PHYSICOCHEMICAL PROPERTIES OF WHEY PROTEIN-STABILIZED EMULSIONS AS AFFECTED BY HEATING AND IONIC-STRENGTH

Corn oil-in-water emulsions (19.6 wt%; d(32) approximate to 0.6 mu m) stabilized by 2 wt% whey protein isolate (WPI) were prepared with a ra nge of pH (3-7) and salt concentrations (0-100 mM NaCl). These emulsio ns were heated between 30 and 90 degrees C and their particle size dis tribution, rheological properties and susceptibility to creaming measu red. Emulsions had a paste-like texture around the isoelectric point o f WPI (approximate to pH 5) at all temperatures, but tended to remain fluid-like at pH >6 or <4. Heating caused flocculation in pH 7 emulsio ns between 70 and 80 degrees C (especially at high salt concentrations ), but had little effect on pH 3 emulsions. Flocculation increased emu lsion viscosity and creaming. Results were interpreted in terms of col loidal interactions between droplets.