Comparison of Microwave Vacuum Drying with Traditional Rice Bran Stabilization Methods: Impact on Extracted Oil Quality

Rice bran requires a stabilization process to prevent the rapid development of rancidity upon rice milling. Common stabilization methods usually take a long time or are harsh, which lead to a decrease in rice bran quality (e.g., nutritional and sensory properties). Microwave vacuum drying is a potential stabilization method for rice bran that generates heat at a lower temperature and allows rapid mass and energy transfer leading to an increased drying rate, thus retaining quality. This study aimed to evaluate the effects of various stabilization methods, i.e., dry heating (DH), microwave heating (MH), vacuum drying (VD) and microwave vacuum drying (MVD), on the quality and antioxidant properties of rice bran oils. It was observed that VD and MVD resulted in better rice bran color retention. Oil extraction yield was significantly increased by MVD and DH compared to unstabilized rice bran. Stabilization of rice bran by MVD, DH and MH resulted in significantly lower free fatty acid content and peroxide values in extracted oils. Total antioxidant capacity and percentage of scavenging activities of rice bran oil samples, as determined using DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) assays, were not significantly different. These results suggest that MVD is an efficient rice bran stabilization method that provides similar oil qualities to those produced using traditional stabilization methods.