The mean of % isomerisation and fructose yield) was

enzymatic and physicochemical properties of GI from several organisms have been
extensively studied. The knowledge of specific properties of the enzyme, such
as its stability, substrate specificity, and metal ion requirement, is
important to prevent its inactivation and to assess its suitability for
application in HFCS production.

Temperature and pH

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The optimum
temperature of GI ranges from 60 to 80oC and increases in the
presence of Co21. The optimum pH range of GI is generally between pH 7.0 and
9.0. The enzyme from Lactobacillus brevis has a lower pH optimum
(between 6 and 7), which is desirable for commercial applications of GI. The
enzyme from Streptomyces spp., Bacillus spp., Actinoplanes
missouriensis, and Thermus thermosulfurogenes is stable at high
temperatures, but that from Lactobacillus and Escherichia spp. is
less stable.


Production of fructose from
glucose isomerization process using commercial immobilised glucose isomerase
(IGI), involved many factors such as a pH, temperature and initial glucose
concentration. Rahman et al (2008) studied the optimization of these factors
for improving formation of fructose. Glucose isomerisation was performed using
12g rehydrated of immobilised glucose isomerase (IGI) in a well mixed 2L batch
bioreactor. Different series concentrations of glucose from 10 to 50%w/v were
prepared. The temperature under study was from 550C to 700C
and for pH from 4 to 9. From the results, the highest desirability, D (geometric
mean of % isomerisation and fructose yield) was obtained when the initial
glucose concentration had 30%w/v, a pH of 8 and at a temperature of 650C.

Tükel and Alagöz reported the catalytic
efficiency of immobilized Glucose isomerase (GI) from Streptomyces rubiginosus in
isomerization of glucose to fructose to be as three fold higher than that of
free GI. The residual activity of immobilized GI after 18 reuses in a batch
type stirred reactor was about 85% of its initial activity. The thermal
stability of immobilized GI was almost same with that of the free GI at
60 °C for 18 h preincubation time. The residual activities of
immobilized GI when stored at 5 °C and 25 °C for four weeks were 72%
and 69% of the initial activity, respectively. However, free GI retained 88%
and 78% of its initial activity at 5 °C and 25 °C upon four weeks
storage, respectively