Carotenoids belong to the tetraterpenes family and are represented by more than 600 known natural sructural variants. They are divided in two categories, carotenes containing only carbon and hydrogen atoms and oxocarotenoids (xanthophylls) which carry at least one oxygen atom. Carotenoids are synthesized in plants, fungi, bacteria and algae. In recent years, medicinal studies indicate that carotenoids play an important role in human health, such as quenching free-radical, improving human immunity, preventin...