SURFACE-FILM PRESSURE OF BETA-LACTOGLOBULIN, ALPHA-LACTALBUMIN AND BOVINE SERUM-ALBUMIN AT THE AIR-WATER-INTERFACE STUDIED BY WILHELMY PLATE AND DROP VOLUME

The surface film pressure (II) of β-lactoglobulin, α-lactalbumin, and bovine serum albumin was studied in simulated milk ultrafiltrate (SMUF) and in water at concentrations from 10-6 up to 1% (w/v) at times from 30 s to 14 h and the results were analyzed with regard to adsorption transport and kinetics. In SMUF at low concentrations, β-lactoglobulin was the most "surface active" protein. There was little difference in the surface film pressure between β-lactoglobulin and α-lactalbumin at high concentrations. Bovine serum albumin showed the lowest surface activity, but did not reach a constant II, even after 14 h. As the pH approached the isoelectric point, the surface film pressure increased, and in the case of bovine serum albumin II increased faster. In water, however, the surface film pressures were lower than in SMUF, and for bovine serum albumin II developed more slowly. The transport to the interface was found to be controlled by diffusion only for a small concentration range of approximately 10-4%. It was controlled by initial flow disturbances at higher concentrations and free convection at lower concentrations. The rate of increase of the surface film pressure was not a simple function of surface film pressure and bulk concentration under any of the conditions studied. © 1992.