Stability of emulsions containing sodium caseinate and dextran sulfate: Relationship to complexation in solution

The effect of addition of the anionic polysaccharide dextran sulfate (DS) on the properties of n-tetradecane-in-water emulsions containing sodium caseinate (CN) has been Studied under different pH and ionic strength conditions. Two methods were used for preparation of the emulsions (20 vol% oil, 0.5 wt% CN, 0.1-1 wt% DS). in 'bilayer emulsions', the DS was added to a CN-stabilized emulsion after emulsification; in 'mixed emulsions', the oil was directly emulsified into the mixed biopolymer solution. At pH = 6, DS Was found to adsorb onto CN-coated droplets, and extensive aggregation due to bridging flocculation occurred at 0.1 wt% DS. Polymeric stabilization was observed Lit higher polysaccharide concentration (1 wt% DS). In the mixed emulsions, no bridging flocculation was observed Lit any DS concentrations. These contrasting results for the two preparation methods indicate that strong interactions are present already Lit a pH value above the isoelectric point of the protein, and that the structure of the adsorbed layer at the oil-water interface is different for the two sets of systems. When the pH of emulsions containing 0.5 wt% DS or less was lowered towards acidic Values, precipitation was observed. The mixed and bilayer emulsions containing 1 wt% DS were found to be more stable at pH = 2 than the emulsion without DS. Mixed emulsions containing 1 wt% DS exhibited good shelf-life stability on quiescent storage for 3 weeks, especially when the emulsion was prepared Lit low pH. Complexes were found to dissociate when 0.1 or 0.5 M NaCl was present, suggesting that associative interactions between CN and DS are mainly clectrostatic. (c) 2007 Elsevier Ltd. All rights reserved.