Immobilised enzyme systems are used where they offer
economic advantages on the basis of total manufacturing
costs. The plant size needed for continuous process is two
orders of magnitude smaller than that required for batch
process using free enzymes. The capital costs are therefore
considerably smaller and a plant may be prefabricated
cheaply off-site. Immobilised enzymes offer greatly
increased productivity on the enzyme weight basis and
also often provide process advantages.
Different supports and methods are constantly being tried
to immobilise various industrial enzymes to get increased
activity and stability in various applications. In the textile
industry, high water and energy costs in wet processing
imposed the implementation of closed-loop processes and
recycling of the textile liquors. For the adequate
processing of textile materials, it is necessary to apply
various additives. The removal of hydrogen peroxide
and hydrolysed dyestuff after the bleaching and dyeing
processes are the two major areas where the washing
liquors can be recycled by means of an appropriate
enzymatic treatment with catalases, laccases, peroxidases,
or azoreductases.
These treatments can be carried out with enzymes in both
free and immobilised form. Usually, low concentration
of the free enzymes is sufficient to achieve the desired
effect. However, the catalyst is not recoverable and
stability problems may arise from the high temperature
and alkalinity of the bleaching, washing or dyeing liquors.
The main disadvantage of using free enzymes is that
the protein remains in the recycled effluent that
is intended to be reused for dyeing. The dyeing is carried
out mostly at temperatures where proteins undergo
denaturation. The transition from globular to random coil
conformation of the protein occurs during denaturation
at elevated temperature. This thermally initiated process
increases the hydrophobic dye-protein interactions.
The denaturated protein binds dye from the dyeing
solution and thereby decreases its concentration.
The presence of denaturated protein does not alter
the dye exhaustion kinetics, but reduces the final
exhaustion level. Use of immobilised enzymes will help
overcome this problem.
Currently, the technology of immobilised enzymes is going
through a phase of evolution and maturation.
Evolution is reflected in the ever-broadening range
of applications of immobilised enzymes. Maturation is
mirrored in the development of the theory of how
immobilised enzymes function and how the technique
of immobilisation is related to their primary structure
through the formation and configuration of their three
dimensional structure.
There still remains much room for the development
of useful processes and materials based on this hard-won
understanding. Immobilised enzymes will clearly be more
widely used in the future. This is just the beginning
of the immobilised enzyme technology era.
