The antioxidant activity of gentisic (GA) and α-resorcylic (α-RA) acids was investigated by considering their molecular structures in various oxidative environments, including DPPH· scavenging assay, stripped olive and soybean oils, and the corresponding oil-in-water emulsions. The mechanism of action in the oils was evaluated in the presence of different concentrations of the antioxidants at 60 °C, using the kinetic parameters the stabilization factor (F), the oxidation rate ratio (ORR), the activity (A), and the average rate of antioxidant consumption (r¯¯AH). GA was significantly more potent antioxidant than α-RA in all the environments. Although the less polar α-RA showed better activity in the emulsions rather than in the bulk oils, GA with an ortho-hydroxy structure had higher capacity to scavenge DPPH·, and LOO· in the oils and emulsions. The lower performance of α-RA was attributed to its participation in side reactions of chain initiation (AH + LOOH → A· + L· + H2O) and propagation (A· + LH → AH + L·) as competed with the main chain termination reaction (LOO· + AH → LOOH + A·).

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