The effect of surfactant type on the rheology of ovalbumin layers at the air/water and oil/water interfaces

The aim of this work is to investigate the simultaneous adsorption of a globular protein, ovalbumin, and two different types of food emulsifiers, non-ionic Tween 60 and anionic Admul DATEM, at the air-water and sunflower oil-water interfaces. A commercial non- purified oil was used, aiming at investigating the behaviour of interfaces close to real systems. A pendant drop tensiometer was used to carry out transient interfacial tension measurements and small amplitude oscillations. A constant protein concentration (0.1 g/l) and different emulsifier/protein ratios (ranging between 0 and 0.6) were used during the tests.Experimental results evidenced that the non-ionic emulsifier replaces the protein on the interface (only a partial replacement was observed in the tested conditions) whereas the anionic molecule interacts with the protein forming complexes which can be almost completely replaced by the single emulsifier. The interfacial layers are characterised by a prevalent solid-like behaviour, which proved to be similar to 3D weakly structured systems. The rheological properties are strongly dependent on the nature of both the emulsifier and the interface, nevertheless it was observed that ovalbumin yields a more structured and stronger layer than Admul and Tween. In mixed systems, increasing the emulsifier concentration, the extension of this 2D network decreases whereas the strength seems to be less dependent and evidences only a slight reduction for Admul addition at the A/W interface.