458 JOURNAL OF COSMETIC SCIENCE has not been elucidated. However, the oxidation of alkenes leads to destruction of the chromophore of carotenoids, causing color loss (62). Isomerization can be caused by heat, acids, and light, but results in only a slight change in color (62). To prevent the oxidation of carotenoids, the inactivation of the oxidative enzyme and the use of antioxidant agents (e.g., citric acid, α-tocopherol, and butylated hydroxytoluene) are recommended (62). Furthermore, to improve their solubility and chemical instabil- ity against environmental factors, such as light, temperature, and pH, spray drying and freeze-drying are used for encapsulating carotenoids (63,64). The most commonly used encapsulation technique is a method of enclosing active compounds in capsules with appro- priate carrier matrices. Spray drying in a maltodextrin-based matrix is the most commonly used encapsulation technique in the cosmetic and food industries (64). In the next section, the definitions, production, and regulations of specific carotenoids will be discussed. Annatto. Annatto is an orange colorant prepared by extracting the outer coating of seeds from the annatto tree (Bixa orellana L.). The principal coloring matters of annatto seeds are bixin (oil soluble) and norbixin (water soluble) (Figure 9) (56). In the manufacturing process, the extraction solvent influences the ratio of bixin and norbixin and the amount of coloring matter. Heating in the extraction process converts the cis-bixin, or cis-norbixin to a more stable isomer, trans-bixin or trans-norbixin (65). Usually, organic solvent extraction provides higher extraction yields on both bixin and norbixin. The bixin undergoes hydrolysis in hot alkaline solution to become norbixin. The EU, the United States, and Korea permit the use of annatto as a cosmetic colorant. Specially, individual specification is determined separately according to the manufacturing process (e.g., solvent, alkali, or oil extraction) in the EU. isoprene unit beta-Carotene Figure 8. Structure of β-carotene. HO O O OMe 9' cis-Bixin HO O O OH cis-norBixin Figure 9. Structure of cis-bixin and cis-norbixin.

459 COSMETIC COLORATION: A REVIEW Lycopene. Lycopene, the precursor of carotene, is a red colorant easily found in tomatoes. The principal coloring matter, lycopene, consists entirely of hydrocarbon and contains 13 trans-double bonds. Lycopene can be extracted from tomatoes and microorganisms (B. trispora) or synthe- sized chemically. Over 60% of lycopene production comes from plant extraction (66). Natu- rally occurring lycopene predominantly exists in an all-trans-configuration, but the trans-cis isomerization process can occur during processing and storage. Synthetic lycopene is synthe- sized via the double Wittig reaction using the strategy C15 + C10 + C10 (Figure 10) (67). Synthetic lycopene costs less than lycopene extraction from tomatoes and microorganisms (66). In the EU, synthetic lycopene is required to contain more than 70% trans-lycopene. Alternatively, lycopene products derived from biomass have been developed as food and cosmetic additives. As an alternative and sustainable source for the production of lyco- pene, the Blakeslea trispora microorganism has been utilized (68,69). ß-Carotene. β-carotene, known for its provitamin A activity, is a highly conjugated compound that makes carrots orange (Figure 8). It is obtained from various natural sources (plants, algae, and fungus) or prepared synthetically. In the EU regulation, four manufacturing methods are permitted to produce β-carotene as a colorant. Traditionally, β-carotene is obtained by solvent extraction from plants. The disadvantage of this process is that it requires high quantities of plants. For example, 2 g of α- and β-carotene requires 50 kg of carrots (70). Synthetically, the Grignard reaction or Wittig reaction is used as a key reaction for obtaining beta-carotene. In the first synthesis, two moles of C-19 aldehydes react with the Grignard reagent followed by dehydration and hydrogenation (71). The other synthesis uses the Wittig reaction of C-15 phosphonium salt and C-10 dialdehyde (71). Regarding the consumer demand for natural sources, β-carotene is also obtained from microorgan- isms such as the mold B. trispora and the algae Dunaliella salina. In the EU, assay values vary according to their sources: more than 96% for synthetic production, 5% for plant extraction. In the United States, regardless of its origin, raw material has to contain at least 96% total β-carotene. O O PPh3X C 10 -dialdehyde C 15 -phosphonium salt + 2 via Wittig reaction Lycopene Figure 10. Synthesis of synthetic lycopene. Adapted from Ernst et al. (67).