Phase behaviour of lactoferrin and β-lactoglobulin complexes: Revealing mechanisms from an integrated experimental and theoretical perspective

Regulating the phase characteristics of milk proteins through pH changes can enhance the quality of milk products. This study investigated the effect of pH on interaction mechanism of lactoferrin-β-lactoglobulin (LF-β-LG) complexes in different phases through experimental characterization and theoretical simulations. As pH varied from 2.0 to 12.0, soluble complexes, insoluble complexes, and co-soluble polymers were generated. The soluble complexes and co-soluble polymers exhibited smaller particles and less aggregation, whereas insoluble complexes displayed larger, irregularly shaped particles. The complex formation enhanced thermal stability of individual proteins, with the most significant improvement observed in the insoluble complexes, which exhibited thermal denaturation temperature of 100.1 °C. Fourier transform infrared spectroscopy and molecular dynamics simulations revealed that electrostatic interactions were the main driving force for the formation of insoluble complexes, while hydrogen bonding, electrostatic and hydrophobic interactions contributed to the formation of soluble complexes and co-soluble polymers. The results of molecular dynamics simulations revealed that strong interaction between LF and β-LG facilitates the generation of insoluble complexes at pH 6.0, while weak interactionn facilitates the generation of co-soluble polymers at pH 10.0, which was also validated by small-angle X-ray scattering analysis. Present work provided valuable insights into the phase behaviour of LF and β-LG.