Antioxidant activity of tannins extracted from bark and tan-bark of Quercus persica Jaub. & Spach fruit in Soybean and Sunflower

Skin tannin and tan-bark of Quercus persica Jaub. & Spach were extracted by two different solvents namely methanol and ethyl acetate. Afterwards, their antioxidant effects were studied on edible vegetable oil compared with synthetic antioxidant Grindox 117 through AOM and Rencimat methods. AOM method was applied in condition of 120 ° C and an air flow of 8:35 l/h while 110 ° C and airflow of 20 l/ h were applied in Rencimat method. Induction period of sunflower oil was increased from 5.30 to 10.85 h by adding 200 ppm extract taken out with methanol 90%. This period was increased up to 10.9 h by adding 200 ppm extract taken out with ethyl acetate 99/99%. Induction period of soybean oil was increased from 5.9 to 8.87 h by adding 200 ppm extract taken out with methanol 90%. This period was increased up to 8.87 h by adding 200 ppm extract taken out with ethyl acetate 99/99%. In another sample of soybean oil, induction period was increased from 4.65 to 7.2 h by adding 200 ppm of a mixture of methanol extract and pure citric acid (ratio1:3). This period was increased up to 7.15 h by adding 200 ppm of a mixture of ethyl acetate and citric acid (ratio1:3).