Optimization and Kinetics of Cellulase Immobilization on Modified Chitin Using Response Surface Methodology

This study was aimed at investigating the immobilization of Aspergillus nidulans cellulase onto modified chitin (MC). The effects of contact time, cellulase concentration, MC dosage, temperature and agitation rate for maximum immobilization percentage and optimum immobilization capacity have been investigated by response surface methodology (RSM) on the basis of a five-level, five-factor central composite design (CCD). The equilibrium nature of the immobilization was described by the Langmuir and Freundlich isotherms. The kinetic data were tested using the first-order and pseudo-second-order kinetic models. The results of thermodynamic investigations indicate spontaneity (ΔG0 < 0), endothermicity (ΔH0 > 0) and irreversibility (ΔS0 > 0) for the sorption process. At 120 rpm, 304.6 K, 23.3 min, 1.12 mg of MC immobilized 18.51 mg/g of cellulase from an initial solution concentration of 16.34 mg/mℓ with a retention of 70% of the native cellulase activity up to 10 cycles in batch hydrolysis experiments. Under optimized conditions, immobilized cellulase had a higher Km value (0.83 mM) and a lower Vmax value (38.2 μmol/min) compared with the free cellulase (0.62 mM and 48.92 μmol/min, respectively), indicating the affinity of cellulase for the MC matrix.