Extraction, Purification, Characterization and in Vitro Hypoglycemic Activity of Polysaccharides from Fruiting Body of Phlebopus portentosus

Abstract

In order to study the structural properties and biological activities of the polysaccharides of Phlebopus portentosus, water-soluble polysaccharides from the fruiting body of P. portentosus were extracted by hot water extraction followed by ethanol precipitation, deproteinized using Sevag reagent, decolorized using macroporous adsorption resin, and purified to homogeneity by successive chromatography on DEAE-52 cellulose and Sephacryl S-400HR columns. The molecular mass of the purified polysaccharides was determined by high performance gel permeation chromatography (HPGPC), and the monosaccharide composition by high performance liquid chromatography (HPLC) following pre-column derivatization with 1-phenyl-3-methyl-5-pyrazolone (PMP). Ultraviolet (UV) absorption spectroscopy was used to examine whether the polysaccharide samples contained proteins or nucleic acids, and the types of functional groups, structure and morphology were characterized by infrared spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and scanning electron microscopy (SEM), respectively. The polysaccharide with high α-glucosidase inhibitory activity was selected to evaluate its inhibition kinetics on α-glucosidase. Furthermore, its in vitro hypoglycemic mechanism and inhibitory type were clarified. The results showed that among four macroporous resins (HP 2MGL, HP 20, SP 850 and SP 825) tested, SP 825 macroporous resin had the best decolorization efficiency. The fraction PPP-0 had a weight average molecular weight (mw) of 31 059 Da. Moreover, it was a heteropolysaccharide mainly composed of galactose, glucose, fucose and mannose that were linked by α- and β-glycosidic bonds. In vitro hypoglycemic experiments showed that the crude polysaccharide and the three purified polysaccharide fractions all exhibited inhibitory activity on α-glucosidase, among which PPP-2 had the highest inhibitory rate, followed by PPP-0. The inhibition was competitive and reversible. This study could provide a theoretical basis for the development of functional foods with hypoglycemic activity and hypoglycemic agents from P. portentosus polysaccharides.

Keywords

• phlebopus portentosus; polysaccharides; separation and purification; structural characteristics; hypoglycemic activity