Chemistry Reference
In-Depth Information
0.1
0
-0.1
S
=
S
0
-0.2
-0.3
c
=
c
*
-0.4
-0.5
-0.6
-1.0
-0.5
0
0.5
1.0
1.5
log (
c
/
c
*)
Fig. 8.2
Flavour/taste suppression by random coil polysaccharides. Results (mean values
of panel scores for sweetness and flavour intensity) are shown for alginate (
), car-
boxymethylcellulose of high (
) and medium (
•
) molecular weight, and guar gum of high
(
) molecular weight. Reproduced from Baines and Morris (1988),
with permission from Oxford University Press.
), medium (
◦
)andlow(
1989) compared the relationship between the perceived flavour and the
concentration of a hydrocolloid. The results showed that perception de-
creased when the concentration of the hydrocolloid c exceeded the c
*
concentration. The latter is the concentration where the hydrodynamic
domains of the polymer coils start to overlap. Above this concentration,
non-Newtonian behaviour becomes much more pronounced because of
disruption of entanglements between coils with increasing shear rate and
the concentration dependence of the zero shear rate viscosity changes
from an approximately linear dependence to a dependence on c
3-4
.
In these studies, magnitude estimation was used by the panel to
estimate the degree of inhibition of taste and flavour perception. This
involved the panel being told to rate the product relative to a value of 100
for the control containing no thickener. Thus, if a thickened product was
perceived as being half as sweet as the control, then it would be given a
score of 50. Fig. 8.2 displays the relationship between the S
/
S
O
,where
SandS
O
is the score for the thickened product and the unthickened
control, respectively, and c
c
*
.
The obvious question is what is the mechanism responsible for this
decrease in perception? One hypothesis is that the release of volatiles
from the solution is decreased once the concentration exceeds c
*
.Fol-
lowing the development of a direct interface between air exhaled from
the nose and a Mass Spectrometer developed by Taylor and Linforth
(Taylor
et al
., 2000), it was possible to test this. For solutions thickened
by hydroxypropylmethyl cellulose (HPMC), the flavour perception mea-
sured by a sensory panel was in agreement with the Baines and Morris
results shown in Fig. 8.2. There was however no significant difference
in the concentration of the volatile detected in the nose as the HPMC
/
