Effects and Prooxidant Mechanisms of Oxidized α‐Tocopherol on the Oxidative Stability of Soybean Oil

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Abstract
ABSTRACT:  α‐Tocopherol was oxidized in methanol containing methylene blue for 30 h under light. The effects of 0, 250, 500, 1000, and 1500 ppm of oxidized α‐tocopherol on the oxidative stability of purified soybean oil in the dark at 55 °C were studied by measuring the peroxide values and headspace oxygen contents in sample bottles. As the concentrations of oxidized α‐tocopherol increased, the peroxide values increased and the headspace oxygen contents decreased during the 6 d of storage. The oxidized α‐tocopherol compounds acted as prooxidant on the peroxide values and headspace oxygen contents of purified soybean oil. Tukey's test showed that oxidized α‐tocopherol had a significant effect on the peroxide value and headspace oxygen disappearance of oil at P < 0.05. The prooxidant mechanisms of oxidized α‐tocopherol may be due to α‐tocopherol peroxy radical, α‐tocopherol oxy radical, hydroxy radical, and singlet oxygen formed from the α‐tocopherol. The oxidized α‐tocopherol containing polar and nonpolar groups in the same molecule may reduce the surface tension of oil to increase the transfer of headspace oxygen to oil and accelerate the oil oxidation.