Phenolics as radical scavengers in Plantago species

The genus Plantago L. (Plantaginaceae) comprises about 275 species found all over the world. Ancient use of plantains as herbal remedies is a consequence of their adstringent, anti-toxic, antimicrobial, anti-inflammatory, expectorant and diuretic properties. Although studies concerning the antioxidant activity of some plantains are available [1, 2], there are no reports on the antioxidant activity of some other Plantago species. The aim of this study was to examine antioxidative properties of methanolic extracts from four Plantago species (P. maior L., P. media L., P. lanceolata L. and P. holosteum Scop.) collected from three different locations in Serbia. The extracts were investigated regarding their composition by different colorimetric techniques, such as the content of total phenolic compounds by the Folin-Ciocalteu assay [3] and flavonoids by AlCl₃ reagent [4]. Their radical scavenger capacity (RSC) was evaluated measuring spectrophotometrically the decrease of DPPH* (diphenylpicrylhydrazyl radical) [5]. The content of total phenolic compounds (expressed as g chlorogenic acid equivalents/g of dry extract) varied from 0.1281 (P. maior location N. Sad) to 0.2774 (P. media-Mt. Kopaonik). Flavonoid content was the highest in P. holosteum, followed by P. media, P. lanceolata and P. maior (from 19.76 to 7.77mg quercetine equiv/g of dry extract, respectively). The most potent extracts of P. media (Mt. Kopaonik) and P. holosteum (Mt. Stara Planina) inhibited the DPPH* by 50% (IC₅₀) at 4.25 and 4.28µg/ml respectively indicating higher activity than the synthetic antioxidant BHT (IC₅₀ 4.62µg/ml). The extracts of P. maior and P. lanceolata also showed significant scavenging capacity. Beside estimated correlation between the scavenging potency and the total phenolic content of the extracts, this study presented P. media and P. holosteum as a possible new source of natural antioxidants.

References: [1] Galvez, M. et al. (2005) J. Agric. Food. Chem. 53(6):1927–33. [2] Pourmorad, F. et al. (2006) Afric. J. Biotech. 5: 1142–1145. [3] Singleton, V.L. et al. (1999) Methods in enzymology, Acad. Press, New York. [4] Chang, C.C et al. (2002) J. Food Drug Anal. 10: 178–182. [5] Soler-Rivas, C. et al. (2000) Phitochem. Anal. 11: 330–338.