Storage performance of non-waxy Japonica rice varieties preferred by Japanese consumers: Evaluation of physicochemical properties and in vitro starch digestibility

This study aimed to evaluate the changes during storage in the composition, texture, and starch digestibility of non-waxy Japonica rice varieties (cv. Yudai 21, Koshihikari, and Milky Queen) preferred by Japanese consumers. Stored grains were prepared by storing fresh grains at 30 degrees C for 6 months. Changes in pH of the rinse water and the color reaction of catalase activity showed a decrease in freshness and significant differences between varieties, between storage periods and by interaction. The total and resistant starch content decreased during storage and had significant correlations with pH and color reaction. Yudai 21 had higher surface adhesiveness, surface adhesion, and overall adhesiveness than Koshihikari with a similar apparent amylose (AA) content and Milky Queen with a lower AA content, regardless of storage. The equilibrium concentration of starch hydrolysis ranged from 84.1% to 94.9% with no significant difference and showed a significant correlation with pH (r = 0.78). The estimated glycemic index (eGI) was significantly affected by variety, with Koshihikari having the highest eGI and Yudai 21 having the lowest eGI, but was not affected by storage. Among the varieties, Yudai 21 was a suitable variety not only for fresh grains but also for stored grains, with high eating quality and low starch digestibility.