Comparative Study of the Impact of Alkali‐Steeping (Na2CO3, K2CO3, NaOH) with Equivalent pH on Rice Flour Processing Properties

Abstract

In this research, the rice grains are soaked in different alkalizing agents (Na2CO3, K2CO3, and NaOH) with a pH of 12 to investigate the influence of traditional alkali processing methods on the physicochemical and processing characteristics of the resultant rice flour. Further, the microstructure, crystalline structure, molecular structure, pasting properties, thermal properties, and rheological properties of the rice flour are analyzed. Soaking the rice in Na2CO3 solution and K2CO3 solution elevates the apparent amylose content in the rice flour, increases relative crystallinity, promotes the degradation of starch molecular chain, and enhances the rice flour's ability to endure stress and heat. The gelatinization enthalpy of Na2CO3‐treated rice flour and K2CO3‐treated rice flour increases, while the viscosity indices of paste gel decrease. The use of alkaline salts during steeping helps mitigate short‐term retrogradation in rice products. However, in comparison to these alkaline salts, NaOH solution with the same pH has minimal impact on the surface and longitudinal section morphology structure of starch–protein in rice grain, pasting properties, thermal properties, and rheological properties of rice flour due to its lower Na+ concentration. This indicates that NaOH solution with the same pH value cannot replace alkaline salt solutions in traditional alkali processing techniques.