Cellulase immobilization properties and their catalytic effect on cellulose hydrolysis in ionic liquid

Abstract

Cellulase was immobilized on chitosan by the method of covalent binding. The optimum immobilized conditions were as follow: the pH value was 5.0, the glutaraldehyde concentration was 0.015 (w/v) and the formaldehyde concentration was 0.15 (w/v). Both the free and immobilized cellulase were characterized by determining the pH, temperature, thermal stability and storage stability. The optimum pH of both the free and immobilized cellulase was found as 4. The immobilized cellulase had optimum temperature of 50 degrees C as compared to 40 degrees C in case of free enzyme. The immobilized enzyme showed higher thermal stability than the free cellulase, after 120 min, the activity of immobilized cellulose and the free enzyme retained 86.5 and 61% respectively. After 11 cycles, the activity of the immobilize enzyme conserved 80.27%. The immobilized enzyme exhibited slightly better storage stability than the free enzyme. The Km and Vm values for the immobilized and free cellulase were 8.1 and 1.84 mg/L and 0.01 and 0.0036 mg/ml/min respectively. Cellulose hydrolysis by immobilized cellulase in the presence of a 88 ionic liquid (IL), 1,3-dimethylimidazolium dimethylphosphate (MMIM-DMP), was investgated. The result showed that the addition of 20% (v/v) MMIM-DMP gave the highest initial rate, which was 1.3 and 13.9 times higher than the hydrolysis rate in citric acid - sodium hydrogen phosphate buffer and in IL, respectively.