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than the other emulsions (in terms of fattiness), when it was only found to
be different in fraction measured above 100 mm/second, thus suggesting
that a sensorial difference can be detected at these speeds. As all samples
had the same bulk viscosity, results indicate that tribology measurements
are a more relevant descriptor. Fat perception, however, does not just
relate to the lubrication experienced in the mouth; this is evident in the
sensory scores for the emulsion containing 1% oil, which are different to
those for pure water (0% oil). This is attributed to flavours and volatiles
present in the oil phase, which can be detected in the mouth even though
the actual lubrication sensation remains the same.
Further to this work, Vingerhoeds
et al
. (2008) looked more exten-
sively into the sensory response of different oils and oil contents in
emulsions. In this study, increasing the fat content led to an increasing
perception of fat-related attributes, but this is believed to be mostly due to
viscosity increases between systems, as stated by Mela
et al
. (1994). This
is somewhat confirmed by results gathered from guar-thickened emul-
sions of matched viscosities; panellists gave the same fattiness scores to
a guar-thickened 10% oil-containing emulsion and an un-thickened 40%
oil-containing emulsion. However, this result affected other attributes,
making the thickened sample, for example, appear 'slimier'.
In order to determine whether tribology can indeed be used as a tool
for the evaluation of emulsions processed under oral conditions, Dres-
selhuis
et al
. (2008a) carried out a series of experiments focusing on the
different measuring aspects of the technique itself. Initially, the study
compared PDMS and a biological tissue material (tongue from pig) in
terms of their efficiency for use as the surfaces in contact during the tri-
bology experiments, in other words, to determine which type of surface
best reflects the characteristics of oral surfaces during food oral pro-
cessing. The findings of this work revealed that there are certain issues
associated with the use of the PDMS surface, namely the differences
in roughness and hardness between the actual oral surfaces and PDMS.
However, the practical implications of using biological materials for this
type of experimentation render their use rather problematic and there-
fore an artificial surface would be more preferable, although in need of
some improvement (Dresselhuis
et al
., 2008a). Another study by Ranc
et al
. (2006), looking at modified PDMS surfaces in tribology, showed
that there is potential to make this type of surfaces more representative
of the mouth, which is extremely important, since the frictions mea-
sured during such a test have been shown to be affected by the surfaces
used. Regardless of this though, good correlations can still be obtained
between sensory and friction measurements even when relatively rough
PDMS surfaces are used (Ranc
et al
. (2006)). The set-up of the equip-
ment used in this work was different to what is commonly used; here a
lower glass plate moves over the 'tongue' or PDMS surface and as such
