Inhibitory Effects of Tocopherols and ?-Carotene on Singlet Oxygen-Initiate D Photooxidation of Methyl Linoleate and Soybean Oil

Methyl linoleate was photooxidized in the presence of chlorophyll at 37°C and the change in the isomeric composition of monohy droperoxides (MHP) produced was measured. The result of increasing the proportions of the 9- and 13-isomers with the elapse of time shows that autocatalytic oxidation occurs with the accumulation of MHP produced by singlet oxygen (1 O2). δ-Tocopherol had the most inhibitory effect on the production of MHP among α-, γ- and δ-tocopherols, by suppressing autocatalytic oxidation and by quenching 1 O2. α-Tocopherol scarcely inhibited the production of MHP, because α-tocopherol disappeared rapidly during photooxidation. β-Carotene retarded the photooxidation of methyl linoleate efficiently. The inhibitory effect of β-carotene was elongated in the presence of δ-tocopherol. It was observed that β-carotene efficiently inhibited the deterioration of soybean oil which was exposed to photoirradiation in the presence of tocopherols.