Rhus verniciflua Stokes flavonoid extracts have anti-oxidant, anti-microbial and α-glucosidase inhibitory effect

We isolated four compounds, fustin, gallic acid, 3',4',7-trihydroxyflavone, and fisetin from Rhus verniciflua. These compounds showed electron donation ability (87-94%) that was stronger than butylated hydroxyanisole (52%). Gallic acid (OD700 = 1.98) showed the highest reducing power, and the other isolated compounds (OD700 = 0.66-1.31) showed stronger activity than alpha-tocopherol (OD700 = 0.21). The ethyl-acetate fraction had the highest phenolic content (723 mg GAE/g), followed by the 80% ethanolic extract (597 mg GAE/g). For Gram-negative bacteria, fisetin had the most potent anti-bacterial activity (MIC=8 mu g/ml) against Escherichia coli. 3',4',7-Trihydroxyflavone (106%), the 80% ethanolic extract (101%), and ethyl-acetate (98%) had the most powerful alpha-glucosidase inhibitory effect at 50 mu g/ml. R. verniciflua extracts have potential as functional food additives. (C) 2009 Elsevier Ltd. All rights reserved.