Antioxidant potency of gallic acid, methyl gallate and their combinations in sunflower oil triacylglycerols at high temperature

•Significant formation of secondary oxidation products over IP at high temperature.•Higher antioxidant efficiency of GA and MG than TBHQ in inhibiting total oxidation.•Higher activity of GA than MG due to more molecular mobility and surface activity.•A best antioxidant synergy between MG and GA at a weight ratio of 75 to 25.

Lipid peroxidation and polar compounds formation in sunflower oil triacylglycerols at 120 °C were investigated in the presence of gallic acid (GA), methyl gallate (MG), MG/GA combinations (75:25, 50:50, and 25:75), and tert-butylhydroquinone (TBHQ). Hydroperoxide-based kinetic parameters (IP, induction period, min; ki, rate constant during IP, meq/kg min) of control sample (38.0; 2.0346) were considerably improved by TBHQ (201.1; 0.0267), followed by GA (163.8; 0.0837), MG (151.2; 0.0983), and the combinations (∼184.4; ∼0.0861) with an average synergy of 18.6%. Regarding the polar compounds inhibition, the best antioxidant performance (the ratio of IP to oxidized triacylglycerol monomers at IP, min/%; time reaching 10% of triacylglycerol dimers and polymers, min) in general belonged to MG/GA 75:25 (42.4; 263.0), GA (43.2; 249.9), MG (38.0; 237.5), and TBHQ (17.7; 214.4), respectively. The kinetic parameters based on the formation of polar compounds than hydroperoxides provided more reliable results to evaluate antioxidant potency at high temperature.