Table Of ContentQuality Factors of Fruits
and Vegetables
In Quality Factors of Fruits and Vegetables; Jen, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
In Quality Factors of Fruits and Vegetables; Jen, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
405
ACS SYMPOSIUM SERIES
Quality Factors of Fruits
and Vegetables
Chemistry and Technology
Joseph J Jen
The University of Georgia
Developed from a symposium sponsored
by the Division of Agricultural and Food Chemistry
at the 196th National Meeting
of the American Chemical Society,
Los Angeles, California,
September 25-30, 1988
American Chemical Society, Washington, DC 1989
In Quality Factors of Fruits and Vegetables; Jen, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Library of Congress Cataloging-in-Publication Data
Quality factors of fruits and vegetables
(ACS symposium series, ISSN 0065-6156; 405)
"Developed from a symposium sponsored by the
Division of Agricultural and Food Chemistry at the 196th
National Meeting of the American Chemical Society, Los
Angeles, California, September 25-30, 1988."
Includes bibliographical references.
1. Fruit—Quality—Congresses. 2. Vegetables—
Quality—Congresses. 3. Food—Analysis—Congresses.
4. Food—Sensory evaluation—Congresses.
I. Jen, Joseph J., 1939- . II. American Chemical
Society. Division of Agricultural and Food Chemistry.
III. American Chemical Society. Meeting (196th: 1988:
Los Angeles, Calif.) IV. Series.
TX557.Q35 1989 664'.807 89-17684
ISBN 0-8412-1663-0
Copyright © 1989
American Chemical Society
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In Quality Factors of Fruits and Vegetables; Jen, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
ACS Symposium Series
M. Joan Comstock, Series Editor
1989 ACS Books Advisory Board
Paul S. Anderson Mary A. Kaiser
Merck Sharp & Dohme Research Ε. I. du Pont de Nemours and
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Purdue University
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Dow Chemical Company
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University of Iowa
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Conoco Inc.
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In Quality Factors of Fruits and Vegetables; Jen, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Foreword
The ACS SYMPOSIUM SERIES was founded in 1974 to provide a
medium for publishin
format of the Serie
IN CHEMISTRY SERIES except that, in order to save time, the
papers are not typeset but are reproduced as they are submitted
by the authors in camera-ready form. Papers are reviewed under
the supervision of the Editors with the assistance of the Series
Advisory Board and are selected to maintain the integrity of the
symposia; however, verbatim reproductions of previously pub
lished papers are not accepted. Both reviews and reports of
research are acceptable, because symposia may embrace both
types of presentation.
In Quality Factors of Fruits and Vegetables; Jen, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Preface
QUALITY OF RAW AND PROCESSED FRUIT AND VEGETABLE PRODUCTS
are sometimes elusive factors and may differ from person to person
based on individual tastes. However, there is no doubt that consumers
want high-quality foods in our fast-moving society. Consumers want
convenient, fresh, light, and nutritious products for their diets. Fruits
and vegetables fit in th
who work with fresh an processe vegetable
high-quality products to consumers economically. It was with this
thought in mind that I organized the symposium on which this book is
based.
I had a second motive in organizing this symposium on quality factors
of fruits and vegetables. Literature and research reports on the subject
appear in many different places: in journals and books that cover food
science, food technology, plant physiology, plant pathology, horticulture,
agricultural sciences, agricultural engineering, and packaging. One
cannot gather the vast amount of information on the quality of fruits
and vegetables in one volume. However, I hope this book can serve as an
important starting reference for researchers working in this field. It may
also serve as a textbook for students interested in fresh and processed
fruits and vegetables.
The book is separated into six sections and 30 chapters. An overview
chapter is provided to introduce the subject. The first three sections deal
with the chemical aspects of the three major quality factors of fruits and
vegetables, that is, color, flavor, and texture. The next three sections deal
with the technological aspects of quality factors of fresh and processed
fruits and vegetables: Section four deals with storage and light processing
of fresh produce; section five deals with quality improvement of further
processed fruits and vegetables; and section six deals with some of the
newer technology used in this field.
With 30 chapters and multiple authors in this book, it is unavoidable
that some minor duplication of coverage may occur. The
comprehensiveness of each chapter will differ. Nevertheless, all authors
are well-known researchers in their respective fields or have published
extensively in the subject. I hope that cross-fertilization among the
authors can help the growth of this scientific field.
xi
In Quality Factors of Fruits and Vegetables; Jen, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Acknowledgments
I want to thank many people for assisting me in bringing this book to
fruition. I want to thank the authors for presenting the papers and for
their cooperation in completing the chapters in a timely manner. Also,
more than 50 scientists served as reviewers. Their comments contributed
greatly to the quality of the book. The editors of the ACS Books
Department worked patiently with me. My wonderful, diligent secretary,
Beth Knight, assisted in the handling of the manuscripts. Last, but not
least, I appreciate the financial assistance provided by the Financial
Committee of the Division of Agricultural and Food Chemistry of the
American Chemical Society, the Agricultural Research Division of
Campbell Soup Company, the Basic Research Division of Kraft, Inc.,
and the Research and Developmen
Company.
