CO-immobilization of cellulase and xylanase on magnetically-separable hierarchically-ordered mesocellular mesoporous silica

Abstract

Lignocellulosic biomass that exist abundantly in nature is a potential source for producing environmentally sustainable biobased chemicals. Lignocellulosic materials can be converted into fuels and value-added chemicals by the method of enzymatic hydrolysis using cellulase and xylanase enzymes. However, the use of free enzymes is hampered by the low storage stability, difficulty in recovery and non-reusability of the enzymes, which leads to the need for enzyme immobilization. Several inorganic carriers are potentially suitable for enzymatic immobilization, by means of several different techniques. Enzyme immobilization in magnetically-separable hierarchically-ordered mesocellular mesoporous silica (M-HMMS) is an alternative method for producing efficient biocatalyst. In this study, cellulase and xylanase were immobilized using three approaches: enzyme adsorption, enzyme adsorption and cross-linking and enzyme adsorption, precipitation and cross-linking (EAPC). The best precipitant, cross-linker and immobilization method for cellulase and xylanase co-immobilization were tert-butanol, glutaraldehyde and EAPC, respectively. The optimum cellulase and xylanase activity retention were achieved using 2 mL of enzymes, 1 mg: 0.15 mL of magnetic silica-to-enzyme ratio, adsorption temperature of 26 ºC, adsorption time of 40 min, adsorption agitation rate of 162 rpm, 1:11 mL volume of enzyme-to-precipitant ratio, 0.05 % v/v of glutaraldehyde concentration, cross-linking temperature of 37 ºC, 2 hours of cross-linking time and cross-linking agitation rate of 300 rpm. The biocatalysts prepared under optimized condition retained the activity more than 90% with improved storage stability (above 60 % after 14 days). Adsorption study showed that the pseudo-second-order kinetic model and Kolmogorov-Erofeev-Kazeeva-Avrami-Mampel model were the best models to represent the kinetic adsorption process of cellulase and xylanase on M-HMMS. The sorption process was found to be physisorption for cellulase and chemisorption for xylanase, as predicted by the activation energies. The results suggest that co-immobilized cellulase and xylanase in M-HMMS is a promising biocatalyst.