Chemistry Reference
In-Depth Information
b-LG soluble aggregates having a similar condensation state using various
cosolutes providing that charge neutralization of the denatured monomers is
achieved. This statement is corroborated by the superimposed values of the
apparent electrophoretic mobility of these aggregates for the three cosolutes
(Figure 5).
The air-water interfacial properties of the soluble aggregates have been
investigated by dynamic pendent drop tensiometry, allowing determination of
the surface viscoelastic parameters. Figure 7 shows a comparison of the
frequency behaviour of the surface elasticity E
0
and the phase angle
d
for
b-LG heated alone or in the presence of cosolutes close to the critical concen-
tration C
cs
* (A50 and N140). The heated b-LG+cosolute dispersions exhibited
a considerable increase in E
0
of more than 100% over the whole frequency
range. The surface viscosity
Z
d
¼
E
00
/o (at 0.01 Hz) exhibited very similar
behaviour, increasing from 160 mN s m
1
for b-LG heated alone to 280 mN s
m
1
when heated with cosolutes (results not shown). The frequency dependence
of
Z
d
can be explained in terms of conformational rearrangements at the
interfacial layer upon deformation. The gel-like character of the interface
composed of soluble aggregates generated in presence of cosolutes is empha-
sized by the change in phase angle from 221 to 91 for b-LG alone and with
cosolutes, respectively (Figure 7).
31
Here, it is important to note that the
viscoelastic patterns for A50 and N140 (conditions with 4 80% of soluble
aggregates) could be superimposed, indicating similar interfacial properties for
aggregates having similar molecular weight, hydrodynamic diameter and
apparent surface charge.
The foaming and foam-stabilizing properties of these soluble aggregates have
been investigated using the Foamscan
TM
apparatus. The foamability of aggre-
gates generated with or without cosolute presence was determined by measur-
ing the average number of bubbles initially present in a given volume of foam
after N
2
sparging. It has been found that 2-3 times more bubbles were present
25
80
20
60
15
40
10
20
5
0
0
0.00
0.02
0.04
0.06
0.08
0.10
0.12
Frequency (f) [s
-1
]
Figure 7 Frequency dependence of surface elasticity E
0
(—) and phase angle (- - - -) at
air-water interface:
K
, heated
b
-LG;
J
, A50 (
b
-LG + 50 mM arginine
HCl);
m
, N140 (
b
-LG + 140 mM NaCl). Vertical error bars represent the
standard deviation
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