Chitosan-based edible coating produced from an emulsion containing the major constituents of oregano essential oil for the control of sour rot in 'Lima' orange.

Sour rot caused by Geotrichum citri-aurantii is one of the most destructive postharvest diseases affecting citrus fruits, mainly the 'Lima' variety, leading to severe economic losses. Beyond its economic impact, the management of postharvest diseases is linked to global efforts to reduce food losses and decrease reliance on synthetic agrochemicals, aligning with the Sustainable Development Goals related to responsible production. In this context, active coating-based strategies have emerged as promising alternatives to conventional fungicides. In this study, in vitro and in vivo experiments were conducted to evaluate the antifungal capabilities of an emulsion produced by mixing a chitosan solution with the major constituents of oregano (Origanum vulgare) essential oil - carvacrol, thymol, and p-cymene. We also treated postharvest oranges with this emulsion to evaluate. The physicochemical quality and defense enzyme activity. The formulated emulsion exhibited a broad oil droplet size distribution in the micrometric range and a good film-forming capacity. In vitro experiments demonstrated complete inhibition of colony formation at 0.25 µL mL⁻¹ and inhibition of mycelial growth at 3.00 µL mL⁻¹, whereas lower antifungal efficacy was observed in the vapor phase. When applied to orange fruit, the emulsion at 7.5 µL mL⁻¹ reduced disease severity. The treatment also maintained higher firmness values and more stable pH and color attributes at the evaluated sampling times. Changes in the activity of enzymes were also observed at specific sampling times following treatment. Overall, the results indicate that the emulsion is a promising alternative for controlling sour rot while preserving the postharvest quality of citrus fruits.