Influence of KCl on the physicochemical properties of whey protein stabilized emulsions

Monovalent K+ and Cl- ions have been determined to be indifferent ions in whey protein stabilized emulsions, because the increase of the ionic strength did not alter the medium isoelectric point of whey proteins. The reduction of zeta-potential and stabilizing repulsive electric forces as a consequence of the increase of ionic strength was attributed to contraction of the electrical double layer around the charged droplets. The particle size distribution, mean droplet size and creaming stability of 0.04 wt% soybean oil-in-water emulsions (d(32) = 0.3 mum) were measured with varying KCl concentrations (0-100 mM) and pH (2.5-7). In the absence of KCl the range of pH values where the droplets tended to aggregate was 4.5 < pH < 5.5, which has been broaden to 4 < pH < 6 when the KCl concentration exceeded 10 mM. To produce an emulsion that is stable to aggregation, its pH must be adjusted to be < 4 or > 6. The numerical calculations by DLVO theory showed a good agreement with the experimental data. (C) 2003 Elsevier Ltd. All rights reserved.