Dynamics of protein adsorption at the oil–water interface: comparison with a theoretical model

A novel procedure of analysis of protein adsorption at liquid interfaces is proposed in terms of the steady state (equilibrium) surface pressure–concentration curves and also the dynamic interfacial tension–time curves obtained for each individual protein concentration. The analysis is performed on the basis of a thermodynamic model that has been recently extended to the study of adsorption dynamics. The procedure presented is based on the modification of the area values given to the protein at the oil–water interface with respect to those used at the air–water interface. This is done in order to account for the differences inferred from the experimental data. In this manner, and in view of the excellent correlation found between theory and experiment, the model substantially deepens the understanding of the adsorption process in two steps. Firstly, the fitting of the equilibrium isotherm provides a set of characteristic parameters that quantifies the interfacial structure adopted by the protein at the oil–water interface in terms of the partial molar area. Subsequently, the optimal set of parameters obtained by this procedure is also used in the fitting of the dynamic curves and similarly the area parameters changed according to experimental findings. Such practice yields as a conclusion a direct relationship between the degree of interfacial unfolding attained by the protein at the tetradecane–water interface and the bulk concentration, representing an innovative quantification of the kinetics of protein adsorption.