The effects of the degree of milling on water mobility and texture of rice during simulated cooking

Abstract

Milling makes rice softer and fluffier by enabling it to absorb more water, which is closely related to the degree of milling (DOM). Thus, this study investigated the effect of differences in water absorption and distribution between rice at different DOM on its texture. The results showed that the water mobility in rice gradually increased with water absorption during soaking and cooking. After soaking, low mobile semi-bound water (T22) accounted for 90.13% of water in the rice. In contrast, this percentage rapidly decreased to 23.34% after cooking for 20 min, with 49.74% and 23.57% more mobile constructed water (T23) and the most mobile free water (T24) respectively. Milling enhanced water mobility in rice by creating more cracks on the grain surface so that T23 rapidly took up 73.7% within 10 min of cooking, resulting in fluffy and soft rice after 20 min of cooking with 67.43% of T24. As the DOM increased, rice's water absorption, moisture status, and texture gradually improved and stabilized at DOM >8.06%. Combined with the structural changes in rice, DOM <8.06% as the moderate milling could retain most of the aleurone layer. The results of the correlation analyses reaffirmed water migration as a new way to judge moderate milling, thus supporting the application of moderate milling in rice industrialization.