Differences in the structure and dynamics of the adsorbed layers in protein-stabilized model foams and emulsions

Abstract

Protein-stabilized food dispersions often contain a range of surface active species. Many of these are of low molecular weight and include lipids or food emulsifiers. Depletion measurements, fluorescence and fluorescence recovery after photobleaching (FRAP) studies have shown that competitive adsorption of these molecules at the interface causes breakdown of protein–protein interactions in the adsorbed layer. This results in partial displacement of adsorbed protein and the initiation of lateral diffusion in the remaining adsorbed fraction However, there are distinct differences between the structure of the adsorbed protein layers found at air/water and oil/water interfaces. This causes differences in behaviour of the adsorbed layer in response to competitive adsorption of low-molecular-weight surfactant. This paper contrasts the behaviour of adsorbed layers formed by the milk proteins, β-lactoglobulin and β-casein, adsorbed at the interfaces of air-suspended thin liquid films and the thin aqueous film between two oil droplets, as a function of increasing concentration of the non-ionic surfactant, Tween 20.