Interaction of silica with cellulase and minimization of its inhibitory effect on cellulose hydrolysis

Abstract

Enzymatic hydrolysis of lignocellulosic biomass to sugar has attracted a lot of attention in recent years. Although lignocellulosic biomasses such as rice husk contain a substantial amount of amorphous silica, the role of silica in enzymatic hydrolysis of cellulose is poorly understood. In this study, the interaction of silica with a cellulase enzyme (CTec2) was studied by addressing the role of silica in cellulase adsorption and cellulose (avicel) hydrolysis. CTec2 adsorption on silica surface was found to be influenced by temperature, pH and contact time. The adsorption equilibrium data fitted the Langmuir isotherm model better than the Freundlich isotherm model. The maximum adsorption capacity (Qm) of silica was found to be as high as 244mg/g at a temperature of 50°C and pH of 4.0, indicating strong interaction between silica and CTec2. This strong interaction inhibited avicel hydrolysis; consequently the maximum sugar yield was only 32%. The inhibitory effect of silica was almost completely minimized by introducing PEG1500, and the sugar yield reached 78%, similar to that (81%) obtained in the silica-free system. The results of this paper could, therefore, be useful in designing cellulase-catalyzed hydrolysis of silica containing cellulosic biomasses.