Industrial Biotransformations

References
Owing to the need for stabilized biocatalysts, a large amount of effort is directed at
improving established immobilization techniques and to develop new ones. A technique
of great interest is the use of cross-linked enzyme crystals (CLEC) and cross-linked
enzyme aggregates (CLEA). For the preparation of CLEAs, protein preparations of even
technical purity can be used [45].
For substrates and products of poor solubility, aqueous–organic mixtures are being
used as reaction media for the biotransformation. The two-phase systems have recently
attracted new attention, as it has been pointed out that not only the logP [46], but also
structural elements of the solvents have to be considered to guide the choice of the solvent
[47].
For compounds with low water solubility the use of new solvent systems such as ionic
liquids [48] or supercritical fluids [49–51] (e.g., carbon dioxide) in industrial biocatalysis
can be foreseen. Owing to the water-free environment in ionic liquids even enzymatic
condensation reactions can be carried out [52]. Alternative techniques for the separation
of the products from the new reaction medium have to be developed: while distillation is
feasible for volatile products, nanofiltration can be used for nonvolatile compounds [53].
Instead of using organic solvents, a two-phase system of water and ionic liquids can also
be used in biocatalysis both with isolated enzymes [54] or whole cells [55].
One of the most important tasks for biocatalysis that has to be considered in the early
stages of industrial development is that of reducing the time-to-market. Thus, in the
future some problems in the process development could frequently be solved in silico
(reactor design, process strategy, kinetic simulations). Scale-up and scale-down operations
will be facilitated by mini- and microreactor technology and parallelization. Isolated
enzymes and whole cells will give rise to new synthetic routes increasing the use of
renewable resources. Using modern shuffling techniques, directed evolution will give
rise to improved enzymes with new biocatalytic properties [56, 57] (see also Chapter 4).
References
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5 Bradford, M.M. 1976, (Rapid and Sensitive
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6 Mulder, M. 1996, Basic Principles of Membrane
Technology, Kluwer Academic,
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7 Noble, R.D., Stern, S.A. 1995, Membrane
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Elsevier, Amsterdam.
8 Flaschel, E., Wandrey, C., Kula, M.-R. 1983,
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Bückmann, A.F., Kula. M.-R. 1980, (Immobilization
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