Effect of protein molecules and MgCl2 in the water phase on the dilational rheology of polyglycerol polyricinoleate molecules adsorbed at the soy oil-water interface

Abstract

The objective of this study was to investigate the effect of inorganic salt and protein in the aqueous phase on the dilational rheology properties of interfacial film stabilized by the hydrophobic emulsifier polyglycerol polyricinoleate (PGPR). The interfacial behavior was investigated using the oscillating drop method. With increased PGPR concentration, the interfacial tension tended to decrease and reached an equilibrium value of 3.3 mN m−1, at 1.0% (w/w) PGPR. With 0.01% (w/w) PGPR in the oil phase, the presence of whey protein isolate (WPI) increased the dilational elasticity modulus of PGPR, but the addition of bovine serum albumin (BSA) decreased the elasticity modulus. This was likely due to competitive adsorption of BSA and PGPR at the soy oil/water interface, resulting in the desorption of BSA from the interface. At 1.0% (w/w) PGPR, both WPI and BSA increased the interfacial dilational elastic modulus and the reason might be that the presence of protein could suppress the diffusion-exchange process of PGPR between bulk phase and interface. The addition of MgCl2 may enhance the adsorption of PGPR molecules at the interface and therefore increased the dilational modulus.