Immobilization and characterization of cellulase enzyme in polyvinyl alcohol gel

In this thesis study, the immobilization of cellulase enzyme from Aspergillus sp. in polyvinyl alcohol by gel immobilization method was investigated. Optimum pH and temperatures, kinetic parameters, thermal and storage stability of free and immobilized cellulase and reuse stability of immobilized cellulase were determined. The optimum pH for free and immobilized cellulase was 5.5 and 5.0, respectively, while the optimum temperature was determined as 45 ˚C for the both preparations. Under optimum conditions, Km and Vmax values for free cellulase were 168.08 mg/mL and 22.62 U/mg protein, respectively, while for immobilized cellulase they were calculated as 39.07 mg/mL and 5.04 U/mg protein. Thermal stabilities of free and immobilized cellulase determined at different temperatures were compared and it was seen that free cellulase retained 4% of its initial activity at 45 ºC and 61% of its initial activity at 55 ºC after 24 hours. The immobilized cellulase retained 15% of its initial activity at 45 ºC and 55% of its initial activity at 55 ºC. It has been determined that it loses 12% of its initial activity at 55 ºC. Storage stabilities of free and immobilized cellulase were investigated at specific time intervals for 30 days. Free cellulase retained approximately 45% of its initial activity after 30 days at 5 °C, while it retained approximately 20% of its initail activity at 25 °C. The immobilized cellulase retained approximately 48% of its initial activity after 30 days at 5 °C and approximately 30% of its initail activity at 25 °C. The reusability of immobilized cellulase was investigated and initial activity of immobilized cellulase decreased below 50% after four reuses.