Oxidation Products of Vitamin E

Abstract

Examination was made of oxidation products of vitamin E (α-tocopherol) during the peroxidation of unsaturated lipids and decomposition of a lipid hydroperoxide. Free-radical scavenging reactions of α-tocopherol take place via the α-tocopheroxyl radical as an intermediate. Should a suitable free radical be present, a non-radical product is formed from coupling of the free radical with the α-tocopheroxyl radical. The reaction products of α-tocopherol with lipid-peroxyl radicals are 8a- (lipid-dioxy) -α-tocopherones. When the supply of oxygen is insufficient, α-tocopherol traps carbon-centered radicals of lipids to form 6-O-lipid-α-tocopherols. The dimer and trimer of α-tocopherol are formed by bimolecular self-reaction of the α-tocopheroxyl radical in a reaction mixture containing excess α-tocopherol. The reaction products of other vitamin E compounds (γ-and δ-tocopherols) with lipid-peroxyl radicals are much the same as those formed from α-tocopherol. The tocopheroxyl radicals of γ-and δ-tocopherols prefer to react with each other to form dimeric products that are still possessing high capacity to function as free radical scavengers.