Phenolic profiles and antioxidant activities of free, esterified and bound phenolic compounds in walnut kernel

•The majority phenolics in walnut kernel were free phenolics.•Acetone was better to extract soluble phenolics, and methanol for insoluble bound phenolics.•Jeuglone, kaempferol, quercetin-7-o-β-D-glucoside and dihydroquercetin were only found in free phenolics.•There was positive linear correlation between antioxidant activities and total phenolic contents.