Modulating dynamic interactions between soy protein isolate and hydroxytyrosol via pH-driven technology: Binding mechanism, structure, and functional characteristics

In this study, soy protein isolate (SPI)-hydroxytyrosol (HT) nanocomplexes were prepared via pH-driven technology under different alkaline conditions to investigate their interaction mechanisms during the alkalization-neutralization process, and their effects on structure and functional properties. The results indicated that pH induced the unfolding-refolding conformational changes in SPI to expose binding sites, thereby facilitating interactions with HT. In addition, HT was bound to SPI mainly by hydrogen bonds, with higher binding affinities during alkalization than during neutralization (binding constants of 9.26 × 10 3 mol -1 L and 1.14 × 10 3 mol -1 L, respectively), altering the secondary and tertiary structure of the protein. As the alkaline pH increased, the nanocomplexes showed smaller particle sizes and lower zeta potential, along with increased surface hydrophobicity and solubility. Notably, nanocomplexes prepared under alkaline conditions at pH 10–11 exhibited optimal emulsifying (EAI and ESI increased by 254% and 82.4%, respectively), foaming (FC and FS increased by 21.8% and 55.5%, respectively), and antioxidant performance. This study elucidated the pH-driven dynamic interaction mechanisms between SPI and HT, providing novel insights into the development of functional food ingredients. • Interaction mechanisms between SPI and HT across the pH-driven process were explored. • Hydrogen bonds were the main driving forces in their interactions. • The binding affinity during alkalization was higher than during neutralization. • pH induced the unfolding-refolding of SPI, facilitating the embedding of HT. • Nanocomplexes prepared at pH 10–11 exhibited optimal functional properties.