Effect of acid induction on structure and physicochemical properties of soybean lipophilic protein and epicatechin complex

The application of epicatechin (EC) in foods is limited by its poor stability and bioavailability. This study investigated whether acid induction (pH 3–7) could improve the structural and functional properties of soybean lipophilic protein (SLP)–EC complexes. The study aimed to elucidate the underlying mechanisms and identify the optimal formation condition. At pH = 4, the SLP–EC complex exhibited the smallest particle size (230.83 nm). It also showed a loose tertiary structure with increased hydrophobic exposure and secondary structure transitions (α-helix decreased, β-sheet increased). These changes, driven by hydrogen bonding and hydrophobic interactions, significantly enhanced functionality: the emulsifying activity index reached 85.2 m 2 /g, with foam capacity at 125%, and DPPH radical scavenging rate at 97.87%. The complex also exhibited high thermal stability (denaturation temperature 351.65 K at pH 5). These findings demonstrate that acid induction at pH 4 simultaneously improves multiple functional properties of SLP–EC complexes, offering a practical strategy for developing high-performance protein–polyphenol ingredients in foods. • Acid induction effectively modulates the structure of SLP-EC complexes. • Structural alterations were confirmed by SDS-PAGE and FTIR analyses. • Optimal physicochemical and functional properties were achieved at pH 4. • Enhanced emulsifying, foaming, and antioxidant activities were obtained.