Abstract
The distribution and the properties of components of rice grain were investigated to optimize the processing of rice under consideration of the characteristics for utilization. The gelatinization properties of the starch in the layers to be polished and the underlying physicochemical properties were investigated on rice grains of three varieties, Habataki, Ohchikara and Kinuhikari and following results were obtained. (1) The components and their properties were varied among the layers for all the three varieties. The contents of moisture, minerals (Mg, K, Fe) and protein were higher in the outer layer, whereas the contents of starch which is the major component was high in the inner layer, and the apparent amylose content was apt to be high. Regards as tone, the brightness (L) was high and the degrees of redness (a) and yellowness (b) were low in the inner layer. The differences in the length variation of chain length distributions of amylopectin were small among layers and varieties. (2) Viscograph of the respective layers revealed that the viscosity was high in the inner layer and the values of characteristics of gelatinization, such as maximum and minimum viscosities, the final viscosity, breakdown, consistency were generally high. The viscosity changed stepwisely and the changes were different among the varieties and the lowering of viscosity was marked in the outer layer. The viscosities changed by four steps for Habataki, by two steps for Ohchikara, and by three steps for Kinuhikari. (3) By analyzing the relationships between the gelatinization properties (viscosity) and the physicochemical properties, it was found that the former properties for each layer were closely correlated to the contents of amylose and protein, and the tone. These results suggested that the contents of starch including the apparent amylose and protein were the important factors affecting the gelatinization characteristics of each layer.
