One-step conversion of cellulose to fructose using coimmobilized cellulase, β-glucosidase,and glucose isomerase

Glucose isomerase was immobilized by itself and coimmobilized with cellulase and β-glucosidase using a polyurethane foam (Hypol® FHP 2002). Approximately 50% of the enzyme added was immobilized. The immobilized enzyme was active at pH values as low as 6.8. When immobilized alone, the K_m for Mg²⁺ increased by 5.5fold and the K_m for fructose increased 62%. The half-life of the immobilized glucose isomerase was approximately 160 h of continuous hydrolysis, with a substantial (about 35–40%) amount of activity remaining even after 1000 h. When all three enzymes were immobilized together, the system was found capable of functioning at pH 7.0 to produce fructose from both soluble and insoluble cellulose substrates. At this pH, the glucose:fructose ratio was 70:30. The advantageous properties of the foam as a support for enzyme immobilization and the efficiency of the one-step conversion process outlined combine to make this system appear valuable for use in high fructose syrup production.