Chemistry Reference
In-Depth Information
0.06
0% oil
1% oil
15% oil
20% oil
0.04
55% oil
100% oil
0.02
0
10
0
10
1
Speed (mm/second)
10
2
10
3
Fig. 10.2
Tribometer curves for o/w emulsions containing different levels of fat at 35
◦
C.
All emulsions were made to have the same viscosity at a shear rate of 100 per second.
All the emulsions were made iso-viscous at a shear rate of 100 per
second. This work showed that the physical sensation of fat tends to be
one of a mixture of thin-film (tribology) and hydrodynamic behaviour,
i.e. the mixed regime. Fig. 10.2 shows how the frictional coefficient
changes for a range of samples (emulsions with oil levels between 1 and
55%, the data obtained for the aqueous phase used and pure vegetable
oil are included for comparision (Malone
et al
., 2003a). As can be
seen, at low rotational speeds (the tribological region - where the gap
between the ball-and-plate is the smallest), the pure water and 1% fat
emulsion have a much higher frictional coefficient than that of emulsions
with 20% oil or more. The emulsion with 15% oil falls between these
two sets of curves. As the rotational speed of the disc increases, the
gap between the ball-and-plate increases and the flow becomes what
is known as a mixed regime (hydrodynamic and tribological). In these
conditions, emulsions with greater than 20% oil match the pure oil.
Finally, at very high speeds, where the gap is greatest (the hydrodynamic
regime), the emulsions with the lowest fat levels give the lowest friction.
This is expected as they contain higher levels of hydrocolloids in this
experiment, as the authors constructed the emulsions to be iso-viscous at
100 per second.
By comparing this data with sensory perception data (from a trained
panel), it has been shown that the best correlation between the rheolog-
ical measurement and the human sensation occurs with speeds between
10 and 100 mm/second (the mixed regime) (Malone
et al
., 2003a).
When considering the eating action and the dimensions of the human
mouth, these speeds seem to be realistic. This data suggests that a lower
