Rice proteins and carboxymethyl cellulose complexes: a tunable system for the creation of novel acid gels

Despite the widespread cultivation of rice globally, the strong hydrophobicity of its proteins is limiting the development and application of rice protein isolates as an ingredient in food. In this research, the acid-induced gelation properties of rice colloidal particles (RCPs) obtained with carboxymethyl cellulose (CMC) and rice protein isolates were evaluated. RCPs were prepared with varying protein-CMC ratios (20:1, 10:1 and 5:1, w/w) by raising the pH to 12.0 and readjusting to pH 7.0. Gels were then prepared by addition of glucono-δ-lactone (GDL). The effects of pH, acidification rate, and RCPs concentration were investigated. In situ rheological analysis indicated that gelation occurred at a pH between 6.0 and 7.0, driven by rice proteins destabilization. The pH of gelation increased with increasing concentration of the particles. Gels formed at a 1 % RCPs concentration exhibited a high degree of syneresis, compared to those formed at higher concentration. A higher amount of GDL resulted in a lower storage modulus near the gelation pH, due to a more extensive and uncontrollable aggregation of the particles. Besides, the higher the CMC content, the lower the gel pH, and the smaller the storage modulus of gels, which indicates protein contributes more to the gel strength than the polysaccharide. Particle gels with different texture and structure were obtained by adjusting protein/CMC ratio, final pH of the gels, and overall concentration of particles. These results provide valuable insights into creating novel, tunable fermented products based on rice protein isolate, or novel functional ingredients derived from rice-polysaccharide colloidal particles.