| Summary: | 碩士 === 國立中興大學 === 農藝學系 === 87 === This study was to understand the change in rice grain quality during ripening stage of different recommended varieties. We examined the changes in grain dry weight, milling quality, grain appearance of brown rice, grain dimension of brown rice, and physicochemical properties of milled rice. The relation between time of maximum grain dry matter accumulation (Tmax) and grain moisture percentage was used in the pursuit of indicative grain characteristics of the appropriate harvesting period of recommended varieties. The results are summarized as follows:
The Tmax of the tested varieties was 22 to 31 days after anthesis. Among them, Taichung Sen 10 had the shortest Tmax of 22 days, while Koshihikari’s 31 days being the longest. The dry grain weight of different varieties and crop seasons were dramatically different. Significant interaction existed between varieties and crop seasons. Which showed that the dry grain weight at Tmax was a grain characteristic and was affected by crop season.
After Tmax, little changes were found in grain dimension of brown rice and physicochemical properties of milled rice. Significant increase in brown rice percentage and milled rice percentage were found in indica rice Taichung Sen 10, while the changes in other japonica rice varieties being insignificant. For immature kernel percentage and whole kernel percentage, all varieties except Koshihikari, which had held constant at Tmax, only ceased to change in 31 to 34 days after anthesis. The differences were significant among varieties and crop seasons, and we could find significant interaction between varieties and crop seasons. Which showed that the change of milling quality after Tmax was also a grain characteristic and was different in different crop seasons.
The grain moisture percentage was 24% to 30% after Tmax. However, all varieties except Koshihikari, which had held constant at Tmax, were still under changes. Milling quality of all varieties was not stable until the grain water percentage was about 20% to 27%. Grain quality had held constant in this range of grain moisture percentage. As a result of this experiment, the proposed grain moisture percentage for harvesting was 24% to 26% for Koshihikari and Tai Ken 8, 25% to 26% for Kaohsiung 142, 22% to 27% for Tai Ken 9, and 20% to 23% of Taichung Sen 10.
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