Physico-ecological studies on quality formation of rice kernel. III. Effects of ripening stage and some ripening conditions on free amino acids in milled rice kernel and in the exterior of cooked rice.

Abstract

Free amino acids (FAA) in the cooked rice exterior and in milled rice kernels (ground milled rice) were studied from the standpoint of taste. The amount and proportion of FAA in the exterior of cooked rice were compared with those in ground milled rice in relation to maturity stages. Moreover, the effects of nitrogen top-dressed at full heading time, air temperature during ripening period and varietal differences on FAA were examined. The amount of FAA was substantial in immature rice but it decreased with maturation, particularly that in the exterior of cooked rice declined continuously till the over-ripened stage. Taste which can be felt by human senses was suggested to be rich in immature rice but poor in over-ripened rice. FAA proportion in the exterior of cooked rice varied considerably during ripening, although that in ground milled rice hardly changed. The amount of FAA was also little in rice of both exceedingly low and high protein content. A low temperature regime produced an increased amount of FAA, as was also seen in immature rice. In terms of variety, rice of good eating quality contained plenty of FAA. This trend was more remarkable in the exterior of cooked rice than in ground milled rice. In good eating quality rice, FAA, especially glutamic acid, easily dissolved out from the cooked kernels in the cooking process.