Effect of Oak fruit extract on oxidative stability of soybean oil during the thermal process

Oak tree fruit is one of the most plentiful fruits of the Iranian forest, which has important medicinal and nutritional quality. In this study, the oak fruit was extracted by ultrasonic method and three solvents including water, water-ethanol (1:1) and ethanol and examined by free radical scavenging capacity (DPPH) and oxidative stability at three concentrations (200, 700 and 1200 ppm). The results indicated that the water-ethanol (1:1) extract in 1200 ppm had higher antioxidant capacity in comparison with other solvents and synthetic antioxidant, BHA. Hence, oxidative stability of water-ethanol extracts at three concentrations 200, 700 and 1200 ppm was determined under thermal conditions (180 °C) for 30 hours as compared with BHA. Soybean oil in specific interval was monitored with conjugate diene, peroxide value, total polar and carbonyl compounds. The results revealed that soybean oil samples including 1200 ppm of water-ethanol Oak fruit extract prevented significantly from the formation of peroxides, polar, conjugated diene and carbonyl compounds in soybean oil during the heating time as compared with 200 ppm of BHA. Consequently, Oak fruit extract in oils, fats and other food products can be used as natural antioxidant to prevent lipid oxidation.