Apocarotenoids bixin

Figure 11.8 Structures of c/s-bixin and norbixin, apocarotenoid pigments in annatto.

Cleavage of carotenoid precursors is likely to explain the formation of bixin and crocetin (Figure 5.71) and, indeed, these are classified as apocarotenoids. Large amounts (up to 10%) of the red pigment bixin are found in the seed... 

Amongst the apocarotenoids with less than 40 carbon atoms in the skeleton there are several examples of naturally occurring carotenoid mono- and dicarboxylic acids [7]. These include crocetin (31) from saffron, bixin (32) from Bixa orellana, azafrin (33) from roots of Escobedria scabrifolia and neurosporaxanthin (4) from yeasts (Neuro-spora sp.), Fig. 13. 

The most important acyclic apocarotenoids are the C2o-diapocarotenoids crocetindialdehyde (27), crocetin, and bixin, which contains 24 carbon atoms in the skeleton. 

The Cio-phosphonium acetals 27 and 28 (Scheme 4) proved their utility in the synthesis of 7,8-didehydroastaxanthin (402) [16] and various diapo- and apocarotenoids [17]. Selective reduction of Cio-dialdehyde 8 with NaBH4 furnished the hydroxyaldehyde 29, which was also used as an intermediate in the synthesis of the methyl ester of natural bixin (533) [18]. 

In terms of quantity, annatto is a very important carotenoid colourant for foodstuffs, which is isolated from the seeds ofthe achiote (also known as aplop-pas , indigenous to the tropics Bixa orellatia) (Fig. 7.33). The principal component is cA-bixin, an apocarotenoid with two carboxylic acid functions, one of which is esterified. Annatto is marketed either as a solution in various edible oils or as a spray-dried powder, and serves as colourant of margarine, pasta, cheese and yoghurt. [63]... 

The coloring principles are carotenoids, mostly bixin (oil-soluble) and norbixin (water-soluble), with bixin (especially the cis isomer) in major concentration (2.5% dry wt.). Norbixin is the principle component of the water-soluble dyes of annatto and is formed by the removal of the methyl esters of bixin. Both a- and P-forms of norbixin are found in water-soluble annatto dye. (—)-Bixin (syn. a-bixin) is unstable and during extraction is usually converted to trans-hixin (syn. P-bixin), the stable isomer, which is also known as isobixin. Bixin is a monomethyl ester of norbixin (a dicarboxylic acid) it is readily hydrolyzed by alkalis during alkali extraction of annatto to the dicarboxylic acid, norbixin (evans MERCK).Annatto also contains P-carotene (6.8-11.3 mg/lOOg), apocarotenoids, diapo-carotenoids, an essential oil (with the sesquiterpene ishwarane as the major component), pentosans, pectin, protein (13-17%), tannins, and others (evans). 

The liposoluble nature of these compounds determines, a priori, the type of food in which they can be incorporated to dissolve efficientiy. 3-Carotene is added to fatty foods, such as butter, cheeses, and oils, although other pigments such as bixin and apocarotenals are also employed. Paprika and oleoresins industrially obtained from red pepper are used directly or as ingredient in the manufacture of sauces and meat products. Saffron, which contains crocin as a major pigment (a diester of crocetin with the disaccharide gentiobiose), is used as a hydrosoluble condiment for soups and to color foods and drinks. Other hydrosoluble preparations of 3-carotene and other pigments such as canthaxanthin and apocarotenoids are used to color drinks. Norbixin, a product derived from the saponification of bixin, is hydrosoluble, and used to color ice cream, cereals, and cheese. 

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