COMPARATIVE STUDY OF WATER-,ORGANOSOLV- AND ALKALI-SOLUBLE HEMICELLULOSES FROM CARAGANA SINICA

摘要

Caragana sinica, a very important shrub species widely distributed in the desert regions of China, may potentially be the source of raw cell wall material to promote a local development in northern China. Hemicelluloses, the main matrix cell wall polymers, were fractionated by successive extractions with distilled water at 80 °C for 2 h, 70% ethanol, 70% ethanol containing 1% NaOH, 1 M KOH, 1 M NaOH, 3 M KOH, and 3 M NaOH at 75 °C for 3 h. The obtained seven hemicellulosic fractions were comparatively studied by sugar analysis, GPC, FT-IR, 1D and 2D NMR spectroscopy. The results showed that the sequential treatments led to a release of 86.7% of the original hemicelluloses. Comparison of these hemicelluloses indicated that the smaller sized and more branched hemicelluloses were dissolved by the hot water treatment, while the larger molecular size and more linear hemicelluloses were extracted by the organosolv and alkali solutions treatments. In addition, the hemicellulosic fraction H3 isolated with 1 M KOH was found to be composed of a linear (1→4)-β-D-xylopyranosyl main chain with a 4-O-methylglucuronic acid substituting the C-2 position of approximately every eight xylose units, which is typical of a hardwood acidic 4-O-methylglucuronoxylan (MGX).