(269d) Temperature and pH Effects on Deposition Kinetics of Beta-Lactoglobulin

Deposition of thin beta-lactoglobulin layers at a solid-liquid interface was monitored in situ by optical waveguide lightmode spectroscopy. The initial step in beta-lactoglobulin deposition is the primary adsorption on the bare surface, which is partially reversible at ambient temperature. Primary coverage density at ambient temperature depends on beta-lactoglobulin concentration and pH. The irreversibly bound part of the primary layer can be partially desorbed at elevated temperatures, but can be resaturated to its original density from the protein solution at ambient temperature. Sustained secondary deposition resulted in multilayer deposits up to several tens of nanometers thick. The measured deposition rates were strongly influenced by temperature and pH. Deposition rates were decreasing with increasing pH from 5.5. to 7.4, in a trend similar to that for non-covalent aggregation of beta-lactoglobulin in solution. Activation energies for deposition rates were decreasing with increasing pH, from 340kJ/mol at pH=5.5 to 230kJ/mol at pH=7.4, and were similar to the activation energies for denaturation of beta-lactoglobulin in solution. These observations can be consistently explained considering interplay of protein denaturation and deposition of the denaturated protein.