In this study, we investigated the starch, pasting, thermo-physical, and iodine absorption spectrum properties of Chou 2418, a new amylopectin long-chain (ALC) rice cultivar developed by crossing a high amylose rice cultivar Koshinomenjiman and amylose extender mutant rice cultivar EM10. Chou 2418 exhibited high apparent amylose content, high pasting temperature, and low breakdown viscosity. The iodine absorption spectrum indicates that Chou 2418 contains long-chain glucans of amylopectin and also has high amylose content. Boiled rice grains of Chou 2418 contained more resistant starch (RS) than those of high amylose rice cultivars. The RS content of Chou 2418 rice grains increased following the retrogradation of starch granules, and the grains became hard and non-sticky. The RS content of Chou 2418 was 25 times higher than that of Koshihikari, the most popular rice cultivar. Taken together, these data suggest that Chou 2418 is a suitable raw material for bio-functional foods that help prevent diabetes.

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The effects of high temperature on rice taste, grain quality, grain physical properties, apparent amylose content, and gelatinization were evaluated for 3 consecutive years using products grown in plots supplied with hot water as high-temperature stress. In the taste sensory evaluation, the comprehensive evaluation, appearance and taste, and the stickiness decreased while the hardness increased by the high-temperature treatment in all varieties. The surface stickiness decreased by 11%, the surface stickiness to hardness ratio decreased by 10% and the overall stickiness to hardness ratio decreased by 6%, whereas the overall hardness increased by 4%. The apparent amylose content decreased by 10%. The rice flour gelatinization starting temperature increased by 1.2°C, and the peak viscosity and holding viscosity increased by 9% and 5%, respectively. The breakdown increased by 11%. To identify the relevant palatability characteristics, we surveyed the correlation between statistical analysis parameters. The surface stickiness and surface stickiness to hardness ratio showed the highest correlation, suggesting that these parameters are indicators of the lower eating quality of rice during high-temperature treatment. The gelatinization starting temperature also showed a high correlation and was considered a useful indicator of taste degradation due to high-temperature treatment. The surface stickiness to hardness ratio, which showed the highest correlation with hardness in the taste sensory evaluation, was considered an indicator of grain hardness.