Structural and physicochemical characterization of hemicelluloses isolated by alkaline peroxide from barley straw

Seven hemicellulosic preparations were obtained from barley straw by extraction with 1.5% H2O2 at pH 12.0 for 14 h at 45 °C with extractant to straw ratios of 10:1, 13:1, 15:1, 18:1, 20:1, 25:1 and 30:1. The respective yields of dissolved hemicelluloses were 28.4 wt%, 28.8 wt%, 29.7 wt%, 30.1 wt%, 30.6 wt%, 30.8 wt% and 30.8 wt% or dry barley straw, corresponding to release of 78.7%, 79.8%, 82.3%, 83.4%, 84.8%, 85.3% and 85.3% of the original hemicelluloses. The polymers were mainly composed of xylose, arabinose, glucose, galactose and 4‐O‐methyl‐D‐glucuronic acid (59.3–62.6%, 19.7–22.0%, 8.8–12.5%, 5.6–6.9% and 5.8–6.7%, respectively) and had weight‐average molecular weights of between 38 470 and 41 050 g mol−1.13 CNMR spectroscopy confirmed the results obtained by chemical methods, and showed that the hemicellulosic fraction was mostly by L‐arabino‐(4‐O‐methyl‐D‐glucurono)‐D‐xylan. More importantly, it was found that lignin provides some protection for the hemicelluloses in barley straw against attack by hydrogen peroxide.