Optimization of Extrusion-Expansion Process of Brown Rice Flour and in Vitro Digestive Characteristics of Its Prepared Protein Bars

In order to improve the processing convenience and stability of brown rice flour, brown rice flour treated by extrusion-expansion technology was studied. The effects of extrusion-expansion parameters on the brown rice flour properties were systematically evaluated, including the moisture content of raw material (material moisture), the extrusion temperature, the screw rotation speed, and the feeding speed. The optimal extrusion-expansion parameters were selected by orthogonal experiments. The changes in physicochemical properties such as nutrient composition, hydration properties, pasting properties, thermal properties and rheological properties before and after extrusion were analyzed using rotational viscosity analyzer (RVA) and differential scanning calorimeter (DSC). The protein bars were created with extruded brown rice flour as the main ingredient, and their in vitro digestive properties were analyzed. The results showed that the optimal process parameters of extruded brown rice flour were 180 ℃ extrusion temperature, 27% material moisture, 200 r/min screw rotation speed and 8 kg/h material feeding speed. Compared with the raw material powder, the total starch, branched-chain starch and fat content of the extruded brown rice flour were decreased by 14.21%, 17.91% and 64.35%, respectively; the protein and ash content were not changed significantly. The water solubility index and water absorption index increased by 2.94 and 1.23 times, respectively, and the color deepened. At the same shear rate, the extruded brown rice flour had lower shear stress, and the RVA and DSC results showed that the peak viscosity, trough viscosity and final viscosity of the extruded brown rice flour decreased by 1536, 909 and 2311 cP, respectively, and the enthalpy of pasting decreased from 9.50 J/g to 0.74 J/g. The protein bars thus created showed a decrease in the stable concentration (C∞), a shrinkage in the area under the curve (AUC), and a decrease in the hydrolysis index (HI), and starch hydrolysis decreased, resulting in protein bars that were digested and absorbed more slowly and provided a longer-lasting feeling of satiety. This study provides technical solutions and theoretical support for the innovation and development of brown rice casual ready-to-eat products.