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

The effects of alkaline pre-treatments of wheat straw have been examined in detail. In particular, treatments with increasing amounts of sodium 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 delignification 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 sequentially extracted with 0.25% ammonium oxalate for the isolation of pectin, acidic sodium chlorite solution for delignification and 24% potassium hydroxide with 2% boric acid (2 h at 20 degrees C) for the determination of remaining hemicellulose and alpha-cellulose. The yields were determined by gravimetric analysis and expressed as a proportion of the starting material. It was found that xylose was the major sugar constituent in all the hemicellulose fractions and the hydrolysates obtained from pre-treatment, while glucose and galactose were present as minor components. The content of arabinose was higher in all the pre-treatment hydrolysates than in hemicellulose fractions isolated from the residues, whereas the relative amount of xylose in remaining hemicellulose was higher than in the hydrolysates material. The content of uronic acid and the range of molecular weights both in remaining hemicellulose and in hydrolysate fractions were also studied. The contents of phenolic acids and aldehydes remaining both in 0.5 h pre-treated (1.5% sodium hydroxide) wheat straw hemicellulose and cellulose were 0.15%.