Whey protein isolate-based amphiphilic surfactin complexes: Structural, antioxidant, and interfacial properties, and molecular docking analysis.

Whey protein isolate and surfactin (WPI-S) complexes were fabricated via non-covalent interactions. Surfactin induced partial unfolding of WPI through hydrogen bonding, electrostatic, and hydrophobic interactions, as evidenced by their structural analysis. Compared to WPI, the complexes exhibited enhanced ABTS and DPPH scavenging capacity (by 3.38-fold and 44.7%, respectively). Interfacial properties were also improved: foaming capacity and stability increasing by 157.14% and 18.95%, oil-holding capacity by 1.98-fold, and emulsifying activity and stability by 5.12-fold and 52%, respectively. WPI-S-stabilized emulsions displayed superior physicochemical characteristics, including reduced droplet size, more negative zeta potential, elevated turbidity, and enhanced homogeneity. Rheological property analysis revealed that all emulsions exhibited shear-thinning behavior, with WPI-S systems consistently showing higher apparent viscosity than WPI. The maximum viscosity was observed at WPI/S mass ratio of 5:2. Oscillatory rheology confirmed solid-like behavior (G' > G″) in most formulations. Molecular docking suggested that hydrogen bonding, hydrophobic interactions, and van der Waals forces are key drivers of complexation. These findings elucidate the molecular mechanism underlying WPI-S interactions and support the potential application of the complexes as functional ingredients in emulsion-based food and pharmaceutical products.