Chemistry Reference
In-Depth Information
saliva. The authors concluded that the ability of an emulsion to first ad-
here to the surface of the tongue and later form a stable film determines
the ability to reduce friction. Although saliva has a significant effect in
removing oil from the hydrophobic tongue, emulsions that are prone
to coalescence during oral processing appear to adhere more strongly
and spread more easily on the surface of the tongue. This would have a
direct effect on the perception attributes of these systems, a hypothesis
confirmed by sensory studies which have shown that emulsions with a
higher sensitivity to coalescence are perceived as more fatty and creamy
(Dresselhuis
et al.
, 2008c).
Therefore, another 'tool' for succussfully designing functional foods
is the introduction of (a level of) mucoadhesive properties into food
formulations, as this could allow for the control of food transit time
(e.g. delay) and manipulation of the coverage of oral surfaces. Malone
et al
. (2003) formulated chitosan stabilised o/w emulsions that could
adhere to the mucus layer, resulting in absorption, even after 5 minutes.
A result of the chitosan absorbing onto the oral mucosa, though, is an
astringent mouthfeel, attributed to complexation and precipitation of
salivary proteins (Rossetti
et al
., 2008).
9.4
IN VITRO MEASUREMENTS OF
SENSORY PERCEPTION
It has been established that there are links between the sensory attributes
of foods and their physical properties, usually in the form of (both bulk
and thin film) rheological properties. However, it should be stressed
that these links tend to be limited to specific products or individual
attributes. This is partly due to the fact that the range of shear rates
experienced in the mouth during oral processing, as reported in the
available literature, is very wide, mainly due to the complexity of the
system under investigation and also because the very nature of oral
processing is quite material-specific. An example of this can be found
in the early study by Shama and Sherman (1973), which demonstrated
that the perceived thickness of a variety of foods could be correlated
with bulk rheology as measured for a shear rate range from 10 to 1000
per second, depending on the material tested; however, correlations were
subject to exceptions at high viscosities for non-Newtonian foods. Work
on emulsions by Akhtar
et al
. (2005) studied the effects on sensory
perception introduced by changes in the emulsions' oil content and
droplet size. Perception did correlate with fat content and viscosity, but
fat content only at high viscosities and not in the presence of thickeners,
thus leaving the conclusions uncertain. Droplet sizes and emulsifier type
