Lipid Controlled Non-Monotonic Assembly and Rheology of an Egg Yolk Protein at Water-Soybean Oil Interface
An essential component of food items like mayonnaise and salad dressing is hen egg yolk. Phosvitin (PVT) is a phosphoprotein, which exists in the granules of this hen egg yolk which stabilizes the food emulsion by preventing phase separation. To understand, how this protein is adsorbed at the interface of water and edible oil in the presence and absence of lipids is essential for improved control in food production. To monitor the kinetics of this adsorption, the dynamic interfacial tension has been determined in the current investigation. The drop in interfacial tension over time indicates the adsorption of protein at interface which is enhanced on increasing the concentration of protein in water phase. However, at higher concentration, the positive activation energy hinders the adsorption process resulting a saturated interfacial tension. The dilation rheology of the macromolecular film at this oil-water interface shows the elastic nature of the film to be greater than the viscous nature, indicating the formation of a soft gel film. At low concentration, the zwitterionic lipid, 1-palmitoyl-2-oleoyl-sn-glycero 3-phosphocholine (POPC), promotes this protein adsorption at the interface. Interestingly, at high concentration, the lipid overtakes the interface removing the protein from there. The lipid-protein composite film again shows the nature of a soft gel. The non-monotonic effects of lipids on assembly of protein at the water-edible oil interface is an important observation to optimize the composition of relevant food products.