title: Arabinan-cellulose composite in Opuntia ficus-indica prickly pear spines.
abstract: The ultrastructure of the spines decorating the cladodes of the cactus Opuntia ficus-indica was investigated by optical microscopy, scanning and transmission electron microscopy, wide angle X-ray, and solid state 13C NMR analyses. Each spine consisted of a compact parallel arrangement of slender cellulosic fibers (0.4 mm in length and 6-10 microm in diameter) with small lumens. The fibers were disencrusted by alkali and sodium chlorite bleaching, yielding a remarkable arabinan-cellulose (1:1) product. X-ray fiber diagrams of the spines before and after purification confirmed the presence of crystalline cellulose domains with molecular axis parallel to the spine axis. CP-MAS 13C T1 NMR data showed a strong interaction at a nanometric level of a fraction of the arabinan and the cellulose crystalline domains. By sequential hydrothermal extractions, followed by a trifluoroacetic acid treatment, a relatively pure cellulose was isolated while the extracted fibers became fibrillated into slender microfibrils having no more than 4-6 nm diameter. The hydrothermal extract yielded the alpha-L-arabinofuranan consisting of a chain of (1-->5)-linked L-arabinosyl residues with branching either at C-2 or C-3 or at both C-2 and C-3. Taken together, these observations suggest that the bulk of the spine fibers consists of an intimate composite of cellulose microfibrils embedded in an arabinan matrix.
authors.affiliation: Centre de Recherches sur les Macromolécules Végétales (CERMAV-CNRS), Université Joseph Fourier, BP 53, 38041 Grenoble 9, France. vignon@cermav.cnrs.fr
authors.forename: M R
authors.initials: MR
authors.lastname: Vignon
authors.forename: L
authors.initials: L
authors.lastname: Heux
authors.forename: M-E
authors.initials: ME
authors.lastname: Malainine
authors.forename: M
authors.initials: M
authors.lastname: Mahrouz
mesh_terms: D001089:Arabinose / Q000031:analogs & derivatives* / Q000737:chemistry; D002482:Cellulose / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004043:Dietary Fiber / Q000032:analysis; D009682:Magnetic Resonance Spectroscopy; D008854:Microscopy, Electron; D029747:Opuntia / Q000737:chemistry*; D010936:Plant Extracts / Q000737:chemistry; D011134:Polysaccharides / Q000737:chemistry*
chemical_list: D004043:Dietary Fiber; D010936:Plant Extracts; D011134:Polysaccharides; C431714:arabinofuranose; C030080:araban; D002482:Cellulose; D001089:Arabinose; C109691:microcrystalline cellulose