and evaluated in terms of glass transition temperature modification and its influence on ascorbic acid retention. State diagrams and sorption isotherms were determined in order to predict freezing storage conditions for the pulps. Glass transition temperature was found to be a function on the composition of the mixture of carbohydrates present on the pulps. As the molecular weight of carbohydrates used for the pulps formulation increased, so did T’ . Maltodextrin M150, which had the highest T’ value, had g g the highest protective effect on ascorbic acid degradation. However, knowledge of T’ alone was g not sufficient to know whether a cryoprotectant is a good cryostabilizer or not. Sensory and textural analysis were recommended in addition to evaluate cryoprotectan effects during frozen storage. INDEX WORDS: Osmotic dehydration, Mango, Quality, Frozen Storage, Thawing, Texture, Sensory Evaluation, Ripeness, Glass Transition Temperature, State Diagram, Sorption Isotherm, Water Activity, Sugar Composition. EFFECT OF PREFREEZING TREATMENTS ON QUALITY OF MANGO (Manguifera Indica L.) DURING FROZEN STORAGE By ANGELA RINCON B.S., America University, Bogota, Colombia, 1999 A Thesis submitted to the Graduate Faculty of The University of Georgia in partial fulfillment on the Requierements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2004 © 2004 Angela Rincon All Rights Reserved EFFECT OF PREFREEZING TREATMENTS ON QUALITY OF MANGO (Manguifera Indica L.) DURING FROZEN STORAGE By ANGELA RINCON Major Professor: William L. Kerr Committee: Robert L. Shewfelt Philip E. Koehler Electronic Version Approved: Maureen Grasso Dean of The Graduate School The University Of Georgia December 2004 DEDICATION I dedicate this thesis to my father, who will live in my heart forever, to my mother and to my sister for their encouragement, love and support. iv AKNOWLEDGEMENTS I am deeply grateful to my major professor Dr. William Kerr for his guidance and encouragement on the development of this project. I also thank Drs. Robert Shewfelt and Philip Koehler for been part of my graduate advisory committee. I also want to express my gratitude to Dr. Milena Corredig who gave me the priceless opportunity to be part of the department of Food Science and Technology. Thanks to my dad for giving me the strength, encouragement and inspiration for the completion of this degree. Thanks to my mom and my sister for their love, this thesis is a symbol of the realization of many of our hopes. I also want to specially thank my uncle Dr. Pedro Villegas for his constant support and for being a model for me and my family, and Angela Villegas for her friendship, hospitality and valuable advices. Thanks to my grandmother Leonor Villegas for being a support and a model of love for the family. I thank my boyfriend Ivan Alvarado for his love and his incredible support when hard times came into my life. I have learned a lot from life being by his side. My appreciation and thanks to Maureen Bishop and Jin Yinhee for their friendship and assistance in the laboratory. I also want to share this achievement with my friends in the department of Food Science and Technology at the University of Georgia (Danitza, Lashkmi…). Finally, I think that this accomplishment would have never been possible without God. Thanks for giving me the opportunity that changed my life!! v TABLE OF CONTENTS Page ACKNOWLEDGEMENTS.............................................................................................................v CHAPTER 1. INTRODUCTION………………………………………………………………………...1 2. LITERATURE REVIEW…………………………………………………………………8 3. INFLUENCE OF OSMOTIC DEHYDRATION, RIPENESS AND FROZEN STORAGE ON PHYSICOCHEMICAL, OPTICAL AND MECHANICAL PARAMETERS OF MANGO (Manguifera Indica L.)………………………………………………………..51 4. SENSORY CHARACTERISTICS OF MANGO FRUIT FROM THREE RIPENING STAGES AFTER OSMOTIC DEHYDRATION AND FROZEN STORAGE…………80 5. THE INFLUENCE OF CARBOHYDRATE COMPOSITION ON VITAMIN C STABILITY, PHASE AND STATE TRANSITIONS OF FROZEN MANGO PULP..106 6. CONCLUSIONS……………………………………………………………………….142 v i CHAPTER 1 INTRODUCTION Consumer demand has increased for processed products that keep more of their original characteristics. In industrial terms, this requires the development of operations that minimize the adverse effects of processing [1]. Freezing of fruits can result in reduced quality, due to inferior texture and enzymatic action [2]. The consequence is, that during frozen storage, a gradual cumulative and irreversible loss of quality occurs in time [3]. Freezing damage is a consequence of many separate processes such as solute concentration damage, dehydration damage, and mechanical damage from ice crystals[4]. However, there are two possibilities for achieving good protection against freezing damage [5]. One is the reduction in the water content of the product before freezing in order to decrease the amount of crystals formed during this process and thus, minor damage of the cellular membranes occurs and a better conservation of the fruit is assumed [6]. The concentration step is generally realized by air drying [7], osmotic dehydration [8], or a combination of both [9]. Another is the formulation of food with appropriate ingredients to elevate the glass transition temperature (T’ ) of the food which is relative to the freezing g temperature (T), enhancing the product stability [10]. f The dehydration pre-freeze treatments are a useful tool to reduce or avoid the detrimental phenomena of loss of cellular structure and exudates loss at thawing, caused by the physical and chemical actions of freezing of food tissues [11]. While some treatments such as freezing have primarily a stabilizing effect, other steps such as partial dehydration allows structural, nutritional, sensory and other functional properties of the raw material to be modified [12]. Osmotic dehydration, better defined as dewatering impregnation soaking in concentrated solutions (DIS) 1 [13], can also allow cryoprotection of the cell during freeze-thawing process. The stability of frozen fruits during process and storage could be dependent upon the ability to store the food at a temperature less than its glass transition temperature or the ability to modify the food formulation to increase glass transition temperatures above storage temperature [14]. Cryostabilization provides a means of protecting products, storing for long periods at typical freezing temperatures (-18oC) from changes in texture, structure and chemical composition [5]. Storage of frozen fruits at temperatures below the glass transition temperature (T’ ) can improve the stability of the thawed product greatly, but this would require very low g temperatures in the freezer (e.g. -50oC). T’ is a function of the molecular weight of water g compatible monomers, oligomers and high polymers [10]. The selection of the ingredients in a fabricated product allows the food manufacturer to manipulate T’ and thus, deliberately g formulate the raising of T’ relative to T, enhancing the food stability [15]. g f Mango is the most heavily produced tropical fruit in the world comprising 40% of the tropical fruit production in 1999 [16]. This climacteric fruit has three defined periods [17], and it is highly perishable, due to, among other causes, the activity of degradative enzymes (such as polygalacturonase and cellulase), that are activated in the maturation period, causing reduction of dietary fiber content [18], and softening of the fruit [19]. Mangoes have poor storage qualities and few technologies for longer term storage. Storage methods for mango have been characterized by variable results and the occurrence of physiological disorders [20]. In spite of this, mangos are more and more appreciated by consumers, not only as fresh fruit but also as an ingredient in processed products such as dairy, ice creams, fruit salads or snacks. Mango processing that maintains the product freshness lengthening its shelf life in the market, would be very convenient to increase commercialization in the non-producing countries [21]. 2