INFLUENCE OF ALKALINE PRETREATMENTS ON THE CELL-WALL COMPONENTS OF WHEAT-STRAW

The effects of alkaline pre-treatments of wheat straw have been examin ed in detail. In particular, treatments with increasing amounts of sod ium hydroxide at a range of temperatures and exposure times have been investigated. A number of other alkaline or oxidizing agents have also been utilized and briefly assessed. Optimal conditions for delignific ation and dissolution of hemicellulosic polysaccharides were found to be pre-treatment with 1.5% sodium hydroxide for 144 h at 20 degrees C. This resulted in release of 60% and 80% of lignin and hemicellulose, respectively. The residues of the pre-treated wheat straw were sequent ially extracted with 0.25% ammonium oxalate for the isolation of pecti n, acidic sodium chlorite solution for delignification and 24% potassi um hydroxide with 2% boric acid (2 h at 20 degrees C) for the determin ation of remaining hemicellulose and alpha-cellulose. The yields were determined by gravimetric analysis and expressed as a proportion of th e starting material. It was found that xylose was the major sugar cons tituent in all the hemicellulose fractions and the hydrolysates obtain ed from pre-treatment, while glucose and galactose were present as min or components. The content of arabinose was higher in all the pre-trea tment hydrolysates than in hemicellulose fractions isolated from the r esidues, whereas the relative amount of xylose in remaining hemicellul ose was higher than in the hydrolysates material. The content of uroni c acid and the range of molecular weights both in remaining hemicellul ose and in hydrolysate fractions were also studied. The contents of ph enolic acids and aldehydes remaining both in 0.5 h pre-treated (1.5% s odium hydroxide) wheat straw hemicellulose and cellulose were 0.15%.