Optimization of enzyme-assisted microwave extraction, structural characterization, antioxidant activity and in vitro protective effect against H2O2-induced damage in HepG2 cells of polysaccharides from roots of Rubus crataegifolius Bunge.

In this study, an enzyme-assisted microwave extraction process was obtained by response surface method of polysaccharide from roots of Rubus crataegifolius Bunge. The optimized extraction process was as follow: enzyme dosage 2 %, enzymatic time was 3.6 h, enzymatic pH 4.9, and microwave time 4.7 min, with the extraction yield of 9.07 %. Four homogeneous polysaccharides (RCP-1, RCP-3, RCP-4 and RCP-5) were purified through column chromatography. Four polysaccharides have the relative higher molecular weights of 1.70 × 106 Da, 5.56 × 106 Da, 4.97 × 106 Da, and 9.80 × 106 Da and mainly consisted of GluN, GluA, Glu, Gal and Arab. FT-IR and NMR spectral analysis confirmed that the purified polysaccharides were polypyranose containing α- and ß-glycosidic bonds. RCP - 1 has a relative high crystallinity. Four purified polysaccharides contained triple helical conformations, and have good antioxidant activities. Among the purified polysaccharides, RCP - 1 was found to reduce the oxidative cell damage induced by H2O2 through increasing of cell viability, inhibition of AST and ALT levels, ROS production and cell apoptosis, increasing of the activities of antioxidative enzymes, as well as reduction of MDA content. Our findings would provide a foundation for purified polysaccharides efficient extraction and demonstrated that the polysaccharides from R. crataegifolius roots could be a promising hepatoprotective agent.