Structural characterization and antioxidant activity in vitro of polysaccharides from angelica and astragalus

• Polysaccharides from angelica and astragalus (AAP) were extracted according to Danggui Buxue Decoction.
• AAP was at first isolated and purified.
• The characterization of AAP-2A was elucidated and the structure of AAP-2A was deduced.
• The ultramicrostructure of AAP-2A was described.
• AAP-2A presented better antioxidant activities when compared with AAP.

In the present study, structural characterization and antioxidant activity of a fraction (AAP-2A) of polysaccharides from angelica and astragalus (AAP) were investigated. Characteriztion assay showed that AAP-2A had molecular weight (Mw), root-mean square (RMS) radius and polydispersity index (Mw/Mn) of 2.252 × 103 kDa, 28.4 nm and 1.038, respectively. There were infrared characteristic absorption peaks of polysaccharides in FT-IR spectroscopy. AAP-2A was composed of rhamnose (Rha), galactose (Gal), arabinose (Ara) and glucose (Glc) with a molar ratio of 1:2.13:3.22:6.18 in GC analysis. Methylation analysis combined with NMR spectroscopic analysis demonstrated that a preliminary structure of AAP-2A was proposed as follows: 1,3-linked Rhap, 1,3-linked Galp, 1,3-linked Araf, 1,5-linked Araf, 1,3,5-linked Araf, 1,4-linked Glcp and 1,4,6-linked Glcp interspersed with terminal Glcp. AAP-2A exhibited a surface with a sheet-like appearance in scanning electron microscope and stronger antioxidant capacity compared with AAP.