Solubility and functionality improvement of rice glutelin by homologous assembling combined with sonication: Potential mechanism

The low solubility of rice glutelin (RG) leads to the poor solubility of rice protein as a whole, which significantly limits its application in liquid foods and protein-based functional ingredients. Therefore, developing efficient methods to enhance the solubility of RG is crucial for expanding the food applications of rice protein. In this study, homologous assembling combined with sonication was utilized to improve the solubility of RG, with assemblies constructed using RGs from japonica and indica rice at different ratios. The solubility, emulsifying, and foaming properties of the assemblies were evaluated. Additionally, the multi-level structures, molecular weight distributions, surface properties, and aggregation state of these assemblies were characterized in order to reveal the potential mechanism underlying the improved solubility of RG after homologous assembling and sonication. The solubility of RG increased up to 8 times after homologous assembling and sonication, while the emulsifying and foaming capacities increased up to 1 and 3 times, respectively, compared to natural RG. The two RGs tend to assemble through hydrophobic interaction (mainly) and electrostatic force, forming assemblies with more charged groups exposed on protein surface. The increased exposure of charged groups further induces strong repulsive forces among molecules, preventing protein aggregation and thereby enhancing water-solubility. With improved water-solubility, the assemblies were easier to be absorbed at water/oil or water/air interfaces, leading to enhanced emulsifying and foaming ability. This study may provide a reference for expanding the utilization of rice protein and other plant proteins with poor water-solubility in the food industry.