3.2. In¯uence of pH and CaCl2 on droplet aggregation
The pH dependence of the mean particle size of pro-
tein stabilized emulsions determined by turbidity mea-
surements is shown in Fig. 3. These measurements were
carried out 24 h after the CaCl2 was added to the
emulsions and they had been stored at 30C. In the
absence of calcium chloride there was a signi®cant
increase in mean particle size around the isoelectric
point (4 < pH < 6) of the whey proteins, which sug-
gested that appreciable droplet aggregation occurred.
The addition of CaCl2 to the emulsions signi®cantly
altered the extent of droplet aggregation. When the
CaCl2 concentration was increased from 0 to 1 mM the
pH at which the droplets aggregated shifted to higher
values (Fig. 3). This is because the isoelectric point of
the emulsion droplets shifted to higher pH (Fig. 1),
presumably because of binding of Ca2+ ions at very low
calcium chloride concentrations. As the CaCl2 con-
centration was increased above 1mM the range of pH
values above the isoelectric point over which the emul-
sions became unstable grew wider. At 20 mM CaCl2 the emulsions were unstable to aggregation at all pH values
above the isoelectric point.