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.

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