Comparison of 11 rice bran stabilization methods by analyzing lipase activities

Abstract

The production of rice bran oil is severely impeded because of the rapid rancidity caused by rice bran lipase. Eleven stabilization treatments including 6 heating treatments and 5 nonheating treatments were carried out in this research. Lipase activities as well as oil colors, oil compositions, and contents of vitamin E and γ-oryzanol after different treatments were investigated to evaluate the effect of stabilization and oil qualities. All the treatments had no significant influence (p > .05) on the oil compositions and γ-oryzanol contents. Among six heating treatments, autoclaving had the best stabilization effect for 10.73% lipase activity remained and other heating treatments held about 30%–35% lipase activities residual except dry heating (68.88%). Heating treatments except steam heating resulted in the significant decreases (p < .05) of oil acid values and significant increases (p < .05) of peroxide values, meanwhile six heating treatments increased oil colors. Among five nonheating treatments, ultraviolet irradiation for 18 hr and extreme low temperature (−80°C) for 72 hr were found 57.08% and 58.85% lipase activities residual, respectively. Peroxide value was significantly increased (p < .05) only by ultrasound. All nonheating treatments had little effect (p > .05) on oil acid values and color. In conclusion, ultraviolet irradiation might be a potential, convenient, and energy-saving stabilization method with high oil quality. Practical applications Rice bran has a potential for producing about 8 million tons of rice bran oil worldwide but nearly 90% rice bran was wasted every year. The processing of rice bran is impeded because of the rancidity caused by lipase, so the stabilization of rice bran is very important. This research provided a new and time-saving method for evaluating stabilization efficacy instead of long time storage. Using this new evaluating method, 11 stabilization methods were compared and methods like microwave, extrusion, and ultraviolet irradiation were considered to be suitable methods for industrial processing. In additional, ultraviolet irradiation was found to be a potential, convenient, and energy-saving stabilization method without influencing oil quality and nutrient content.