本實驗是以臺中農業改良場生產之三種稻米(臺農67號、臺中189號和臺中秈17號)探討其在開花後30天、35天和40天之米粒構造及理化性質。結果顯示，此三種稻米在開花後30天、穀粒已充實，米粒外型、干粒重及糙米碾製率皆不因收割期不同而有太大差異。但不同收割期，對精白米碾製時之碎米粒的產生，則有影響放品種之不同而有所差異。化學成份方面，粗脂肪含量會隨收割期之增長而遞減，但粗蛋白及粗灰分含量則不大受影響;又、米粒中之澱粉含量隨收割期之延長而增加， 80%乙醇可溶性醣量則遞減，三種米澱粉中之直鏈澱粉含量皆以開花後三十五天收割者含量最高。以SEM觀察米粒橫切面時，臺農67號及臺中189號在35天便有複合澱粉顆粒(compound starch granule)出現，而臺中秈17號則須等至闐天才有類似構造顯出。由Brabende「連續粘度圓判斷，不同收割期對米澱粉之糊化性質影響不大;同時以DSC所測出之糊化溫度及糊化大含亦不因不同收割期而期大差別。此外，品種間之異同處亦有探討，綜合上述桔果，此三種稻米似以35天為最適收割期。 Threeeties of rice (Tianung 67, TN 67; Tiachung 189, TC 189, and Taic-hung Sheng 17, TCS 17) grown at Taichung Agricultural Improvement Station were applied as the samples to examine the structures of the rice grains and their physicochemical properties at 30, 35, and 40da.vs alter Aowering (DAF). The results indicated that the rice kernels of all three varieties were already fully grown at 30 DAF; there were, consequently no signihcant differences on the shapes of rice grains, the thousand kernel weights and the milling yield of brown rice for the samples harvested from various DAF, but not For the head milling yield and the total milling yield of the polished rice. However, the contents of crude fats would decrease with the harvest time prolonged; but the contents of crude proteins and crude ash would not be affected signihcantly. The starch contents were increased and the carbohydrate contents of the 8096 ethanol extractable were decr- eased as the harvest time delayed. The amvlose contents of all three varieties gave the highest amounts at 35 DAF. The compound starch granules were obser-ved from the SEM on the both cross-sections of TN67 and TC189's rice kernels at 35 DAF, and the similar observation was seen until 40 DAF for TCS17. Thedifferent harvest times would not inHuence much on the pasting behaviors of the rice starches, based on the results of the Brabender amyiograms. From DSC anal ysis, the gelatinization temperarures and the gelatinization enthalpies of all three starches would not be aft'ected signihcanrly by the different harvest times. The comparison of the differences among the varieries oF rice were also investigated. From the above data, it Could be concluded-that the 35 DAF was the optimal harvest time.