Abstract
Six common Japanese cultivars of ordinary (non-glutinous) rice (Oryza sativa subsp. japonica), namely Koshihikari, Hitomebore, Akitakomachi, Kinuhikari, Nipponbare and Hinohikari, were obtained from public agricultural experiment stations to investigate the production of reducing sugars during rice soaking, as well as related starch-degrading enzyme activities. Polished rice samples were ground to make rice flour consisting of 13% outer endosperm and 87% inner endosperm. Samples were soaked in water, and the amount of reducing sugars formed was then measured using the Somogyi-Nelson method. α-Glucosidase, α-amylase, and β-amylase activities for all samples were also measured. As a result, significant differences in the production of reducing sugars were found among cultivars. This research also suggested the possibility of region-dependent differences in the generation of reducing sugars. As for enzyme activities, α-glucosidase contributed the most to reducing sugar levels in all cultivars. The enzyme contributing the second most differed depending on the cultivar. Within the inner rice endosperm, which showed the greatest influence on reducing sugar formation, the top two enzymes contributed to reducing sugar formation nearly equally. Enzyme activities showed differing characteristics depending on the cultivar, suggesting the existence of cultivar-dependent differences in the formation of reducing sugars.
