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Effect of Steam Treatment on the Chemical Composition of Wheat Straw

A study was carried out on the effects of steam treatment at 120°C/2 bar for different periods of time on the chemical composition of wheat straw cell wall material. The contents of weakly acidic pectic polysaccharide (WAPP), 80% ethanol soluble material, lignin, hemicelluloses and α-cellulose were determined by successive extractions with 0.25% ammonium oxalate solution, 80% ethanol, acidic sodium chlorite solution and 24% potassium hydroxide with 2% boric acid solution from the residues of 15, 30, 60, 120, 180 and 300min steam treated wheat straw, respectively. The yields of WAPP, hemicellulose, cellulose and lignin extracted from the treated straw ranged from 1.8 to 2.6%, 29.8 to 34.0%, 42.1 to 45.6% and 20.0 to 22.7%, respectively. The neutral sugars in the extracts were measured by gas chromatography. The contents of phenolic acids and aldehydes resulting from alkaline nitrobenzene oxidation of lignin remaining in hemicellulose and cellulose extracted from steam treated wheat straw ranged between 0.14 and 0.33%. The results showed that steam treatment removed some portion of pectic substances and hemicelluloses. In addition, for treatment periods greater than 120min, the treated straw contained higher amounts of lignin and cellulose than untreated straw.