Phytochemical analysis of different species of gentiana from Nepal

Abstract

Nepal houses 44 different species of Gentiana. Plants belonging to genus Gentiana are very well-known for their pharmacological properties. Ethnopharmacological data show that various species of Gentiana have been effectively used in herbal medicine to treat various ailments. They are known to possess potent therapeutic compounds like iridoids, xanthones and glucoflavones. This study attempts to evaluate phytochemical, antioxidant and antibacterial activities and estimate three bioactive compounds: swertiamarin, amarogentin and mangiferin in different species of Gentiana collected from different parts of Nepal. Methods: Total phenolic and flavonoid contents were quantified spectrophotometrically and in vitro DPPH free radical scavenging assay was measured. Agar well diffusion method was employed for antibacterial assays. Thin Layer Chromatography was performed on TLC Aluminium plates pre-coated with silica gel 60 for identification and estimation of swertiamarin, amarogentin and mangiferin. Semi-quantitative estimation was done using GelQuant.NET software using the standard compounds. Results: The quantitative phytochemical analysis showed presence of higher amounts of polyphenol and flavonoid in methanol extracts as compared to the aqueous extract of various Gentiana species. Among methanol extracts highest concentration of polyphenol was observed in G. depressa (79.2±19.19mgGAE/gm) while G. capitata (44.6±3.97 mgGAE/gm) showed the lowest content. Similarly, G. capitata recorded the highest total flavonoid content (19.09±0.97mgQE/gm) and G. ornata (11.31±0.49 mgQE/gm) showed the least content. Likewise, the methanol extracts showed more promising antioxidant activity compared to the aqueous extracts. The methanol extract of G. depressa showed the best antioxidant activity among the different Gentiana sps with an IC 50 value of39.57±0.95 µg/ml. Semi-quantitative analysis showed that swertiamarin was present in higher quantities than amarogentin and mangiferin. Highest concentration of swertiamarin and mangiferin was identified in G. ornata (0.109±0.013 mg/gm DW and 0.018±0.001 mg/gm DW respectively) while G. capitata possessed highest concentration of amarogentin (0.075±0.005 mg/gm DW). Antibacterial assay showed varying degree of sensitivity to various pathogenic microorganisms. G. ornata was showed highest activity among all plant species against K. pneumonia and E. feacalis while G. depressa showed maximum sensitivity to S. aureus and moderate sensitivity to K. pneumonia. These results clearly show that crude methanol and aqueous extract of various Gentiana species possess potent pharmacological compounds, and justified the folkloric use of these plants in digestive and respiratory ailments. Keywords: Gentiana, antioxidant, antibacterial, amarogentin, swertiamarin, mangiferi