Exploring the Green Power Unleashed by ZnO-Immobilized Aspergillus oryzae Cutinase for the Degradation of Insecticide and Polyester Waste

The present study deals with the enhanced production of cutinase (E.C. 3.1.1.74) by Aspergillus oryzae ISL-9 under submerged fermentation and its immobilization on ZnO nanocrystals for improved stability. The wild-type (ISL-9) was optimized for various parameters viz. substrate level (2%), sucrose concentration (1%), time of incubation (72 h), size of inoculum (3%), and pH (6). The activity was further enhanced by immobilization on ZnO nanocrystals. The UV–Vis spectrum showed an absorption band for both immobilized and free enzymes at 310 nm and 290 nm, respectively. The results of XRD showed the crystalline nature of ZnO nanocrystals. In FTIR, the observed bands from 1120.6 cm⁻¹, 590.2 cm⁻¹, 601.7 cm⁻¹, and 1105.2 cm⁻¹ showed the stretching vibrations of nanocrystals of immobilized and free enzymes, respectively. The SEM images confirmed the particle size of the ZnO nanocrystals of 120–149 nm. Further, the polyester hydrolysis and insecticide degradation potential of the cutinase produced by wild-type ISL-9 was also evaluated. Under the optimized conditions of 0.6 ml of crude enzyme extract, 30 mg ZnO nanocrystals, and 30 min incubation, an overall 16.236% of polyester was hydrolyzed and 26.62% of insecticide was degraded by the enzyme. The immobilized enzyme showed a 1.19-fold and 1.35-fold increase in enzyme activity for polyester and insecticide hydrolysis, respectively, when compared with the free enzyme. The results are highly significant indicating the commercial availability of the process after the scale-up studies.