There are several hundred additional natural pigments that are not as widely represented in foods as the previously discussed coloring substances. Among them are the quinones and xanthones, which are yellow pigments. An example of a quinone is juglone, which is present in walnuts and pecans. Mangiferin, a representative of xanthones, is found in mangoes. Tannins include two types of pale yellow to light brown compounds, characterized by their property to convert animal hides to leather. One type consists of condensed tannins, to which referencewas made in relation to the leucoanthocyanidins, and the other type comprises hydrolyzable tannins, which are esters of a sugar, usually glucose, with gallic acid, ellagic acid, or both. Corilagin is an example of a gallotannin, in which glucose is esterified with three gallic acid molecules. A yellow pigment that has attracted much attention because of its toxicity to humans and nonruminant animals is gossypol. It is present in cottonseeds, which are used as animal feed and have been considered a potential source of protein for human use. Several biologically very important food constituents are colored, such as phytochrome (yellow), vitamin B2 (riboflavin, orange-yellow), and vitamin B12 (red), although their contribution to food coloration is negligible.
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