Physicochemical properties of whey protein-stabilized emulsions as affected by heating and ionic strength

Corn oil-in-water emulsions (19.6 wt%; d₃₂ ≃ 0.6 μm) stabilized by 2 wt% whey protein isolate (WPI) were prepared with a range of pH (37) and salt concentrations (0-100 mM NaCl). These emulsions were heated between 30 and 90°C and their particle size distribution, rheological properties and susceptibility to creaming measured. Emulsions had a paste-like texture around the isoelectric point of WPI (≃pH 5) at all temperatures, but tended to remain fluid-like at pH >6 or <4. Heating caused flocculation in pH 7 emulsions between 70 and 80°C (especially at high salt concentrations), but had little effect on pH 3 emulsions. Flocculation increased emulsion viscosity and creaming. Results were interpreted in terms of colloidal interactions between droplets.