Preparation, characterization and in vitro antioxidant activities of a homogeneous polysaccharide from Prunella vulgaris.

Prunella vulgaris is a medicinal and edible homologous plant, commonly used as a folk medicine to treat diseases. The Prunella vulgaris polysaccharides (PVPs) are reported with the antioxidant activity. This work was designed to isolate, characterize, and test the antioxidant activity of purified PVPs from P. vulgaris. A new homogeneous polysaccharide (PVP-1) was prepared by the DEAE column from PVPs, and diverse chromatography/spectroscopy and chemical methods were simultaneously employed to characterize the fine structure of PVP-1. The result showed PVP-1 had a triple helix structure, and the repeating structural unit of PVP-1 was composed of →6)-β-D-Galp-(1→6)-β-D-Galp-(3,1→6)-β-D-Galp-(1→6)-β-D-Galp-(1→ as the main chain, together with →6)-β-D-Galp-(1,3→1)-α-D-Araf-(5→1)-β-D-Galp-(4→1)-α-D-Galp-(2→ and →6)-β-D-Galp-(1,3→1)-α-D-GlcAp-(4→1)-α-D-Glcp-(4→1)-α-D-Galp as the branch chains. The main monosaccharides of PVP-1 were galactose (Gal, 41.25 %), galactose-OMe (Gal-OMe, 27.73 %), arabinose (Ara, 10.63 %), mannose (Man, 9.86 %), glucose (Glc, 3.88 %), glucuronic acid (GlcA, 2.86 %), ribose (Rib, 1.79 %), and xylose (Xyl, 1.76 %). In addition, the scanning electron microscopy (SEM) displayed that the surface of PVP-1 was rough and porous. PVP-1 gave the scavenging rates of the DPPH, ABTS, and hydroxyl radical lower than vitamin C at the same concentration, with the highest scavenging rate of DPPH radical at 82.71 % ± 4.19 % (5 mg/mL).