Perspectives on Chemicals from Renewable Resources - Sustainable Biotechnology: Sources of Renewable Energy - page 207

separation techniques. IE is effective in the separation of complex mixtures of amino
acids, however, for (very) large scale applications costs are anticipated to be high
due to elution times and the need for regeneration. ED shows potential of being an
economically technique for the separation of charged species and has already been
demonstrated at large scale for a number of applications [46]. ED separates ions in
aqueous solution under the influence of a (electric) potential gradient therefore the-
oretically all amino acids could be separated on the basis of their isoelectric point
(IP) and a number of studies have examined the isolation of amino acid containing
materials using ED [47-49]. In practice, due to similarity in IP, only three different
groups of species are isolated (acidic, basic and neutral amino acids). Thus strate-
gies developing novel separation techniques need to be developed in order to effect
greater separation.

5.4 Amino Acid Application and Modification

Once separated, what is the best application of a specific amino acid? For amino
acids such as methionine, perhaps the most useful application is to use it for its
nutritional value. The traditional method for the production of methionine is via
chemical synthesis and the product cost is high. Some amino acids have similar
chemical structures to chemical products currently on the market. For example ser-
ine if decarboxylated is converted to ethanolamine that is, amongst other things,
an intermediate in ethylenediamine synthesis used in the production of chelating
agents, some polymers, pharmaceuticals and agrichemicals. The question of which
type of “transformation” technology should be used? Since an amino acid may be
obtained in an aqueous environment, it would be useful to not need to remove the
water and carry out (if possible) some of the synthetic procedure in the aqueous
phase. For some transformations the use of enzymes are very useful. For example
decarboxylation is often a valuable step and can be specifically carried out with the
use of the correct enzyme at ambient conditions. In the above example serine can be
decarboxylated to ethanolamine using serine decarboxylase. While enzymes offer
this useful option they are prone to deactivation. Thus prolonged and/or repeated
use can be troublesome. Some of these problems may be reduced with the aid of
immobilisation of the enzyme. However, costs per kg product produced generally
tend to be higher with enzyme technology compared to chemical transformation. In
most cases the required enzyme is not commercially available and development is
required to engineer them and allow production in microorganisms for application
and also to reduce the costs. However, one should not be discouraged, as a num-
ber of viable processes have been developed for the production of industrial (bulk)
chemicals using enzymes e.g. the production of acrylamide from acrylonitrile using
nitrile hydratase.
Lysine, produced by fermentation, has been discussed as a raw material for

ε -caprolactam [11]. Developments in plant breeding and genetic engineering has

allowed the enhanced production of lysine in planta . The accumulation of lysine
in potato has been well investigated [50-53]. Lysine biosynthesis was increased by