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 the phase behavior and the rheology of oil-in-water emulsions. Already at low EPS concentrations the phase separation occurs. The phase line can be described by depletion interaction theory. At high EPS concentrations and dispersed 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 decreases with increasing oil content due to hydrodynamic effects. This rate depends strongly on the concentration of EPS, which is related to the strength of the depletion interaction and the viscosity of the continuous phase. At low EPS concentration the creaming rate strongly increases with EPS concentration because of the stronger attraction. At higher EPS concentrations creaming is slowed down by the viscosity increase of the continuous phase and of the particle network which is formed. At high EPS concentrations this network becomes so strong that the gel prevents creaming. The rheological behavior of the "gel" was studied by measuring flow curves, which could be interpreted by a theoretical model for weakly aggregating particles. Copyright 1999 Academic Press.