Enhancement of fungal cellulase production using pretreated orange peel waste and its application in improved bioconversion of rice husk under the influence of nickel cobaltite nanoparticles

Cellulases are the enzymes of enormous industrial interests. In this study, solid-state fermentation (SSF) of alkali-pretreated orange peel waste has been evaluated to produce fungal cellulase. Different concentrations of alkali solution for the pretreatment of substrate and its impact to maximize the cellulase production have been investigated. Furthermore, process parameters of SSF including different substrate amount, different particle size of substrate, and impact of different moisture contents have been analyzed to achieve maximum cellulase production under the optimized conditions which include pretreatment using 1.0% alkali solution, 7.0 g substrate, 2.2 mm particle size of substrate, and 65% moisture content, wherein fungal strain Emericella variecolor NS3 exhibited the highest cellulase production of 39 IU/gds FP (filter paper cellulase), 236 IU/gds EG (endoglucanase), and 197 IU/gds BGL (β-glucosidase). The produced raw enzyme holds improved thermal and pH stability up to 3.5 h at 65 °C and over pH 4.0–6.0 in the presence of 1.0% nickel cobaltite nanoparticles (NiCo 2 O 4 NPs). Consequently, NiCo 2 O 4 NP–stabilized enzyme exhibited improved hydrolytic efficiency for alkali-pretreated rice husk as compared to control enzyme system. This work may be potentially applied for the mass-scale production of enzyme using orange wastes at industrial scale. Graphical abstract