Abstract: In this study, the total phenol and flavonoid contents of the ethanol extract of green walnut husks were determined as (21.71 ± 0.98) and (22.16 ± 0.45) mg/g, respectively. Using ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS) and high performance liquid chromatography (HPLC), nine major compounds in the extract were identified including quercitrin, avicularin, astragalin, hyperoside, isoquercetin, quercetin, caffeic acid, ferulic acid and juglone. The extract had a protective effect against 2,2’-azobis-2-methyl-propanimidamide dihhydrochloride (AAPH)-induced oxidative damage to biological macromolecules. The extract at 1 mg/mL had a significant protective effect against oxidative damage to bovine serum albumin (BSA), and at 0.5 mg/mL, it could protect plasmid DNA from oxidative damage. The extracts had antibacterial activity against Escherichia coli, which could increase the permeability of the bacterial cell membrane and destroy its integrity, thereby resulting in the leakage of intracellular nucleic acid and proteins. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results showed that the damage to cellular proteins could be another antibacterial mechanism of the extract. In addition, the extract inhibited the respiration of E. coli, and the percent increase in respiration rate with the extract alone compared to that with its combination with trisodium phosphate was the lowest. The extract significantly reduced the activity of glucose-6-phosphate dehydrogenase. Therefore, it can be inferred that the extract exerts an antibacterial effect mainly by participating in regulating the respiratory metabolism of the pentose phosphate pathway.

Key words: ethanol extract from green walnut husks; polyphenols; oxidative damage; antibacterial activity; respiratory metabolism