Chemistry Reference
In-Depth Information
(a)
(b)
(c)
(d)
Fig. 8.4
Mixing behaviour of (a) a polymeric thickener (HPMC) and (b) a particulate
thickener (swollen suspension of granular starch) with a viscosity of 380 mPa
s measured
at 50 per second and 25
◦
C and locust bean gum at a concentration of (c) 0.5% and
(d) 0.6%. Adapted from Ferry etal., 2006a. Copyright 2006, with permission from Elsevier;
and Koliandris et al. (2008). Copyright 2008, with permission from Elsevier.
·
mouth. Nevertheless, the authors consider it as a valuable experiment in
predicting differences in perception between high-viscosity liquid foods.
8.4.2
Microstructure
Clearly, if it is accepted that good mixing is desirable for good per-
ception, then it will be important to understand the microstructure that
is required to promote this. The hypothesis is that solutions which are
thickened by swollen particles, most obviously starch granules but prob-
ably also plant fibres (there is increasing interest in the latter as an
alternative to hydrocolloids), will mix well, whereas polymers in solu-
tion will mix poorly when the c
*
concentration is exceeded. Evidence
in support for this comes from a study on the mixing of gelatinised
starches from different sources and the effect of amylase activity on
starch-thickened systems. It is easy to show that amylase activity re-
duces starch viscosity on time scales relevant to oral consumption (Ferry
et al
., 2004). A consequence of the enzymes' attack on a swollen starch
granule is a disruption of the structure, resulting in a partial change
in solution microstructure from a suspension of swollen particles to a
polysaccharide solution. Waxy maize starch that contains no amylose
