POLISHING PROPERTIES OF WHITE-CORE AND NO N-WHITE-CORE GRAINS FRACTIONATED FROM THE SAME VARIETY OF RICE

White-core and non-white-core rice grains have been accurately fractio nated by a shape-analyzing system on the basis of a principle of image analysis. The hardness of white-core grains was lower than that of no n-white-core grains when comparing grains of the same variety of rice having the same true polishing ratio, and there was a tendency for the hardness of grains to decrease and for white-core grains to be polish ed at a higher rate than non-white-core grains as polishing time incre ased. The rate of water absorption of white-core grains was higher tha n that of non-white-core grains but the absorbed water contents of the two types of grains were approximately the same after 120 min steepin g. Loss of polishing ratio of white-core grains was significantly lowe r than that of non-white-core grains at 50% polishing ratio. This tend ency was the same in the case of the practical polishing mill used in sake-making. Moreover, we obtained vertically cracked rice, which allo wed for the observation of the white-core on the surface of the cracke d rice grains. The white-core showed a pair of are shape and white-cor e was not appeared in the center of the are.