The antioxidant activity of tocopherols in vegetable oils was shown to chiefly depend on the amount and the tocopherol homolog present. However, the most effective ratio of tocopherol homologs with regard to the antioxidant capacity has not been elucidated so far. The present study analyzed the effect of different tocopherol concentrations, homologs and ratios of homologs on markers of lipid oxidation in the most commonly consumed vegetable oils (canola, sunflower, soybean oil) stored in a 12 h light/dark cycle at 22 ± 2 °C for 56 days under retail/household conditions. After 56 days of storage, the α-tocopherol-rich canola and sunflower oil showed the strongest rise in lipid peroxides, yielding 25.1 ± 0.03 meq O₂/kg (+25.3-fold) and 24.7 ± 0.05 meq O₂/kg (+25.0-fold), respectively. ESR experiments, excluding effects of the oils' matrices and other minor constituents, confirmed that a food representative tocopherol ratio of (γ + δ)/α = 4.77, as represented in soybean oil, led to a more pronounced delay of lipid oxidation than a lower ratio in canola (1.39) and sunflower oil (0.06). An optimum (γ + δ)/α -tocopherol ratio contributing to the oxidative quality of vegetable oils extending their shelf life has to be investigated.
Keywords: hexanal; lipid oxidation; oxidative stability; tocopherol ratio; vegetable oils.