The carotenoids are red, orange, and yellow pigments synthesized by all green plants and some microbes. They have an essential function in photosynthesis and in attracting the attention of animals. Several of these pigments also have an important nutritional function for animals and some of the familiar colors of animals are derived from plant or microbial carotenoids they consume.

Structure and Occurrence

Carotenoids are synthesized in the plastids of a plant cell and typically contain forty carbon atoms derived from eight subunits of the five-carbon compound, isoprene. Larger and smaller carotenoids do occur. Two categories of carotenoids occur in nature. These are the carotenes that contain only carbon and hydrogen, and the xanthophylls (also termed oxycarotenoids) that contain carbon, hydrogen, and oxygen atoms. Each carotenoid has its own distinctive color. Their chemical structure makes carotenoids very insoluble in water, but they are fat-soluble. Therefore they are usually associated...