ANTIOXIDANT REACTIONS OF BETA-CAROTENE - IDENTIFICATION OF CAROTENOID-RADICAL ADDUCTS

beta-Carotene and other carotenoids are thought to exert disease preve ntive actions by scavenging reactive free radicals, but the mechanisms of these reactions are poorly understood. We detected products formed by reaction of beta-carotene with alkyl, alkoxyl, and alkylperoxyl fr ee radicals generated by thermolysis of azobis(2,4-dimethylvaleronitri le) (AMVN) in benzene. Analyses by atmospheric pressure chemical ioniz ation mass spectrometry identified two previously unknown classes of b eta-carotene oxidation products. Substitution products contain one AMV N-derived radical adduct group and result from hydrogen transfer from the carotenoid polyene followed by radical recombination. Addition pro ducts contain two AMVN-derived adduct groups and result instead from s equential radical additions to the polyene. These product structures p rovide the first mechanistic explanation for the radical scavenging re actions of carotenoids.