Yields in phenylpropanoids and antioxidant properties of different aqueous extracts of lemon verbena (Lippia citriodora K.)

Lemon verbena (Lippia citriodora K.) contains several flavonoids and phenylpropanoids mainly represented by verbascoside [1]. In order to develop a rich phytocomplex of such constituents' different aqueous extracts (i.e. a decoction obtained 5min. boiling, one obtained after 20min. boiling and a tea) were prepared from the dried plant and liophylised. Quantification of constituents in the dried extracts was carried out by HPLC-DAD-MS and the chromatographic conditions were the following: a binary system H₂O (pH 3.2 by HCOOH) and CH₃CN using a multi-step linear solvent gradient elution method. Total time of analysis was 28min and flow rate was 0.8 mL/min. The column was a Varian Polaris ^TM C18-E (250×4.6mm i.d., 5µm) mantained at 26°C with a pre-column of the same phase. By UV and MS spectral data were identified the constituents of the 3 extracts. The qualitative profiles of the three extracts was quite similar, 9 constituents were identified, mostly of them represented by verbascoside and its analogues, besides luteolin and apigenin derivatives and one iridoid, verbenalin. However, the yield of such constituents and in particular phenylpropanoids was very different being in the lyophilized infusion 8.3% with respect to the decoctions, 1.7 or 4.4%. The lowest content of phenylpropanoids in the liophilised decoctions was probably due to the heat instability of verbascosides and analogs. In view of the pharmacological interest of verbascoside and analogs as antioxidants, the DPPH test was also carried out according to Son and coworkers [2].

Acknowledgments: The financial support of MIUR (PRIN 2004) is gratefully acknowledged.

References: 1. Valentao, P. et al. (2002), Biol. Pharm. Bull. 2: 1324–1327. 2. Son, S., Lewis, B.A. (2002), J. Agric. Food Chem. 50: 468–472.