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Instituto de Recursos Naturales y Agrobiología de Sevilla, CSIC, P.O. Box 1052, E- 41080 Seville, Spain E-mail address: delrio@irnase.csic.es (J.C. del Río), The chemical composition of leaf fibers of abaca (Musa textilis), which are commonly used for high-quality paper pulp production, was thoroughly studied. The results revealed that the lignin content was 13.2 % of the total fiber. The analysis of abaca fibers by Pyrolysis coupled to gas chromatography-mass spectrometry (Py-GC/MS) released predominantly compounds arising from lignin and p-hydroxycinnamic acids, with high amounts of 4-vinylphenol. The latter compound was demonstrated to arise from p-coumaric acid by pyrolysis of abaca fibers in the presence of tetramethylammonium hydroxide (TMAH), which released high amounts of p-coumaric acid (as the methyl derivative). Products from p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) propanoid units, with a predominance of the latter (H:G:S molar ratio of 1.5:1:4.9) were also released after Py-GC/MS of abaca fibers. Sinapyl and coniferyl acetates, which are thought to be lignin monomer precursors, were also found in abaca. The extractives content of the abaca fiber (0.4 %) was low, and the most predominant compounds were free sterols (24% of total extract) and fatty acids (24% of total extract). Additionally, significant amounts of steroid ketones (10%), triglycerides (6%), ω-hydroxyfatty acids (6%), monoglycerides (4%), fatty alcohols (4%) and a series of p-hydroxycinnamyl (p-coumaric and ferulic acids) esterified with long chain alcohols and ω-hydroxyfatty acids were also found, together with minor amounts of steroid hydrocarbons, diglycerides, α-hydroxyfatty acids, sterol esters and sterol glycosides., This study has been supported by the Spanish Ministerio de Ciencia y Tecnología (MCYT) (projects AGL2002-00393 and AGL2005-01748). We thank Isabel M. Rodríguez for sample preparation and technical support. We also thank J.M. Gras and G. Artal (CELESA, Spain) for providing the abaca leaf fibers.

Instituto de Recursos Naturales y Agrobiología de Sevilla, CSIC, P.O. Box 1052, 41080-Seville, Spain; E-mail address: delrio@irnase.csic.es (J.C. del Río), The chemical composition of lignin and lipids of bast fibers from kenaf (Hibiscus cannabinus) used for high-quality paper pulp production was studied. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) of fibers showed a lignin with high syringyl:guaiacyl ratio (5.4) and minor amounts of p-hydroxyphenyl units. Simultaneously, sinapyl and coniferyl acetates were also identified, indicating that this lignin is partially acetylated. p-Hydroxycinnamic acids were only found in trace amounts. The main lipids identified by GC/MS of extracts from kenaf fibers were series of long chain n-fatty acids, waxes, n-alkanes and n-fatty alcohols. Free and esterified sterols and triterpenols, steroid hydrocarbons, steroid and triterpenoid ketones, as well as steryl glycosides were also found. Finally, the fate of the main constituents of kenaf fibers in alkaline pulping was also investigated., This study has been supported by the Spanish Ministerio de Ciencia y Tecnología (MCyT) and FEDER funds (project AGL2002-00393). A.G. acknowledges a "Ramón y Cajal" contract of the Spanish MCyT. We thank CELESA (Tortosa, Spain) for providing the kenaf and pulp samples, S. Camarero (CIB, CSIC, Madrid) for Klason lignin and hemicellulose analyses and A. T. Martínez (CIB, CSIC, Madrid) for critical reading of the manuscript.