Antioxidant activity and mechanism of action of some phenolic acids at ambient and high temperatures

Abstract

The antioxidative properties of syringic, 3,4-dihydroxybenzoic, sinapic and caffeic acids were studied in the concentration range 0.002–0.02% (0.9×10 −4–1.3×10 −3 M) during autoxidation of triacylglycerols of sunflower oil at 22 and at 90 °C. The stabilization factor (F) as a measure of effectiveness, the oxidation rate ratio (ORR) as a measure of strength, and the activity (A) which combines the above two factors were determined. The effectiveness of the phenolic acids increased in the following order: syringic acid <3,4-dihydroxybenzoic acid <sinapic acid <caffeic acid. The molecules of syringic, 3,4-dihydroxybenzoic and synapic acids at both temperatures, and the molecules of caffeic acid at 90 °C participated in one side reaction with hydroperoxides. The molecules of caffeic acid did not participate in side reactions at room temperature. The radicals of 3,4-dihydroxybenzoic, sinapic and caffeic acids participated in one reaction of chain propagation at both temperatures, whereas the radicals of syringic acid participated in more than one reaction of chain propagation. The complex kinetic parameter activities, A, for syringic and 3,4-dihydroxybenzoic acids, were practically the same at both temperatures, whereas sinapic and caffeic acids showed a greater activity at 90 °C than at ambient temperature.