Annatto

Annatto (CI Natural Orange 4, CI No. 75120, EEC No. E 160b) is found in the outer layers of the seeds of the shrub Bixa orellana, a tropical plant grown in South America, India, East Africa, the Philippines, and the Carribbean. Peru and Brazil are the dominant sources of supply. Annatto is one of the oldest colorants and has been used in antiquity for coloring foods, cosmetics, and textiles. It has been used for more than a hundred years in the United States and Europe primarily as a colorant for dairy products. The colorant is prepared by leaching, with gentle mechanical friction, of the seeds with various solvents, including vegetable oil, fats, and alkali aqueous and alcoholic solutions. Depending on the application, the crude extract may be refined by precipitation with acids and/or recrys-tallization. Spray-dried powders are also available in both water-soluble and oil-soluble forms. The Food and Drug Administration (FDA) approved procedures for extraction are specified in the 21 CFR section 73.30 for Annatto Extract.

The pigments in annatto are a mixture of bixin, the monomethyl ester of a dicarboxylic carotenoid, and nor-bixin, the dicarboxylic derivative of the same carotenoid (Fig. 2). Both bixin and norbixin normally occur in the cis form, but small amounts of the more stable trans form are formed on heating. A yellow degradation product termed C17 yellow pigment (Fig. 2) is also produced on heating. The cis forms are redder than the trans forms or the C17 compound; thus, a source of red and yellow pigments are available. The carboxylic portion of the molecule contributes to the solubility in water, and the ester form contributes to oil solubility. This has provided flexibility in applications, and annatto has been used in a wide variety of applications.

Annatto is available in both water-soluble and oil-soluble liquids and powders. The oil-soluble form is somewhat unstable under oxidative conditions, and degradation is increased by exposure to light and is catalyzed by metals. Addition of antioxidants, such as ascorbic acid, tocopherols, and polyphenols, helps to minimize oxidative degradation. Annatto shows more stability to exposure to air than other carotenoids and is moderately stable to heat. Little change in color occurs with pH changes, but products with a low pH may show a pinkish tinge due to isomeri-zation of the pigments.

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