Chemistry Reference
In-Depth Information
Table 1 Transition enthalpy change
D
H, transition point temperature, transition
temperature range and transition entropy change
D
S of the endothermic
events occurring on heating of the control samples and in the presence of
increasing quantities of solubilized phytosterols
Temperature
(1C)
D
H
(J g
1
)
Temperature
(1C)
D
H
(J g
1
)
D
S
(J g
1
K
1
)
L
b
L
a
L
b
L
a
L
a
Q
L
L
a
Q
L
L
a
Q
L
2.79-8.53
a
17.33-21.12
a
Q
L
15.91
1.16
0.06
6.04
b
19.32
b
3.03-8.08
a
14.94-20.99
a
Q
L
+ 0.2-wt%
phytosterols
13.63
1.24
0.0645
5.66
b
19.14
b
2.98-8.16
a
16.92-20.61
a
5.6
10
2
Q
L
+ 1.4-wt%
phytosterols
4.17
0.0030
5.63
b
18.74
b
2.55-8.17
a
Not observed
c
40.003
c
Q
L
+ 2.5-wt%
phytosterols
1.09
5.68
b
a
Range of peak.
b
Centre of peak.
c
Difficult to measure.
The cooling stage (from 40 to
101C) exhibits only one exothermic event,
corresponding to the crystallization from liquid crystal phase to gel lamellar
phase. The formation of the gel lamellar phase occurred at a lower temperature
than during the heating scan (Figure 6 and Table 2). The lower crystallization
point reflects the supersaturation effect, which is common in all fats and lipids.
The transition temperatures were even lower in the presence of increasing
contents of solubilized phytosterols. Similarly, the enthalpy values were found
to decrease for > 0.2 wt% of phytosterols.
It is thus understood that a moderately high level (> 0.2 wt%) of solubilized
phytosterol lowers the order in the Q
L
phase. Phytosterols at high content
destabilize the Q
L
phase, and so the transition is observed at lower temperatures.
The SAXS measurements reveal that phytosterols solubilized into the
Q
L
phase have a progressive concentration-dependent effect on the nano-
structure of the phase. At low solubilizate concentration, the guest molecules
exhibit an ordering effect, so that the SAXS diffractions became sharper,
better resolved and the peaks are intensified (Figure 7). The diffractions reveal
the existence of a series of six Bragg peaks with calculated reciprocal spacing
ratios of 1 :
O
2:
O
3:
O
4:
O
5:
O
6. The reciprocal d space (1/d
hkl
)ofthesix
reflections versus (h
2
+ k
2
+ l
2
)
1/2
intercepts the axis of the origin with a very
small deviation of 2.7
10
4
and high linearity of 0.9991. The indexation
indicates the existence of the P4
2
32 space group and the lattice periodicity
spacing is 94.9 A
˚
. Therefore we can conclude that a solubilization level of 0.2
wt% of phytosterols enhances the order in the structure, since a very good
matching of the actual diffractions and the permitted reflections was clearly
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