Development and characterization of a chitosan-stabilized pickering emulsion incorporating thyme essential oil to extend the shelf life of strawberries during cold storage

The practical use of plant essential oils in postharvest fruit preservation remains challenging due to their physicochemical instability and rapid degradation under storage conditions. In this study, a chitosan-based nanogel modified with fatty acid was formulated to encapsulate thyme essential oil (TEO). The nanogel was synthesized using an emulsion-gelation method and characterized through Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Different coating treatments, including free TEO and TEO-loaded nanogels, were applied to Camarosa strawberries, which were stored at 4 °C for 16 days. FTIR analysis indicated hydrogen bonding interactions between chitosan and essential oil components, while SEM images confirmed a uniform and spherical morphology of the nanogels. The release profile of TEO exhibited a biphasic and sustained pattern. Application of the coating significantly reduced weight loss, maintained fruit firmness, and stabilized changes in total soluble solids (TSS), titratable acidity (TA), and pH. Furthermore, TEO-loaded coatings preserved anthocyanin and ascorbic acid contents and maintained a higher antioxidant capacity compared to the control group. Additionally, the coating suppressed the activity of polyphenol oxidase (PPO). In contrast, it significantly enhanced the activities of defense-related enzymes, including catalase (CAT) and peroxidase (POD), indicating an upregulated antioxidant defense system. Overall, the chitosan-based nanogel encapsulating thyme essential oil demonstrates high potential for extending the shelf life and preserving the postharvest quality of fresh strawberry fruits.