Immobilization quantities are needed to compensate for the

Immobilization of Glucose
Isomerase

One of the
ways to reduce the cost of production of GI is to recover it efficiently and
reuse it several times. Immobilization of GI offers an excellent opportunity
for its effective reuse. The largest market for GI is for its immobilized form.
Development of immobilized GI has been a subject of great interest. The use of
GI is expensive because it is an intracellular enzyme and large quantities are
needed to compensate for the high Km for glucose. Therefore, it is
important to immobilize GI for its industrial applications. Several methods for
immobilizing GI have been described. However, only a few are economical and
yield enzyme preparations with properties that are suitable for commercial
production of HFCS. Two main methods are used for immobilization of GI:
cell-free enzyme immobilization and whole-cell immobilization.

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Cell-free
immobilization. Soluble
enzymes that are immobilized to a support structure have excellent flow
characteristics suitable for continuous operations, in contrast to whole-cell immobilized
supports, and offer considerable savings in terms of capital equipment. Materials
for immobilization includes

·        
DEAEcellulose.

·        
Porous alumina

·        
Controlled-pore alumina in the
presence of Co21

·        
Coimmobilized GI on large-pore
polyethylene discs by permeating the discs with a solution of polyacrylonitrile
in dimethyl sulfoxide and finally fixing it with glutaraldehyde.

·        
Cellulose acetate

Whole-cell
immobilization. Because
GI is an intracellular enzyme, whole-cell immobilization is the method of
choice for most of the commercially available immobilized GIs. Methods of
achieving this includes:

1.      Spray-drying whole cells containing GI, adding inorganic salts such
as magnesium hydroxide to the fermentation broths of Streptomyces or Arthrobacter
species, filtration and drying of the cake is a straightforward method to
immobilize cells.

2.      Physical entrapment of whole cells in polymeric materials was used
as an immobilization method

3.      Chemical entrapment of cells in a membrane followed by cross-linking
with glutaraldehyde was used to prepare an immobilized GI.