BETA-CAROTENE

Carotenoids are plant pigments that involve in light harvesting to participate in energy transfer process in photosynthesis. They absorb light in the 400-500 nm region of the visible spectrum and impart coloration of yellow, orange, red, and purple. They are widely distributed in nature including vegetables, fruits, insects, fishes, and birds. Animals are incapable of synthesizing carotenoids, which should be obtained through diet. Chlorophyll is the generic name for green plant pigments which includes the open-chain bile pigments and the large ring compounds. The structure of chlorophyll molecule has four nitrogen-containing pyrrole rings bonded to a central magnesium atom, and the fifth ring containing only carbon atoms, and various long hydrocarbon tails attached to the pyrrole rings. Carotenoids contain sequences of conjugated isoprene units, alternating double and single carbon bonds. They are sometimes terminated by cyclic end-groups (rings) complemented with hydroxylated, oxidized and hydrogenated groups. The conjugated double bonds absorbs light and UV. The more number of double bonds result in the absorbance of red color wavelength. Changes in geometrical configuration about the double bonds result in the existence of many cis- and trans- isomers. Carotenoids are usually located in quantity in the grana of chloroplasts in the form of carotenoprotein complexes which give blue, green, purple, red, or other colors to the outer surfaces in plants, or eggs of crustaceans, such as the lobster and crab. Carotenoids are classified into carotenes (un-oxidized carotenoids, orange pigments) or xanthophylls (yellow pigments) which contains oxygen and are alcohol-soluble. It is known that more than 600 carotenoids are isolated from natural sources.

Carotene: though carotene is the simplest of a group of natural pigments called carotenoids, it has an unsaturated and long aliphatic hydrocarbon chain. It is found as a fat-soluble pigment in many higher plants of dark green leafy and yellow vegetables such as carrots, collards, turnips, sweet potatoes, and squash, and in yellow fruits such as apricots, oranges, peaches, and cantaloupes. Carotene is thought to transport light energy for photosynthesis or contribute to reduction reaction. It is important in animal biology as it is are converted to retinol in the body by an enzyme in the intestinal wall and the liver. Carotene occurs in several isomeric forms: alpha, beta, gamma, delta, epsilon, and zeta of which the form of beta acts as an antioxidant nutrient protecting the body from damaging molecules called free radicals and an immune system booster as it is converted to vitamin A (retinol), important in animal biology as the main dietary source. One molecule of beta-carotene splits into two molecules of vitamin A and thus Beta-carotene is called provitamin A. Cryptoxanthin is a yellow carotenoid widely distributed in egg yolk, green grass, yellow corn which can be converted into vitamin A in the body. Cryptoxanthin is the major precursor of vitamin A together with beta-carotene in humans.