The antioxidant activities and xanthine oxidase inhibition effects of walnut fruit, stem and leaf were studied in this work. The total phenolic contents were in a descending sequence: shell extract > leaf extract > stem extract > defatted walnut kernel (DWK) extract > green husk extract (GHE). The sequence of total phenolic contents was in agreement with the sequence of antioxidant capacities evaluated by ferric reducing antioxidant power and oxygen radical absorbance capacity (ORAC) assays except for DWK extract. The walnut shell extract showed the highest phenolic content (14.81 gallic acid equivalent g/100 g dry extract) and the best antioxidant activity (the ORAC value was 3423.44 ± 142.52 μmol Trolox equivalents g−1). All tested samples possessed xanthine oxidase inhibitory (XOI) effects, the inhibition percentages of which were >50% at 2 mg mL−1 except for stem and DWK extracts. The contents of the major compound (hydrojuglone) in all extracts were in a descending order: GHE > walnut stem extract > walnut shell extract > walnut leaf extract > DWK extract.Summary
Walnut (Juglans regia L.) fruit (including green husk, shell and defatted kernal), stem and leaf.