Enhancing Nutraceutical Quality and Antioxidant Activity in Chili Pepper (Capsicum annuum L.) Fruit by Foliar Application of Green-Synthesized ZnO Nanoparticles (ZnONPs).

The application of zinc oxide nanoparticles prepared by green synthesis (GS-ZnONPs) has demonstrated essential benefits in boosting the clean and sustainable production of agricultural crops worldwide. In this part of the study we evaluate the effect of GS-ZnONPs foliar spraying on the yield, nutraceutical quality, capsaicin concentration, and antioxidant metabolism of chili fruit (Capsicum annuum L., CHISER-522 variety) grown under greenhouse conditions. GS-ZnONPs treatments were applied at concentrations of 10, 20, 30, 40, and 50 ppm every 15 days post-transplant, with the control group treated only with distilled water. The results indicated that treatments with 40 and 50 ppm of GS-ZnONPs significantly improved fruit yield, length, and fruit amount. At the same time, the concentrations of 30 and 40 ppm significantly increased the levels of vitamin C, bioactive compounds, and antioxidant capacity, indicating a better nutraceutical quality of the fruit. In addition, an increase in the catalase activity and the content of macro and micro-minerals in the fruit treated with GS-ZnONPs was observed. Our results suggest that the foliar application of GS-ZnONPs acts as a nanobioestimulant, offering an excellent biotechnological tool for developing agroecological strategies to increase the nutraceutical and antioxidant quality of chili pepper fruit.