Mechanism of emulsion stabilized by an ultrasonically prepared protein–polyphenol-polysaccharide complex: structure, functional properties and interfacial behavior

Based on the mechanism that polyphenols and polysaccharides can modulate protein conformation through non-covalent interactions such as hydrogen bonding and hydrophobic forces, the construction of ternary complexes offers a promising strategy for developing efficient emulsion-based delivery systems. This study employed soy protein isolate (SPI), (-)-epigallocatechin gallate (EGCG), and polydextrose (PD) as raw materials to fabricate SPI, SPI-EGCG, SPI-PD, and SPI-EGCG-PD complexes via ultrasonic treatment. These complexes were then used to stabilize emulsions, and their structural characteristics, functional properties, and interfacial behavior were systematically investigated. The results indicated that the protein secondary structure of the ultrasonicated samples underwent significant alterations compared to SPI and the complexes (SPI-EGCG, SPI-PD, SPI-EGCG-PD). Specifically, the contents of α-helix and β-sheet decreased significantly, while the content of random coils increased significantly. Also, their emulsifying capacity and antioxidant activity were both significantly enhanced (p < 0.05). The emulsion stabilized by the ultrasonically prepared SPI-EGCG-PD complex exhibited superior stability, as evidenced by the highest emulsion stability index (89.6 min), the smallest particle size (599.6 nm), the highest absolute ζ-potential value (-37.4 mV), the greatest interfacial adsorbed protein content (4.89 mg/mL), the best oxidative stability (5.31 μmol/L), the lowest interfacial tension (20.89 mN/m), and the best storage stability. This study elucidates the mechanism by which ultrasonic treatment promotes the synergistic adsorption of proteins, polyphenols, and polysaccharides. It further examines the role of the interfacial behavior of ultrasonicated proteins and their complexes in maintaining emulsion stability, thereby providing a theoretical foundation for developing highly stable delivery systems for bioactive substances.