Effect of water structure makers and breakers on the adsorption of β-casein at the air—water interface

Abstract

The kinetics of adsorption of β-casein at the air—water interface was studied in the presence of kosmotropic (water structure maker) and chaotropic (water structure breaker) salts. It was found that while 1 M NaCl increased the rate and the equilibrium adsorption of β-casein, 1 M NaSCN caused a decrease compared to the 20 m M phosphate buffer control. Analysis of the data indicated that the adsorption was primarily diffusion controlled in both cases. It was also found that even though the rate and equilibrium adsorption of β-casein was affected by the structure maker (NaCl) and structure breaker (NaSCN), the surface equation of state was not affected by these salts. These results are discussed in terms of the hydrophobic effect which is related to the state of bulk water structure and its interaction with the nonpolar surfaces of the protein.