192 Produce Degradation: Reaction Pathways and their Prevention
Generally, appearance includes geometric and color characteristics. The determina-
tion of appearance may be made by visual observation and instrumental measure-
ments. Detailed general principles and discussion of appearance and its measurement
may be found in the classic monograph by Hunter (1975). Additional concepts related
to appearance were advanced by Hutchings (1999). Due to the large number of
attributes and their interdependence in the case of plant products it would be not
practical to attempt a comprehensive appearance description. Only attributes that
are critical to quality should be selected and determined. However, it should be kept
in mind that consideration of produce color alone without appropriate attention to
other attributes of appearance such as size, shape, surface characteristics, and others
might lead to superficial, incomplete, and erroneous judgments. In this chapter the
emphasis will be on chemical aspects of produce color. The major classes of com-
pounds contributing to the color of fruits and vegetables include carotenoids, chlo-
rophylls, benzopyran derivatives, and betalains.
7.2 CAROTENOIDS
The carotenoids are yellow, orange, and red pigments widely distributed in nature.
Most of the more than 100 million tons of annual production of these compounds
(Isler, 1971) takes place in the oceans via synthesis by seaweeds and algae. On land,
carotenoids are formed by plants and almost always occur together with chlorophylls.
The importance of these compounds comes from their multifarious functions, includ-
ing light energy absorption, protection against photosensitized oxidation, and oxygen
transport. Carotenoids are also singlet oxygen quenchers and regulators of plant
growth. A separate area of interest is the role of these compounds in nutrition,
promoting health and disease prevention. Some carotenoids are vitamin A precursors.
The provitamin A activity remains the most important function of a selected group
of carotenoids, especially beta-carotene (see Figure 7.1). Vitamin A deficiency is
still a cause of blindness, premature death, and other health problems in numerous
underdeveloped countries. In recent years attention of many researchers has been
focused on carotenoids as compounds preventing development of cancer and heart
diseases. An important aspect of carotenoids is their contribution to the aesthetic
value of food. In produce, carotenoids make up a class of pigments contributing to
the beautiful yellow to red spectrum of colors stepwise synthesized during the
development stages of fruits and vegetables, culminating in ripening, and degrading
during senescence. Genetic nature, environmental conditions, and agricultural cul-
tivation practices significantly influence the qualitative and quantitative composition
of carotenoids in produce. Postharvest treatments, packaging, industrial processing,
and storage affect retention and changes of these compounds in food products.
FIGURE 7.1β-Carotene.