Carotene, C40H56

an orange-yellow pigment of the carot-enoid group; a precursor of vitamin A. It is synthesized by plants; it is particularly abundant in leaves as the plants begin to bloom. Carrot roots are rich in carotene (hence the name; it was first isolated from them, and in some varieties it constitutes 31 mg percent of raw substance). The pigment is also present in the fruit of the dog rose (2–16 mg percent), currant, mountain ash, sea buckthorn, and vines of the genus Actinidia.

Plants contain mainly ²-carotene, which as a precursor of vitamin A is twice as active as its isomers, ±- and ³-carotene. Vitamin A is biosynthesized only in animals. The liver of whales and some fish is particularly rich in this vitamin (100 kg of whale liver contains about 100 g of vitamin A, the daily dose for 50, 000 persons). Carotene increases the fertility of animals, accelerates the growth and development of young animals, and prevents xerophthalmia in animals.

The role of carotene in plants is rather obscure. It appears to play an important part in photosynthesis, respiration, and growth. Carotene readily forms peroxides in which a molecule of oxygen is bound at a double bond and can then participate in the oxidation of various compounds.