Phase separation, creaming, and network formation of oil-in-water emulsions induced by an exocellular polysaccharide

We have investigated the effect of an exocellular polysaccharide (EPS) on t he phase behavior and the rheology of oil-in-water emulsions, Already at lo w EPS concentrations the phase separation occurs. The phase line can be des cribed by depletion interaction theory. At high EPS concentrations and disp ersed phase volume fractions above 10% there is a stable "gel"-like region in the phase diagram. A kinetic study showed that the rate of creaming decr eases with increasing oil content due to hydrodynamic effects. This rate de pends strongly on the concentration of EPS, which is related to the strengt h of the depletion interaction and the viscosity of the continuous phase. A t low EPS concentration the creaming rate strongly increases with EPS conce ntration because of the stronger attraction. At higher EPS concentrations c reaming is slowed down by the viscosity increase of the continuous phase an d of the particle network which is formed. At high EPS concentrations this network becomes so strong that the gel prevents creaming. The rheological b ehavior of the "gel" was studied by measuring flow curves, which could be i nterpreted by a theoretical model for weakly aggregating particles, (C) 199 9 Academic Press.