Objective This study aimed to prepare a nano-cerium oxide (CeO₂)/gelatin (GE)-pullulan (PU) composite coating, to evaluate its preservation effect on postharvest papaya under ultraviolet (UV) irradiation, and to determine the optimal CeO₂ doping ratio, thereby providing a green and efficient preservation strategy for climacteric tropical fruit.

Method Using GE and PU as film-forming substrates, composite coatings were prepared with 0.25%, 0.5%, and 1% nano-CeO₂, respectively. Five treatment groups were established: CK (UV and distilled water), T1 (UV combined with GE/PU), T2 (UV combined with GE/PU containing 0.25% CeO₂), T3 (UV combined with GE/PU containing 0.5% CeO₂), and T4 (UV combined with GE/PU containing 1% CeO₂). After coating, papaya fruits were stored at room temperature (25℃, RH 85%) for 16 days and irradiated with UV (365 nm) for 2 min on days 0 and 8. Postharvest quality attributes, including appearance colour, decay rate, weight loss, firmness, total soluble solids (TSS), titratable acidity (TA) and vitamin C (Vc) content were measured periodically.

Result All composite coating treatments delayed the quality deterioration of papaya fruits, and the T3 group showed the best performance. By day 16 of storage, the decay rate, weight loss and firmness of the T3 group were 66.16%, 13.02% and 4.65 N, respectively. Compared with the CK group (88.61 %, 15.35% and 3.26 N) (P < 0.05), the T3 group showed significantly lower decay rate and weight loss and significantly higher firmness (P < 0.05). Regarding colour, the changes of a* and b* values on day 8 were -12.52 and 36.67, respectively, which were significantly lower than those of CK (-2.33 and 54.35) (P < 0.05). At the end of storage, the CI (46.98) was significantly lower and the h* value (87.17) was significantly higher in the T3 group than in the CK group (65.24 and 74.30), indicating that peel color conversion and yellowing were significantly delayed. In terms of nutritional quality, the Vc content of the T3 group reached 771.73 mg/kg, which was significantly higher than that in CK (625.00 mg/kg) (P < 0.05). Moreover, the TSS and TA contents were maintained at 12.43% and 0.55%, respectively, indicating a good sugar-acid balance.

Conclusion The UV-assisted CeO₂/gelatin-pullulan composite coating inhibited postharvest decay, softening, and color deterioration of papaya, effectively maintained the nutritional and flavor quality of postharvest fruit, and extended the shelf life. Among the treatments, the coating doped with 0.5% CeO₂ showed the best preservation effect.