Effect of Extrusion Process on the Nutritious and Physicochemical Properties of Purple Brown Rice Flour

Using purple brown rice as raw material, extruded purple brown rice flour was prepared by twin-screw extrusion technology, the changes of nutrition, hydration properties, gelatinization properties, thermal properties and rheological properties of purple brown rice flour before and after extrusion were analyzed. The results showed that , compared with the raw materials, the total starch, amylopectin and fat content of the extruded purple brown rice flour decreased by 12.45%, 16.03%, and 67.45% respectively, the protein, total amino acid, calcium and zinc content changes were not change significantly (P>0.05). Besides, the content of total phenols, total flavonoids and total anthocyanins were reduced by 23.70%, 28.34% and 29.16% respectively, and the antioxidant activity was weakened. The water solubility index and water absorption index were increased by 2.80, 1.07 times respectively, and the color became deeper. Under the same shear rate, the extruded flour has lower shear stress, which easier to stir. The results of RVA and DSC showed that the peak viscosity, lowest viscosity, attenuation value, final viscosity and retrogradation value of extruded purple brown rice flour decreased by 3528.50, 2038.83, 1489.00, 3975.33, 1937.00 cP, the gelatinization degree was 93.15%, and the enthalpy reduced from 5.23 J/g to 0.74 J/g, indicating that most of the starch has been gelatinized. According to this, the nutritive value retention of the extruded purple brown rice flour was still at a relatively high level, the hydration capacity was significantly improved, the taste was good, and it had good application value.