Immobilization of indigenous holocellulase on iron oxide (Fe₂O₃) nanoparticles enhanced hydrolysis of alkali pretreated paddy straw

The holocellulase from Aspergillus niger SH3 was characterized and found to contain 125 proteins including cellulases (26), hemicellulases (21), chitinases (10), esterases (6), amylases (4) and hypothetical protein (32). The crude enzyme was immobilized on five different nanoparticles (NPs) via physical adsorption and covalent coupling methods. The enzyme-nanoparticle complexes (ENC) were screened for protein binding, enzymatic activities and immobilization efficiency. Magnetic enzyme-nanoparticle complexes (MENC) showed higher immobilization efficiency (60–80%) for most of the enzymes. MENC also showed better catalytic efficiencies in term of higher V_max and lower K_m than free enzyme. Saccharification yields from alkali treated paddy straw were higher (375.39 mg/gds) for covalently immobilized MENC than free enzyme (339.99 mg/gds). The immobilized enzyme was used for two cycles of saccharification with 55% enzyme recovery. Hence, this study for the first time demonstrated the immobilization of indigenous enzyme and its utilization for saccharification of paddy straw.