Miscellaneous Natural Food Colors
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.
