Biomedical Engineering Reference
In-Depth Information
Figure 13. Oxidation processes of polyunsaturated fatty acids and their ascorbates at 65
o
C and nearly
0% relative humidity. (a) n-6 series: (
z
)
γ
-linolenic acid, (
{
)
γ
-linolenoyl ascorbate, (
) dihomo-
γ
-
linolenic acid, (
) dihomo-
γ
-linolenoyl ascorbate, (
S
) arachidonic acid and (
U
) arachidonoyl
ascorbate; (b) n-3 series; (
¡
)
α
-linolenic acid, (
)
α
-linolenoyl ascorbate, (
T
) eicosapentaenoic acid,
(
V
) eicosapentaenoyl ascorbate, (
X
) docosahexaenoic acid and (
Z
) docosahexaenoyl ascorbate.
5. Emulsifier Property of Acyl Ascorbate
The surface tensions of the aqueous solutions of acyl ascorbates were observed at the
various concentrations and at 25
o
C by the Wilhelmy method [26]. The critical micelle
concentration for each acyl ascorbate, CMC, was estimated from the results. The surface
excess,
Γ
, was evaluated according to the following equation:
d
γ
−
=
2
.
30
Γ
RT
(6)
d
log
C
where γ is the surface tension, and
C
is the concentration of acyl ascorbate. The residual area
per molecule,
a
, was calculated from the
Γ
value by:
1
N
a
=
(7)
Γ
A
where
N
A
is Avogadro's number. The CMCs of the ascorbates with longer acyl chains were
lower, while the
Γ
values scarcely depended on the acyl chain length. The CMCs and
a
values of acyl ascorbates are plotted versus the carbon number of the acyl chains in Figure 14,
together with the CMCs at 25
o
C for 6-
O
-acyl mannoses [42] and 1-alkyl
β
-D-glucosides [53].
The change in the CMC as a function of the chain length
n
is expressed by [54]:
