Enhancement of Functional and Flavor Attributes of Soy Protein Isolate–Chitosan Coacervates via Ultrasonic Processing

Soy protein isolate (SPI)-based foods were limited by beany flavors and suboptimal emulsifying performance. Conventional flavor-mitigation strategies were often accompanied by losses in protein functionality, and the potential of ultrasound to simultaneously modulate structure, functionality, and flavor release of SPI–chitosan (SPI–CS) coacervates remained unclear. In this study, SPI–CS complexes were prepared and subjected to ultrasound at amplitudes of 20%, 50%, and 80% for 2 min, 5 min, or 10 min, after which their physicochemical properties, emulsifying properties, and the release of beany-flavor compounds were characterized. Coacervation with CS was found to increase particle size, decrease solubility, and enhance emulsifying indices while reducing beany-flavor release relative to SPI alone. Ultrasound treatment further decreased particle size, increased the absolute ζ-potential and surface hydrophobicity, and induced changes in secondary structure that were associated with improved solubility and emulsifying properties. Moderate amplitudes (20%, 50%) were more effective in enhancing emulsifying activity and alleviating flavor release, whereas prolonged treatment at 80% amplitude resulted in partial reaggregation and compound-dependent flavor behavior. Overall, ultrasonic processing was demonstrated to be a tunable, green strategy for engineering SPI–CS coacervates with concurrently improved functional and flavor attributes.