Structural characterization and isolation of lignin and hemicelluloses from barley straw

Structural characterization and isolation of lignin and hemicelluloses from crops are very important for industrial utilization. In this paper, the sequential treatments of barley straw using 90% dioxane, 80% acidic dioxane, 100% dimethyl sulfoxide, and 8% NaOH released total 93% of original lignin and 87% of original hemicelluloses. The extractions with acidic dioxane and dimethyl sulfoxide produced the original hemicelluloses and high-condensed lignin mainly from the middle lamella. FT-IR and NMR analyses show that the hemicelluloses of barley straw contain acidic arabinxylans as the major polysaccharides, which are substituted by α-l-arabinofuranose, 4-O-methyl-glucuronic acid, acetyl group (DS = 0.13), and xylose at O-3 and/or O-2 of xylan, and lignin contains β-O-4′ as a predominant interunit linkage with high amounts of β-5′ and β-1′. The guaiacyl and syringyl units are more etherified, and the proportion of erythro-β-O-4′ is slightly higher than that of threo-β-O-4′ in the lignin of barley straw.