Interaction of Light and Temperature on Tocopherols During Oxidation of Sunflower Oil

Light and temperature effects on tocopherols during the oxidation of sunflower oil were studied. The oxidation was performed at 40, 60, or 80 A degrees C for 30, 15, and 6 days, respectively, in the dark or under 1,700 lux light. Oil oxidation was analyzed with peroxide values and conjugated dienoic acid contents, and tocopherols in the oil were separated and quantified by HPLC. The oxidation of sunflower oil was increased with temperature increase, and the light decreased the temperature dependence of the oil oxidation. Sunflower oil before oxidation contained tocopherols with a total of 737.96 mg/kg, with alpha- and gamma-tocopherol at 726.41 and 11.56 mg/kg, respectively, and the tocopherol contents decreased during the oil oxidation. Degradation of tocopherols increased with the temperature increase, and its dependence on the temperature was lower under light than in the dark. gamma-Tocopherol showed higher stability than alpha-tocopherol during oxidation of the oil in the dark and under light. Residual amounts of tocopherols showed a relatively good correlation with the degree of oil oxidation, and the dependence of alpha-tocopherol degradation on the oil oxidation was higher than that of gamma-tocopherol, and light decreased the dependence on the oil oxidation in both tocopherols.