Immobilization ofAspergillus ficuumInulinases on Porous Glass

The thermostable inulinases from the fungus Aspergillus ficuum were immobilized by covalent binding on porous glass beads of different porosities (pore diameter 125 to 1170 Å). The highest retention of activity (60%) and highest activity per g of support (300 IU/g) were obtained with the support with an average pore diameter of 120 Å. The immobilized inulinase preparation showed no changes in pH-activity profile but the optimum temperature was higher (70°C instead of 60°C) compared to the free enzymes. Very similar apparent Michaelis constant and activation energy for free and immobilized enzymes suggested the lack of diffusional limitations of the inulin substrate inside the glass beads. A complete inulin hydrolysis was obtained in batch reactors using substrate concentrations of 5–15% (w/v) and a temperature of 40°C. At higher temperatures (50 and 60°C), enzyme inactivation resulted in higher conversion time. A continuous reactor operated with an inulin concentration of 5% and at a high substrate conversion (more than 99%) showed an operational half-life of 17.9 days.