Oxidation Products of β-Carotene during the Peroxidation of Methyl Linoleate in the Bulk Phase

Methyl linoleate containing β-carotene was autoxidized or photooxidized at 37°C in the bulk phase, and the oxidation products of β-carotene were analyzed by high-performance liquid chromatography. Formyl β-carotenes, β-carotene 5,6-epoxide, and cyclic ethers of β-carotene were detected as the oxidation products during the peroxidation of methyl linoleate initiated by a free radical initiator. These products, which were also detected in the methyl linoleate autoxidized without an initiator, were detectable only in much smaller amounts than the consumed β-carotene. In the chlorophyll-sensitized photooxidation process, the products were β-carotene 5,8-endoperoxide and β-carotene 5,6-epoxide. α-Tocopherol partially inhibited the formation of the 5,6-epoxide, but had no effect on the main product, the 5,8-endoperoxide. These results indicate that β-carotene reacted with singlet oxygen to form the 5,8-endoperoxide as the primary product during the photooxidation of methyl linoleate, and that β-carotene trapped lipid-peroxyl radicals to form oxygenated products which decomposed immediately during the autoxidation process.