Extraction, purification, and bioactivities analyses of polysaccharides from Glycyrrhiza uralensis

Glycyrrhiza uralensis is an important traditional Chinese herbal medicine. Polysaccharide is one of active components of G. uralensis. In this paper, the extraction conditions of crude polysaccharides from G. uralensis (GPs0) were optimized by central composite design (CCD), and Three purified polysaccharide fractions (GPs1, GPs2 and GPs3) were studied based on physicochemical property, monosaccharide composition, molecular weight, structures characteristics and antioxidant activities. Results showed that the yield of GPs0 reached at the maximum of 4.23%, when the optimum extraction process was 1:13 g/mL (solid-liquid ratio), 600 W (ultrasonic power) at 70°C for 85 min. Except for GPs2, the others (GPs0, GPs1 and GPs3) are non-reducing sugars. They don't contain starch. GPs0 and GPs1 contain protein. The molecular weight, monosaccharide composition and Fourier transform infrared spectroscopy (FT-IR) assay showed that GPs1, GPs2 and GPs3 are pyran polysaccharides with a weight average molecular weight (Mw) of 4.513 × 103, 1.378 × 105 and 2.084 × 105 g/mol, respectively. GPs1, GPs2 and GPs3 mainly contain glucose and galactose, respectively. Scanning electron microscope (SEM) demonstrated that GPs1, GPs2 and GPs3 are flaky with a pore structure. Atomic force microscopy (AFM) displayed GPs1 and GPs2 have a large number of dispersions and a small amount of smaller globular aggregates, while GPs3 is the opposite of the abovementioned result. Besides, the antioxidant activity assay of these polysaccharides illustrated that GPs1 has a strong scavenging effect on DPPH radicals and superoxide radical.