Characterization of hemicelluloses isolated with tetraacetylethylenediamine activated peroxide from ultrasound irradiated and alkali pre-treated wheat straw

Post-treatment with 2% H2O2-0.2% tetraacetylethylenediamine (TAED) at pH 11.8 for 12 h at 48 degreesC solubilized 27.1-28.1% of the original hemicelluloses and 43.3-46.2% of the original lignin from the ultrasound irradiated and alkali pre-treated wheat straw. It was found that the bleaching activator TAED forms peracetic acid with hydroperoxide anion in aqueous alkali and improves the brightness of the solubilized hemicelluloses. Xylose was a predominant sugar in all the hemicellulosic preparations, comprising 72.0-73.1% of the total sugars. Arabinose (13.4-13.9%) and glucose (6.7-7.9%) were detected as the second and third major neutral sugar constituents. In addition, the hemicelluloses also contained a noticeable amount of 4-O-methyl-D-glucuronic acid (6.0-7.0%) together with a small amount of galactose (4.3-4.9%) and minor quantities of rhamnose (1.5-1.8%) and mannose (0.5-0.8%). Furthermore, the hemicellulosic preparations obtained by TAED activated peroxide extraction showed a relatively lower content of associated lignin (3.8-4.4%), but a higher molecular weight (34,210-40,310 gmol(-1)). No significant differences in the structural features such as oxidation of the hemicelluloses by TAED were observed as compared to those obtained by alkaline peroxide without bleaching activator. (C) 2002 Elsevier Science Ltd. All rights reserved.