Rice Starch Isolation by Neutral Protease and High-Intensity Ultrasound1

The efficacy of neutral protease and combinations of neutral protease and highintensity ultrasound on rice starch isolation was investigated. Rice flour slurry (33%) was treated with neutral protease at 0.01, 0.03, or 0.05% (on flour basis) or combinations of 0.03% neutral protease and high-intensity ultrasound at 25, 50, or 75% amplitude for 15, 30, or 60 min concurrently or sequentially. The starch yield greatly improved to 79.8%-86.7% with 0.50-0.96% residual protein content and 0.98-1.87% damaged starch content when neutral protease treatment was combined with highintensity ultrasound. The preferred combinations were neutral protease digestion for 2 hr followed by sonication at 75 or 50% amplitude for 15 or 30 min. The starch structure analyzed by a high performance size-exclusion chromatography and a scanning electron microscope revealed no damaged on the molecule structure or on the surface of starch granules. The combination of neutral protease and high-intensity ultrasound was an effective technique for rice starch isolation without generating salt wastes.