Influence of sodium dodecyl sulfate on the physicochemical properties of whey protein-stabilized emulsions

The influence of sodium dodecyl sulfate (SDS) on the flocculation of drople ts in 20 wt.% soybean oil-in-water emulsions stabilized by whey protein iso late (WPI) was investigated by light scattering, rheology and creaming meas urements. The SDS concentrations used were low enough to prevent depletion flocculation by surfactant micelles and extensive protein displacement. In the absence of SDS, emulsions were prone to droplet flocculation near the i soelectric point of the proteins (4 < pH < 6), but were stable at a higher and lower pH. Flocculation led to an increase in emulsion viscosity, pronou nced shear thinning behavior and accelerated creaming. When the surfactant- to-protein molar ratio was increased from 0 to 10, the emulsion instability range shifted to lower pH values due to binding of the negatively charged SDS molecules to the droplets. Our results indicate that the physicochemica l properties of protein-stabilized emulsions can be modified by utilizing s urfactant-protein interactions. (C) 2000 Elsevier Science B.V. All rights r eserved.