Antioxidant and antimicrobial characteristics of black Raspberry (Rubus occidentalis) leaves extract and its effect on stability of soybean oil

Nowadays, finding new resources of vegetal antioxidants in order to use them in food (as an additive or alternative with artificial antioxidants) is an important research subject in the field of food science and technology. In this research methanolic extracts of green and black raspberry leaves were examined in antioxidant properties, total phenolic content (TPC) and antimicrobial activity against Escherichia coli, Staphylococcus aureus, Entherococcus faecalis, Salmonella typhimurium, Yercinia enthrocolitica and Shigella dysenteria. then, three concentrations of each extract (200, 400, and 600 ppm) were applied in free antioxidant-purified soybean oil. The oils were kept in 60° C for a period of one month. After storage, Peroxide index, Iodine index, and Acidity value of oil samples were determined. According to the results, in all concentration of extracts, green leaves extract (GLE) had more antioxidant activity (0.7- 87%) and TPC (103±0.1 mg/g dry matter) significantly than black leaves extract (BLE). In antimicrobial activity, GLE in the minimum concentration of 7.12 mg/ml had an antimicrobial effect on Staphylococcus aureus and in the minimum concentration of 28.5 mg/ml inhibited the growth of Salmonella typhimurium, Yercinia enthrocolitica. But BLE did not show any effects on growth of investigated microbes. In the quality tests of oil samples, with an increase in the concentration of GLE, acidity, Iodine index, and peroxide index increased significantly. At the end, it was concluded that oil samples containing 200 ppm, had better quality and stability than samples containing 200 ppm Propyl Gallate (market soybean oil).