α‐, γ‐ and δ‐Tocopherol Effects on Chlorophyll Photosensitized Oxidation of Soybean Oil

The effects of 0, 1.0, 2.0 and 4.0 (x 10 −3 M) α‐, γ‐ or δ‐tocopherol on chlorophyll b photosensitized oxidation of soybean oil in methylene chloride were studied by peroxide values and headspace oxygen. As concentrations of tocopherols increased, peroxide values decreased and headspace oxygen increased (P < 0.05). At 1.0 × 10 −3 M, α‐tocopherol showed highest antioxidant effect, γ‐tocopherol second and then δ‐tocopherol. α‐ and ‐γ‐Tocopherols had similar effects and δ‐tocopherol had lower effect at 2.0 × 10 −3 M (P < 0.05). However, the three tocopherols were not different (P > 0.05) at 4.0 × 10 −3 M. α‐Tocopherol quenched singlet oxygen to reduce the photosensitized oxidation of oil. The quenching rate constants of α‐tocopherol were 2.7 × 10 7 M −1 sec −1 by peroxide value and 2.6 × 10 7 M −1 sec −1 by headspace oxygen.