Correlation between surface activity and foaming properties of individual milk proteins in dependence of solvent composition

Through the use of protein-free milk serum (PFMS) in comparison with deionised water (DW) or deionised water with lactose (DWL), the respective impact of lactose and milk salts on surface activity and foaming properties of selected individual milk proteins and relevant milk protein mixtures was evaluated. Against expectation, the lactose-dependent increase in solution viscosity did not impede protein diffusion and surface adsorption. Instead of molecular flexibility, protein interaction potential (inherent or milk salt-induced) correlated with foamability. Lactose and milk salts contributed to increased foam stabilities, which was also reflected in time-dependent evolution of bubble sizes as well as reduced drainage exponents. Generally, maxima in foamability and foam stability resulted when PFMS was used, which indicates the significance of pronounced protein–protein interactions as well as high packing densities at the air/water interface. The main contribution of lactose to foam volume gain and stabilisation was attributed to the reduction of coalescence.