Fractionation and characterization of alkali-extracted hemicelluloses from peashrub

Alkali-soluble hemicelluloses were extracted from delignified peashrub (Caragana korshinskii) by sequential treatments with 0.5, 1.0 and 2.0 mol L−1 KOH under a solid to liquid ratio of 1:25 (g mL−1) at 25 °C for 10 h. The successive treatments resulted in a total dissolution of 64.1, 15.6, and 12.5% of the original hemicelluloses, respectively. The released hemicelluloses were separated into linear and branched hemicellulosic subfractions by the iodine-complex precipitation technique. Their chemical and physical characteristics were determined by HPAEC, GPC, FT-IR and 1H and 13C NMR spectroscopy. It was found that the hemicelluloses precipitated by iodine-potassium iodide solution were more linear as shown they contained more xylose and less uronic acid than the hemicelluloses remaining in the solution, which were more branched and contained higher amounts of arabinose, galactose and glucose. In addition, the linear hemicellulosic subfractions with a low arabinose/xylose ratio had higher molecular weights than those of the branched hemicellulosic subfractions in solution.