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(a)
1000
100
10
0.01
0.1
1
10
Speed (mm/s)
(b)
600
500
400
300
200
100
0
0
200
400
600
Surface load (Pa)
Figure 5 Surface friction as a function of (a) sliding speed (at constant surface load of
482.5 Pa) and (b) surface load (at a constant sliding speed 1 mm s
1
) for heat-
set whey protein gels containing different amounts of xanthan:
J
, none;
D
, 0.05
wt%;
B
, 0.25 wt%
Separate CLSM observations with both the protein and the polysaccharide
labelled separately have also been made to examine the surface distribution of the
xanthan. Figure 7 shows the CLSM images of the surface of the gel containing
0.05 wt% xanthan. In Figure 7(a) we can see the polysaccharide distribution is
oriented towards the surface in the form of highly concentrated stripes. Peaks of
protein aggregates are clearly identifiable in Figure 7(b), with the open valleys
appearing just at the positions where xanthan stripes are located. The combina-
tion of Figures 7(a) and 7(b) gives the dual-stained image shown in Figure 7(c).
Now we clearly see a rather dense surface layer with segregated protein and
xanthan regions. It appears that the outer part of the hydrocolloid regions
protrudes slightly further out from the surface than does the protein.
Figure 8 shows the ESEM surface images for the gel containing (a) no
xanthan and (b) 0.05 wt% xanthan. We observe completely different topo-
graphical microstructure for the two gels. For the gel with no xanthan addition,
its surface layer was composed of rather regularly spaced protein aggregates
separated by holes and void spaces (Figure 8(a)). We presume that these holes
and void spaces extend well into the bulk phase of the gel and that they
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