Theenzymatic and physicochemical properties of GI from several organisms have beenextensively studied. The knowledge of specific properties of the enzyme, suchas its stability, substrate specificity, and metal ion requirement, isimportant to prevent its inactivation and to assess its suitability forapplication in HFCS production.OptimumTemperature and pHThe optimumtemperature of GI ranges from 60 to 80oC and increases in thepresence of Co21. The optimum pH range of GI is generally between pH 7.0 and9.0.
The enzyme from Lactobacillus brevis has a lower pH optimum(between 6 and 7), which is desirable for commercial applications of GI. Theenzyme from Streptomyces spp., Bacillus spp., Actinoplanesmissouriensis, and Thermus thermosulfurogenes is stable at hightemperatures, but that from Lactobacillus and Escherichia spp. isless stable. Production of fructose fromglucose isomerization process using commercial immobilised glucose isomerase(IGI), involved many factors such as a pH, temperature and initial glucoseconcentration. Rahman et al (2008) studied the optimization of these factorsfor improving formation of fructose. Glucose isomerisation was performed using12g rehydrated of immobilised glucose isomerase (IGI) in a well mixed 2L batchbioreactor.
Different series concentrations of glucose from 10 to 50%w/v wereprepared. The temperature under study was from 550C to 700Cand for pH from 4 to 9. From the results, the highest desirability, D (geometricmean of % isomerisation and fructose yield) was obtained when the initialglucose concentration had 30%w/v, a pH of 8 and at a temperature of 650C.
Tükel and Alagöz reported the catalyticefficiency of immobilized Glucose isomerase (GI) from Streptomyces rubiginosus inisomerization of glucose to fructose to be as three fold higher than that offree GI. The residual activity of immobilized GI after 18 reuses in a batchtype stirred reactor was about 85% of its initial activity. The thermalstability of immobilized GI was almost same with that of the free GI at60 °C for 18 h preincubation time. The residual activities ofimmobilized 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 weeksstorage, respectively