Carotenoids form a large group that contains hundreds of related compounds and are usually in red, orange or yellow colours. They may be divided into the carotenes, which are hydrocarbons, and the xanthophylls, which contain oxygen in addition to hydrogen and hydrocarbon. Unlike anthocyanin, carotenoids are insoluble in water. Most are fairly stable to heat and pH extremes but may be destroyed by oxidation due to the presence of double bonds as seen in Figure 4. In intact tissues little oxidation takes place, but in processed foods in which tissues have been disrupted, carotenoids may be auto-oxidized by atmospheric oxygen. Oxidation rate may be affected by light, heat, pro-oxidants and antioxidants. Vitamin A activity is expressed relative to β-carotene, which is set at 100. Note the conjugated double bond sequences.

 

Natural extracts and synthetic carotenoids are used to colour margarine, butter, oils, beverages, soups dairy and meat products, syrups and macaroni. Bixin, a carotenoid present in annatto seeds, is widely used to produce a yellow colour in cheese. Three synthetic carotenoids currently approved by the FDA for food uses are β-carotene (yellow to orange), β-apo-8-carotene (orange to red) and canthaxanthin[1] (red). The advantages of synthetic carotenoids include high purity, better control of concentrations and tolerances and freedom from contamination substances.