Insights from alpha-Lactoalbumin and beta-Lactoglobulin into mechanisms of nanoliposome-whey protein interactions

The complexation between nanoliposomes and two dominant monomers in whey proteins, i.e. alpha-Lactoalbumin (α-La) and beta-Lactoglobulin (β-Lg), were investigated to reveal the mechanisms of nanoliposome-whey protein interactions. The UV–vis spectra showed that nanoliposomes could significantly interact with the two monomeric proteins. The red shift phenomenon and intensity decrease were observed in the endogenous fluorescence spectra. It indicated that the exposure of hydrophobic groups in α-La/β-Lg increased, and the endogenous fluorescence was quenched. Synchronous fluorescence results showed that Trp fluorescence intensity decreased more significantly than that of Tyr, and more powerful interactions between monomeric proteins and nanoliposomes occurred in the regions around Trp residues. CD spectra showed an increase of β-sheet secondary structures of α-La and β-Lg in content at the cost of a decrease in α-helix and random coil in the two monomeric proteins after complexation. FTIR results indicated that the secondary structures of monomeric proteins altered, and the main interaction forces were hydrogen bond and hydrophobic forces. Surface hydrophobicity and free sulfhydryl content of monomeric proteins enhanced after complexation with nanoliposomes. Molecular docking theoretically demonstrated that the main interaction forces between nanoliposomes and monomeric proteins were hydrogen bond and hydrophobic forces. The interaction between nanoliposomes and α-La was more strong than that between nanoliposomes and β-Lg. The natural properties, such as amino acid composition, advanced structure and surface hydrophobicity, could play a critical role in the interaction between nanoliposomes and monomeric proteins. These findings could deepen the understanding of the interaction mechanisms between nanoliposomes and whey proteins.