SLURRY VISCOSITY AS A POSSIBLE INDICATOR OF RICE QUALITY

Abstract

Forty‐one rice varieties belonging to eight quality types were examined. The viscosity of a 5% rice flour slurry dispersed in 2% carboxymethylcellulose, measured with an Ostwald capillary viscometer, was remarkably constant among varieties within the same quality type but increased significantly from type I (high‐amylose) through type VIII (little or no amylose) rice. Slurry viscosity was strongly affected by particle size, being higher for finer flour, but it appeared independent of the age of the rice after harvest. Slurry, as well as paste viscosity, was affected by kernel chalkiness in rice, chalky grains showing lower viscosity than vitreous grains. Chalky rice grains contained less amylose and hydrated more in ambient water than nonchalky ones. When ground under a constant condition, high‐amylose rice yielded slightly coarser flour than intermediate‐ or low‐amylose rice, suggesting differences in grain hardness.