Pigments in fruits

Flavonoids are a large class of plant natural products of low molecular weight. Over 3,000 different flavonoids have been chemically characterised and novel ones are still being reported. Flavonoids are aromatic molecules synthesised from the amino acid phenylalanine and an acetate-derived precursor as malonyl-coenzyme A (Fig. 11.1) (Winkel-Shirley 2001). This reaction is carried out by the enzyme chalcone synthase (CHS) to produce chalcone. The chalcone can subsequently be isomerised by the enzyme chalcone flavone isomerase (CHI) to yield a flavanone. From these intermediates the pathway diverges into several side branches yielding different subclasses of flavonoids, as summarised in Fig. 

Anthocyaiuns are widely distribnted in nature, occurring in most higher plants and found in all parts of the plants, being most important in flowers and fruits. Analysis of anthocyanins in fmits has revealed that the profile of the anthocyanin content varies among different species, and even within one species. Thus, differentiation of different grape species (species of Vitis vinifera) has been possible through the study of the anthocyanin composition. In general, 

In contrast to flavonoids and carotenoids, which are widespread in the plant kingdom, betalains are found exclusively in one group of angiosperms, the Caryophyllales (including beetroot and Amaranthus). Betalains are derivatives 

/3-Carotene is the major dietary precursor of vitamin A and therefore represents a fundamental component in our diet. The later steps of carotenoid biosynthesis in plants involve the formation of xanthophylls, which are oxygenated derivatives. Among these, capsanthin results from the activity of a bifunctional enzyme, the capsanthin-capsorabin synthase (CCS), that catalyses the conversion of the ubiquitous antheraxanthin and violaxanthin, into capsanthin and capsorubin (Fig. 11.3). 

Efforts have also been made to introduce genes in plants to produce carotenoids other than those that ate already present in the transformed species. 

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Gross, J., Chlorophylls, in Pigments in Fruits, Gross, J., Ed., Academic Press Inc., London, 1987, chap. 1. 

Gross, J., Pigments in Fruits, Academic Press, London, 1987. 

Gross J. 1987. Pigments in Fruits. London Academic Press. 

J. Gross. Pigments in Fruits. Food Science and Technology. A Series of Monographs. Academic Press, London, p. 87 (1987). 

Other natural pigments existing in selected pi. nt foods include tannin, betalain, leucoanthocyanin, quinone and xanthone. Table I lists the color and stability of natural pigments in fruits and vegetables (10). 

Table I. Summary of Characteristics of Natural Pigments in Fruits...

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