Plants are important sources of new natural products, including many prescription drugs, herbal medicines, and nutritional supplements. However, less than 10% of the estimated 250,000–500,000 species have been screened for medicinal purposes. Our efforts focused on two of the most promising classes of new medicines: antimicrobial and antioxidant agents. Plants studied were Juglans nigra (black walnut), Quercus alba (white oak), and Quercus rubra (red oak).

Leaves from each species were collected, air dried, ground, and extracted with methanol to give crude fractions which were further purified by suspension in water and filtration or hexane extraction. Aqueous fractions were lyophilized. Further purification was achieved by column chromatography.

Crude and aqueous fractions were assayed for antibacterial activity against Bacillus cereus, Escherichia coli, Enterococcus faecalis, Staphylococcus epidermidis, and Pseudomonas aeruginosa on Mueller-Hinton agar using the disc diffusion method. All lyophilized extracts showed partial activity against all organisms tested ranging from 1mm to 2.6 cm (inhibition zone diameters). Crude extracts showed selective activity with a range of 0 to 2.9 cm. Tetracycline positive controls had zones ranging from of 1.1 cm to 3.5 cm.

Crude and lyophilized fractions were assayed for antioxidant activity using the DPPH (1,1-diphenol-2-picrylhydrazyl) and xanthine oxidase (XO) assays. Lyophilized fractions of each species yielded slightly better inhibition in the DPPH assay (< 82%) than the ascorbic acid control (77%). Methanol extracts of J. nigra reduced XO activity by 99%, compared to methanol alone.

Future work will seek to identify compounds which showed high activity in the antibiotic and antioxidant assays.