Molecular Modeling of the Adsorption of an Egg Yolk Protein on a Water-Oil Interface.

Egg yolk contains several molecular species with emulsifying properties, such as proteins and phospholipids. In particular, these molecules have both polar and nonpolar parts and thus can act as surfactants. One of the most surface-active proteins from egg yolk low-density lipoproteins is the so-called Apovitellenin-1. Experimental studies have been hindered by difficulties in isolating individual species from egg yolk lipoproteins. The purpose of this work was to assess the emulsifying properties of Apovitellenin-1 and any potential cooperative or competitive behavior in the presence of phospholipids. To do so, molecular simulations were carried out in a liquid-liquid interfacial system consisting of water and soybean oil, with varying concentrations of phospholipids and for different spatial configurations. To evaluate the conformational stability of the protein at the water-oil interface, the Gibbs free energy was computed from Metadynamics simulations as a function of the distance from the interface and of the radius of gyration. Moreover, a detailed analysis was also performed to determine which peptide residues were responsible for the protein adsorption at the oil-water interface as well as the lowering of the interfacial tension. Lastly, we combined the simulation results with a thermodynamic model to predict the interfacial tension behavior at increasing protein bulk concentration, which cannot be measured experimentally.