A deeper insight into the characteristics of double-layer oil-in-water emulsions stabilized by Persian gum and whey protein isolate

Whey protein isolate (WPI) is an excellent emulsifier. However, WPI-stabilized emulsions tend to flocculate at pH values close to their isoelectric point. In this work, a layer by layer (LBL) technique was used to develop double layer oil in water emulsions using a mixture of WPI and water-soluble fraction of Persian gum (WSPG). Polysaccharide concentration and pH were found to have a major impact on the stability of the final system. At a constant total biopolymer concentration, increasing the amount of WSPG significantly (p < 0.05) improved the emulsion physical stability. An appropriate stability was obtained at 0.5 wt% WPI, 1 wt% WSPG, and pH 5.0. At high ionic strength, the emulsions became unstable with a higher sensitivity to CaCl2 than NaCl. Confocal laser scanning microscopy and zeta-potential measurements confirmed the electrostatic adsorption of WSPG onto the WPI-stabilized oil droplets. The results of interfacial tension and dilatational rheology measurements revealed a slight decrease in the interfacial tension after the adsorption of WSPG as the second layer and a predominantly elastic behavior (E′ > E″), at the interface especially at pH 5.0. The results showed that WSPG is an appropriate candidate for improving the physical stability of WPI-stabilized emulsions at pH values close to isoelectric point.