Influence of pH and CaCl 2 on the stability of dilute whey protein stabilized emulsions

Abstract

The influence of pH and CaCl 2 on the physical stability of dilute oil-in-water emulsions stabilized by whey protein isolate has been studied. The particle size, zeta potential and creaming stability of 0.05 wt% soy bean oil-in-water emulsions ( d ≈ 0.53 μm) were measured with varying pH (3 to 7) and CaCl 2 concentration (0 to 20 μM). In the absence of CaCl 2 extensive droplet aggregation occurred around the isoelectric point of the whey proteins (4 < pH < 6) because of their low electrical charge, which led to creaming instability. Droplet aggregation occurred at higher pH when CaCl 2 was added to the emulsions. The minimum concentration of CaCl 2 required to promote aggregation increased as the pH increased. Aggregation was induced in the presence of CaCl 2 probably because of the reduction in electrostatic repulsion between droplets, caused by binding of counter ions to droplet surfaces and electrostatic screening effects.