Bitter Gentian Teas: Nutritional and Phytochemical Profiles, Polysaccharide Characterisation and Bioactivity

Abstract

As a result of the wide distribution of herbal teas the data on nutritional characterisation, chemical profile and biological activity of these products are required. The decoctions of Gentiana algida, G. decumbens, G. macrophylla and G. triflora herb teas were nutritionally characterized with respect to their macronutrients, demonstrating the predominance of polysaccharides and low lipid content. Gentian decoctions were also submitted to a microcolumn RP-HPLC-UV analysis of phytochemicals demonstrating a high content of iridoids (177.18-641.04 μg/mL) and flavonoids (89.15-405.71 μg/mL). Additionally, mangiferin was detected in samples of G. triflora tea (19.89 μg/mL). Five free sugars (fructose, glucose, sucrose, gentiobiose, gentianose) were identified in all gentian teas studied, as well as six organic acids (malic, citric, tartaric, oxalic, succinic, quinic). Pectic polysaccharides with a high content of rhamnogalacturonans and arabinogalactans were also identified and characterized in gentian decoctions for the first time. Gentian tea decoctions and their specific compounds (gentiopicroside, loganic acid-6'-O-β-d-glucoside, isoorientin, isoorientin-4'-O-β-d-glucoside, mangiferin, water-soluble polysaccharides) showed a promising antimicrobial, anti-inflammatory and antioxidant potentials. Evidences obtained indicate the prospective use of gentian herb teas as food products and medicines.

Keywords: Gentiana algida; Gentiana decumbens; Gentiana macrophylla; Gentiana triflora; anti-inflammatory; antimicrobial activity; antioxidant; flavonoids; iridoids; polysaccharides.

Figure 1

FT-IR spectra of water-soluble polysaccharide fraction of G. algida bitter tea.

Figure 2

Anti-inflammatory activity of four gentian teas and individual compounds on carrageenan-induced paw edema in rats after 1 and 4 h after injection. Bars show the values of edema volume (mL). Values of edema shown are mean ± SD (n = 12). Asterisks indicate statistically significant values from the control (*—p < 0.05; **—p < 0.01; ***—p < 0.001). On cuts—percentage of edema inhibition (A—aspirin, G.a.—G. algida, G.d—G. decumbens, G.m.—G. macrophylla, G.t.—G. triflora, G—gentiopicroside, LG—loganic acid-6′-O-β-d-glucoside, ⁱO—isoorientin, ⁱOG—isoorientin-4′-O-β-d-glucoside, WSPF—water-soluble polysaccharide fractions).

Figure 3

HPLC chromatograms of G. algida and G. triflora teas decoctions before and after prechromatographic reaction with DPPH-radicals. Compounds: 1—loganic acid-6′-O-β-d-glucoside; 2—loganic acid; 3—swertiamarin; 4—isoorientin-4′-O-β-d-glucoside; 5—gentiopicroside; 6—sweroside; 7—mangiferin; 8—saponarin; 9—isosaponarin; 10—isoorientin; 11—isovitexin; 12—isoscoparin.