Rheology and adsorption behaviour of β-casein and β-lactoglobulin mixed layers at the sunflower oil/water interface

This paper investigates the adsorption behaviour of two milk proteins, β-casein and β-lactoglobulin, both alone and in binary mixtures, at the sunflower oil-water interface (O/W) in order to better understand the emulsifying functionality of protein mixtures commonly used in the manufacture of milk protein-stabilised emulsions. A commercial non-purified oil was used, to analyse the behaviour of interfaces close to real systems. A constant protein concentration (1 g/l) and different β-lactoglobulin:β-casein ratios (1:3; 1:1; 3:1) were used during the tests and interfacial protein interactions were studied with a pendant drop tensiometer. Experimental results evidenced that the adsorption and the interfacial rheological properties of β-casein/β-lactoglobulin adsorbed layers are mainly affected by the presence of β-casein molecules, which is probably the most abundant protein at interface, as also suggested by the application of two rheological models, commonly adopted for the description of bulk properties of mixed systems. Dynamic data evidenced a solid-like behaviour for the interfacial layer similar to 3D weakly-structured systems.