Identifying Antibacterial Compounds in Black Walnuts (Juglans nigra) Using a Metabolomics Approach

• Main Authors: Khanh-Van Ho, Zhentian Lei, Lloyd W. Sumner, Mark V. Coggeshall, Hsin-Yeh Hsieh, George C. Stewart, Chung-Ho Lin
• Format: Article
• Language: English
• Published: MDPI AG 2018-09-01
• Series: Metabolites
• Subjects: black walnut; Juglans nigra; antibacterial; metabolomics approach; compound identification
• Online Access: http://www.mdpi.com/2218-1989/8/4/58

Black walnut (Juglans nigra L.) is one of the most economically valuable hardwood species and a high value tree for edible nut production in the United States. Although consumption of black walnut has been linked to multiple health-promoting effects (e.g., antioxidant, antimicrobial, anti-inflammatory), the bioactive compounds have not been systematically characterized. In addition, the associations between different black walnut cultivars and their health-promoting compounds have not been well established. In this study, the kernels of twenty-two black walnut cultivars selected for nut production by the University of Missouri Center for Agroforestry (Columbia, MO, USA) were evaluated for their antibacterial activities using agar-well diffusion assay. Among the selected cultivars, four black walnut cultivars (i.e., Mystry, Surprise, D.34, and A.36) exhibited antibacterial activity against a Gram-positive bacterium (Staphylococcus aureus), whereas other cultivars showed no effect on the inhibition of this bacterium. The antibacterial compounds showing the strongest activity were isolated with bioassay-guided purification and identified using a metabolomics approach. Six antibacterial bioactive compounds responsible for antimicrobial activity were successfully identified. Glansreginin A, azelaic acid, quercetin, and eriodictyol-7-O-glucoside are novel antibacterial compounds identified in the kernels of black walnuts. The metabolomics approach provides a simple and cost-effective tool for bioactive compound identification.