title: NMR and rheological study of Aloe barbadensis partially acetylated glucomannan.
abstract: The structural and rheological properties of the Aloe extract (AE) and the polysaccharidic fraction (PF) obtained from the leaves pulp of Aloe barbadensis Miller were investigated. Structural analyses carried out by composition, methylation analysis and NMR spectroscopy showed that PF is mainly constituted by a partially acetylated 4-linked β-d-glucomannan. The acetyl groups are located at C-2, C-2 and C-3, C-3 and/or C-6. The acetylation pattern of this type of polysaccharide was for the first time established using bidimensional NMR analyses. AE and PF aqueous solutions at 25°C showed a non-Newtonian behavior (with pseudoplastic characteristics), however PF showed higher apparent viscosity than AE. Dynamic oscillatory analyses showed that both samples, at the same concentration, behaved as a concentrated solution. PF presented higher values of G' compared with those of AE and this behavior could be consequence of its higher content in partially acetylated glucomannan.
authors.affiliation: Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Paraná, P.O. Box 19046, CEP 81531-980, Curitiba, Paraná, Brazil.
authors.forename: L H
authors.initials: LH
authors.lastname: Campestrini
authors.forename: J L M
authors.initials: JL
authors.lastname: Silveira
authors.forename: M E R
authors.initials: ME
authors.lastname: Duarte
authors.forename: H S
authors.initials: HS
authors.lastname: Koop
authors.forename: M D
authors.initials: MD
authors.lastname: Noseda
mesh_terms: D000107:Acetylation; D000504:Aloe / Q000737:chemistry*; D001938:Brazil; D002236:Carbohydrate Conformation; D004548:Elasticity; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008351:Mannans / Q000737:chemistry* / Q000302:isolation & purification; D010936:Plant Extracts / Q000737:chemistry* / Q000302:isolation & purification; D018515:Plant Leaves / Q000737:chemistry*; D012212:Rheology; D014783:Viscosity
chemical_list: D008351:Mannans; D010936:Plant Extracts; C022901:(1-6)-alpha-glucomannan