Fractional Isolation and Physico-Chemical Characterization of Hemicelluloses by a Two-Stage Treatment from Haloxylon ammodendron and Elaeagnus angustifolia

Abstract

The cell wall material of Chinese shrubs Haloxylon ammodendron and Elaeagnus angustifolia was fractionated by successive extractions with ethanol/H₂O (60:40, v/v) under acidic conditions (0.2 N HCl) at 70 °C for 4 h, and 2% H₂O₂ at pH 11.5 for 16 h, respectively. The sequential two-step treatment resulted in the dissolution of 83.9% and 87.6% of the original hemicelluloses from dewaxed H. ammodendron and E. angustifolia, respectively. Xylose, glucose, and galactose were the major sugar constituents in the two acidic organosolv-soluble hemicellulosic preparations. The two alkaline peroxide-soluble hemicellulosic fractions were shown to be composed primarily of xylose, comprising over 80% of the total sugars. The results also showed that the two alkaline peroxide-soluble hemicellulosic fractions were more linear and acidic, and had higher molecular mass and thermal stability than the two acidic organosolv-soluble hemicellulosic preparations. The 2% H₂O₂ posttreatment did not result in any significant changes in the macromolecular structure of the isolated hemicelluloses. It is probable that lignin protects hemicelluloses and cellulose from being attacked by peroxide. Keywords: Hemicelluloses; ethanol/H₂O; alkaline peroxide; Haloxylon ammodendron; Elaeagnus angustifolia