Chitosan–Zinc Oxide Nanoparticle Composite Coatings Preserve Postharvest Quality of ‘Rosada’ Cherry Tomato

The postharvest quality of cherry tomato (Solanum lycopersicum L. var. cerasiforme) is often limited by rapid ripening and the early onset of senescence. Thus, there has been an increasing interest in exploring edible coatings to replace commercial wax-based and fungicides to preserve the postharvest quality of fresh produce. The current study assessed the effect of chitosan (CS) enriched with green-synthesized zinc oxide nanoparticles (ZnO-NPs) on preserving the postharvest quality of ‘Rosada’ cherry tomato fruit. The ZnO-NPs were synthesized using cancer bush (Lessertia frutescens L.) leaf extract and incorporated into CS (1.5% w/v) at 0%, 0.3%, 0.6%, and 0.9% to form the CS, CS + ZnO-NP 0.3%, CS + ZnO-NP 0.6%, and CS + ZnO-NP 0.9% composite coatings, respectively. Uniform fruit without any visible defect were gently dipped for 1 minute in the respective coatings, and the uncoated fruit were used as the control. Thereafter, fruit were air-dried at ambient temperature (21 ± 1^°C and 60.0 ± 5% relative humidity) for 1 hour. Fruit were then packed in open-top commercial boxes to assess postharvest quality during the 25 days of shelf life at room temperature. Incorporation of ZnO-NPs in CS coating effectively preserved postharvest quality of cherry tomato during shelf life compared with the postharvest quality of CS alone and the control. Chery tomato coated with ZnO-NPs had higher fruit texture and lower total sugars, thus reducing the sugar content, titratable acidity (TA), and ripening index (RI) during shelf life compared with those of cherry tomato coated with CS alone and the control. At the end of shelf life, fruit coated with 0.9% ZnO-NP and 0.6% ZnO-NP had a lower respiration rate, mass loss, total carotenoids, malondialdehyde, and hydrogen peroxide as well as high TA, ascorbic acid, total phenolic content, antioxidant activity, and antioxidant enzymes compared those of fruit coated with ZnO-NP 0.3%, CS, and control. Therefore, enriching the CS coating with ZnO-NPs using a range of 0.6% to 0.9% is recommended for preserving postharvest quality and extending the shelf life of cherry tomato at ambient conditions.