Food Biochemistry and Food Processing

(Ben Green) #1

21


Biochemistry of Fruits


G. Paliyath and D. P. Murr

487

Introduction
Biochemical Composition of Fruits
Carbohydrates, Storage, and Structural Components
Lipids and Biomembranes
Proteins
Organic Acids
Fruit Ripening and Softening
Carbohydrate Metabolism
Cell Wall Degradation
Starch Degradation
Glycolysis
Citric Acid Cycle
Gluconeogenesis
Anaerobic Respiration
Pentose Phosphate Pathway
Lipid Metabolism
Proteolysis and Structure Breakdown in Chloroplasts
Secondary Plant Products and Flavor Components
Isoprenoid Biosynthesis
Anthocyanin Biosynthesis
Ester Volatile Biosynthesis
General Reading
References


INTRODUCTION


Fruits and various products derived from fruits are at
the center stage of human dietary choices in recent
days, specifically because of various health benefits
associated with the consumption of fruits and fruit
products. The selection of trees that produce fruits
with ideal edible quality has proceeded throughout
human evolution. Fruits are developmental manifes-


tations of the seed-bearing structures in plants, the
ovaries. After fertilization, the hormonal changes
induced in the ovary result in the development of the
characteristic fruit, which may vary in ontogeny,
form, structure, and quality. Pome fruits such as ap-
ple and pear are developed from the thalamus in the
flower. In general, drupe fruits such as cherries,
peaches, plums, and apricots are developed from
the ovary wall (mesocarp) enclosing a single seed.
Berry fruits such as tomato possess seeds embedded
in a jelly-like pectinaceous matrix, with the ovary
wall developing into the flesh of the fruit. Cucum-
bers and melons develop from an inferior ovary.
Citrus fruits belong to the class hesperidium, where
the ovary wall develops as a protective structure sur-
rounding the juice-filled locules, which are the edi-
ble part of the fruit. In strawberry, the seeds are
located outside the fruit, and it is the receptacle of
the ovary (central portion) that develops into the edi-
ble part. The biological purpose of the fruit is to
attract vectors that help in the dispersal of the seeds.
For this, the fruits have developed various organ-
oleptic (stimulatory to organs) characteristics that
include attractive color, flavor, and taste. The bio-
chemical characteristics and pathways in the fruits
are structured to achieve these goals. The nutritional
and food qualities of fruits arise as a result of the
accumulation of components derived from these in-
tricate biochemical pathways. In terms of produc-
tion and volume, tomato, orange, banana, and grape
are the major fruit crops used for consumption and
processing around the world (Kays 1997).

Food Biochemistry and Food Processing
Edited by Y. H. Hui
Copyright © 2006 by Blackwell Publishing
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