- A class of carotenoids, yellow-red pigments (lipochromes) widely distributed in plants and animals, notably in carrots, and closely related in structure to the xanthophylls and lycopenes and to the open-chain squalene; of particular interest in that they include precursors of the vitamins A (provitamin A carotenoids). Chemically, they consist of 8 isoprene units in a symmetrical chain with the two isoprenes at each end cyclized, forming either α-c. or β-c. (γ-c. has only one end cyclized). The cyclic ends of β-c. are identical β-ionine-like structures; thus, on oxidative fission, β-c. yields 2 molecules of vitamin A. The cyclic ends of α-c. differ: one is an α-ionone, the other a β-ionone; on fission, α-c., like γ-c., yields 1 molecule of vitamin A (a β-ionone derivative).
* * *car·o·tene 'kar-ə-.tēn n any of several orange or red crystalline hydrocarbon pigments (as C40H56) that occur in the chromoplasts of plants and in the fatty tissues of plant-eating animals and are convertible to vitamin A see BETA-CAROTENE
* * *n.a yellow or orange plant pigment - one of the carotenoids - that occurs in four forms: alpha (a), beta (b), gamma (g), and delta (d). The most important form is b-carotene, which is an antioxidant and can be converted in the body to retinol (vitamin A). Foods containing b-carotene (for example, milk and some vegetables) are therefore a source of the vitamin.
* * *car·o·tene (karґə-tēn) [L. carota carrot] one of four isomeric pigments (α-, β-, γ-, and δ-carotene), having colors from violet to red-yellow to yellow, found in many dark green, leafy, and yellow vegetables, as well as yellow fruits. They are fat-soluble, unsaturated aliphatic hydrocarbons that are converted to vitamin A in animals by an enzyme in the intestinal wall and the liver. β-Carotene is the major precursor (provitamin) of vitamin A in humans, although it is less well absorbed than is retinol. See also retinol equivalent, under equivalent.
Medical dictionary. 2011.