Nutrient Loss 237
8.7 FACTORS INFLUENCING NUTRIENT CONTENT
OF FRUITS AND VEGETABLESNutrient content of fruit and vegetables is influenced by many factors such as stage
of maturity, degree of ripeness, storage and handling conditions, and packaging
materials and methods.
8.7.1 MATURITY AND RIPENESS
During maturation, the last stage of development, fruits and vegetables attain full
size and optimum eating quality. Ripening is the terminal period of maturation when
fruits develop the flavor, texture, and aroma that contribute to optimum eating quality.
Thus, a fruit can be mature but unripe, and indeed many fruits are harvested while
mature but unripe. This process is accompanied by softening, loss of astringency,
biosynthesis of aroma volatiles, and conversion of starch to sugar. The ripening
process in climacteric fruits is usually initiated by a growth regulator, ethylene.
Ethylene, which is physiologically synthesized in the fruit, must reach a certain
concentration/level before the ripening process can be triggered (Klein, 1989;
Saltveit, 1999). Some growth regulators in fruits have been shown to promote
ethylene synthesis. During the course of ripening, enzymes are synthesized that are
used in the ripening process, but the enzymes cannot act until enough ethylene is
present (Ryall and Pentzer, 1974). The stage of maturity of a fruit has a big influence
on the nutritional quality. A substantial amount of research has been done on the
composition of fruits and vegetables at different stages of development, mostly on
apples and pears, but also on various other fruits and vegetables.
The important changes as the fruit goes through the last stages of maturity and
ripening, including an increase in sugars; a decrease in acidity; a decrease in starch
(apples, pears, and bananas); an increase in oil content in the case of avocados and
nuts; changes in pectic constituents that result in softening, loss of tannins, and
astringency; development of volatiles that contribute to flavor and aroma; formation
of pigments in the skin and flesh; loss of the green pigment chlorophyll in the skin
and flesh; an increase in ascorbic acid followed by a decrease; and an increase in
β-carotene (provitamin A) (Watada et al., 1976). For example, the β-carotene (pro-
vitamin A) content of tomatoes has been shown to vary directly with the ripeness
of the fruit at harvest (Watada et al., 1976). However, fruits harvested mature-green,
the stage at which most fresh market tomatoes are harvested, did not differ in vitamin
A activity among various cultivars. The skin of many fruits also develops wax as
they mature, giving the fruit protection against moisture loss. The percentage of
soluble solids increases in fruits as sugar content increases. Some of these properties
of fruits have been used as indices for harvest maturity and standardization for
marketing. Notably, the sugar:acid ratio of citrus fruits, oil content of avocados,
sugar content of grapes, and the firmness of the flesh and color of pears, peaches,
and plums have been used as indices for nutritional and market quality (Aked, 2002).
Vegetables for fresh use and for processing should be of a satisfactory size and
texture. Optimum maturity differs depending on the type of vegetable and the method