Effect of Pretreatment and Low-temperature Extrusion on the Physicochemical Properties of Embryonic Rice Flour

The embryonic rice flour was roasted, pre-gelatinized, and extruded at a screw speed of 100 r/min, a moisture content of 30%, and an extrusion temperature of 50~90 ℃. The effects of different extrusion temperatures on the physicochemical properties of embryonic rice flour were investigated in the pre-gelatinization-low temperature extrusion process. The results showed that with the increase of extrusion temperature, the pasting degree of embryonic rice flour gradually increased. The contents of starch, fat, protein, and GABA decreased, while the contents of soluble dietary fiber increased significantly after the temperature exceeded 70 ℃. The water absorption index of embryonic rice flour decreased significantly (P<0.05), the water solubility index and swelling potential increased. The total color difference increased first and then decreased. The particle size increased significantly (P<0.05). The analysis of differential scanning calorimetry showed that the enthalpy of heat absorption decreased from 1.14 to 0.82 J/g, and the degree of pasting increased gradually at the starting temperature (T₀), peak temperature (T_P), and termination temperature (T_C) of embryonic rice flour. Fourier infrared spectroscopy showed that no new groups or chemical bonds were formed in the starch structure of rice flour at all extrusion temperatures. The above results showed that pre-gelatinization-low temperature extrusion had a significant effect on the physicochemical characteristics of embryonic rice flour, and the appropriate extrusion temperature reduced the loss of nutrients.