Biomedical Engineering Reference
In-Depth Information
ascorbates in the effluent are plotted in Figure 6(a). For each acyl ascorbate, the concentration
of more than 18 mmol/L was attained at τ ≥ 175 min. Therefore, the reactor was operated at
the residence time of 175 min for the long-term production of the acyl ascorbates. The long-
term operational stability of the immobilized enzyme was examined for the synthesis of the
decanoyl, lauroyl and myristoyl ascorbates at τ = 175 min. As shown in Figure 7, the
productivity of lauroyl ascorbate for 5 days was constant, and was determined to be
ca
. 57
g/L-reactor
·
day. The productivities of decanoyl and myristoyl ascorbate were calculated to be
ca
. 53 and 66 g/L-reactor
·
day, respectively. The decanoyl and myristoyl ascorbates were also
produced at similar conversions. The immobilized enzyme was stable and the reactor was
steadily operated for at least 11 days.
Figure 7. Continuous production of (
S
,
U
) decanoyl, (
T
,
V
) lauroyl or (
X
,
Z
) myristoyl, (
{
)
arachidonoyl, (
) oleoyl, and (
) linoleoyl ascorbate using the CSTR (closed symbols) or PFR (open
symbols) with immobilized lipase, Chirazyme
®
L-2 C2, at 50
o
C. The flow rates were 2.0 mL/min for
the CSTR and 0.5 mL/min for the PFR, respectively. The fatty acid concentration was 200 mmol/L.
The curves were empirically drawn.
A decanoic, lauric, myristic, oleic, linoleic or arachidonic acid solution dissolved in
acetone was fed to the PFR system at a flow rate of 0.5 mL/min, which corresponded to a
surperficial residence time in the immobilized-enzyme column, τ, of 5.0 min. After a steady
state was achieved, the concentration of the corresponding acyl ascorbate in the effluent was
determined. For every fatty acid, the product concentration increased as the fatty acid
concentration in the feed increased, and it reached the maximum value at the fatty acid
concentrations higher 200 mmol/L. Because the solubility of ascorbic acid in acetone at 50
o
C
was 25.3 mmol/L, the molar ratio of a fatty acid to ascorbic acid at the inlet of the
immobilized-enzyme column would be
ca.
8. The concentrations of oleoyl and linoleoyl
ascorbates were lower than those of other ascorbates at any fatty acid concentration. This
would be due to the lower purity of oleic and linoleic acids used (
ca.
90%). In the subsequent
experiments, the fatty acid concentration in the feed was fixed at 200 mmol/L. A fatty acid
solution was fed through the ascorbic acid column to the column packed with the
immobilized lipase at various flow rates, and the corresponding acyl ascorbate concentration
in the effluent at a steady state was measured. Figure 6(b) shows the relationship between the
