Influence of dextran sulfate and NaCl on the flocculation of oil-in-water emulsions stabilized by a nonionic surfactant

The creaming stability and viscosity of 10 wt % soybean oil-in-water emulsions stabilized by Tween 20 were monitored as a function of 500 kDa dextran sulfate (DS) concentration (0-5 wt %) and NaCl concentration (0-1 wt %). In the absence of salt, DS increased the apparent viscosity of the emulsions and promoted droplet flocculation above a critical concentration (CFC similar to 0.08 wt % DS). Above the CFC, the creaming rate decreased with increasing DS because of the enhanced viscosity of the continuous phase. The addition of salt decreased the apparent viscosity of emulsions, increased the CFC, and increased the creaming rate above the CFC. These results can be explained by the reduction in the effective radius of DS molecules due to electrostatic screening by the salt. Emulsions with specific physicochemical properties can be developed by carefully controlling salt and biopolymer concentration.