Ultrafiltration isolation, hypoglycemic activity analysis and structural characterization of polysaccharides from Brasenia schreberi

Brasenia schreberi (B. schreberi) is a rare and precious vegetable, which coat with a gelatinous mucilage. This study is aiming to investigate the relationship between structural characteristics and hypoglycemic activities of polysaccharides with different molecular weight (Mw) range. Three polysaccharides fractions, namely BSP-U100 (50-100 kDa), BSP-U50 (10-50 kDa) and BSP-U10 (<10 kDa), were isolated from B. schreberi mucilage using ultrafiltration method. Compared to other polysaccharide samples, only BSP-U100 had a triple helix structure and existed as the ordered structure in aqueous solution. Furthermore, BSP-U100 exhibited higher α-amylase (IC50 = 0.4414 mg/mL) and α-glucosidase (IC50 = 0.5993 mg/mL) inhibitory activity. A heteropolysaccharide BSP-1a, which average Mw was 83.98 kDa, was purified from BSP-U100 by DEAE Sepharose Fast Flow and Sephadex G-75 column. D-galactose (66.85%), d-glucose (2.05%) and D-mannose (1.65%) were three main monosaccharides of BSP-1a. Structural characterization of BSP-1a showed that BSP-1a might be a kind of L-D-pyranose type galactose and mainly composed of α-1 → 6-linked Galp, α-1 → 3-linked Manp and α-1 → 4-linked Glcp. This study provided a theoretical basis for the development and application of B. schreberi polysaccharides as a potential anti-diabetic supplement.