Abstract
Reducing postharvest losses (PHL) caused by phytopathogenic fungi is critical for sustainable agriculture. Raspberry pomace (RP), banana peel (BP), and rooibos tea (RT) were valorized as phytochemical-rich mediating agents for the green synthesis of bioactive ZnO nanoparticles (ZnO-RT, ZnO-RP, and ZnO-BP), respectively. Structural characterization using X-ray diffraction (XRD), UV-visible spectroscopy (UV-Vis), and transmission electron microscopy (TEM) confirmed highly crystalline wurtzite ZnO nanoparticles with absorption maxima between 366 and 371 nm and average particle sizes of 48.69, 35.86, and 46.99 nm for ZnO-RT, ZnO-RP, and ZnO-BP, respectively. The nanoparticles were predominantly spherical, with ZnO-RP exhibiting the smallest particle size, superior dispersion, and the highest synthesis yield. Antimicrobial evaluation showed that all ZnO NPs were most effective against Enterococcus faecalis among the tested food-borne bacteria. Against the postharvest fungi Botrytis sp., Mucor sp., and Rhizopus sp., fungal susceptibility differed significantly (p < 0.05) with nanoparticle type. ZnO-RP demonstrated the highest inhibition of Mucor sp. (41.97%), Botrytis sp. (73.19%), and Rhizopus sp. (42.93%), while microscopy revealed pronounced structural damage to fungal hyphae. Overall, RP-mediated ZnO nanoparticles showed superior performance, demonstrating the role of food waste composition in tailoring nanoparticle functionality for postharvest preservation.