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100
10
1
0.1
0.01
0.001
0.02
0.03
0.04
0.05
0.06
0.07
0.08
c (w/v %)
Figure 10 Comparison of viscosities determined by particle tracking in the phase-sepa-
rated regions of emulsions (30 vol.% oil, 1.4 wt.% sodium caseinate, pH 6.8)
as a function of the concentration c of xanthan in the aqueous phase:
J
,
xanthan-rich aqueous regions;
K
, flocculated oil-droplet-rich regions
under gravity - and not the viscoelasticity of the xanthan-containing micro-
regions (with or without dispersed oil droplets).
20.4 Concluding Remarks
The use of particle tracking combined with confocal microscopy appears to
offer new opportunities for understanding the texture and stability of food
colloids and for systematically controlling the processing and shelf life of food
products. Here we have illustrated the application of the technique for the case
of a protein-stabilized emulsion with added hydrocolloid thickening agent.
From qualitative visual observations of the particle diffusive motions, and from
quantitative analysis of trajectories in the viscous regime, we have demon-
strated unequivocally that the viscosity in the oil-droplet-rich regions is very
much greater than in the xanthan-rich phase. Hence we assert that the kinetics
of phase separation in this type of emulsion system is predominantly deter-
mined by the rheological behaviour of the interconnected oil droplet regions.
These findings complement our confocal microscopy study
14
of the evolving
morphology of the xanthan-containing blobs. The shape relaxation time
determined by image analysis can now be unambiguously related to the
dominant viscoelasticity of the surrounding regions of the concentrated pro-
tein-coated oil droplets, and not to the viscosity of the xanthan-rich blobs
themselves. Owing to the flexibility of the weak interdroplet bonds, the floccu-
lated droplet network undergoes reorganization and rearrangement under the
combined influence of Brownian motion and gravity. Eventually, the restruc-
turing and reorganization of the flocculated droplets leads to a loss of connec-
tivity in the aggregated microstructure and the transient network collapses. The
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