Comparative Studies of Hemicelluloses Solubilized during the Treatments of Maize Stems with Peroxymonosulfuric Acid, Peroxyformic Acid, Peracetic Acid, and Hydrogen Peroxide. Part 1. Yield and Chemical Characterization

Summary Treatment of the water-extracted maize stems with peroxymonosulfuric acid at 20 °C for 144 h, peroxyformic acid at 80°C for 6 h, peracetic acid at 50°C for 6 h, and 2% hydrogen peroxide at 45°C for 12 h at pH 1.5, 4.4, 9.5, 11.5, 12.0, and 12.6, respectively, solubilized 47.1%, 91.3%, 33.3%, 16.6%, 15.9%, 17.4%, 86.2%, 87.7%, and 91.3% of the original lignin, and hydrolysed or dissolved 12.1%, 99.1%, 4.5%, 2.7%, 3.1%, 3.1%, 63.3%, 64.7%, and 83.0% of the original hemicelluloses, respectively. Substantial lignins and hemicelluloses were degraded or released during the treatment with peroxyformic acid and alkaline peroxide at pH ≥ 11.5, while an insignificant effect on delignification and hemicellulose solubilization was observed by using peroxymonosulfuric acid, peracetic acid, and hydrogen peroxide in acidic, natural, and weak alkaline media. The optimum condition for extraction of hemicelluloses was found to use 2% H2O2 at 45°C for 12 h at pH 11.5–12.0, which yielded 63.3–64.7% of the original hemicelluloses having much lighter color than those obtained by peroxymonosulfuric acid and peracetic acid under conditions used and 2% H2O2 at pH 1.5, 4.4, 9.5, and 12.6. Xylose and arabinose were the major sugar constituents in these hemicellulose preparations, whereas glucose, galactose, mannose, rhamnose, and fucose were present as minor components. The α-ether linkages between lignin and hemicelluloses in the cell wall of maize stems were substantially cleaved during the treatment with 2% H2O2 at pH ≥11.5 as shown by a minimal amount of associated lignin (2.9–3.9%), rich in syringyl units, in the solubilized hemicelluloses.