Milling affects rheological and gel textural properties of rice flour

Background and objectiveGenerally, most milled rice is consumed as cooked grain. Nevertheless, a steady increase in new processes and products involving rice flour as a fundamental ingredient can be observed, which imposes a need for deeper knowledge of the properties of milled rice flours. The objective of this study is to investigate the effects of combinations of milling speed (750, 950, and 1,050 r/min) and milling time (20, 40, and 60 s) on the rheological and gel textural properties of waxy, low-, and high-amylose rice of flour. FindingsSteady shear rheological measurements revealed that a positive relationship exists between milling revolution (speed x time) and the consistency coefficient values or hysteresis area of rice flour pastes; that is, the more the total milling revolutions, the higher the viscosity and stronger the thixotropic properties. During rheological measurement, waxy and low-amylose rice flour pastes from milled rice with higher storage moduli and lower the ratio of storage moduli and loss moduli delta exhibited more elastic properties and higher gel strength than those from unmilled rice, indicating that a more rigid structure was formed. As milling speeds and durations increased, the hardness of waxy and low-amylose rice flour gels increased, but the adhesiveness decreased. ConclusionsThis study showed that milling speed had more pronounced effects on the extent of change than did milling time regarding steady flow and textural properties. Meanwhile, both milling speed and duration could change the properties of rice flour to different extents. Significance and noveltyThese findings provided fundamentals for the effects of combinations of milling speed and milling time on the rheological and gel textural properties of the flours produced from waxy, low-, and high-amylose rice grains. Moreover, this research may help enable rice millers to produce improved functional rice products with minimal processing by precise control of suitable milling conditions.