Antioxidative activity of fermented solid-waste soybean on soybean oil oxidation

Soybean and soyfoods were known to contained isoflavones that had antioxidative activity. Solid-waste soybean was the unextracted soybean in the tofu processing. Solid-waste soybeans were fermented with Neurospora sitophila , Rhizopus oligosporus , and R. oryzae for 5 days. The fermented solid-waste soybeans were extracted with 80% methanol and defatted with 50% methanol-hexane (1:2;v/v). The methanol extracts were dried into dried extracts and added into soybean oils. The soybean oil oxidation was obtained based on weighing method. The dried extracts (100, 200, 300, and 400 ppm) of 2, and 3 days fermented solid-waste soybeans with N. sitophila , R. oligosporus , and R. oryzae that showed strongest inhibited of lipid oxidation were added into soybean oils and oxidized at 170°C for 15 min. The antioxidative activities of fermented solid-waste soybeans were calculated. The antioxidative activities of fermented solid-waste soybeans were increased following increased of the dried extract concentrations of fermented solid-waste soybeans in soybean oil. The antioxidative activity of 400 ppm fermented solid-waste soybeans with N. sitophila , R. oligosporus , and R. oryzae were 97.7, 98.0, and 95.3%, respectively.