Mechanism of galacturonic acid-rich Schisandra Chinensis polysaccharide in improving emulsifying properties of soy protein hydrolysate: Insights from interfacial behavior and molecular interactions.

In this study, Schisandra Chinensis polysaccharide (PSCP, 85.19% purity) was identified as an acidic heteropolysaccharide featuring excellent stability and favorable rheological properties. For the first time, we systematically elucidated the structure of PSCP through multiple analytical techniques, identifying a characteristic fragment: [→4)-α-D-GalpA-(1 → 4)-α-D-GalpA-(1 → 4)-β-D-Glcp-(1→]. PSCP significantly enhanced the emulsifying properties of soy protein hydrolysate (SPH, 6% hydrolysis degree) emulsions. The optimal emulsifying properties of SPH emulsion were achieved when PSCP concentration was 1 mg/mL, pH was 6.0, and ionic strength was in the range of 0-200 mM. The galacturonic acid-rich (Gal A-rich) PSCP increased the negative charge density on droplet surfaces, promoting strong electrostatic repulsion and inhibiting droplet aggregation. Interfacial tension and rheological analyses confirmed that PSCP reduced equilibrium interfacial tension, enhanced interfacial pressure and adsorption kinetics, and strengthened interfacial film viscoelasticity (increased G' and G") and structural integrity, all of which synergistically improve emulsifying activity and stability. Experimental analysis showed that the binding of PSCP to 7S/11S in SPH was spontaneous and exothermic, driven by hydrogen bonds, electrostatic interactions, and van der Waals forces. Molecular dynamics (MD) simulations confirmed that PSCP can form stable complexes with 7S/11S, and that PSCP induced secondary structural changes in the 7S/11S, consistent with FT-IR. This work not only uncovers the mechanism by which PSCP improves SPH emulsifying properties but also lays a theoretical and practical basis for precise engineering of stable plant protein emulsions via Gal A-rich polysaccharides.