Influence of pH and carrageenan type on properties of beta-lactoglobulin stabilized oil-in-water emulsions

The influence of pH and carrageenan type (iota, kappa, and lambda) on the properties of P-lactoglobulin (beta-Lg) stabilized oil-in-water emulsions was investigated by particle charge, particle size distribution, creaming stability, and optical microscopy measurements. Emulsions containing droplets stabilized by beta-Lg were produced by homogenization, and then adjusted to a particular pH (3, 5 or 6) before carrageenan solution (0 to 0.15 wt%) of the same pH was added. At pH 3 and 5, there was a pronounced decrease in droplet charge with increasing polysaccharide concentration for all carrageenan types, suggesting adsorption of carrageenan to the droplet surfaces. Extensive droplet aggregation and creaming were observed in these emulsions when the carrageenan concentration exceeded a particular level, indicating that carrageenan destabilized the emulsions. At pH 6, the droplet charge decreased when iota- or lambda-carrageenan were added to the emulsions suggesting surface adsorption, but did not significantly change when kappa-carrageenan was added. The mean particle diameter remained relatively small in all emulsions at pH 6 indicating no strong flocculation or coalescence occurred, however only the emulsions containing iota-carrageenan were stable to creaming after 1 week storage. We propose that iota-carrageenan, which had the most densely charged helix structure, was most effective at creating highly charged interfacial membranes, thereby reducing the tendency for depletion flocculation to occur. (C) 2004 Elsevier Ltd. All rights reserved.