Chemistry Reference
In-Depth Information
Table 8.1
Pearson's correlation coefficients
between salivary amylase activity and sensory
scores for salt perception by a sensory panel
Thickener type
Saltiness
0.11
a
HPMC
0.20
b
Waxy maize starch
−
0.43
c
Modified waxy maize starch
−
0.25
c
Wheat starch
−
Reproduced from Ferry et al. (2006b), copyright 2006,
with permission from the American Chemical Society.
a
Not significant at a level of 5%, p
>
0.05.
b
Significant at a level of 5%.
c
Significant at a level of 1%.
8.4.3
Mouthfeel
More than 40 years ago, Szczesniak and Farkas (1962) attempted to
relate the mouthfeel of hydrocolloid solutions to solution rheology.
They matched the viscosity of a wide range of hydrocolloid and starch
'solutions' where this viscosity was measured semi-empirically at a
shear rate which would be lower than the value of 50 per second, which
as discussed above is often considered to be the shear rate prevalent in the
mouth. The sensory panel was asked to evaluate these solutions in terms
of sliminess, where a slimy solution was considered to be one difficult
to swallow. The hydrocolloid solutions were split into three classes on
the basis of their degree of shear thinning. At higher levels of shear
thinning, the solutions were perceived as increasingly less slimy, i.e.
easier to swallow. It has been argued that these differences simply reflect
difference in dynamic viscosity or shear viscosity at the appropriate
values for perception in the mouth (Richardson
et al
., 1989). However,
it is interesting that this class of least slimy solutions contains the starch
systems, which would be expected to maintain a granular microstructure
after gelatinisation (maize starch and high-amylose starch were used in
this study), and xanthan gum, whereas waxy maize starch was in the
slimy category. Returning to the mixing argument, it seems a useful and
testable hypothesis that mouthfeel improves with the ease of mixing.
Swallowing will be easier for a viscous solution which mixes more
readily with saliva compared to something that maintains a semi-gel-like
consistency in the mouth. As so often happens, xanthan gum does not
seem to fit the hypotheses. This polysaccharide would be expected to mix
in a polymeric fashion, i.e. poorly; however, observations on its in-mouth
behaviour reveal a behaviour more akin to that of a particulate system. It
is possible that this is because of its dramatic shear thinning behaviour
causing the concentration required to match the viscosity at in-mouth
shear rate of the other hydrocolloids to be below the entanglement
