Lipid chemistry of rice bran and residual bran on milled rice

The relative free fatty acid (FFA) formation, lipid oxidation, and volatile compounds formation of commercially milled head and broken rice samples were determined during storage at 37°C and 70% relative humidity. The effects of rough rice drying conditions on the surface lipid and FFA content of head and broken rice were evaluated. The effect of water washing on lipid and FFA content of rice bran and residual bran on milled head and broken rice was also examined. The physicochemical and functional properties of rice bran aqueous extracts were evaluated.;The relative rates of FFA formation, lipid oxidation, and volatile compound formation for commercially milled broken rice were significantly greater than those obtained in head rice. Pentanal, pentanol, hexanal, pentylfuran, octanal, and nonanal were the major volatile compounds identified by GC-MS analysis in both head and broken rice. The concentration of volatile compounds was greater in broken rice than in head rice. The most severe drying condition reduced the rice surface lipid contents when compared with mild drying condition. The drying treatments had no effect on FFA development beyond affecting surface lipid contents. Water washing reduced the rates of FFA formation, lipid oxidation, and volatile compound formation of both head and broken rice. Water washing also extracted emulsified oil from rice bran and reduced FFA and CD formation during storage. The rice bran aqueous extract was rich in phenolics and antioxidant capacity. The rheology and droplet size distributions of the rice bran aqueous extract were similar to that of native bovine milk.;The high concentration of surface lipids and volatile compounds in broken rice was responsible for the greater off-flavor development and lower quality of broken rice relative to head rice. Water washing appears to be a simple and practical means to lower the rates of FFA formation, lipid oxidation, and volatile compound formation in broken rice. The composition and functional properties of rice bran aqueous extracts show potential as a food-grade emulsion.