Effect of Temperature at Ripening Period on the Eating Quality of Rice : Effect of temperature maintained in constant levels during the entire ripening period

[摘要] Rice varieties from Hokkaido, Tohoku and Hokuriku were cultivated at different temperatures during the ripening period. The maximum viscosity of starch and yield of starch from milled riece which seemed to be the two main factors affecting the eating quality of the harvested rice were investigated. 1. Maximum viscosity of starch correlated most strongly with amylopectin content. And the lafger the amount of phytin in milled rice, the smaller the alkali decomposition of milled rice, and the fewer the appearance of milky white rice kernels, the higher was the maxlmum viscosity of starch, respectively. 2. Maximum viscosity of starch was increased by higher temperature during the ripening period. It was high in early varieties and palatable varieties. In amylogram, peak viscosity was correlated most signifiCantly with break down and significantly with rising temperature and minimum viscosity. Peak viscosity was negatively correlated most significantly with setback and significantly with consistency. 3. Amylose content was decreased by higher temperature during the ripening period. It was also low ln early varieties and in palatable varieties. At lower temperature, amylose content showed more highly negative correlation with maximum viscosity. 4. Phytin content in milled rice was increased by high temperature during the ripening period. It was also high in palatable varieties and in Hokkaido varieties. At low temperature, phytin content was lowly correlated with maximum viscosity. 5. The rice kernels of high alkali decomposition is estimated to be ripened at low temperature, because the degree of alkali decomposition was much higher when ripening temperature was lower. Within the same temperature of ripening period, the rice grains with lower maximum viscosity were more readily decomposed, and this tendency seemed to be due to the higher amylose content. 6. The occurrence of milky white rice kernels was negatively correlated with maximum viscosity of starch. White core rices occurred at high temperature and the percentages of white core rice appeared to be in parallel with the varietal difference of milky white rice kernels. 7. The starch yieid obtained from milled rice was negatively correlated with protein content, with high significance. The starch yield was low in the early or inferior taste varieties. 8. The amount of protein in milled rice was higher in the case of early varieties and small grain varieties. The starch of lower maximum viscosity was yielded from the rice grains ripened at lower temperature when compared at the same level of protein content.

[学科分类] 农业科学（综合）