Effects of the degree of milling on the quality characteristics of rice ‘Nuruk’

Abstract

This study aimed to investigate the effects of the degrees of milling of rice (0-50%) on the physicochemical properties and enzymatic activities of rice ‘Nuruk’. As results, the contents of the general components of milled rice, except for the starch value (85.13-90.99%) decreased as the degree of milling increased. The moisture content of rice with different degrees of milling ranged from 11.04 to 12.68% and significantly decreased as the degree of milling increased. Furthermore, the hydration rate increased as the degree of milling increased. The pH of rice ‘Nuruk’ was the lowest at 5.32 in the 0% milled rice ‘Nuruk’ and highest at 5.98 in the 30% milled one, which indicated no correlation between pH and degree of milling. By contrast, the soluble solid and reducing sugar contents which are correlated with the starch value of rice increased as the degree of milling increased. For the enzymatic activities of each rice ‘Nuruk’, there was no clear trend for the α-amylase and acidic protease activities with respect to the degree of milling, whereas the glucoamylase activity decreased with increasing degree of milling. Correlation analyses indicated that the activity of glucoamylase decreased as the starch value of rice increased, but increased as the crude protein content of rice increased. The activity of acidic protease had a negative correlation with the crude lipid content of rice.