Polysaccharide Composition of Fraxinus angustifolia Leave Infusions
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The use of plant infusions with medicinal purposes, such as the ones from members of the Fraxinus genus, is an ancient practice that has been reported by popular medicine [1]. The health benefits are associated with the presence of phenolic compounds and polysaccharides, among others [2]. Although phenolic compounds have been studied in detail for more than two decades, the characterization of the polysaccharides present in plant infusions and their involvement in the health benefits is still incipient.
The polysaccharides of F. angustifolia dried leaves were recovered by dialysis (12-14 kDa cut-off). The high molecular weight material comprised approximately 2% of the total soluble material obtained from the infusions. Total sugars in fraction were 27%, with a monomeric composition rich in Ara (15.2 ± 1.9 %), Gal (17.7 ± 0.4 %), Glc (30.1 ± 1.3 %) and uronic acids (18.9 ± 2.9 %). Analysis of the glycosidic linkage composition showed the presence of (1→6)-, (1→3,6)- and (1→3)-Gal with a proportion of 5:3:1, respectively, and also a high percentage of Ara terminally linked, diagnostic of the presence of Type II arabinogalactans [3]. Similar features have been reported in biological active Type II pectic arabinogalactans obtained from aqueous extracts of the roots of C. tinctorium [4].
The EC50 for the antioxidant activity (DPPH radical assay) was 0.34±0.04 mg/mL, showing lower antioxidant activity than that reported for aqueous extracts of hazel leaves (0.16-0.20 mg/mL) [5], but higher than that reported for the table olives ‘‘alcaparras’’ aqueous extracts (0.47± 0.03) [6].
The high molecular weight material was fractionated by ethanol precipitation in four distinct fractions: WI, a cold water insoluble residue (20.3% yield); Et50, material precipitated with 50% ethanol (17.9%); Et75, material precipitated with 75% ethanol (21.1%); and SN, material that remained soluble in 75% ethanol solution (40.7%). Fractions Et50, Et75 and SN were submitted to solid phase extraction (C18 cartridge). The Et50 and Et75 C18 non-retained fractions were rich in Ara (13.5-17.2%), Gal (27.1-35.7%) and uronic acids (25.9-35.2%), suggesting the occurrence of heterogeneous pectic arabinogalactans.
NMR experiments are in progress in order to evaluate the detailed structure of the type II pectic arabinogalactans isolated from the infusions of dried leaves of F. angustifolia.
The use of plants with medicinal purposes is an ancient practice, which is still very common all around the world and that has been largely increasing over the last decades. Data from the World Health Organization indicate that 80% of the total human population still treat their health problems with traditional remedies [1]. Consequently, a large number of ethnobotanical research studies focused on the flora of diverse countries can be found in the literature [1,2]. According to these ethnobotanical studies, the infusion is one of the most frequently cited preparation processes. The infusions of “freixo“ (Fraxinus angustifolia) dried leaves protects against high levels of cholesterol, blood pressure, and uric acid, and act against rheumatism [3]. These health benefits are associated with the presence of several physiologically active substances, such as phenolic compounds, essential oils, and polysaccharides, among others [4]. Although phenolic compounds have been studied in detail for more than two decades, the characterization of the polysaccharides present in plant´s infusions and their involvement in the health benefits is still incipient. The aim of this work is to provide a first insight into the polysaccharide composition of the infusions from Fraxinus angustifolia dried leaves.
