Effects of air, microwave, and microvacuum drying on brown rice quality

Proper hulling and drying are critical components of brown rice quality. Two medium grain rice varieties were examined for grain qualities including husking, cracking, germination ratio, color, hardness, and fat acidity after drying with 15, 30, and 45°C air, as well as at 100 and 200 W microwave, and microwavevacuum, respectively. Unlike impeller dehuller, rubber roller dehuller could not process rice with 22% moisture content. Brown rice varieties with 22% moisture content after dehulling were dried at 15, 30, and 45°C until moisture content reached 15%; the drying ratios for each temperature were 1.02, 2.55, and 3.46 %/h, respectively. When brown rice varieties were dried at below 30°C, no significant changes were observed in physico-chemical properties, whereas the cracking ratio increased significantly. Microwavevacuum drying resulted in higher reductions of germination ratio and fat acidity than with the microwave only at 100 W as well as reduced drying time over microwave drying.