Green Synthesis and Characterization of Zinc Oxide Nanoparticles Using Citrus limetta Peels Extract and Their Antibacterial Activity Against Brown and Soft Rot Pathogens and Antioxidant Potential

The production of food waste such as fruit peels and organic solid waste from municipal sources can be used in the emerging field of nanotechnology. The current research was conducted to study the in vitro and in vivo antagonistic potential of zinc oxide nanoparticles synthesized from Citrus limmeta peel extract against plant pathogenic bacteria (Erwinia carotovora, Ralstonia solanacearum, Clavibacter michiganensis). The nanoparticles synthesized by the green method were characterized by various characterization techniques such as UV-vis spectroscopy, X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), high resolution scanning electron microscopy (HR-SEM) and energy dispersive X-ray (EDX). The UV-vis spectrum observed from the synthesized nanoparticles was at 339 nm, and the ideal absorption spectrum for zinc oxide nanoparticles (ZnO NPs) lies in the region from 290 to 400 nm. XRD examination reveals that the synthesized ZnO NPs have a crystalline nature with an average size of 16.58 nm. FT-IR spectrums of the extract and the biosynthesized ZnO NPs revealed the disappearance of different functional groups that were modified after the formation of zinc oxide nanoparticles. The results obtained from SEM images revealed that the synthesized NPs were mostly irregularly spherical in shape. EDX spectroscopy of the nanoparticles quantified the percentage of zinc (72.27%) and oxygen (8.35%) which indicated the presence of ZnO NPs synthesized from peels of Citrus limetta. The in vitro antagonistic potential of the biosynthesized ZnO NPs was checked by the disc diffusion method at different concentrations, such as 100, 250 and 500 mu g/ml. Moreover, the in-vivo antagonistic potential of the synthesized nanoparticles was evaluated on potato tuber slices. The nanopriming results showed complete elimination of soft and brown rot infections in comparison to nonprime potato tuber slices. On the basis of this study, it is proposed that the nanoparticles synthesized from the peels of C. limmeta have inhibitory activity against brown and soft rot pathogens in potato. Different concentrations of ZnO using peels of C. limetta caused increments in the scavenging of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals, 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and reducing power. Furthermore, these NPs can also be used to analyze their antibacterial, and antioxidant potential.