VARIATIONS IN CHEMICAL-COMPOSITION AND STRUCTURE OF MACROMOLECULAR COMPONENTS IN DIFFERENT MORPHOLOGICAL REGIONS AND MATURITY STAGES OF ARUNDO-DONAX

Arundo donax plants were manually separated into fractions of differen t morphological regions (internodes, nodes and foliage) at different s tages of maturity and submitted to chemical composition studies. Gener al chemical composition was determined by established methods. The pol ysaccharides were fractionated by successive extractions of holocellul ose with aqueous KOH solutions. The sugar composition was determined b y hydrolysis of polysaccharides followed by GC analysis of neutral sug ars as alditol acetates and spectrophotometric determination of uronic acids. In situ lignins, milled wood lignins (MWL) and dioxane lignin were characterised by permanganate oxidation followed by GC and GC-MS analysis of the methylated oxidation products and by quantitative C-13 NMR spectroscopy. The results of general chemical analysis evidenced the different relative abundance of holocellulose, lignin, proteins, e xtractives and ashes in internodes, nodes and foliage, at different st ages of maturity. In internodes, nodes and foliage about 70-80% of hem icelluloses (21-30% o.d. material) were easily extracted with 5% KOH a queous solutions. The analysis of hemicelluloses indicated that they a re constituted mainly by arabinoglucuronoxylans with a xylose:arabinos e:uronic acid ratio of 91-93:5-7:2 for internodes. The high content of xylose in Arundo donax stem (24-27% o.d. material) and the easy extra ction of hemicelluloses opens new perspectives for the use of this ree d as a source of pentosans. The results obtained by the permanganate o xidation method indicated that Arundo donax lignins are essentially H- G-type with approximate H:G:S proportions of (32-36):(59-61):(5-8) in internodes. The H units are constituted mainly by esterified p-coumari c acid. These results were confirmed by quantitative C-13 NMR spectros copy of isolated dioxane lignin. The quantity of condensed structures in in situ lignin decreases from the older to the younger parts of the stems and is much higher in nodes than internodes. (C) 1997 Elsevier Science B.V.