CHARACTERIZATION OF SOME CELL-WALL COMPONENTS OF UNTREATED AND OZONE-TREATED COTTON STALKS

Untreated (CS) and ozone-treated (OCS) cotton stalks were studied to d etermine the effects of ozonation on the content of water-soluble phen olics, on the chemical features of cell wall (CW) matrix complexes (MC ), and on in situ structure! and chemical properties as reflected in s olid-state cross-polarization/ magic angle spinning (CP/MAS) C-13 NMR spectroscopy. The concentrations of water-soluble total monomeric phen olics were 20.1 and 48.2 mg/100 g of dry matter in the CS and OCS mate rials, respectively. The major increase was in protocatechuic acid (PA ), whose concentration increased nearly 10-fold. Matrix complexes extr acted by N NaOH from neutral detergent fiber (NDF) of CS and OCS pretr eated by ball-milling plus Trichoderma reesei cellulase were analyzed by high-performance size exclusion chromatography (HPSEC) to assess th e molecular weight distribution. Two-thirds of the MC of CS were in th e molecular weight range 800-10 000 with a weight-average molecular we ight (M(w)) of 8500. The MC isolated from OCS showed a more dispersed pattern, with a higher proportion of molecules in the range higher tha n 10 000 and a (M(w)) of 15 000. The MC isolates from CS and OCS conta ined 54% and 39% carbohydrates, respectively, with xylose as the major component and uronic acid as the major potentially branching unit. So lid-state CP/MAS C-13 NMR spectroscopy Of NDF preparations of CS and O CS showed that the 89 and 65 ppm peaks (the ''crystallinity peaks'') w ere affected by ozonation. The intensity of the signals found in the 1 60-110 ppm chemical region, assigned to aromatic carbons, declined. Th e quantitative data on carbon distribution in the various chemical ent ities of the NDF samples analyzed by solid-state CP/MAS C-13 NMR showe d a decline in the proportion of aromatic carbons from 13% in CS to 7. 4% in OCS. This is the first evidence to show that CS lignin degradati on by ozone is mediated via ring cleavage.