Differences and similarities of albumins from japonica rice bran, japonica, indica, and javanica rice endosperm in the suppressive effect of postprandial blood glucose elevation

Abstract Suppression of rapid increase in blood glucose level using food components can prevent diabetes. To use functional food components from natural resources, information regarding the plant varieties and plant parts where the component exists is important for the effective extraction and the effective use of biological resources. We have previously found that proteins from the albumin fraction of rice endosperm are indigestible and adsorb glucose to suppress postprandial blood glucose elevation in vivo. However, the variety and location of this functional protein remain unknown. We investigated whether water‐soluble fraction from the endosperm of indica and javanica rice and red and middle bran of japonica rice contains functional albumin observed in the endosperm of japonica. Middle bran was found to possess an indigestible albumin with the same molecular weight as that in the endosperm of japonica and adsorb a large amount of glucose. Middle‐bran albumin suppressed postprandial blood glucose elevation after oral glucose loading in animal experiments, as well as the rice‐endosperm albumin. As middle bran is the outer layer of the endosperm, many functional components are distributed. Our study can aid the effective use of middle bran, which is predominantly discarded in the process of making rice wine, as a functional food material for the prevention of diabetes mellitus.