Optimization of Matrix Components for Improved Catalytic Activities of Cellulase Immobilized on Biochar-Chitosan Beads

Abstract

Bioethanol is a renewable energy that is gaining popularity globally. It’s biochemical production requires the use of enzyme, especially cellulase. Cellulase is an enzyme that catalyzes the degradation of cellulose and related polysaccharides which finds applications in food, textiles, detergents, biofuels etc. However, the worldwide use of cellulase is limited by its relatively high production costs and low biological activity. This study was design to locally produce biochar-chitosan beads at optimized conditions to immobilize cellulase for improved thermal and storage stability as well as ensure reusability of the enzyme so as to improve biological activity and avoid the continuous production of free cellulase thereby reducing the production cost. Biochar was produced by pyrolyzing sugarcane bagasse in a local airtight chamber for 1 hour. Beads were formed from different ratios of biochar and chitosan in varying concentrations of calcium chloride solution as generated by design expert software version 13. The beads were dried in an oven at 50 0C for 24 hours and functionalized in 25% glutaraldehyde (GDA). The beads were loaded with enzyme (10.06 µmole/min/mL) at room temperature (27 ± 3 oC). Enzyme activity, thermal stability, storage stability and reusability tests were carried out according to standard procedures. The half-life and activation energy were also evaluated. The result showed that the optimum activity of the loaded enzyme (2.63 µmole/min/mL) was obtained when 2.46 g of porous biochar was mixed with 2.48 g chitosan in 5 % Calcium chloride aqueous solution. The immobilized enzyme was able to maintain thermal stability between 30 oC and 70 oC while the activity for free enzyme started declining after 50 oC. Also, the activation energy for immobilized cellulase enzyme (23.17 KJ/mol) was lower than the activation energy (55.146 KJ/mol) for free cellulase. The half-life, when stored at ambient Temperature (27 ± 3 oC), for free enzyme was 0.4 days while the half-life for immobilized enzyme was 3.59 days. Therefore, cellulase immobilized on support locally produced at optimal conditions had improved catalytic properties when compared to the free enzyme. Hence, more indigenous materials and practices may be employed for a cost effective and cheaper industrial processes.