NUTRITIONAL EVALUATION OF OSMOTIC AND ... EVALUATION OF OSMOTIC AND NON-OSMOTIC SOLAR GREENHOUSE...

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  • Nutritional evaluation of osmotic and non-osmotic solar greenhouse dehydrated peaches

    Item Type text; Thesis-Reproduction (electronic)

    Authors Abougou, Jean-Claude

    Publisher The University of Arizona.

    Rights Copyright is held by the author. Digital access to this materialis made possible by the University Libraries, University of Arizona.Further transmission, reproduction or presentation (such aspublic display or performance) of protected items is prohibitedexcept with permission of the author.

    Download date 09/07/2018 18:36:51

    Link to Item http://hdl.handle.net/10150/566323

    http://hdl.handle.net/10150/566323

  • NUTRITIONAL EVALUATION OF OSMOTIC AND NON-OSMOTIC SOLAR GREENHOUSE

    DEHYDRATED PEACHES

    byJean-Claude Abougou

    A Thesis Submitted to the Faculty of theDEPARTMENT OF NUTRITION AND FOOD SCIENCEIn Partial Fulfillment of the Requirements

    For the Degree ofMASTER Of "SCIENCE

    In the Graduate CollegeTHE UNIVERSITY OF ARIZONA

    1 9 8 0

  • /

    STATEMENT BY AUTHOR

    This thesis has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

    Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the copyright holder.

    SIGNED: V V f - r Is ff'A.

    APPROVAL BY THESIS DIRECTORThis thesis has been approved on the date shown below:

    Asst. Professor of Nutrition and Food Science

  • To my mother who taught me the basic principles of reading and writing. To my father who has always emphasized the importance of education to me.

    iii

  • ACKNOWLEDGMENTS

    The author wishes to express his thanks to Dr.Ralph L. Price for his guidance, encouragement, helpfulsuggestions and constructive criticisms throughout the elaboration of this thesis.

    Acknowledgment is made to Dr. Warren J. Stull andDr. James W. Berry for their helpful assistance in correcting the manuscript, thus allowing the final achievement of this thesis.

    Special thanks to the staff of the African American Institute who have provided funds for my education in the U.S.A.

    Deepest appreciation to my brothers and sisters for their notion of unity.

    Unlimited thanks to Miss Dyer (my nurse) for her understanding, encouragement and love.

  • TABLE OF CONTENTS

    PageLIST OF TABLES...................... . . . viLIST OF ILLUSTRATIONS................................ viiABSTRACT............................................. viii

    CHAPTER1. INTRODUCTION ................................. 12. LITERATURE REVIEW ............................. 4

    Importance of Chemical Analyses .......... 4Factors Affecting the Quality of RawFruits and Vegetables ................. 7

    Effects of Food Preparation on the Qualityof Fruits and Vegetables.............. 10

    Effects of Water Removal and Storage on theQuality of Fruits and Vegetables . . . . 14

    3. MATERIALS AND METHODS.................... .. . 28Preparation and Dehydration of Autumn Gem

    Peaches .......................... 28Methods of Analyses .............. 30

    Moisture, Sulfur Dioxide and 3-caroteneAnalysis . . . . . . . 30

    Titratable Acidity Analysis .......... 31Sugar Analysis .................... 31Ascorbid Acid Analysis .............. 34

    4. RESULTS AND DISCUSSION .............. 395. CONCLUSION ................................. 53

    LIST OF REFERENCES . . ................ 56

    v

  • LIST OF TABLES

    Table Page1. Relation of ascorbic acid content to ripeness

    of peaches . . . . . . . . . 92. Preparation of standard solution of ascorbic

    acid .................... . . . . . . . . . 363. Moisture and solid contents of fresh and dried

    peaches................. .................. 404. Free sulfur dioxide levels of dried peaches . . 425. Titratable acidity in fresh and dried

    peaches ...................... 446. Ascorbic acid content of fresh and dried

    peaches................. ................... 477. Sugar content of osmotic and non-osmotic dried

    peaches.............................. 498. Provitamin A content of fresh and dried

    peaches................. ................... 51

    vi

  • LIST OF ILLUSTRATIONS

    Figure Page1. Moisture Content versus Water Activity Curve

    for Foods in General, Showing the TypicalSorption Isotherm Behavior in the LowerRegion.......... 21

