Composition and properties of pectin polysaccharides of St. John’s wort Hypericum Perforatum L.

Abstract

Three fractions of acidic water-soluble polysaccharides (concentration of glucuronic acid 10–65%) were obtained from the above-ground part of St. Johns wort Hypericum perforatum L. by serial extraction with water and 0.7% aqueous solution of ammonium oxalate. Enzymatic hydrolysis of these polysaccharides using endo-polygalacturonase indicates that their carbohydrate chains contain the units of galacturone formed by 1,4-α-linked residues of non-substituted D-galacturonic acid. The extracted polysaccharides have been purified by means of gel filtration. It has been shown that water-soluble polysaccharides obtained by extraction with water manly contain the residues of galactose, mannose, glucose, and arabinose (the concentration of glucuronic acid being 10–27%) while the polysaccharide fraction extracted using 0.7% aqueous solution of ammonium oxalate is presented by pectin polysaccharides. Only the residues of galacturonic acid (55–72%) have been identified among glucuronic acids in its composition using chromatography/mass spectrometry of trimethylsilyl derivatives. In addition, this fraction contains the residues of the neutral monosaccharides which are typical for pectins: arabinoses, galactoses, rhamnoses, and glucose; there are also minor concentrations of residues of xylose and mannose. IR spectra of pectin polysaccharides of St. John’s wort have absorption bands in the ranges 1740, 1640–1620, 1236–1200, and 1200–1000 cm−1 which are typical for pectins. It has been demonstrated that aqueous solutions of pectin polysaccharides of St. John’s wort (2 mg/mL) have pronounced antioxidant activity (44% of the activity of trolox taken for 100%).