Postharvest Quality Preservation of Carica papaya L. Using Sodium Alginate Coatings Incorporating Thymus vulgaris Essential Oil-Loaded Polymeric Nanocapsules

Polymeric nanoparticles combined with coatings have emerged as a promising strategy to preserve fresh produce. This study evaluated a sodium alginate coating incorporating polymeric nanocapsules loaded with Thymus vulgaris L. essential oil (NC-EOt), with the aim of preserving the postharvest quality of papaya (Carica papaya L.). NC-EOt, obtained by nanoprecipitation using Eudragit L 100-55, was evaluated by FTIR-MID spectroscopy, antioxidant activity assays (DPPH and ABTS), and physical stability during six months of storage. The nanocapsules were incorporated into a sodium alginate coating (AL-NC-EOt), whose mechanical properties (adhesion, elongation, and tensile strength) were determined before application to whole papayas stored at 25 °C. Fruit quality was assessed through firmness, titratable acidity (TA), total soluble solids (TSS), color parameters, and visible microbial spoilage. NC-EOt exhibited a mean particle size of 153.9 ± 4.7 nm and remained physically stable for six months while retaining the main components of EOt. Nanoencapsulation enhanced the antioxidant activity of EOt, reducing IC50 values from 423.16 ± 56.69 to 279 ± 22.82 μg/mL in the ABTS assay and from 828.74 ± 15.17 to 324.54 ± 34.76 μg/mL in the DPPH assay. Mechanical characterization showed improved adhesion, elongation, and tensile strength in AL-NC-EOt compared to alginate alone. Papayas coated with AL-NC-EOt maintained higher firmness and titratable acidity, showed smaller increases in total soluble solids (TSS) during storage, and exhibited no visible signs of fungal growth after 13 days at 25 °C. -NC-EOt effectively preserved papaya quality and represents a promising postharvest technology for tropical fruits.