Role of Protein-Stabilized Interfaces on the Microstructure and Rheology of Oil-in- Water Emulsions - Food Colloids: Self-Assembly and Material Science - page 392

size distribution and a lack of flocculation. Because the size distribution of both
emulsion systems was identical, the oil droplets moved from the sub-phase at a
very similar rate. The region showing the most distinct differences is within the
cream layer over the first 8 h of the experiment. In the case of the surfactant-
stabilized system [Figure 3(b)], the density of the cream gradually increases from
the base to the top of the layer. However, in the case of the protein system, there
is a 'pseudo' plateau of lower density at the base of the cream that disappears
after about 8 h. This suggests a delay in the rearrangement into a more densely
packed layer. After this 8-h period, the ascending droplets seem able to pack into
the denser state more directly. This may be a result of the polydispersity of the
emulsion, leading to larger droplets ascending into the cream layer first and
showing a delay in rearranging. A further difference to note between the
behaviour of the two samples is that the final phase volume at the top of the
cream layer is some 5% greater in the surfactant-stabilized system than in the
protein-stabilized system. This is shown in more detail in Figure 4. Here the oil
volume fraction of the top 20 mm of the cream layer is shown as a function of
time. The initial rapid creaming seems to be similar for the two samples, but after
about 5 h the density of the WPI emulsion equilibrates quickly, whereas the
surfactant emulsion continues to increase in density over the course of the
experiment. This highlights a difference between the two emulsion systems, as
the bulk moduli of the WPI emulsion cream layer are almost an order of
magnitude greater than those of the surfactant emulsion cream layer (Figure 2),
despite the fact that the former has a lower phase volume (Figure 4).

0.8

0.75

0.7

0.65

0.6

0.55

1

0.5

0.45

0.4

0.35

0.3

0 10 20 30 40 50 60

Time (h)

Figure 4 Dispersed phase volume of upper 20 mm of cream layer as a function of time for
emulsions stabilized by WPI (solid line), SDS (dotted line), Brij 35 (dashed
line) and SDS/Brij35 (dashed/dotted line)