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HPLC determination of chlorogenic acid in Verbena officinalis L. extract and its in-vitro antibacterial activity

Zhonghao Zhang, Taowen Pan

To investigate the method for quantitatively determining chlorogenic acid in Verbena officinalis L. extract; and to determine its content and in-vitro antibacterial activity. Cylinder-plate method and MIC assay were employed to compare the antibacterial activity between different concentrations of Verbena officinalis L. extracts; and to evaluate the antioxidant activity of various extracts in the DPPH radical system, hydroxyl radical system and anti-lipid peroxidation system. Verbena officinalis L. extracts exhibited inhibitory zone diameters all reaching above 15 mm against Escherichia coli, Proteus vulgaris and Bacillus subtilis at a mass concentration of 100 mg/ml, with MICs all ≤ 100 mg/ml. In various radical systems, different concentrations of Verbena officinalis L. extracts all exhibited weak scavenging effect on superoxide anion radicals, but manifested strong effect in scavenging DPPH and hydroxyl radicals and in inhibiting lipid peroxidation. With mass concentration IC₅₀ of sample solution corresponding to a 50% scavenging rate as a comparative index, IC₅₀ of high dose extract for these three free radicals were calculated to be 0.20, 0.15 and 2.69 mg/ml, respectively. Chlorogenic acid content in Verbena officinalis L. extract was 30.23%. The present method is accurate, sensitive and highly specific, which can be used for determination of chlorogenic acid content in Verbena officinalis L. and its extract. Verbena officinalis L. extract has strong antibacterial activity against Gram-negative bacteria, and further study is needed to clarify its antibacterial mechanism. Verbena officinalis L. extract is suitable for in-depth exploitation as a botanical antioxidant.