Inhibition of cholesterol autoxidation by the nonsaponifiable fraction in rice bran in an aqueous model system

The inhibition of cholesterol autoxidation by nonsaponifiable fraction from rice bran oil (700, 1400, and 2100 ppm) was studied in an aqueous model system for 16 h at pH 5.5 and 80°C. Antioxidant effectiveness was investigated by following the loss of cholesterol and the formation of 7‐keto‐cholesterol. The changes in levels of vitamin E vitamers and γ‐oryzanol in the system were determined during cholesterol autoxidation. The 2100 ppm treatment produced a 92% reduction of 7‐ketocholesterol, 1400 ppm an 82% reductions and 700 ppm a 64% reduction after 16 h, whereas without the nonsaponifiable fraction, the samples showed almost complete degradation of cholesterol. Vitamin E vitamers decreased (P<0.05) in all treatments, but γ‐oryzanol was not significantly (P<0.05) reduced in the 2100 ppm treatment.