    2. Relation between Water Activity and Rate ofDestruction of Ascorbic Acid ........ 24

    3. Retention of Ascorbic Acid in Processed Peas . 254. Flowsheet of the Processing of Osmotic and

    Non-osmotic Dried Peaches 295. GLC Standard Curves of Sugars 326. GLC Pattern of Standard Sugars , 337. GLC Pattern of Non-osmotic Tunnel Dried

    Peaches 338. Standard Cuver of Vitamin C . . . . . . . . . 37

    vii

  • ABSTRACT

    Chemical and nutritional changes were studied in osmotic and non-osmotic peaches dried in a greenhouse solar energy collector, in its adjacent tunnel, and in a control forced-air oven. A sharp decrease in the moisture contents of dehydrated fruits and a general increase in their solid quantities were noted. Osmotic dried peaches showed higher levels of total sugar than non-osmotic dried samples. An overall decrease in acid content was noticed. The lower acidity level of osmotic dried fruits in comparison to non- osmotic was probably a result of the leaching action of syrup during osmotic dehydration. The levels of sulfur dioxide were too low to protect ascorbic acid and g-carotene from oxidation. Osmotic dehydration was not superior to non-osmotic dehydration processing in retention of the nutrients g-carotene and ascorbic acid and tunnel dried peaches were superior in this regard to greenhouse dehydrated samples.

    viii

  • CHAPTER 1

    INTRODUCTION

    Generally foods are processed commercially for one of the following reasons: (1) to extend the shelf-life ofthe processed form, (2) to alter the characteristics of the products, (3) to separate components from the complex mixture of biochemicals, and (4) to improve the nutritional characteristics of the processed food.

    In the special case of processing fruits and vegetables to extend the shelf-life, several methods of drying are available; it is the responsibility of the food processor to choose the most appropriate one. Until recently the two most important bases for evaluation of adequacy of a processing method were the cost of the method and the quality of the product. More recently, two additional bases which have also been considered are energy utilization and waste generation (Lund 1979).

    Because of the rising fossil fuel costs, solar energy dehydration will be of increasing importance in the production of dried fruits. According to the United States Department of Energy, solar energy will certainly cover 50 percent of the energy requirement within agriculture by the

    1

  • year 2000 (ERDA 1975). Experiments currently underway at The University of Arizona have shown that collection of energy by greenhouse can be efficiently used for drying of peaches and apples (Price et al. 1979).

    Also of interest is the dehydration of fruits by osmosis. This method, used in the past for the drying of fruits and vegetables, consists of removing water from the aqueous hypotonic solution of a fruit or vegetable by placing it in a hypertonic solution of sugar. By itself, this method necessitates a low capital investment; however, it should be associated with another means of dehydration to lower the moisture level so that food is stable against enzymatic, microbial and chemical deterioration. Vacuum drying has been used in association with odmotic dehydration in a method called osmovac (Ponting 1966, 1973). This two-step method of drying is cheaper than freeze-drying but more expensive than vacuum-drying.

    In an effort to produce dried fruits at less cost, Price et al. (1979) have modified Ponting's osmovac process by substituting a less expensive drying method: solar energy greenhouse dehydration for the vacuum drying (second step). However, to ascertain the superiority of osmotic solar energy greenhouse dehydration over other methods of drying a second criteria should be used in addition to the

  • cost factor: quality evaluation of these dried fruitsshould be performed.

    Thus, the purpose of this thesis is to study the chemical and nutritional changes between osmotic and non- osmotic peaches dried in a greenhouse solar energy collector and in its adjacent tunnel, and in a control forced-air oven. To meet this objective, analysis of moisture, sugars, titratable acidity, ascorbic acid, g-carotene and sulfur dioxide were run on the above dried peaches.

  • CHAPTER 2

    LITERATURE REVIEW

    Importance of Chemical Analyses In general, the evaluation of thermal processing

    (i.e., solar greenhouse dehydration) with regard to quality factors can be done on two bases. First, nutrient retention of some thermolabile nutrients such as ascorbic acid and 3-carotene can be used as a criteria for the adequacy of a processing method. Second, color, texture and flavor deterioration can be used to evaluate a processing method. Lund (1979) showed that the temperature dependence of the destruction reactions of nutrients are quite similar to those of color, texture and flavor deterioration reactions.

    The chemical analyses utilized are important not only as indicators of the adequacy of the solar g