Quenching Effect of Tocopherols on the Methyl Linoleate Photooxidation and Their Oxidation Products

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Abstract
The quenching effect of α-, γ- and δ-tocopherols on the methylene blue sensitized photo- oxidation of methyl linoleate was investigated, and the 1O2. quenching ability of tocopherols was determined. The 1O2 quenching rate constants for α-, γ- and δ-tocopherols in ethanol were estimated to be 2.6 × 108 m−1 sec−1, 1.8 × 108 m−1 sec−1 and 1.0 × 108 m−1 sec−1, respectively. And the rate constants for the chemical reaction between each tocopherol and 1O2 were 6.6 × 106 m−1 sec−1, 2.6 × 106 m−1 sec−1 and 0.7 × 106 m−1 sec−1 for α-, γ- and δ-tocopherols, respectively. The results show that α-tocopherol is the most effective compound toward 1O2 among the three tocopherols. The photooxidation of each tocopherol produced two peroxides which, after chemical reduction, were identified to be tocopherol hydroquinone by gas chromatography-mass spectrometry analysis. The photooxidation mechanism of these tocopherols was assumed to be different from that of autoxidation.

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