Antibacterial and Antioxidant Activities of Leaf Extracts from Juglans sinensis, and its Phenolic Compositions

The beneficial properties of walnut depend on climate, genotype, and farming practices. We investigated the antibacterial and antioxidant activities of Juglans sinensis Dode cultivars grown in South Korea. Antibacterial activities were assessed using the minimum inhibitory concentration method and antioxidant activities using the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) assays. Ethyl acetate and chloroform extracts of J. sinensis leaves showed the highest antibacterial activity against Staphylococcus aureus SG511, Klebsiella aerogenes 1522E, and/or Enterobacter cloacae P99. DPPH and ABTS radical scavenging activities were found to be highest in the ethyl acetate extract. The total flavonoid and polyphenolic contents in the extract were 219.27 mg/g quercetin equivalents and 245.11 mg/g of gallic acid equivalents, respectively. Phenolic acids (gallic and vanillic) and flavonoids (catechin, rutin, and juglone) were detected by high performance liquid chromatography. We conclude that J. sinensis cultivars provide accessible sources of natural antibacterials and antioxidants.