Effects of moisture changes on physicochemical properties of rice flour during semidry grinding

In this study, the effects of moisture changes on rice grain crack, volume and hardness during the semidry grinding process, as well as the damaged starch, microstructure, hydration, and pasting properties of rice flours prepared with different semidry grinding conditions were studied. Moisture changes of semidry grinding showed a "decrease-increase-decrease" pattern which represents hot-air treatment, tempering and drying process, respectively. With the moisture changes of semidry grinding, severe cracks occurred on the rice grains after hotair treatment, and the hardness of the rice grains decreased rapidly in the first 15 min of tempering. For rice flours, the hot-air treatment and tempering were beneficial to reduce the content of damaged starch, and the tempering process had the greatest influence on the hydration and pasting properties of the rice flours among the three processes of semidry grinding. Moreover, the drying process had a positive effect on thermal paste stability and the resistance of retrogradation of the rice flours. These findings indicated that the "decrease-increasedecrease" pattern of moisture changes during the semidry grinding process affected the rice flour qualities, and could be used to guide the semidry grinding production of specific rice flours.