Starch characteristics and enzyme digestibility of steamed rice grains grown at high air temperature during grain filling in 2010

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  • イネ登熟期が記録的な猛暑となった平成22年産米のデンプン特性及び蒸米酵素消化性
  • イネトウジュクキ ガ キロクテキ ナ モウショ ト ナッタ ヘイセイ 22 ネンサンマイ ノ デンプン トクセイ オヨビ ムシゴメ コウソ ショウカセイ

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Abstract

The mean temperature in August 2010 was the highest ever recorded in Japan. Previous studies showed that higher temperatures during rice grain filling cause a higher retrogradation of gelatinized starch due to longer side chains of amylopectin, as well as lower enzymatic digestibility during sake making. Thus, the effect of extremely high temperatures during the 2010 season on starch characteristics of rice grains for sake making and the enzyme digestibility of steamed rice grains was examined. The gelatinization temperatures of rice samples harvested during the 2010 season were higher than those harvested in the 2007 (a hot summer but cooler than 2010) and 2009 (a cooler summer) seasons. The decreasing degree of enzymatic digestibility of steamed rice grains after partial retrogradation of starch was higher in 2010 than in 2007 and 2009. On the other hand, even in the rice samples harvested in the same prefectures, gelatinization temperatures and the enzyme digestibility of rice grains varied among samples. Especially, the rice samples whose heading date was late showed lower gelatinization temperatures and higher enzyme digestibility of steamed rice grains than early heading samples. Moreover, the polished rice grains harvested during the 2010 season showed lower alkali solubility than those harvested in 2009. The present study suggests that the enzyme digestibility of steamed rice grains can be predicted by mean air temperature after heading even in historic high air temperature such as the 2010 summer, and the alkali solubility method can be useful for examining the starch characteristics of rice grains conveniently.

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