Seasonal variations of phenolic profiles and antioxidant activity of walnut (Juglans sigillata Dode) green husks

The phenolics content and antioxidant activity of walnut (Juglans sigillata Dode) green husks were analysed during different stages of development. Contents of total phenolics and total flavonoids decreased from April 25th to June 7th, then increased during June and July, and decreased again at the beginning of August. Thirteen types of phenolic compounds were identified using HPLC of which juglone had the highest content. Because of seasonal variations, the trends of different phenolic compounds were different. Contents of both total phenolics and total flavonoids were strongly correlated with antioxidant activity; however, compared with totals, less significant correlations were observed between individual phenolic compounds and antioxidant activities.