Fractional and structural characterization of hemicelluloses from perennial ryegrass (Lolium perenne) and cocksfoot grass (Dactylis glomerata) Original Research Article

Sequential three-stage treatments with 80% EtOH containing 0.2% NaOH, 2.5% H2O2–0.2% EDTA containing 1.5% NaOH and 2.5% H2O2–0.2% TAED containing 1.0% NaOH at 75 °C for 3 h released 8.0% and 10.4%, 79.1% and 77.0% and 12.9% and 12.5% of the original hemicelluloses from perennial grass and cocksfoot grass, respectively. It was found that the four alkaline peroxide-soluble hemicellulosic fractions contained higher amounts of xylose (33.4–38.2%), uronic acids (9.3–15.3%) and rhamnose (3.0–3.9%), but were lower in glucose (25.1–28.3%), galactose (13.3–15.3%) and mannose (0.4–1.5%) than those of the two alkaline EtOH-soluble hemicellulosic fractions in which glucose (32.9–36.0%), xylose (20.1–22.6%), arabinose (14.1–21.4%), galactose (16.6–19.9%), mannose (4.1–9.9%) and uronic acids (3.4–7.4%) were the major sugar components. 13C NMR spectroscopy confirmed that all the six hemicellulosic fractions were composed of galactoarabinoxylans, 4-O-methylglucuronoarabinoxylans and β-glucan. In addition, the studies showed that the four alkaline peroxide-soluble hemicellulosic fractions were more linear and acidic and had larger molecular weights (Mw, 28,400–38,650 g mol−1) than those of the two alkaline EtOH-soluble hemicellulosic fractions (Mw, 16,460–17,420 g mol−1).