Chemistry Reference
In-Depth Information
10
-3
×
8
2 hours - ionic
24 hours - ionic
2 hours - acid
6
24 hours - acid
4
2
0
0
0.5
1 1.5
Concentration (%)
2
2.5
Fig. 10.19
Comparison of the concentration dependence of T
2
relaxation time (i.e.
extent of ordering) of ionic and acid gels, together with how these properties change with
time after the gels had been formed (adapted from Norton et al., 2006a).
be used to induce self-structuring of food-grade hydrocolloids (Norton
et al
., 2006a). A number of different polysaccharides are known to be
acid sensitive and so could be used to form structures as they enter
the stomach. However, in order to make them applicable, it will be
necessary to control the structure produced, the rate of structuring and
the structural breakdown of the materials used throughout the human
GI tract.
Acid gelation of alginate in environments close to stomach condi-
tions have been studied and compared with simple viscosifying systems
(Fig. 10.19). This figure shows that when guar is used, the stomach
contents become diluted and more water-like with time. However, when
alginate is used, the T
2
becomes shorter with time in the acid conditions,
indicating an increased amount of structuring. In principle, the design
idea is to have systems that undergo self-structuring in the stomach to
gel the whole stomach contents. The work by Rayment
et al
. (2009)
has in principle tried to investigate this, but unfortunately there was no
attempt to control acid gelation rates or even when gel beads were used,
cross-linking of the beads in acid conditions was also not considered.
This meant that in both studies, no real control of stomach gelling was
obtained and as a consequence, no real difference between meals with
or without alginate was observed.
One of the major problems with alginate is gaining control of the
gelation kinetics. This is proving very difficult even with selected or
modified alginates. However, control is likely in the fullness of time. As
a consequence of these difficulties, investigators have started to look at
other materials. One of the best candidates is gellan.
