The rice grain localization of endosperm enzyme activity

Abstract

Rice endosperm enzyme activity affects the qualities of cooked rice. In this study, we aimed to investigate the differential localization of various enzymes in the endosperm of milled rice. Using hydrolytic enzyme analysis, we confirmed the activities of amylase, protease, and lipase. We milled brown rice to yields of 30-90%, at intervals of 10%, and then extracted enzymes from the milled rice. Total protein content was reduced by about 43% with 60% removal of the outer layer, resulting from the decrease in milling yield from 90-30%. However, the watersoluble protein content was only approximately 0.3% in both the inner and outer layers. Moreover, the activities of esterase (C4), acidic and alkaline phosphatase, leucine allyl amidase, naphthol-AS-BI-phosphodiester hydrolase, α- and β-galactosidases, N-acetyl-β-glucosaminidase, debranching enzyme, β-amylase, and α-glucosidase were similar between the inner and outer layers. In contrast, the activities of esterase lipase (C8), valine allyl amidase, cystine allyl amidase, trypsin, β-glucosidase, α-mannosidase, α-amylase, and polygalacturonase were greater in the outer layer. Thus, these results showed that measurement of rice endosperm enzyme activity could be used to assess enzyme localization.