PROTEIN-POLYSACCHARIDE INTERACTIONS AT THE OIL-WATER INTERFACE

Electrophoretic mobilities of emulsion droplets of di-n-butyl phthalat e formed in the presence of methemoglobin alone, methemoglobin plus al ginate or carboxymethyl cellulose, bovine serum albumin alone and bovi ne serum albumin plus alginate have been measured. At pHs below the pr otein isoelectric points addition of the polysaccharide conferred a ne t negative charge on the emulsion droplets. For pHs less than or simil ar to 2 units above the isolectric point the mobilities of the polysac charide containing emulsion droplets were substantially more negative than for the protein covered droplets. At higher pHs the observed mobi lities 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 protei n 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 sugge sted that low concentrations of polysaccharide destabilise emulsions b y bridging rather than depletion flocculation.