Influence of pH value and locust bean gum concentration on the stability of sodium caseinate-stabilized emulsions

Sodium caseinate emulsions of 20% sunflower oil in water were prepared at various pH and Locust Bean Gum concentrations (LBG). The presence of LBG was examined to assess the stabilizing properties in relation to flocculation, creaming and coalescence, in the initial emulsions as well as freeze-thawed and freeze-dried/reconstituted samples. We found the initial emulsions to be stable at pH 6.0 and 6.5, both in the absence or presence of LBG, against creaming. However we found evidence for the aggregates of emulsion droplets in the presence of LBG. Strong shear thinning behavior, even at low shear rates, and micrographs indicated that the presence of LBG may promote flocculation by mediating depletion forces between the oil droplets. However, the absence or low concentrations of LBG resulted in creaming followed by the emulsion break-up for the freeze-dried/reconstituted emulsions, particularly at lower pH. We have also detected a proliferation in the number of very small sub-micron particles in the particle size distribution, for samples containing higher concentrations of LBG, following the freeze-thaw cycle. We believe these to be LBG aggregates nucleating during the freezing phase of the process as the polysaccharide solubility declines with temperature.