The structure of mixed β-lactoglobulin/Tween 20 adsorption layers was studied by surface shear rheological and dynamic surface tension measurements. Surface shear rheology was carried out with a torsion pendulum set-up which provides information about the surface shear viscosity and elasticity in one single experiment.
The adsorption layer structure is controlled by the interactions between the protein molecules and the surfactant. The corresponding dynamic surface tension measurements confirm the peculiarities found by the shear rheology, which suggests dramatic changes of the mixed adsorption layer structure. With increasing surfactant at constant protein concentration the mixed surface film approaches, step-by-step, a state identical to a pure surfactant adsorption layer where the protein is completely removed.