Viscosity, a crucial characteristic for rice palatability, is affected by endosperm characters. We compared correlations between differences in viscosity of japonica rice with various palatability and endosperm characters. Changes in apparent amylose and protein contents (AAC% and PC%, respectively) and amylopectin side-chain distribution and the relationship of these traits with palatability were investigated in superior and inferior spikelets of good cultivars with low amylose content from Hokkaido and common cultivars from northeastern Japan, using rapid visco analyzer characteristics and rice-grain microstructures. Significant differences occurred in PC%, AAC%, breakdown, setback, peak time, and pasting temperature of different cultivars and grain positions. Amylopectin components showed remarkable differences in grain surfaces, surface layers, and section structure between the grain varieties. Hokkaido cultivars showed better viscosity than northeastern cultivars, particularly initial stage grains. Correlation analysis indicated viscosity was mainly AAC%-dependent, whereas differences in endosperm characteristics between spikelet positions were mainly due to grain-filling temperature.

Background and objectives Rice with very low amylose content tends to have a good taste, while germ‐remaining rice is nutritive because it retains nutrient‐rich embryos. We cultivated a batch of new germ‐remaining rice varieties with very low amylose content, and good nutrition and taste. We tested the differences in taste quality between superior and inferior grains. Findings The plumule ratio of superior grain was significantly higher than that of inferior grain. The elasticity of the surface layer and whole layer of superior grains was greatly reduced, whereas quality of balance (stickiness/hardness) and tackiness were increased. The proportion of apparent amylose content (AAC) and amylopectin long‐chain branching (Fb3) decreased, whereas the proportion of medium‐length branches (Fb1+2) increased significantly. Correlation analysis showed that small value of aspect ratio and low proportion Fb3, especially the former, can improve the quality of balance of rice. Moreover, plumule ratio showed a high correlation with grain shape and filling degree. Conclusions Therefore, for the specially developed rice, plumule ratio and edibility can be improved by promoting grain plumpness and weight ratio of the embryo, especially the inferior grain. Significance and novelty For rice taste improving, the contribution of grain filling was greater than that of chemical changes in the endosperm composition, and breeders should pay attention to grain shape improvement and filling to improve the taste of rice.