Biomedical Engineering Reference
In-Depth Information
0.5
A1
Megrim
0.4
0.3
Cod
Tuna
0.2
Temperature
variation
0.1
0.0
−
5
35
30
25
10
Temperature (
°
C)
20
15
5
0
Helix formation in gelatin aqueous solution (c = 4.5% w/v) versus temperature, for gelatins
with various sources. Cooling rate
Figure 7.6
0.5°C min
−
1
. Adapted from Joly-Duhamel et al.(
2002b
)
© 2002 American Chemical Society.
−
0.8
T
(
°
C)
c
=
4.7 %w/v
c
=
1 %w/v
10.5
0.6
20.5
χ
0.4
26.5
28.2
0.2
0
1
10
Time (hours)
10
−
2
10
−
1
10
2
10
3
Helix fraction versus time (logarithmic scale) at various temperatures (T = 10.5, 20.5, 26.5,
28.2°C) and concentrations (1% and 4.7% w/v). Adapted from Djabourov et al.(
1988a
) with
permission from EDP Sciences.
Figure 7.7
such as sugars and glycerol enhance helix formation as they decrease the solubility of
gelatin. Other chemicals such as KSCN, LiBr, CaCl
2
, urea and phenols have the power
to completely prevent gelation when they are present in suf
cient concentration; see,
for instance, Ward and Courts (
1977
).
*
Kinetic effects: helix formation proceeds after the nucleation step, but slows down
progressively while the network is formed. An
evolution characterizes
helix formation in gelatin, as shown, for instance, in
Figure 7.7
for various concen-
trations and temperatures. This slow evolution or physical ageing in gelatin gels was
'
in
nitely long
'
first reported and analysed by te Nijenhuis (
1981a
,
1981b
).
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