Exploration of dynamic interaction between β-lactoglobulin and casein micelles during UHT milk process

The protein aggregation induced by UHT treatment shortens the shelf life of UHT milk. However, the mechanism of β-Lg induced casein micelle aggregation remains unclear. Herein, the dynamic interaction between β-Lg and casein micelles during UHT processing was investigated by experimental techniques and molecular dynamics simulations. Results showed that β-Lg decreased the stability of casein micelles, increased their size and zeta potential. Raman and FTIR spectra analysis suggested that hydrogen and disulfide bonds facilitated their interaction. Cryo-TEM showed that the formation of the casein micelle/β-Lg complex involved rigid binding, flexible linking, and severe cross-linking aggregation during UHT processing. SAXS and MST demonstrated β-Lg bound to κ-casein on micelle surfaces with a dissociation constant (Kd) of 3.84 ± 1.14 μm. Molecular docking and dynamic simulations identified the interacting amino acid residues and clarified that electrostatic and van der Waals forces drove the interaction. UHT treatment increased hydrogen bonds and decreased total binding energy. The non-covalent binding promoted the formation of disulfide bonds between β-Lg and casein micelles under heat treatment. Ultimately, it was concluded that non-covalent interaction and disulfide bonding resulted in casein micelle/β-Lg aggregates. These findings provided scientific insights into protein aggregation in UHT milk.