Tannins and Antioxidant Activities of the Walnut (Juglans regia) Pellicle.

The total phenolic content and antioxidant activities of the acetone extract and derived fractions from the walnut (Juglans regia) pellicle were estimated. The BuOH fraction exhibited the strongest antioxidant activity with the highest phenolic content. A phytochemical investigation of this fraction led to the isolation of three tannins, 2,3-hexahydroxydiphenoylglucose (1), pedunculagin (2) and 2,3,4,6-tetragalloylglucose (3). Pedunculagin showed high content and powerful activity, which implied that this compound plays an important role in the antioxidant activity of the walnut pellicle.