Multiscale investigation of the structure, interaction mechanism, and physicochemical properties of α-Lactalbumin and soybean lecithin complexes: integrating spectroscopy, molecular dynamics, and density functional theory

To expand the application potential of α-lactalbumin (α-LA) in functional foods, this study investigated the interaction mechanisms and physicochemical property of noncovalent complexes formed between α-LA and soybean lecithin (SL). SL addition quenched the intrinsic fluorescence of α-LA, increased hydrophobic group exposure, and induced a transition of protein secondary structure from ordered to more disordered conformations. Negative ΔG, ΔH, and ΔS values indicated that the binding process was spontaneous and exothermic. Molecular docking and dynamics simulation revealed the binding site resides within the hydrophobic region of α-LA, primarily driven by hydrogen bonds (Trp60) and hydrophobic interactions (Leu105, Lys108). Density functional theory reveals that the complexes involved weak interactions characterized by electron cloud transfer between α-LA and SL, resulting in a HOMO-LUMO energy gap of 0.125 eV. At an SL concentration of 0.4 mg/mL, the α-LA-SL complexes exhibited the smallest particle size (453.80 ± 4.82 nm), highest emulsifying activity index (30.09 ± 0.09 m 2 /g), and highest emulsion stability index (77.88 ± 2.85 min). Meanwhile, protein oxidative modification and surface tension were reduced. Correlation analysis indicated that the decrease in surface tension was a key factor in enhancing the complex's functionality, while interfacial adsorption-related protein oxidative changes were closely related to its functional enhancement. Oil-in-water model emulsions stabilized by α-LA-SL complexes were further prepared, and the 0.4 mg/mL SL group showed improved storage stability during accelerated storage. Overall, α-LA and SL formed noncovalent complexes with improved structural and functional properties, providing a theoretical basis for constructing food emulsion systems.