Carboxylic Carotene, structure

ANNATTO FOOD COLORS. These colors are natural carotenoid colorants derived from the seed of the tropical annatto tree (Bixa nrellana). The surface of the seeds contains a highly colored resin, consisting primarily of the carotenoid bixin. The bixin is extracted from the seed by a special process to produce a pure, soluble colorant. Bixin, one of the relatively few naturally occurring cts compounds, has a chemical structure similar to the nucleus of carotene with a free and esterified carboxyl group as end groups. Its formula is CM LoCL. (See Fig. I). 

Abscisic acid (ABA) is a 15-carbon acid, related in structure to one end of a carotene molecule [83], Four stereoisomers exist, differing in the orientation of the carboxyl group and the sidechain attachment to the ring. The natural ABA is the c/y-(+)-isomer shown in Fig. le. It is made from zeaxanthin via xanthoxin, probably in plastids (see Chapter 8). ABA can be made in all parts of a plant, with the leaves and the root cap being sites of extensive synthesis. It can be metabolized into phaseic acid, which is active in some, but not all ABA-sensitive processes [83]. 

The structures of these compounds have numerous conjugated double-bonds and cyclic end groups thus, carotenoids present a variety of stereoisomers with different chemical and physical proprieties [5]. Carotenoids can be divided in two groups carotenes, constituted by polyunsaturated hydrocarbons C40 (Fig. 135.1), and xanthophylls their oxygenated derivatives and main contain epoxy, carbonyl, hydroxy, methoxy, or carboxylic acid functional groups (Fig. 135.2). 

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