Abstract
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.
Highlights
Tocopherols are characterized by a chromane ring with a hydroxyl group and a hydrophobic side chain
These vegetable oils showed a great variation in their (γ + δ)/α -tocopherol ratio, with canola, corn olive, soybean and sunflower oil exhibiting ratio of 1.55, 1.32, 0.43, 4.29 and 0.20, respectively
With respect to the tocopherol homologs, our findings indicate a lower antioxidant potential of α-tocopherol compared to γ- and δ-tocopherol in vegetable oils, which has been reported earlier [7,8]
Summary
Tocopherols are characterized by a chromane ring with a hydroxyl group and a hydrophobic side chain. In particular fats and oils, either γ- or δ-tocopherol have been reported being the most potent antioxidant [6,7,8,9]. Another aspect that has not been clarified yet is whether the quantity of tocopherol homologs and their ratio to each other determines their antioxidant potential in a food matrix. In addition to the absolute and relative amount of tocopherol homologs, the food matrix, processing and storage conditions, among other factors, have a major impact on the oxidative stability in fats and oils [10,11,12]
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