Revealing the interaction mechanism and emulsion properties of carboxymethyl cellulose on soy protein isolate at different pH

In this study, carboxymethyl cellulose (CMC) was introduced to reduce the instability and poor functional properties of soy protein isolate (SPI) in low pH environment. The SPI–CMC systems containing 0–0.5% CMC were prepared at pH 4.0 and 5.0. By exploring the interaction mechanism between them, the optimal formation conditions of the composite systems were revealed. The results showed that CMC was continuously adsorbed on the surface of SPI at pH 4.0, in which electrostatic behavior and hydrogen bonds played an important role. The emulsion properties were the best at 0.4% CMC, and the emulsion activity index (EAI) and emulsion stability index (ESI) were increased by 48.91 m2/g and 91.41 min compared with SPI emulsion. The optical microscope images showed that the emulsion interfacial proteins were formed and the droplets were evenly distributed at 0.4% CMC. At pH 5.0, the stability of the SPI–CMC systems was highly dependent on the steric hindrance and high viscosity of CMC. The EAI and ESI of the emulsion at 0.5% CMC were the highest, which increased by 49.08 m2/g and 83.79 min compared with SPI emulsion. The optical microscope images confirmed that the addition of 0.5% CMC significantly inhibited the accumulation of oil droplets. In conclusion, this study provides an effective strategy for stabilizing SPI emulsions in low pH environments, which has important practical application value.