Effects of hot air-assisted radio frequency heating on enzyme inactivation, lipid stability and product quality of rice bran

Rice bran (RB) is a valuable by-product of rice milling but highly susceptible to lipid rancidity induced by inherent lipase (LA) and lipoxygenase (LOX) activities. Therefore a stabilization step is required to reduce activities of these enzymes to ensure RB quality. Effects of hot air-assisted radio frequency (HAARF) heating on enzyme inactivation, lipid stability and product quality of RB were investigated. Influence of water activity (a(w)) in stabilized RB on lipid rancidity during storage was also evaluated. Results showed that average residual LA and LOX activities in RB treated by RF heating at electrode gap of 10 cm and to 100 degrees C with holding in hot air for 15min decreased to 19.2% and 5.5% of their original values. Free fatty acid content and peroxide value of RB oil extracted samples treated under these conditions remained below acceptable limits even following 60d storage at 35 degrees C. The lowest reaction rate for RB rancidity during storage occurred at a(w) value of 0.241. No significant adverse quality changes in RB were observed immediately following HAARF heating, and subsequent storage stability of RB was also enhanced by HAARF heating. HAARF heating can potentially provide rapid and effective methods for RB stabilization without adverse impact on product quality.