Chemistry Reference
In-Depth Information
Table 4.4
Key aspects to be considered for enzyme immobilisation, adapted from Reference [
41
]
Technique
Aspects to consider
Any
Interfering compounds in the formulation
Enzyme stability during immobilisation conditions
Stability of the carrier and enzyme under operating conditions
Support-substrate interactions
Availability and cost of the support/carrier
Adsorption/deposition
Presence of compatible regions (e.g. hydrophobic/hydrophilic) on
enzyme
Ionic interactions
Enzyme pI, and pH and ionic strength of the immobilisation solvent
Surface charged residues on the enzyme
Covalent binding/
cross-linking
Location of the bonding/linking residues
Conditions of immobilization
Encapsulation
Size of 'cavity' and the enzyme
Synthesis and immobilisation conditions
improved activity and stability compared with individual methods. Therefore, as
with cross-linking, enhancements may be made by combining approaches [
41
].
Agarose and poly (
N
-isopropylacrylamide) hydrogels have also been successful
at entrapping lipase. The entrapped lipase maintained good activity, and displayed
very good reuse potential and improved stability compared to free enzyme, particu-
larly in organics [
24
].
Lipase has also been entrapped in a siliceous mesocellular foam, which made use
of a pressure-driven mechanism to bring about immobilisation, rather than conven-
tional stirring. The immobilised material displayed high activity, little leaching and
improved thermal stability compared to free enzyme. The pressure-driven mecha-
nism also resulted in higher enzyme loadings and reduced leaching (and therefore
improved reuse potential) than stirring [
22
].
In summary, a variety of immobilisation techniques are available and we have
discussed each by using lipase as an example. These examples are presented in
Table
4.3
for a quick overview. It is clear that for immobilisation, the choice of sup-
port/carrier used for enzyme immobilisation as well as the techniques employed
depend on the enzyme, substrate, product and operating conditions and as such,
one generic rule cannot be applied [
41
]. In addition, several considerations need
to be taken into account when selecting immobilisation supports and techniques
and they are listed in Table
4.4
. As outlined, many of the current approaches to im-
mobilisation suffer from several problems such as long preparation times, tedious
multistep procedures, use of toxic/hazardous chemicals and loss of enzyme activity
during immobilisation. Due to the materials and techniques involved, many could
also not be classed as green. These drawbacks therefore restrict their industrial
applications [
7
]. There does, however, appear to be much scope for improved en-
zyme immobilization techniques through the use of bioinspired silica. Due to its
mild, rapid and controlled protocol, biologically inspired silica has recently been
demonstrated as a green method for enzyme immobilisation via
in situ
entrapment
of enzymes [
69
,
74
,
75
].
