COMPETITIVE DISPLACEMENT OF PROTEINS IN OIL-IN-WATER EMULSIONS CONTAINING CALCIUM-IONS

The influence of calcium ions on the time-dependent competitive adsorp tion of phosvitin and beta-casein at pH 7 has been investigated at the emulsion droplet surface by monitoring the protein content of the aqu eous phase. In the absence of calcium ions, addition of beta-casein to a phosvitin-stabilised oil-in-water emulsion (0.5 wt.% protein, 20 wt .% n-tetradecane) results in 70% of the originally adsorbed phosvitin becoming displaced within a few minutes, followed by the loss of a fur ther 10% over a 48 h period. In contrast, when calcium ions are presen t at a concentration sufficient to cause droplet aggregation in the mi xed emulsion, no phosvitin is desorbed, despite substantial adsorption of the added beta-casein. But, when calcium ions are present in insuf ficient quantity to cause aggregation, displacement of phosvitin by be ta-casein is facilitated. The incorporation of calcium ions prior to h omogenisation increases the amount of phosvitin at the emulsion drople t surface. The interfacial shear viscosity of an adsorbed phosvitin fi lm at the planar oil-water interface is markedly increased when calciu m ions are present.