Chemistry Reference
In-Depth Information
appeared to increase considerably with increase in b-lactoglobulin concentra-
tion up to 0.42 wt.%, with very little change above this concentration.
There were no significant changes in d
32
values or creaming stability with
an increase in the b-lactoglobulin concentration in the emulsions (data not
shown), suggesting that these emulsions remained very stable despite major
changes in the net charges of the droplets. There was no evidence of droplet
aggregation, even at 0.42 wt.% b-lactoglobulin addition, which corresponded
to the compositions where there was almost complete charge neutralization.
This suggests that steric repulsion may play a more important role than
electrostatic interactions in the stabilization of these emulsions.
11.3.3. Addition of Lactoferrin to
b
-Lactoglobulin-Stabilized
Emulsions
In the absence of lactoferrin, the
z
-potential of the b-lactoglobulin-stabilized
droplets (1 wt.% protein, pH 7.0) was about
50 mV (Figure 5), indicating that
these emulsion droplets had a relatively high negative charge. The
z
-potential
became increasingly less negative and eventually changed from a negative value
to a positive value as the lactoferrin concentration in the emulsion was increased.
A slightly positive value was obtained when the lactoferrin concentration was
about 0.83 wt.%; the
z
-potential continued to become more positive with further
increase in lactoferrin concentration.
The surface protein coverage of the emulsion droplets was found to increase
almost linearly from
3.5 mg m
2
with increase in the lactoferrin
concentration up to 1.2 wt.%, and to reach a plateau thereafter (Figure 6). The
B
1.5 to
B
60
40
20
0
-20
-40
-60
0
0.125
0.25
0.5
1
1.5
2.5
Lactoferrin concentration(%)
Figure 5
Influence of the addition of lactoferrin into emulsions formed with 1 wt.%
b
-lactoglobulin (30 wt.% soya oil, pH 7.0) on the
z
-potential of the emulsion
droplets
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