Optimal tocopherol concentrations to inhibit soybean oil oxidation

The optimal concentration for tocopherols to inhibit soybean oil oxidation was determined for individual tocopherols (alpha-, gamma-, and delta-tocopherol) and for the natural soybean oil tocopherol mixture (tocopherol ratio of 1:13:5 for alpha-, gamma-, and delta-tocopherol, respectively). The concentration of the individual tocopherols influenced oil oxidation rates, and the optimal concentrations were unique for each tocopherol. For example, the optimal concentrations for alpha-tocopherol and gamma-tocopherol were similar to100 and similar to300 ppm, respectively, whereas delta-tocopherol did not exhibit a distinct concentration optimum at the levels studied (P < 0.05). The optimal concentration for the natural tocopherol mixture ranged between 340 and 660 ppm tocopherols (P < 0.05). The antioxidant activity of the tocopherols diminished when the tocopherol levels exceeded their optimal concentrations. Above their optimal concentrations, the individual tocopherols and the tocopherol mixture exhibited prooxidation behavior that was more pronounced with increasing temperature from 40 to 60degreesC (P < 0.05). A comparison of the antioxidant activity of the individual tocopherols at their optimal concentrations revealed that alpha-tocopherol (similar to 100 ppm) was 3-5 times more potent than gamma- tocopherol (similar to300 ppm) and 16-32 times more potent than delta-tocopherol (similar to1900 ppm).