Antioxidant Activity of Amaranth Protein Hydrolysate Against Thermal Oxidation of Vegetable Oils

The antioxidant capacity of amaranth protein hydrolysate (AH) during the thermally induced oxidation of two different vegetable oils, sunflower oil (SO) and canola oil (CO), was assessed by differential scanning calorimetry by means of isothermal and non‐isothermal assays. Interactions between AH and tocopherols were also analyzed. In both oils, AH (10 % w/w) produced an increase in the induction period in isothermal assays, presenting a synergistic effect with tocopherols. In the case of non‐isothermal assays, thermograms of oils with AH showed a significant diminution in the second exothermic peak, suggesting an inhibition of the decomposition of primary to secondary oxidation products. In addition, AH produced an increase in the oxidation rate constant (k) value at low temperatures being more evident in the case of canola oil. However, this effect decreased as a function of the temperature increase, which suggests that AH would have a pro‐oxidant effect at low temperatures but a heat stabilizing effect at high temperatures (above 210 °C for SO and 190 °C for CO).