462 JOURNAL OF COSMETIC SCIENCE Carmines. Carmine is a red colorant obtained by aqueous or alcoholic extraction from the dried bodies of the female cochineal insect (Dactylopius coccus). Three terms–cochineal, carminic acid, and carmines–are often used interchangeably. Strictly, a cochineal is the crude body of a cactus insect, carminic acid is the principal red colorant, and carmine is an aluminum lake of carminic acid (83). Carminic acid is an anthraquinone derivative possessing a C-glycoside (Figure 14). A C-glycosidic bond at C 7 offers stability against acid hydrolysis. According to the specification requirements for a carmine, the carminic acid content is required to be more than 50%. In the United States and Korea, cochineal extract is not permitted for use in cosmetics. Furthermore, carmines are required to be pasteurized or otherwise treated to destroy all viable salmonella microorganisms. Compared to other natural colorants, carmines exhibit high stability against light, heat, and oxidation. For this reason, carmines have been extensively used in the cosmetic indus- try. However, numerous studies have reported allergic reactions to carmine colorants but not enough to harm the public (84). In addition, the use of insect bodies in cosmetics has been a controversial issue because it requires 80,000 to 100,000 insects to produce 1 kg of cochineal (56). Apart from the traditional manufacturing process using insects, alternatives such as microbial production are being developed (85). Anthocyanins. Thousands of anthocyanins are found commonly in red-, purple-, and blue-colored vegetables and edible fruits (86). They consist of a sugar moiety and antho- cyanidins (aglycone) from glycosylation (Figure 15). The sugar moiety includes glucose, rhamnose, xylose, galactose, arabinose, and fructose (87). According to the substituents (OH or OCH 3 ) in the B ring, there are six anthocyanidins used in the cosmetic and food colorants: cyanidin, delphinidin, pelargonidin, peonidin, malvidin, and petunidin (88). Figure 13. Possible structures of Cu-chlorophyllin complexes. Figure 14. Structure of carminic acid.
463 COSMETIC COLORATION: A REVIEW Anthocyanins are included on the colorant positive lists of the countries studied except in the United States. Only the EU has established specifications for anthocyanins. They clarify that the origin of anthocyanins should be vegetables and edible fruits. However, the sugar moiety of anthocyanins is not defined, but the permitted anthocyanidins are defined in the regulation. Stability of anthocyanin is a major drawback of their use as a colorant. Temperature, pH, and light affect the color of anthocyanin. In a highly acidic aqueous solution, a flavylium cation that exhibits the typical red (or orange) color predominates. When the oxonium ion in the flavylium compound accepts the nucleophilic attack of water, the colorless form of carbinol, a pseudo-base, dominates (Figure 16 (1)) (56). Eventually, the ring-opened chalcone compounds are found in the basic solution. Moreover, a free hydroxyl group at position 7 or 4’ in the flavylium cation facilitates a proton transfer to form blue quinoidal bases in weakly acidic or neutral solutions (Figure 16 (2)) (56). Additionally, the temperature influences anthocyanins’ degradation. It was reported that the manufacturing and storage temperatures influence the pigment color (77). Storing the pigment at 4°C increases its half-life 8–10 months, which is six times longer than for storing it at room temperature (77,89). The mechanism of degradation from the heat is not fully elucidated. However, it has been suggested that the degra- dation starts with the hydrolytic opening of the pyrylium ring in the flavylium com- pound, which leads to chalcone (90). There have been a number of studies on enhancing the stability of anthocyanin. The use of polymeric compounds (e.g., gum, pectin, and whey protein), phenolic compounds, and metallic ions have been shown to stabilize anthocyanins by forming molecular complexes (91). Figure 15. Structure of anthocyanin. Figure 16. Structures of anthocyanins in aqueous solution. Adapted from Delgado-Vargas et al. (56).
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