In addition to the carotenes, we also have the family of carotenoids known as xanthophylls, or oxycarotenoids, containing at least one oxygen function in the molecule. A compound because it contains an unsubstituted beta-ionone ring, which is also common in retinol and retinoic acid. This structure is necessary for provitamin A activity. There are more than 500 carotenoids in nature, and about 50 are provitamin A carotenoids. Each carotenoid can exist in a minimum of 282 different geometric isomers.
Carotenoids have three functions that are essential for the well-being of living organisms.
They act as accessory pigments in photosynthesis, they protect against photosensitized damage, and finally, certain carotenoids are provitamin A compounds. Excentric cleavage can take place at virtually any double bond within the molecule, excluding the ring double bonds. Excentric cleavage forms intermediates known as apo-carotenals. They are aldehydes that can be oxidized to carotenoic acids, and ultimately end up as retinoic acid. The formation of retinol, retinal, and retinoic acid are the best documented functions of carotenoids in human biology.