Products Formed by Peroxyl Radical-Mediated Oxidation of Canthaxanthin in Benzene and in Methyl Linoleate

Abstract

Canthaxanthin was reacted with peroxyl radicals generated by thermolysis of 2,2‘-azobis(2,4-dimethylvaleronitrile) (AMVN) in benzene. The reaction products were separated by reversed-phase high-performance liquid chromatography, and their structures were identified as a mixture of 12-formyl-11-nor-β,β-carotene-4,4‘-dione (1a) and 15‘-formyl-15-nor-β,β-carotene-4,4‘-dione (1b), 15‘,13-epoxyvinyleno-13,15‘-dihydro-14,15-dinor-β,β-carotene-4,4‘-dione (2), 13,15‘-epoxyvinyleno-13,15‘-dihydro-14,15-dinor-β,β-carotene-4,4‘-dione (3), and 11,15‘-dihydrooxepino-β,β-carotene-4,4‘-dione (4). Compounds 1−4 could be accounted for almost all the consumed canthaxanthin at an early stage of the reaction mixture. The peroxidation of methyl linoleate initiated by AMVN in bulk phase was suppressed by the addition of canthaxanthin. The reaction products of canthaxanthin, 1−4, were also formed during the antioxidant process of canthaxanthin, although their yields were low. The result indicates that the peroxyl radical addition occurred in the antioxidant process of canthaxanthin during the AMVN-initiated peroxidation of methyl linoleate. Keywords: Canthaxanthin; carotenoids; lipid peroxidation; antioxidant; free radical