Chemistry Reference
In-Depth Information
0.1 M
0 M
10
4
10
4
10
3
10
3
0.1
1
0.1
1
q (nm
-1
)
q (nm
-1
)
Figure 7 The q-dependence of the X-ray scattering intensity during heating of
b
-LG
solutions (C
¼
100 g L
1
,pH
¼
7) at two NaCl concentrations (0 and 0.1
M).
45
The intensity increases at low q and decreases at high q. A well-defined
iso-scattering point is observed at all NaCl concentrations
Figure 8 Electron micrographs of aggregates and gels formed at pH
¼
7 in the absence of
added salt: (a) cryo-TEM image of concentrated OA aggregates;
42
and (b)
TEM image of BSA gel.
16
The total width of each image is 0.7
m
m
The characteristic length-scale for gels that show a scattering peak is less than
a few tens of nanometres. Therefore it can only be observed using small-angle
neutron or X-ray scattering. When the degree of order decreases, the scattering
peak disappears and the intensity increases with increasing q in the range
covered by light scattering. The scattering intensity becomes important at
smaller q-values, which means that more visible light is scattered at wide angles.
Consequently less ordered gels are more turbid. The order can be reduced by
adding more salt to the solutions or by setting the pH closer to the isoelectric
point, which for many globular proteins used in food systems is close to pH
¼
5,
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