Effect of melatonin on ripening of ?Pearl? guava fruit at ambient temperature

In this study, fruit quality and activities of antioxidant and cell wall degrading enzymes, were investigated to explore the effect of exogenous melatonin on preservation of postharvest guava during storage at room temperature (25 degrees C). The results showed 500 mu M melatonin treatment could effectively delay the softening and yellowing of guava fruit, and maintain high soluble sugar and vitamin C content, to keep the appearance and nutrient quality. Moreover, the treatment could inhibit PPO (polyphenol oxidase) enzyme activity to prevent browning, but promote POD (peroxidase) and CAT (catalase) enzyme activities to improve the resistance of fruit during storage. Furthermore, PG (polygalacturonase) and PL (pectate lyase) enzyme activities were effectively suppressed to protect the structural integrity of the cell wall in fruit, and delay the softening process. These findings indicate, 500 mu M exogenous melatonin treatment could delay the ripening of postharvest guava fruit, and present application value of preservation.