Free and Bound Polyphenols in Mango Fruit Peel as Functional Food Ingredients with High Antioxidant Activity

The peel of mango fruit has been found to be a good source of health promoting phytochemicals such as polyphenols and dietary fiber. In this study the effects of maturity and ripening condition on the free and bound phenolic contents and their antioxidant activities in mango fruit were studied. Mango fruits (‘Nam Dok Mai’) were harvested at young, immature, and mature stages, and separated into three groups: those at harvest, stored at 5°C for 15 days and 25°C for seven days after harvest. The polyphenol content and antioxidant activity in the flesh of mango fruit harvested at commercial harvesting stage and stored at 25°C lower than in the peel. The pale brown parts of the peel was lower than that of yellow parts, indicating that the polyphenol content and antioxidant activity decrease with peel browning in over-ripened fruit. Using the peel, the polyphenol content and antioxidant activity were analyzed. The polyphenol content in methanol extract was markedly higher in the peel of fruit stored at 25°C than that of fruits at harvest or stored at 5°C in all stages of maturity. When the peel was heated with HCl and extracted with methanol, the polyphenol contents were higher than in the peel that was not heated with HCl (control) regardless of maturity stage at harvest, demonstrating that the bound phenolics were hydrolyzed by HCl. The comparatively small difference in polyphenols between the HCl-treated and control peel stored at 25°C suggested that part of bound polyphenols was solubilized during storage at 25°C. Antioxidant activities were significantly higher in peel stored at 25°C at all stages of maturity, and related to the polyphenol content of the peel. From the results, the most appropriate material as a functional food ingredient with a higher polyphenol content and antioxidant activity is fruit peel stored at 25°C with a yellow color.