Isolation and structural characterization of hemicelluloses from the bamboo species Phyllostachys incarnata Wen

Water and alkali-soluble polysaccharides, isolated by sequential extractions with distilled water, 0.5% and 1% NaOH, 60% ethanol containing 1% NaOH, and 3%, 5% and 8% NaOH, were prepared at 60 °C for 3 h from dewaxed bamboo Phyllostachys incarnata Wen. The yields of the seven fractions together accounted for 80.1% of total available hemicellulosic polysaccharides. Sugar composition studies showed that the water-soluble polysaccharides consisted mainly of glucose units, while xylose, arabinose and glucuronic acid were the major sugars in alkali-soluble hemicelluloses. Moreover, the molecular weights of these polymers varied between 3760 and 36,000 g/mol as revealed by GPC. Furthermore, the structure of the hemicellulosic fraction extracted with 3% NaOH was determined by 1H and 13C NMR spectroscopy along with 2D HSQC. It was found that the bamboo hemicelluloses were O-acetyl-(4-O-methylglucurono)-arabinoxylans, and the structural element could be identified as below: 1,4-β-D-[2-O-Ac][2,3-di-O-Ac][4-O-Me-α-D-GlcpA-(1 → 2)][α-L-Araf-(1 → 2)(1 → 3)]-xylp.