Biomedical Engineering Reference
In-Depth Information
k
a
k
p
k
b
k
q
E
.
F
+
EA
B
E
.
FB
E
+
A
E
P
Q
Figure 14.3
Enzymatic reactions in anhydrous medium.
surface should be treated as
c = c
0
m
, where
m
is the emulsifier concentration and
c
0
represents the endogenous active surface at
m
= 0 (no emulsifier present).
Lipase-catalyzed reactions do not necessarily require water as the second reactant. An
immobilized enzyme is often stable in anhydrous media (Sharma
et al
., 2001 ) and can use
different alcohols as the secondary acceptors of fatty acids. The concentration of alcohol is
relatively low and cannot be treated as a constant. Consequently, the reaction obeys the
bisubstrate ping-pong mechanism (Cheirsilp
et al
., 2008 ; Mitchell
et al
., 2008 ; Xiong
et al
.,
2008) as shown in Figure 14.3. The corresponding equation of the reaction rate in the
absence of products is:
+
kk
.
Kk
Kk
V
pq
aq
bp
v
=
;
V
=
;
K
=
;
K
=
(14.12)
mA
mB
KK
kk
+
kk
+
kk
+
1
+
mA
+
mB
p
q
p
q
p
q
a
b
where
a
corresponds to the concentration of acyl substrate, for example monoacylglycerol
(MAG), and
b
is the concentration of alcohol, for example methanol. It should be empha-
sized that substitution of one substrate (
b
= methanol) by its analogue (
b
= butanol) changes
not only
K
mB
but also
K
mA
of the other substrate due to a different value of
k
q
. At the same
time, the ratios
V/K
mA
and
V/K
mB
remain the same after substitution of either
B
or
A
.
The current and most used method to analyze kinetics of lipase-catalyzed transesterifica-
tion involves regression analysis of the time-dependent conversions of TAG, DAG, MAG
and fatty acid to the corresponding alcohol esters (Cheirsilp
et al
., 2008 ; Mitchell
et al
.,
2008). Yet, the reliability of these calculations is not very high because a reasonably good
fit of 30-50 experimental points is not necessarily stipulated by one unique combination of
15-20 parameters. Other combinations, not explored by the authors, can prove equal within
the same significance level.
14.4 ENZYMES IN INDUSTRIAL APPLICATIONS
Applications of enzyme technology in various industries have seen a rapid growth in the last
decade. Table 14.1 shows some of the enzymes that are used in various industries.
The food industry is a traditional market for enzymes with the frequent discovery of new
enzymes applications. Pazczola (2001) provided a comprehensive review on the latest
enzyme applications in the food industry. Lipase-catalyzed modifications of oils and fats,
including lipase-catalyzed production of margarine, coco butter equivalents and structured
lipids, represent some of those technologies that have been industrialized (Xu, 2004a).
In the pharmaceutical industry, enzymes have significantly reduced the number of steps
required for syntheses of desired compounds, by-product and waste formation in drugs
manufacturing, which subsequently decreased the overall production cost. For example, the
company DSM has developed a four-step enzymatic semi-synthesis of cephalexin from
cephalosporin C, which is a reduction from the ten-step conventional manufacturing process.
Search WWH ::
Custom Search