Relationship between starch digestibility and physicochemical properties of aged rice grain

The purpose of this study was to investigate the relationship between starch digestibility and physicochemical properties of aged rice grains. Fresh rice (FR), aged rice (AR), and accelerated aged rice (AAR) grains were prepared and used as samples. Freshness evaluations of pH and L* based on lipid deterioration showed that polished AR and AAR were degraded samples. Crude protein and apparent amylose contents and molecular weight profiles of proteins did not differ between polished rice. Although there was no significant difference in surface firmness between cooked grains, cooked AAR grains had significantly lower surface adhesiveness and adhesion than cooked FR and AR grains. Microscopic observations showed that intracellular disruption of the aleurone layer tended to increase in the order of polished AR > AAR > FR grains. No significant differences were found in the equilibrium concentration of starch hydrolysis (111.69-112.82%), kinetic constant (k) (7.57 x 10- 3-8.61 x 10-3 min-1), and estimated glycemic index (eGI) (88.78-93.27) of the cooked grains. However, k and eGI showed significant linear correlations with pH and L*, respectively. These results revealed that changes in the tissue structure of polished grains due to aging affected lipid deterioration, correlating with the starch digestibility of cooked grains.