THE COMPETITIVE DISPLACEMENT OF BETA-LACTOGLOBULIN BY TWEEN-20 FROM OIL-WATER AND AIR WATER INTERFACES

The binding of Tween 20 to β-lactoglobulin variants A and B and a mixture of variants A and B, was measured by fluorescence titration. These data were used to interpret the behaviour of β-lactoglobulin at the interfaces of air-water-air and oil-water-oil films in the presence of competing Tween 20. These films serve as good models for foam lamellae and the structures separating creamed or concentrated emulsion systems. Distinct differences were observed in the film drainage characteristics and equilibrium film thicknesses. A fluorescence recovery after photobleaching technique (FRAP) was used to investigate the surface diffusion of adsorbed FITC-β-lactoglobulin as a function of Tween 20 concentration at the interfaces of both types of thin film. The results demonstrated that disruption of protein-protein interactions and the onset of protein surface diffusion occurred at much lower molar ratios of Tween 20 to protein in the oil-water-oil film compared to the air-water-air film. Explanation of these observations came from direct measurement of surface displacement of β-lactoglobulin by Tween 20 which confirmed that the composition of the adsorbed layers was different in the two types of film. © 1993 by Academic Press, Inc.