Tribology as a Tool to Study Emulsion Behaviour in the Mouth - Food Colloids: Self-Assembly and Material Science - page 459

3

2

1

0

0 1 2 3

D 32 ( µ m)

Figure 5 Viscosity of emulsions stabilized by 1 wt% WPI, containing 10 wt% sunflower
oil or 10 wt% solid fat, as function of the mean droplet size d 32 at three shear-
rates: & , 51.3 s 1 ; m , 90.1 s 1 ;and J , 1030 s 1

0.25

0.20

0.15

0.10

0.05

0.00

Oil, S Oil, L Solid fat, S Solid fat, L

Figure 6 Friction force measurements of emulsions sheared between pig's tongue
and glass. The emulsions contained either 10 wt% sunflower oil, having small
(Oil, S) or large (Oil, L) droplets, or 10 wt% solid fat, having small (Solid
fat, S) and large (Solid fat, L) droplets. Error bars indicate calculated
standard error

friction force data show that the samples with solid fat give rise to a lower
friction force than the samples containing sunflower oil (Figure 6). This
indicates that the samples with solid fat are better lubricants than the samples
with sunflower oil. The samples with the larger droplets give a lower friction
upon shearing. These results are explained by the difference in sensitivity to
coalescence and subsequent oil release.
Studies relating friction of emulsions to sensory perception are up until now
limited. So far most friction results have been obtained with thickened oil-in-
water emulsion systems such as custards. De Wijk and Prinz 15 found an