Chemistry Reference
In-Depth Information
120
100
80
60
40
20
0
Viscosity at 0.01 per second
Gel strength (N)
Fig. 5.8
Effect of preparation procedure on the viscosity of 0.5% xanthan gum in 0.5%
NaCl and the gel strength of 1% 60:40 xanthan:LBG gels in 1% NaCl, (
NaCl added
NaCl added at 87
◦
C).
prior to heating and
or other salts of equivalent ionic strength will raise the transition tem-
perature to greater than 90
◦
C, which is the temperature required to fully
hydrate the LBG and will maximise the gel strength.
When mixed xanthan-LBG gels are made under optimum conditions
(salt addition prior to heating), the gel strength increases with increas-
ing salt concentration up to
∼
100 mM for the monovalent ions. This
is equivalent to
0.58% as sodium chloride and 0.75% as potassium
chloride (see Fig. 5.9). Gels prepared with potassium ions are slightly
stronger than those with sodium. Gels prepared with calcium are signif-
icantly weaker.
∼
5.4.2
Acids (pH)
There are two questions that need to be answered when considering the
effect of pH on a gum solution:
(i) How does the viscosity change as a function of pH?
(ii) How stable is the viscosity as a function of time at any given pH?
The first can be considered to be a question of sensitivity, and the second
can be considered to be a question of stability.
