Antioxidant activity of grapefruit seed extract on vegetable oils

Abstract

The antioxidant activities of a grapefruit seed extract (GFSE) which contains tocopherols, citric acid and ascorbic acid, were investigated in vegetable oils. Different amounts of GFSE in powder were dissolved in a mixture of soybean oil-sunflower oil. The oxidation was carried out in an AOM equipment at temperatures of 98.7°C, 75°C and 66.5°C. The results indicated prooxidant effects of GFSE at 97.8°C and 75°C possibly due to a blockade effect of a hydroxyl compound by tocopherol. The inhibitor reaction order at these temperatures were 0.902 and 0.465, respectively, while at 66.5°C the oxidation rate was inverse to GFSE concentration with reaction order of -0.420. These results seem to indicate different reaction mechanisms depending on temperature conditions. The blockade effects was explained on the basis of a proposed complex between tocopherol and citric acid molecules.