Cellulase entrapment into alginate-PEG beads cross-linked with glutaraldehyde: Optimization of the immobilization conditions and kinetic characterization of the immobilized enzyme

Abstract

Immobilization methods for cellulase entrapped into alginate beads with glutaraldehyde (GA) cross-linking were investigated. Cellulase entrapped into alginate-polyethylene glycol beads with glutaraldehyde cross-linking (SA-PEG-E) showed more superiority both in terms of catalytic performance and reusability than other methods. Several conditions during SA-PEG-E immobilization such as cellulase concentration, GA amount, pH of immobilization, cross-linking time and hardening temperature were evaluated to study their effect on immobilized enzyme activity, immobilization yield and immobilization efficiency. Based on the results, GA amount, pH of immobilization and hardening temperature were selected for process optimization of SA-PEG-E using the Box-Behnken design of response surface methodology. The results showed that the optimum immobilized conditions were obtained with a GA amount of 0.8 mL, pH of immobilization 4.7, and hardening temperature of 47.5 °C when the cellulase concentration was 7.5 mg/mL and cross-linking time was 2 h. Then, the characterization of SA-PEG-E was studied. The optimum pH of SA-PEG-E was observed to be 4, 1 unit lower than that of the free enzyme (pH 5). The optimum temperature was the same for both free and immobilized cellulase at 50 °C. In addition, the SA-PEG-E exhibited broad pH and temperature adaptability.