The effect of the presence of KCl on the adsorption behaviour of whey protein and caseinate in oil-in-water emulsions

Abstract

Emulsions were prepared containing 20% soya oil and 2% protein, which was either caseinate or whey protein isolate (WPI). At pH 7 oil droplets in emulsions made using WPI showed small increases in the diameter with increasing concentration of KCl in the range 0–200 mM, but at pH 3 concentrations of KCl >50 mmol/dm 3 caused very large increases in the diameters of the particles and the emulsions appeared viscous. This effect of KCl was not reversed by dilution. In emulsions prepared with mixtures of proteins, the proportions of proteins adsorbing from WPI and caseinate were affected by the presence of KCl. This was reflected also in the composition of adsorbed protein on emulsion droplets made originally with WPI, and subsequently resuspended in caseinate. In these resuspended emulsions all of the α-lactalbumin was displaced by caseins, and the amount of β-lactoglobulin displaced depended on the age of the WPI emulsion when caseinate was introduced. The thickness of the adsorbed layer depended on (i) the type of protein that was used to make the emulsion, and (ii), whether more protein was added after homogenization and (Hi), the age of the emulsion when further protein was added. This behaviour reflected different structures of the adsorbed layer.