ABSTRACT
Carotenoids are an important class of naturally occurring compounds that are widely distributed in nature. They are a class of hydrocarbons (carotenes, e.g., β-carotene, lycopene) and their oxygenated derivatives (xanthophylls, e.g., lutein, β-cryptoxanthin) consisting of eight isoprenoid units joined in such a manner that the arrangement of isoprenoid units is reversed at the center of the molecule so that the two central methyl groups are in a 1,6-positional relationship and the remaining nonterminal methyl groups are in a 1,5-positional relationship [1]. All carotenoids may be formally derived from the acyclic C40H56 structure having a long central chain of conjugated double bonds by (i) hydrogenation, (ii) dehydrogenation, (iii) cyclization, or (iv) oxidation, or any combination of these processes. Carotene comes in two primary forms designated by characters from the Greek alphabet: alpha-carotene (α-carotene) and beta-carotene (β-carotene). Gamma, delta, epsilon, and zeta (γ-, δ-, ε-, and ζ-carotene) exist as well. The rules for the semisystematic nomenclature can be found elsewhere [1,2]. As hydrocarbons that contain no oxygen, carotenes are fat-soluble but insoluble in water (in contrast with other carotenoids, such as xanthophylls, which are slightly less chemically hydrophobic).
