PROTEIN-POLYSACCHARIDE INTERACTIONS AT THE OIL-WATER INTERFACE

Electrophoretic mobilities of emulsion droplets of di-n-butyl phthalate formed in the presence of methemoglobin alone, methemoglobin plus alginate or carboxymethyl cellulose, bovine serum albumin alone and bovine serum albumin plus alginate have been measured. At pHs below the protein isoelectric points addition of the polysaccharide conferred a net negative charge on the emulsion droplets. For pHs less than or similar to 2 units above the isolectric point the mobilities of the polysaccharide containing emulsion droplets were substantially more negative than for the protein covered droplets. At higher pHs the observed mobilities were similar for both systems. Measurements of alginate surface loadings confirmed that polysaccharide was located at the surface of the oil droplets stabilised with methemoglobin at pHs above the protein isoelectric point. The surface concentration of alginate was similar to 2 mg/m(2), independent of pH in the region pH 5.0-8.0. It is suggested that low concentrations of polysaccharide destabilise emulsions by bridging rather than depletion flocculation.