Effect of the additive amount of extruded pregelatinized rice flour on the physicochemical properties of rice flour

In this study, extruded pregelatinized rice flour was added to rice flour with mass fractions of 0%, 2.5%, 5.0%, 7.5%, 10.0%, and 12.5%, then, the changes in the quality of the mixed rice flour and rice paste were determined, including water hydration, freeze-thaw stability, pasting, thermodynamics, rheological properties, static and dynamic rheological properties. The results showed that the addition of pregelatinized rice flour increased the water absorption index of rice flour by 2.10%, and the regain, peak and valley viscosities of rice flour gels were reduced by 3.99%, 4.94%and 3.05%, respectively. The peak value, valley value and final viscosity of the mixed system decreased significantly with the increase of pregelatinized rice flour addition, and the attenuation value and regeneration value of the rice flour gel decreased significantly, but the effect on the pasting temperature was small. After the addition of pregelatinized rice flour, the water precipitation rate of the mixed rice flour decreased significantly from 60.43% to 56.44%, hence there was a negative correlation between the water precipitation rate and the amount of pregelatinized rice flour added. The differential scanning calorimeter results showed that the addition of pregelatinized rice flour increased the peak temperature and decreased the enthalpy of pasting by 7.62%, hence, the thermal stability of rice flour was reduced by the addition of pregelatinized rice. The energy storage and loss modulus of the rice flour gels decreased, the consistency factor K of rice paste increased by a factor of 0.69, and the thixotropy of the rice paste increased with the addition of pregelatinized rice flour. The energy storage modulus and loss modulus of the rice paste decreased, but the loss angle tangent increased. In summary, the addition of pregelatinized rice flour to rice flour resulted in a certain improvement in hydration characteristics and freeze-thaw stability, and a reduction in the regrowth value as well as enthalpy, which can reduce the ageing and cooking or baking time of rice products.