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jug other provitamin A compounds + —

1.2 fig other provitamin A carotenoids.

a-Carotene on the preceding basis would be half as active as /?-carotene. The metabolism of a-carotene has been shown to result in the liver storage of retinol and avitamin A. The latter compound does not combine with retinol binding protein (RBP). It can induce hypervita-minosis A because it is not delivered to the tissues. There is some confusion in regard to the capacity of the diepox-ide to serve as a vitamin A source. The compound is listed as active in vivo but not active in vitro. Recently, radioactive /?-carotene-5,6,5',6'-diepoxide and luteochrome (5,6,5',8'-/?-carotene-diepoxide) were fed to rats and C14 retinol was not detected in the liver. The absorption or conversion to retinal is enhanced by bile salts, proteins, lipids, and zinc. It is not clear what the effect of various nonprovitamin A compounds have on the bioavailability of the provitamin A compounds. Lycopene is reported to enhance carotene uptake. It was found that nonprovitamin A compounds may decrease the utilization of provitamin A pigments, whereas yS-cryptoxanthin and a-carotene promote utilization.

Because of the uncertainty of some of the artificial pigments and because of the delisting of several (eg, Red No. 2 in the United States, Red No. 40 in the United Kingdom), interest has increased for using carotenoids as food colorants.

We can consider the use of carotenoids as following a direct or an indirect route. As a case of the former, margarine might be colored with /J-carotene. Examples of the latter might be the coloring of poultry skin, or eggs, or salmon flesh with the appropriate pigment. Some confusion exists regarding natural and artificial pigments. The infrared fingerprints for synthetic and natural ^-carotene are identical. Many people prefer the term nature-identical to describe the synthetic carotenes.

One of the most common natural coloring preparations is obtained by extracting the seeds of the Bixa orellana tree, which grows in the tropics. The apo-compound bixin is the main component of the oil-soluble annatto preparations, and nor-bixin is the 6,6'-diapo-dicarboxylic acid (bixin has one methyl ester). Bixin is most stable at pH 8 and shows a diminished stability in the 4 to 8 pH range. In general, annatto extracts have a good shelf life. Annatto oil applications include the coloring of butter, bakery products, and salad oil. Combined with paprika, annatto oils are used to color cheese. Water-soluble preparations may be used in ice cream.

Saffron consists of the dried stigmas of Crocus sativus. It contains crocin, the digentiobioside of crocetin. The preparation is yellow in color. Saffron is also used as a spice and is widely accepted in such foods as soups, meat products, and cheese. Formerly, it was used in cakes and other bakery products.

Tomato extracts Eire red because of the pigment lycopene. The color of the product would be red to orange depending on the medium. Lycopene is not stable, and its use is limited.

Carrot extracts, carrot oil, and red palm oil contain large amounts of a- and /^-carotene. These were used in fat-based products. They have the advantage of being natural but have limited use because of the lower price of synthetic /^-carotene. Recently, hypersaline algae have been cultured for their /?-carotene content.

Oleoresin paprika is an oil extract of paprika. The main carotenoids are capsanthin and capsorubin. The color of products colored by paprika vary from red to pinkish yellow. Oleoresin paprika can be used in salad dressings, sauces, meat products, and processed cheeses. The indirect coloring of trout with oleoresin paprika resulted in a yellow rather than a red hue of the flesh.

The synthetic pigments have a number of advantages over the natural product extracts. Although the principal advantage is price, it should not be overlooked that the large variation in quality is not a problem with the synthetic FDC dyes. The major synthetic carotenoids that are marketed include /^-carotene, /?-apo-8'-carotenal, and can-thaxanthin. All occur naturally, and only canthaxanthin does not have vitamin A activity.

f)-Carotene is widely encountered in nature. In foods it has been used in butter, margarine, salad oil, popcorn, baked goods, confections and candy, eggnog, coffee whit-eners, juices, and soups to name a few. /?-apo-8' -carotenal has been isolated from oranges and several natural sources. However the main source is the chemical synthesis. It is also yellow, and its uses are similar to those for /?-carotene.

Canthaxanin (rosanthin) (4,4'-diketo-/?-carotene) is used where a red color is desired. It was first isolated from the mushroom, but it is also a widely distributed animal pigment. Many crustaceans, especially brine shrimp, and birds, notably the flamingo, contain canthaxanthin. One of its main uses is as a pigmenting agent for salmon. Although a red color is obtained, it has been observed that the pigment tends to cook out. Recently canthaxanthin has been used in simulated meats, shrimp, crab, and lobster products.

Synthetic astaxanthin is now available and is approved for use in Europe and the United States. This is the major pigment in a number offish and shellfish species. The color tends to be more stable than canthaxanthin. When shrimp are raised in intensive culture, often the blue carotenopro-tein is found. This can be corrected by feeding more green algae or astaxanthin. Marigold flowers contain mainly lutein and are fed to chickens to supply yellow-orange pigments for the skin and egg yolks.

The crystalline carotenoids are not absorbed or metabolized by animals. This problem has been solved by the development of special water-soluble forms marketed to satisfy various product needs. Two approaches have been primarily employed: the production of oil suspensions of micropulverized crystals and the development of emulsions or beadlet forms containing the carotenoid in supersaturated solution or finely colloidal forms in liquid or dry products.

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