Optimization and kinetics of ultrasound-assisted solvent extraction of gamma oryzanol from dried rice bran soapstock

Abstract

The effect was investigated of ultrasound-assisted solvent extraction (UASE) parameters on gamma oryzanol recovery from dried rice bran soapstock (DRBS) using a mixture of ethyl acetate and ethanol. The UASE parameters were ultrasound power (0.5 W/g, 2.5 W/g, 4.5 W/g), extraction temperature (35°C, 45°C, 55°C) and sonication time (4 min, 15 min, 26 min). The study used ethyl acetate:ethanol ratios (volume per volume; v/v) of 100:0%, 95:5%, 90:10%, 85:15%, 80:20% and 75:25% and the optimal ethyl acetate:ethanol mixture was 85:15% v/v. In the study, the UASE parameters were first optimized using a response surface method (RSM)-based, face-centered, composite design for maximum DRBS gamma oryzanol recovery. Subsequently, the kinetic behavior of the UASE process was characterized using a second-order kinetic model based on variable ultrasound power and extraction temperature, for a given sonication interval. The optimal RSM-based UASE condition was 4.0 W/g ultrasound power, 50°C extraction temperature and 21.50 min sonication time, achieving maximum predicted and experimental gamma oryzanol recoveries of 98.03% and 98.15%, respectively, which were in good agreement. The simulated and experimental kinetic results were also in agreement (coefficient of determination > 0.972), validating the applicability of the kinetic model for characterizing the effect of UASE parameters on DRBS gamma oryzanol recovery.