JOSEPH J. JEN
Department of Food Science and Technology
The University of Georgia
Athens, GA 30602
April 25, 1989
xii
In Quality Factors of Fruits and Vegetables; Jen, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Chapter 1
Chemical Basis of Quality Factors in Fruits
and Vegetables
An Overview
Joseph J. Jen
Department of Food Science and Technology, The University of Georgia,
Athens, GA 30602
Color, flavor, texture
generally recognized as the four quality factors of
fruits and vegetables. The natural pigments,
chlorophylls, carotenoids and anthocyanins, form the
chemical basis of color. Enzymatic and non
-enzymatic browning contribute to coloring of certain
processed fruits and vegetables. Various volatile
aroma and nonvolatile compounds give fruits and
vegetables special flavors. Cell wall components and
turgor pressure are the two entities that provide the
texture of fruits and vegetables. Pectic substances
and pectic enzymes are closely related to firmness
and softening of many fruits and vegetables.
Celluloses and lignins are associated with toughness
and woody texture. The roles of hemicelluloses and
extinsins in fruits and vegetables are not clear.
Vitamin C and minerals are the major nutrients of
fruits and vegetables. Processing often alters the
quality of fruits and vegetables but does not change
the chemical basis underlining the factors.
Fruits and vegetables constitute an important part of the human
diet. It is one of the four major groups of food our body needs to
ingest daily. The current consumer trend is towards fresh,
natural, minimally processed, and, yet, convenience foods. This
situation increases the opportunities for this segment of diet to
play an increased role in our health and well-being. Consumers
purchase foods on the basis of quality. To improve quality of
fruits and vegetables, we must understand the chemical basis of the
quality factors. Many books and chapters have been written on food
quality although few have been devoted solely on fruits and
vegetables (1, 2). Brief summaries of the subject matter can
usually be found in food chemistry books (3). The purpose of this
chapter is to provide an overview of the chemical bases of quality
0097-6156/89/0405-0001$06.00/0
c 1989 American Chemical Society
In Quality Factors of Fruits and Vegetables; Jen, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
2 QUALITY FACTORS OF FRUITS AND VEGETABLES
factors in fruits and vegetables. Subsequent chapters will provide
detailed information on many specific topics. The flavor and
nutritive value of foods are often the subject of many symposia and
books. This volume will emphasis color and texture of fruits and
vegetables.
Color
With few exceptions, the coloring matters of fruits and vegetables
belong to one of the following four categories of chemical
compounds (4):
1. Tetrapyrrole derivatives: chlorophylls, pheophytins
2. Isoprenoid derivatives: carotenoids, xanthophylls
3. Benzopyran derivatives: anthocyanins, flavonoids, and
related compounds
4. Certain artifacts
The first three groups are natural pigments while the last group is
reaction products of enzymatic and non-enzymatic browning reactions
from natural physiological changes or from processing of fruits and
vegetables.
The chlorophylls are responsible for the green color of nearly
all fruits and vegetables. The isomers, chlorophyll a. and
chlorophyll b^, exist in a 3:1 ratio in higher plants. They have
slightly different visible spectra and color shades. Chlorophylls
are magnesium-chelated tetrapyrroles with an esterified 20 carbon
alcohol, phytol. The phytol gives the pigments a unique ability to
be embedded in the cell organelle chloroplasts. The naturally
existing chlorophyllases can convert chlorophylls to water-soluble
chlorophyllides, without the phytol, but do not significantly alter
the green color. Acidic conditions can cause the replacement of
hydrogen for magnesium and make the chlorophylls into pheophytins.
The pheophytins are brown in color and are normally undesirable in
most foods. The loss of green color in green vegetables is an
important problem in certain thermal processing operations.
The chlorophyll chemistry has been the subject of several
investigations. The conversion of chlorophylls to pheophytins
follows first-order reaction kinetics (5). The photooxidation of
chlorophylls have slow reaction rates (6). Organic acids released
from the destruction of intact cells can cause conversion of
chlorophylls to pheophytins in processed plant foods. Acids are
also formed during processing of certain green leafy vegetables
(7). Various methods developed to preserve the green color of
processed food have undesirable effects of one form or another.
Green metallocomplexes of chlorophyll derivatives formed during
thermal processing offer a possible solution to some vegetables.
A chapter dealing with this subject is included in this book.
The carotenoids are a group of lipid-soluble pigments
responsible for the yellow, orange, and red color of many fruits
and vegetables. Most plant foods contain a variety of carotenoids
that differ mainly in their content of double bonds and oxygen
atoms. The mevalonic acid pathway derived isoprenoids may also
occur in combination with reducing sugars via glycosidic bonds.
In Quality Factors of Fruits and Vegetables; Jen, J.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
