Fructose production from Jerusalem artichoke using mixed inulinases

Mixed inulinases of the fungus Aspergillus niger TISTR 3570 and the yeast Candida guilliermondii TISTR 5844 were used in producing fructose from freshly prepared extracts of Jerusalem artichoke (Helianthus tuberosus). Fructose production was optimized using the Taguchi method involving five factors at four levels. The optimal conditions for maximizing the concentration and yield of fructose were: a mixed inulinase concentration of 4 U/g substrate; a fungus and yeast inulinase activity ratio of 25:1; pH 4.5; 40 °C; and a 24 hr reaction time. Under these conditions, the peak concentration of fructose was 46.9 g/L, the yield on the substrate was 0.60 g/g and the productivity was 1.84 g/L hr. The most important factor was the reaction time for maximizing the final concentration and yield of fructose, whereas the factor significantly affecting fructose productivity was enzyme concentration. All the experimental factors had a significant effect on the production of fructose. The identified optimal conditions for a batch operation were used in the fed-batch production of fructose which had a fructose concentration of 117.6 g/L at a productivity of 1.03 g/L hr. Glucose was the sole by-product with a relatively low concentration of 30.2 g/L.