title: Structural characterisation of underivatised olive pulp xylo-oligosaccharides by mass spectrometry using matrix-assisted laser desorption/ionisation and electrospray ionisation.
abstract: Purified olive pulp glucuronoxylans, with a Xyl/GlcA ratio of 7:1, were subjected to mild acid hydrolysis and the mixture of oligosaccharides obtained was fractionated by size exclusion chromatography. One elution fraction representative of low molecular weight oligosaccharides was analysed by mass spectrometry using matrix-assisted laser desorption/ionisation (MALDI) and electrospray ionisation (ESI) as ionisation methods, in the positive mode. Both types of spectra showed cationised molecules [M + Na](+) of xylo-oligosaccharides in a range below m/z 1,000. The xylo-oligosaccharide structures identified were series of neutral oligosaccharides of xylose (Xyl(n), n = 3-7), of acidic oligosaccharides substituted by one glucuronic acid (Xyl(n)GlcA, n = 3-5) and by two glucuronic acid residues (Xyl(n)GlcA(2), n = 2 and 3), and also of acidic oligosaccharides substituted with one 4-O-methylglucuronic acid residue (Xyl(n)meGlcA, n = 2-4). The proposed structures were confirmed by tandem mass (MS/MS) spectra obtained using collision induced dissociation of the molecular ions. Fragmentation of cationised adducts of neutral Xyl(n) yielded C- and A-type fragments, while ammonium adducts mainly yielded B-type fragments. The fragmentation of the sodium adducts of acidic oligosaccharides (Xyl(n)meGlcA, Xyl(n)GlcA) resulted in the loss of the substituting residue (GlcA or meGlcA) as the predominant fragment, while the corresponding ammonium adducts yielded B-type fragments.
authors.affiliation: Chemistry Department, University of Aveiro, Campus Santiago, 3810-193 Aveiro, Portugal.
authors.forename: Ana
authors.initials: A
authors.lastname: Reis
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Coimbra
authors.forename: P
authors.initials: P
authors.lastname: Domingues
authors.forename: A J
authors.initials: AJ
authors.lastname: Ferrer-Correia
authors.forename: M Rosário M
authors.initials: MR
authors.lastname: Domingues
mesh_terms: D002240:Carbohydrate Sequence; D008969:Molecular Sequence Data; D015394:Molecular Structure; D008970:Molecular Weight; D031658:Olea / Q000737:chemistry*; D009844:Oligosaccharides / Q000032:analysis / Q000737:chemistry*; D010936:Plant Extracts / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D009844:Oligosaccharides; D010936:Plant Extracts