Exotic Fruit Peel Extracts as Green Resources for Bioactive Silver-Based Materials with Plant Protection Potential

Fruit peels represent an abundant source of bioactive compounds with potential applications in green nanotechnology and plant protection. This study comparatively evaluated ethanolic extracts obtained from pomegranate (Punica granatum L.), orange (Citrus sinensis Osbeck), and persimmon (Diospyros kaki L.) peels and the corresponding silver nanoparticle (AgNP)-containing phytosynthesis preparations. The extracts were characterized for phytochemical and antioxidant properties and used for AgNP phytosynthesis, followed by UV-Vis, FTIR, BF-STEM, and EDS characterization. Their effects on Triticum aestivum L., Zea mays L., and Cucumis sativus L., as well as their antifungal activity against selected fungal strains, were comparatively assessed. Pomegranate peel extract showed the highest total phenolic content (147.52 mg g−1 fw) and the strongest antifungal activity against Penicillium hirsutum, with an inhibition zone of 30 mm, followed by orange (27 mm) and persimmon (17.33 mm) peel extracts. The AgNP-containing preparations generally produced lower inhibition zones than the corresponding crude extracts. Antioxidant activity also decreased following phytosynthesis, with the most pronounced reduction observed for the orange peel system (90.72% to 35.17%). Plant responses were species- and treatment-dependent, with maize showing the lowest overall sensitivity to the investigated treatments. Overall, the results demonstrate that conversion of fruit peel extracts into AgNP-containing preparations does not necessarily enhance their biological activity and emphasize the importance of considering both the phytochemical characteristics of the starting extracts and the biological target when developing fruit-waste-derived systems for potential plant-protection applications.