Upcycling opuntia ficus-indica wastes as green mediators for functional nanomaterials: metabolomic profiling of cladode peel and mucilage residue and ZnO nanoparticle synthesis for controlling foodborne pathogens

Agricultural waste management poses significant environmental challenges, necessitating innovative strategies for repurposing biomass. Opuntia ficus-indica (OFI) cladode wastes, comprising 57% of the plant’s biomass, offer a sustainable route for green nanoparticle synthesis due to their high phytochemical content. In this study, zinc oxide nanoparticles (ZnO-NPs) were synthesized using extracts from OFI cladode peels (ZnO-CPW) and mucilage residue wastes (ZnO-MRW). Metabolic profiling identified approximately 38 phytochemicals, with flavonoids and polyphenols more abundant in CPW, contributing to nanoparticle stabilization. Structural characterization via x-ray diffraction (XRD) confirmed the wurtzite crystalline phase, while scanning and transmission electron microscopy (SEM/TEM) revealed spherical nanoparticles with some rod-like structures, which were more prominent in ZnO-MRW. ZnO-CPW exhibited smaller particle sizes (24 nm) compared to ZnO-MRW (32 nm) but showed greater agglomeration. Antioxidant studies demonstrated that ZnO-CPW had superior radical scavenging potential, with IC 50 values of 0.0253 mg ml⁻¹ (DPPH) and 0.0375 mg ml⁻¹ (ABTS), whereas ZnO-MRW exhibited 0.0272 mg ml⁻¹ and 0.1082 mg ml⁻¹, respectively. Antimicrobial studies against Escherichia coli, Enterococcus faecalis, Candida albicans, and Staphylococcus aureus showed that ZnO-CPW exhibited higher inhibition, likely due to its smaller size facilitating better microbial interaction. These findings underscore the potential of ZnO-NPs synthesized from OFI cladode wastes as bioactive agents for antimicrobial and antioxidant applications, particularly in active food packaging. The study highlights the feasibility of utilizing agricultural waste for nanomaterial synthesis, promoting sustainability in food preservation technologies.