Improvement of the solubility and emulsifying properties of rice bran protein by phosphorylation with sodium trimetaphosphate

Rice bran protein (RP) could represent an important component of the protein resources in daily life because a large amount of it remains after rice processing. At present work, RP underwent phosphorylation using sodium trimetaphosphate under hydrothermal treatment at different pH values (3.0, 5.0, 7.0, 9.0 and 11.0), and the utilization of phosphorylated products in emulsions was also assessed. Phosphorylated RP at pH 9.0 showed the highest solubility and emulsifying activity. According to the results of the phosphorus content, zeta potential, infrared spectroscopy and X-ray photoelectron spectroscopy analysis, phosphate groups were introduced to RP, and the phosphate esters (P = O) were detected. With the analysis of surface hydrophobicity, intrinsic fluorescence, and circular dichroism spectra, phosphorylation by hydrothermal treatment changed the secondary and/or tertiary structure of proteins and increased the solubility and emulsifying activity. Emulsions prepared with phosphorylated RP at pH 9.0 were stable over a range of environmental conditions: pH 7-9, NaCl < 50 mM, and temperatures < 90 degrees C were studied. It shows that RP phosphorylated by sodium trimetaphosphate could be utilized in the formulation and production of natural emulsion-based products as emulsifier.