Identification of antioxidant peptides released from defatted walnut (Juglans Sigillata Dode) meal proteins with pancreatin

•We had defatted walnut meal protein hydrolyzed by pancreatin with excellent antioxidant activity.•We evaluated antioxidant activity of peptides by in vitro chemical assay and cellular antioxidant assay.•Chemical assay was based on single-electron-transfer or hydrogen-atom-transfer.•We identified fourteen antioxidant small peptides, most of them contain Tyr or Cys.•The fourteen small peptides were first found from defatted walnut meal protein hydrolysate.

Defatted walnut (Juglans Sigillata Dode) meal (DWM) is the main by-product after oil extraction of walnut seed, which contains 40-45% proteins with abundant essential amino acids. In this research, the protein of defatted walnut meal was subjected to enzymatic hydrolysis by pancreatin. The hydrolysate was found to possess excellent antioxidant capacities. Also, high cytoprotective activities against H2O2-induced oxidative damage to PC12 cells were observed, with 83% cell viability at 0.1 mg/mL of peptides, and no cytotoxicity was detected against native PC12 cells. The peptides could scavenge total reactive oxygen species in rat pheochromocytoma cell line. Defatted walnut meal protein hydrolysates (DWMPH) were isolated and purified by gel filtration chromatography and reverse phase high performance liquid chromatography. By electron spray ionization-tandem mass spectrometry (ESI-MS/MS), the chemical structures of fourteen antioxidant peptides from two fractions were identified, and all of them were novel peptides were found from walnut protein hydrolysate.