Evaluating the application feasibility of thyme oil nanoemulsion coating for extending the shelf life of papaya (Carica papaya cv. Tainung No. 2) with postharvest physiology and quality parameters

Abstract Papaya ( Carica papaya L.) is a typical climacteric fruit with a brief shelf life due to the rapid degradation of quality during post-ripening, necessitating appropriate postharvest management to address this challenge. This study aimed to investigate the characteristics of thyme oil nanoemulsion (TO-NE) coating and utilize its benefits for preserving papaya. This study also investigated the physiological properties and quality changes of papaya storage at 20 ℃ and, in parallel, examined the effects of TO-NE coating to mitigate microbial infection of papaya during storage. The postharvest papaya was soaked in different concentrations (0.1, 0.25, and 0.5 mg/g) of TO-NE for coating. At the same time, the decay loss rate and effective shelf life were also evaluated. This study revealed that polygalacturonase (PG) and pectinesterase (PME) activities were inhibited during the storage of papaya treated with 0.25 mg/g TO-NE coated compared to the control group. This resulted in the preservation of the firmness of papaya fruits, in addition to a higher ascorbic acid content, delayed total soluble solids (TSS) accumulation, and total chlorophyll content (TCC) degradation, with a lagging color change for two days. The respiration rate and ethylene production were suppressed, while the 0.25 mg/g TO-NE coated group at day 14 (ethylene peak) were 63.2 mg CO 2 kg −1 h −1 and 7.3 µL kg −1 h −1 , lower than control. The 0.25 mg/g TO-NE coating treatment significantly reduced the decay rate for 10 days of storage, preserving their appearance and facilitating ripening. This is a viable option for extending Tainung No.2 papaya shelf life. Graphical Abstract