The heteroxylan from sisal (Agave sisalana), an O-acetyl-(4-O-methylglucurono)xylan with a molecular weight (Mw) of 18 kDa, was isolated by extraction of peracetic holocellulose with Me2SO and thoroughly characterized by wet chemistry, and NMR spectroscopy. The heteroxylan backbone is composed of (1→4)-linked β-D-xylopyranosyl units (Xylp) partially branched with terminal (1→2)-linked 4-O-methyl-α-D-glucuronosyl (MeGlcpA, 9%mol.) and a small proportion of α-D-glucuronosyl (GlcpA, <1%mol.) residues. Roughly 61%mol. of Xylp residues are acetylated (DS =0.70). During soda/AQ pulping of sisal fibers, MeGlcpA and GlcpA are mostly removed or converted to 4-deoxy-β-L-threo-hex-4-enopyranosyluronic acid (HexA), although about 15% of the initially present MeGlcpA was maintained intact upon cooking. The major part of acetyl groups (95%) was hydrolyzed during pulping. It was proposed that during bleaching, a low molecular weight xylan fraction associated to residual lignin was removed from pulp and small proportion of MeGlcpA was additionally converted to HexA. The profiles of uronosyl residues in xylans from TCF and ECF bleached sisal pulps were rather different.

This study has been supported by the Spanish Projects AGL2005-01748 and AGL2008-00709 and the EU BIORENEW project (NMP2-CT-2006-26456). We thank CELESA (Tortosa, Spain) for providing the samples. G.M. thanks the Spanish Ministry of Education for a FPI fellowship.

Instituto de Recursos Naturales y Agrobiología de Sevilla, CSIC, P.O. Box 1052, 41080-Seville, Spain and CICECO and University of Aveiro, Department of Chemistry,3810-193 Aveiro, Portugal E-mail address: gisela@irnase.csic.es (G. Marques)

Peer reviewed