ISOLATION AND CHARACTERIZATION OF HEMICELLULOSE-B AND CELLULOSE FROM PRESSURE REFINED WHEAT-STRAW

The hemicellulose and cellulose were extracted with 24% KOH and 2% bor ic acid at 20 degrees C for 2 h from pressure refined wheat straw holo cellulose. The yields were 26.2-28.4% and 41.8-43.0%, respectively. Th e hemicellulosic material was further fractionated into hemicellulosic type A-C. The contents of neutral sugars, uronic acids and molecular- average weights of hemicellulosic fractions B were measured. Xylose wa s the major sugar in the hemicellulosic fractions, while galactose and glucose were the minor constituents and arabinose appeared in noticea ble amounts. The contents of phenolic acids and aldehydes, obtained by alkaline nitrobenzene oxidation, in hemicellulose B were 0.33 (> 300 mu m TMP fiber) and 0.49% (less than or equal to 300 mu m TMP fiber), respectively. The methylation analysis and C-13 NMR measurement showed that hemicellulose B, isolated from pressure refined wheat straw(> 30 0 mu m TMP fiber), appeared to be essentially a (1 --> 4) linked beta- D-xylan with 4-O-methyl-alpha-D-glucopyranosyluronic acid attached at position 2, while L-arabinofuranosyl and D-xylopyranosyl groups attach ed at position 3. (C) 1998 Elsevier Science B.V.