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 °C 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 g mol⁻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.