graduate student Nihon University Fujisawa, Kanagawa, Japan
Although rice bran is known to be rich in dietary fiber and protein, it is mainly used for low-value-added products such as feed and fertilizer, and approximately 500,000 tons are discarded annually. We have already shown that rice endosperm albumin (RA) is resistant to digestion and adsorbs glucose like dietary fiber. If rice bran contains albumin that has an RA-like property, it can be used in various foods as a functional food material to control blood glucose concentration. In this study, we evaluated the glucose adsorption capacity of rice-bran albumin and the digestibility.
Brawn rice was polished 10% from the surface to give red bran, and the next 10% afforded middle bran. After water-soluble fraction was extracted from each bran, albumin was obtained by ammonium sulfate precipitation. The amount of glucose adsorbed on rice-bran albumin was evaluated in vitro by measuring the diffusion rate of glucose from the solution containing rice-bran albumin in the upper chamber through semipermeable membrane to the lower chamber. The digestibility was evaluated by SDS-PAGE after treating albumin solution with pepsin and pancreatin.
Glucose-diffusion rate decreased in the presence of red or middle-bran albumin. The decrease in glucose diffusion rate by bran albumins was larger than that by RA and carboxymethyl cellulose. After pepsin and trypsin treatment, high-molecular-weight peptide of 14 kDa remained only in case of middle-bran albumin.
In conclusion, middle-bran albumin adsorbed glucose and was resistant to digestion, being expected to suppress glucose absorption in the small intestine in vivo like RA.