Characterization of magnetic nanoparticle–immobilized cellulases for enzymatic saccharification of rice straw

Abstract

Cellulases convert lignocellulosic biomass into fermentable sugars which further act as substrate for ethanol production. Our previous research was focused on enzymatic hydrolysis of rice straw by free cellulases for production of fermentable sugars. Immobilization is a powerful tool to increase the stability and reusability of cellulases besides improving the economy of ethanol production process from rice straw. In the present study, cellulase produced from Aspergillus fumigatus was immobilized on magnetic nanoparticles by using glutaraldehyde cross linker with a binding efficiency of 65.55%. The electron microscopy and spectroscopy tools confirmed the enzyme immobilization process on magnetic nanoparticles. The immobilized cellulase exhibited filter paper, carboxymethyl cellulase and cellobiase activities of 11.82, 21.36 and 10.81 IU, respectively. The free and immobilized cellulase exhibited identical pH optima (pH 5.0) while different temperature optima of 50 °C and 60 °C, respectively. The immobilized enzyme retained 56.87% of its maximal activity after 6 h of pre-incubation at 60 °C. Km (Michaelis constant) and Vmax (maximum velocity) of immobilized enzyme were 11.76 mM and 1.17 μmol min−1 ml−1, respectively. The immobilized cellulase hydrolysed pre-treated rice straw with saccharification efficiency of 52.67%. Further, it could be reutilized for up to four saccharification cycles with retention of 50.34% activity. Therefore, the improved properties of magnetic nanoparticle-immobilized cellulase and its reusability benefits offer a promising potential for industrial production of fermentable sugars and ethanol from rice straw.