We examined the appearance quality and palatability of milled rice for each grain-thickness group. The rice cultivars, Nipponbare and Hinohikari, were cultivated at the paddy field of Field Science Center, Okayama University in 2009. For high-temperature treatment, both sides of the transparent chamber were opened when the temperature exceeded 36 degrees C, and closed when lower than 25 degrees C, and 50% shading treatment with black cloth was applied during the grain-filling period. After harvesting, the grains of brown rice were sorted according to thickness using a rice grader, and classified
into eight grain thickness groups, less than 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, and over 2.2mm. The appearance quality of grains was measured, and milled grains were cooked, and the palatability and physical properties were measured. The brown rice yield in high-temperature plots was 10-21% less than control due to the decrease in the ripening percentage and 1000-grains weight. Yield in the shading plot dropped to 16-24% less than control mainly due to the decrease in the ripening percentage. The percentage occupation of grains with 1.8-1.9mm thickness was higher in Hinohikari than Nipponbare. In high-temperature plots, thickness of 1.8-2.0mm decreased and thickness of higher than 2.0mm increased in both cultivars. The shading treatment increased thickness of lower than 1.9mm markedly. It was
cleared that the shading decreased grain thickening growth and grains was distributed more among thinner groups, and high-temperature promoted the grain thickening growth despite the decrease in 1000-grains weight. In both cultivars, the lower the grain thickness group, the lower the percentage of perfect grain due to the increase in the percentage of chalky grain. The palatability value of milled rice
was greater in Hinohikari than Nipponbare. The lower the grain thickness group, the lower the palatability value and stickiness, and those tendencies were remarkable in Nipponbare than Hinohikari. The shading and high-temperature treatments decreased the palatability value and the stickiness, especially in Nipponbare. The palatability value decreased with lower the grain thickness group due to an increase in the percentage occupation of chalky grains.