Physicochemical and structural characteristics of grain associated with palatability in japonica rice

To elucidate the major components of rice quality associated with the palatability in japonica, twelve japonica rice cultivars were examined for several physicochemical properties, endosperm structure of rice grain and physical characteristics or sensory palatability of cooked rice. The rice materials used showed narrow varietal variation in grain size and shape, alkali digestibility, gel consistency and amylose and protein contents, but considerable difference in appearance and texture of cooked rice in two years. Significant variations in varieties (V), harvested years (Y), and V x Y interaction were recognized in most of the physicochemical properties except alkali digestibility, volume expansion rate and texturogram of cooked rice. There was relatively larger coefficients of variation for both varieties and years in Mg/K ratio, iodine blue value of extracted solids and amounts of extracted solid matter during cooking, breakdown and setback viscosity, and short chain ratio of amylopectin. The physicochemical properties significantly associated with glossiness or global palatability score of cooked rice were the peak, hot paste and consistency viscosities of viscogram with year difference. The high-quality rice variety “Ilpumbyeo” showed less portion of amylose on the outer layer of milled rice grain and less and slower change in iodine blue value of extracted paste during twenty minutes of boiling. This highly palatable rice also exhibited very fine net structure in outer layer and fine-spongy and well-swollen shape of gelatinized starch granules in inner layer and core of cooked rice kernel compared with the poor palatable rice. Global sensory score of cooked rice could be estimated by multiple linear regression formula, deduced from relationship between rice quality components mentioned above and eating quality of cooked rice, with high probability of determination in two years. Inconsistent distribution of tested japonica rices over years on the plane of two integrated quality components indicated that there were some different high-quality rice types and those environmental response on grain quality was greatly different.