Chemistry Reference
In-Depth Information
0
50
100
150
200
A
0
50
100
150
200
B
0
50
100
150
200
C
0
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150
200
D
Fig. 8.5
Mixing efficiency of viscous systems with solutions containing an increasing
amount of R-amylase. Viscous samples (480 mPa
s at 50 per second) of different starches
(wheat, A; modified waxy maize, B; waxy maize, C; HPMC, D) were stirred into distilled
water or solutions containing 50, 100, 150, and 200 U
·
mL
−1
of amylase and pho-
tographed after 1 minute. Reproduced from Ferry et al. (2006b), copyright 2006, with
permission from American Chemical Society.
·
has a weak granule structure which is easily disrupted during processes
involving heating and shearing. For this reason, waxy maize starches
are often chemically cross-linked or physically treated to maintain gran-
ule integrity. For amylose-containing starches, such as wheat or maize,
following gelatinisation, there will be a release of some amylose into
solution following gelatinisation, but the swollen granule will be much
'stronger' than unmodified waxy maize starch.
If viscosity was the dominant factor, an increase in perception with
amylase activity would be expected, since it has been shown that flavour
perception normally increases with decreasing viscosity. If for these
systems microstructure through its influence on mixing 'overrides' vis-
cosity as the dominating effect, then perception should decrease with
increasing amylase activity. The latter view is supported by the second
study by Ferry
et al
. (2006b).
For systems thickened with wheat starch, native waxy maize starch,
a waxy maize starch modified to maintain granule integrity following
gelatinisation and HPMC, Figs. 8.5 and 8.6 illustrate the change of
mixing efficiency with amylase concentration in the water to which
the stained viscous 'solution' was added. Figure 8.5 shows observed
mixing efficiency. The quantitative data plotted in Fig. 8.6 are based
on monitoring the concentration of K
+
with a specific ion electrode
inserted into the top surface shortly after mixing (KCl and not NaCl was
used since the amylase preparation added to the water contained Na
+
).
