Effects of differential protein removal on the properties of early indica rice flour

ObjectiveTo investigate the mechanism of the effect of deproteinisation on the physicochemical and functional properties of rice flour.MethodsEnzymatic and alkaline methods were used to remove protein from early rice flour, and the damaged starch content, size distribution, morphology, solubility, swelling power, pasting characteristics and textural characteristics of the deproteinized rice flour were analyzed.ResultsSodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and confocal laser scanning microscope (CLSM) showed that the alkaline method equally removed the protein subunit where as the enzymatic method showed a better homogeneity of protein removal from the surface of starch.The size distribution of the control showed a majorpeak at ca.70 μm and it shifted to 6μmafter protein removal. With the reduction of the protein content, and the damaged starch content of the deproteinized rice flour decreased while its elasticity and hardness increased. The deproteinized rice flour with 3.0% of protein ([email protected]), which was treated by alkaline method, showed a most uniform particle distribution, and a minimum D90 of 23.58 μm was observed. When compared to the control, its damaged starch content decreased from 3.32% to 1.48% while the elasticity and hardness increased by 54.55%, 52.60%, respectively. The deproteinized rice flour had lower peak viscosity, breakdown viscosity and final viscosity than the control, and the [email protected] had minimum breakdown and setback viscosities, which indicated that it exhibited best paste stability and was difficult to retrograde.ConclusionThe protein removal by alkaline and enzymatic methods can improve the properties of early indica rice flour. The enzymatic method has mild reaction conditions and the result and products has better protein and size distribution and are more difficult to retrograde than the rice flour that treated by alkaline method.