EXTRACTION, FRACTIONATION, AND CHARACTERIZATION OF STRUCTURAL POLYSACCHARIDES FROM WHEAT-STRAW

Wheat straw polysaccharides were fractionated into water soluble, pect ic, 80% ethanol soluble, sodium chlorite soluble, hemicellulosic, and cellulose fractions using essentially gravimetric methods. The hemicel lulosic material was further separated into a dimethyl sulfoxide solub le fraction and hemicellulose types A-C. The sugar and uronic acid com positions of each fraction were determined by gas chromatography after hydrolysis and conversion to trimethylsilyl ether derivatives and by a spectrophotometric method. The average molecular weights (M(w)) of h emicellulosic fractions were estimated using gel permeation chromatogr aphy. The major polysaccharides in wheat straw were found to be cellul ose (37.19-38.55%), followed by hemicellulosic fractions (30.28-35.01% ) and small amounts of water soluble, pectic, 80% ethanol soluble, and sodium chlorite soluble materials. Xylose was found to be the major s ugar in all of the hemicellulosic fractions with arabinose, glucose, a nd galactose as minor constituents. From hemicellulosic fractions A to C, the relative amount of xylose decreased, while the contents of ara binose, glucose, and galactose increased. The contents of phenolic aci ds and aldehydes remaining in wheat straw hemicellulosic fractions A a nd B and in cellulose were 0.72, 0.85, and 0.19%, respectively.