Influence of pH and ionic strength on the physical and rheological properties and stability of whey protein stabilized o/w emulsions containing xanthan gum

The influence of pH (3-7) and ionic strength (0-250 mM NaCl) on the physical and rheological properties and stability of soybean oil-in-water emulsions containing whey protein isolate (WPI) as an emulsifier and anionic polysaccharide (xanthan gum, XG) as a stabilizer was studied. The influence of ionic strength was found to be dependent on whether the pH was below or above the isoelectric point (pI ≈ 4.6) of the emulsion droplets. At pH below the pI, the ζ-potential of the emulsions increased from negative to positive values with increasing ionic strength. The emulsions exhibited more extensive droplet flocculation, more viscous, and more structured, but less creaming stability at low ionic strength than at high ionic strength. At pH above the pI, the ζ-potential of the emulsions was always negative and its magnitude decreased with increasing ionic strength. The emulsions exhibited a slight increase in droplet flocculation, decrease in viscosity, viscoelasticity, and creaming stability with increasing ionic strength. This study could potentially serve for applications in the food industry to design the emulsion-based food products with improved physical and rheological properties and stability over a wide range of pH and ionic strength conditions.