The comparative protective effects of gallic acid with well-known synthetic antioxidants (tert-butylhydroquinone, butylated hydroxylanisole, propylgallate) on the thermal oxidations of corn and soybean oils during heating for 8 h at 180°C were studied. The quantitative effects of gallic acid at three different concentrations on the time-course thermal oxidations in the two different vegetable oils were also studied for a prolonged heating of 6 days at 180°C. Gallic acid at 200 ppm exhibited higher protective activity than the synthetic antioxidants at the same concentration. Gallic acid also exhibited persistently strong protective activity, in a concentration dependent manner, on the changes in oxidation indices in corn and soybean oils throughout the prolonged heating period (6 days) at 180°C. The present results clearly suggested that gallic acid would be a potential natural substitute of synthetic antioxidants for the protection of vegetable oils during high temperature heating.
Keywords: frying temperature; gallic acid; synthetic antioxidants; thermal oxidation; vegetable oil.