The kinetic behavior of antioxidant activity and the stability of aqueous and organic polyphenol extracts from navel orange peel

The kinetic behavior of the antioxidant activity of aqueous/organic polyphenol extracts from navel orange peel was evaluated using DPPH and FRAP assays to assess their capacity to scavenge DPPH and ferric reducing antioxidant power. The stability of polyphenol extracts, including the influencing factors of temperature, pH, light, and the correlation of total phenolic content and antioxidant activity were also investigated. The kinetic reaction results showed that the antioxidant activity i.e. DPPH radical scavenging capacity and ferric reducing antioxidant power depended on concentration and reaction time. Its stability in aqueous phase and organic phase was influenced by temperature, pH and light in varying degrees. 50 °C was a key temperature point above which the total polyphenol content and antioxidant ability decreased remarkably. The phenolic compounds were not stable at pH 7, but showed a strongest DPPH radical scavenging capacity in both aqueous and organic phases. Acidic conditions seemed to be better for maintaining antioxidant ability of extracts from navel orange peel than alkaline conditions in aqueous and organic phases. Avoiding light kept the extracted phenolic compounds stable. There is a significant correlation between total phenolic content and antioxidant activity. These results provide some basic understanding of extracts from navel orange peel and promote the application of the extracted polyphenol from navel orange peel as antioxidants.