Coalescence of Expanding Bubbles: Effects of Protein Type and Included Oil Droplets - Food Colloids: Self-Assembly and Material Science - page 377

were also motivated by the desire to produce whippable emulsions with reduced
saturated (solid) fat, as part of other ongoing work. 18
Figure 4 shows some initial results of single bubble layer experiments at
pH ¼ 7with1wt%b-L for three different expansion rates and including different
volume fractions ( f ) of oil droplets. These systems did not contain added sugar as
thickener and the bubbles were formed by the injection method. In Figure 4 (and
the subsequent figures), as an aid to clarity in comparing the different data sets,
we show the estimated mean error as a single error bar in the top left of the plot.
It can be seen that, at very low f the systems containing oil droplets were slightly
more stable (lower F c ) compared with no addition of droplets at all, while at high
f there was a slight decrease in stability back to that for f ¼ 0. The trends for SC-
stabilized bubbles were similar, but for OA-stabilized bubbles, which were not
very stable anyway, all additions of oil droplets decreased the stability further.
Because of this, and because of the further complication that the added emulsion
had to be stabilized with SC anyway, the OA systems were not studied further.
More detailed measurements with b-L and SC were performed at f ¼ 0.25, since
this was found to be approximately the highest value of f giving some increase in
stability at neutral pH.
Figure 5 shows the results of single bubble experiments for 1 wt% SC and
b-L where the pH of the system was adjusted with GDL. The systems were not
thickened with syrup. In all cases the expansion rate was (dlnA/dt) ¼ 0.07 s 1
and the expansion ratio was A/A 0 ¼ 3. We see that both proteins show a slight
decrease in stability (increase in F c ) from pH ¼ 7topH

6. But there is a
marked increase in stability, to almost F c ¼ 0, at a pH between 5.4 and 5.6.
Below this pH range the curves diverge significantly. For b-L the value of F c
remains low as the pH is reduced further to the lowest pH tested (pH

E

4.7),
whereas for SC there is a marked decrease in stability again, with the system
becoming almost completely unstable below pH

E

5. (In fact, few stable
bubbles could actually be formed on injection in this pH range.)

E

1.0

0.5

0.0

10 -3 10 -2 10 -1 10 0

0

φ

Figure 4 Fraction of coalescence (F c ) in single bubble layer experiments with 1 wt% b -L
at different volume fractions ( f )of b -L-stabilized oil droplets, at three different
expansion rates (dlnA/dt): 0.007 s 1 ( K ); 0.07 s 1 ( , ); and 0.35 s 1 ( ' )