Ultrastructure and Composition Analysis of the Pericarp of Six Melon Varieties with Different Storage Characteristics

Objective: To explore the relationship between the structure and composition of melon pericarp and its storability. Methods: We observed the surface and cross-sectional ultrastructure of the pericarp of six different melon varieties with different storage characteristics using scanning electron microscopy (SEM). The composition and antioxidant capacity of the pericarp were analyzed. Results: The wax content, the number of outer epidermis cell layers, cell arrangement and cuticle thickness of melon pericarp were closely correlated with fruit storability. There was a positive correlation between pericarp hardness and fruit storability. The polygalacturonase (PG) in the pericarp degrades the composition of the cell wall and consequently causes a decrease in the hardness of the pericarp, affecting the storability characteristics of the fruit. The antioxidant substances such as total polyphenols and flavonoids in the pericarp of different melon varieties, as well as the activities of antioxidant enzymes such as peroxidase (POD) and superoxide dismutase (SOD), affected their storability characteristics. Conclusion: Principal component analysis (PCA) showed that pericarp hardness, total pectin (TP) content, protopectin (PP) content, PG, pectin methylesterase (PME) and peroxidase (POD) activities had a significant impact on melon storability.