Investigation on the Adding Effect of Subcritical Water Extracts from Pistachio Hull for Increasing the Stability of Soybean Oil

Background and Objectives: Nowadays given to the fact that a large volume of agricultural waste is produced annually in different parts of industry and agriculture and most of these wastes are abandoned or burned without any change in nature, the need to use and find the application of agricultural waste has become particularly important.  Materials and Methods: One of the agricultural products with about 40 % of the waste is pistachio. Therefore, in this study, phenolic compounds in pistachio hull were extracted using subcritical water (SCW), and radical scavenging, reduction power and induction period in edible soybean oil for extracts were measured. The extraction process by SCW was carried out in 120–180 °C with 1:20 (sample:solvent) ratio and constant pressure of 30 bar conditions, and the results were compared with the extract obtained by maceration. As a positive control, BHT, ascorbic acid, and alpha-tocopherol antioxidants were used to better compare the results. Results: The results showed that the amount of phenolic compounds increased by increasing from the temperature from 120 to 150°C. The extract obtained from the maceration method had the highest concentration required for the reduction of 50% of trivalent iron ions to bivalent capacity. The extract obtained at 180°C using SCW had the same ability of BHT for stabilizing soybean oil as the synthetic antioxidant. Conclusion: The overall results indicated that the optimum temperature for the extraction of phenolic compounds from pistachio hull by SCW was 150°C, and radical scavenging ability and reduction power of the extracts had a good correlation with the total phenolic compounds.