Chemistry Reference
In-Depth Information
140
120
100
80
60
40
20
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Tween 20 content (pbw)
Figure 1 Effect of the partial replacement of lecithin, with starting level 1 part by weight
(pbw) of formulation, by Tween 20 on the texture of an instant emulsion also
containing 1 pbw caseinate, 8 pbw starch, 50 pbw sunflower oil, 45 pbw water,
1.2 pbw NaCl and 0.65 pbw buffer salts. Measurements were made using a
Stevens Texture Analyser equipped with a standard mesh probe head
the caseinate + Tween 20 system did not increase the viscosity of the emulsion
either, suggesting that Tween 20 may also be interacting with the caseinate, to
reduce its structuring potential. Figure 1 shows the effect that sequential
substitution of lecithin by Tween 20 has on the 'texture' as measured by a
Stevens Texture Analyser.
28.3 Emulsion Stabilization
The example described above serves to show how an acidified protein-contain-
ing emulsion can be stabilized. An alternative strategy is to speed up the
creation of smaller stable oil droplets. The influences of shear and time were
investigated. When the mixture of oil slurry and water is shaken, then the
structuring and viscosity increase takes place in the region of 10-20 s. The fast
increase in viscosity traps the emulsion and prevents any further 'working' of
the system. However, if the mixture is sheared gently, with hand mixing, the
system can be agitated for a prolonged period of time. This allows smaller
droplet formation, and also additional time for the caseinate to hydrate and
participate at the interface. The confocal micrographs in Figure 2 show the
effect of shaking and shearing on the oil droplet-size distribution.
Another way to reduce the droplet size is to increase the continuous water-
phase viscosity. Grace
20
has shown that droplet break-up can be induced by
changing the relative viscosities of the continuous and dispersed phase. The
addition of a readily hydratable viscosifier (e.g., guar gum) can increase the
aqueous phase viscosity. The effect of increasing the concentration of guar gum
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