Structural Characterization and Hypoglycemic Activity of Polysaccharides from Polygonatum sibiricum Subjected to Nine Steaming-Drying Cycles

This study focuses on the purification, structural characterization and hypoglycemic activity of polysaccharides from Polygonatum sibiricum undergoing nine steaming-drying cycles. Crude polysaccharides were obtained by water extraction followed by alcohol precipitation and purified/fractionated by DEAE-52 cellulose chromatography into three homogeneous polysaccharides, named SPGK, SPGK2, and SPGK3, whose structural characterization was performed by measuring their molecular mass and monosaccharide composition as well as using Fourier transform infrared (FTIR) spectroscopy, methylation followed by gas chromatography-mass spectrometry (GC-MS), and nuclear magnetic resonance (NMR) spectroscopy. Enzyme inhibition assays were conducted to study the hypoglycemic activity of the three polysaccharides. The results showed that the molecular masses of SPGK, SPGK2, and SPGK3 were 12.74, 68.72, and 10.25 kDa, respectively. SPGK contained six monosaccharides: fucose, rhamnose, arabinose, galactose, glucose, and mannose, in a ratio of 0.07:0.04:0.50:89.44:1.58:8.37, with galactose being the major monosaccharide component, and its structural units included →4)-α-D-Galp-(1→, →4)-β-D-Galp-(1→, →4,6)-β-D-Galp-(1→, and T-β-D-Galp-(1→. SPGK2 contained eight monosaccharides: fucose, rhamnose, arabinose, galactose, glucose, mannose, galacturonic acid, and glucuronic acid, in a ratio of 0.27:7.62:7.51:76.59:3.12:1.19:3.28:0.42, with rhamnose, arabinose, galactose, and glucose being the major components. Its structural units included →2,4)-α-L-Rhap-(1→, →5)-α-L-Araf-(1→, →4)-α-D-Galp-(1→, →4)-β-D-Galp-(1→, →4,6)-β-D-Galp-(1→, T-β-D-Glcp(1→, and T-β-D-Galp-(1→. Likewise, SPGK3 contained eight monosaccharides: fucose, Rhamnose, arabinose, galactose, glucose, mannose, galacturonic acid, and glucuronic acid, in a ratio of 0.55:24.59:5.54:37.65:2.90:1.35:26.97:0.45, with rhamnose, galactose, and galacturonic acid being the major components, and its structural units included →3)-α-L-Rhap-(1→, →2,4)-α-L-Rhap-(1→, →4)-α-D-GalAp-(1→, →4)-β-D-Galp-(1→, →4,6)-β-D-Galp-(1→, →4)-β-D-Glcp-(1→, and T-β-D-Galp-(1→. All three polysaccharides exhibited inhibitory activities against α-amylase and α-glucosidase. At a concentration of 2 mg/mL, the inhibition rates against α-amylase were 41.53%, 83.60%, and 56.15%, respectively, while those against α-glucosidase were 28.03%, 83.97%, and 65.76%, respectively. In conclusion, these polysaccharides from P. sibiricum possess potential hypoglycemic effects, providing a theoretical basis for their product development and application in hypoglycemic treatments.