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would result in emulsion droplets with little overall charge density. The
z
-potential data confirm that emulsion droplets stabilized by lactoferrin +
b-lactoglobulin have a very low overall net charge.
It is noteworthy that the emulsion droplets formed by a mixture of lac-
toferrin + b-lactoglobulin at total protein concentrations above 1 wt.% were
stable, as shown by the emulsion droplet size data and creaming measurements
(not shown), even though their charge density was very low or close to zero.
This suggests that the interfacial layers formed by these binary protein com-
plexes provide good steric stabilization.
At low protein concentration (
o
1 wt.%), some droplet flocculation was
evident in the emulsions formed with a mixture of lactoferrin + b-lactoglobulin
(Figure 1). This was probably because of the formation of a complex between
these proteins in aqueous solution, prior to emulsion formation, reduced the
number concentration of protein molecules available for adsorption, and also
increased the molecular weight of the protein complexes. Larger droplet sizes
were probably formed, mostly as a result of bridging flocculation of the
emulsion droplets, whereby one protein complex is adsorbed on to more than
one droplet. Some re-coalescence may have also occurred during emulsion
formation under those conditions.
11.3.2 Addition of
b
-Lactoglobulin to Lactoferrin-Stabilized
Emulsions
Figure 3 shows
z
-potential values of emulsions formed with lactoferrin (1 wt.%
protein, pH 7.0) and then diluted with aqueous phase containing a range of
b-lactoglobulin concentrations.
60
40
20
0
-20
-40
-60
0
0.125
0.25
0.5
1
1.5
Concentration of
β
β
-lg (%)
Figure 3
Influence of the addition of
b
-lactoglobulin into emulsions made with 1 wt.%
lactoferrin (30 wt.% soya oil, pH 7.0) on the
z
-potential of the emulsion droplets
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