Optimization of Extraction and Purification of Polysaccharides from Veronicastrum axillare , and Evaluation of Their Biological Activities

Veronicastrum axillare polysaccharides (VAP) were isolated by cellulase‐assisted digestion. The optimum conditions (2 % cellulase, 47 °C for 2.5 h, then, 95 °C for 2.5 h, pH 4.1, solid/liquid ratio 1 : 7.6) were identified by a combination of single factor optimization and response surface DOE (design of experiment) methods, and achieved a yield of 4.7 %. Treatment with 1 % TCA for 10 min, then, 2 % DEAE‐cellulose removed protein and colored impurities. Purified VAP retained most of the radical‐scavenging activities and GES‐1 cell protection capability in vitro , indicating VAP were the key active components of V. axillare . Some molecular features were identified by FT‐IR and NMR analyses. The molecular weight was estimated from DOSY NMR experiments to be around 21 kDa. There were 6.3 % uronic acid residues in the VAP. The constituent sugars after TFA hydrolysis were identified by HPLC to include glucose, arabinose, rhamnose, galactose, and xylose in a molar ratio of 405 : 259 : 82 : 42 : 1.