A group of yellow and red dyes belonging to the tetraterpenes with wide distribution in the plant and animal kingdom. Chemically, they are highly saturated hydrocarbons, the majority of which consist of 40 carbon atoms and are composed of 8 isoprene units.
As lipoid-soluble compounds, carotenoids are usually associated with fats and oils.
In plants, carotenoids are mainly found in the leaves (> 90 %). Their physiological significance lies in their involvement in photosynthesis. There they serve the transfer of energy and protect cells from the damaging effects of light.
Carotenoids (above all beta-carotene, alpha-carotene, beta-cryptoxanthin) are absorbed in the intestine with plant food. The carotenes are cleaved in the intestine by the enzyme beta-carotene 15,15′ monooxygenase (BMO) to form retinal (in the case of beta-carotene these are 2 molecules retinal - see vitamin A below).
Carotenoids are divided into:
While carotenes are pure hydrocarbons, xanthophylls are oxygenated. They have a yellow colour.