Changes in Extractable and Non-extractable Polyphenols and Their Antioxidant Properties during Fruit On-tree Ripening in Five Peach Cultivars

To evaluate the changes of total phenolic content and antioxidant capacities of five peach cultivars, this work measured them separately in extractable polyphenols and non-extractable polyphenols during the last month of ripening. Total phenolic content was detected using the Folin-Ciocalteau reagent, while total antioxidant activity was detected by DPPH and FRAP assay. In addition, the contribution of extractable polyphenols and non-extractable polyphenols to the total antioxidant activity of peaches was investigated. It is noted that ripening caused a decrease of total phenolic content associated to extractable polyphenols and non-extractable polyphenols by 45.1%-74.6%, 20.7%-41.7%, respectively. Additionally, total antioxidant activity decreased over the ripening period with a high correlation with total phenolic content. Extractable polyphenols contributed more than 50% to the total antioxidant activity, while the non-extractable antioxidants contributed around 31.3%-45.7% (DPPH) or 12.6%-25.4% (FRAP), which suggests that the antioxidant properties of peaches may be undervalued in previous researches.