Effect of oxyanions on the d-glucose isomerase catalysed equilibrium: 2. Effect of germanate on the equilibrium of d-glucose and d-fructose with immobilized d-glucose isomerase

The addition of germanate anions to high d-glucose feed syrups, which are passed through an immobilized d-glucose isomerase [xylose isomerase, d-xylose ketol-isomerase, EC 5.3.1.5] column, displaces a ca. 50/50 d-glucose/d-fructose mixture (produced in the absence of germanate) in favour of d-fructose. A maximum conversion of 94% from a d-glucose feed (40% w/v) is obtained with no detrimental effect on the enzyme. This is related to the germanate: sugar ratio. Optimization of the d-fructose yield from d-glucose germanate substrate has been carried out. The effects due to temperature, pH and concentration were taken into consideration. Confirmation of the quantitative identification of the d-fructose was obtained by isotope dilution analysis. The theory behind the displacement is also discussed, and shows close agreement with practical results.