CHARACTERIZATION OF SOME CELL-WALL COMPONENTS OF UNTREATED AND SO(2)-TREATED WHEAT-STRAW

Chemical and physical properties of cell walls (CW) and CW components have been studied in untreated wheat straw (WS) and SO2-treated wheat straw (SO2-WS). The concentration of water-soluble total free monomeri c phenolics was 47.1 mg per 100 g and 129 mg per 100 g straw dry matte r in WS and SO2-WS, respectively. The major solubilizing effect of the SO2 treatment was exerted on ferulic acid, the concentration of which increased tenfold. Matrix complexes extracted by 1 N NaOH from CW of wheat straw subjected to ball-milling plus Trichoderma reesei cellulas e pretreatment underwent high-performance size exclusion chromatograph y to assess the molecular weight distribution. Most (84%) of the matri x complexes extracted from WS were in the range of 1600-23 000 Da, whe reas those originating from SO2-WS showed a more dispersed pattern, wi th molecular weights of up to and beyond 125 000 Da. The weight averag e molecular weight (M(wt)BAR) was 10 500 Da and 35 000 Da for the matr ix complexes of WS and SO2-WS, respectively. Total monosaccharide cont ent of matrix complexes was 36.4 g per 100 g and 42.5 g per 100 g in W S and SO2-WS, respectively, with xylose as the major (70-80%) componen t. Solid-state cross-polarization-magic angle spinning C-13 NMR spectr oscopy of neutral detergent fiber preparations of wheat straw showed a decline in the intensity of signals at 89 ppm and 65 ppm in response to SO2 treatment and in vitro digestion, respectively. The distributio n of carbons in CW chemical groups and components as determined by the NMR analysis was found to be close to values obtained by wet chemistr y.