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Advisor(s)
Abstract(s)
The study carried out in this work concerns the structural characterization of pectic polysaccharides from plum (Prunus domestica L.) and pear (Pyrus communis L.) cell walls and commercial pectin, obtained from Citrus. The -(1→4)-D-galacturonic acid backbone was submitted to a selective hydrolysis with endo-polygalacturonase (EPG) and the fractions with low molecular weight (< 1000 kDa) obtained by size-exclusion chromatography were analysed by mass spectrometry using electrospray ionisation (ESI-MS). The ESI-MS spectra obtained revealed the presence of several [M+Na]+ ions of pectic oligosaccharides identified as belonging to different series, including oligosaccharides constituted only by galacturonic acid residues (GalAn, n=1-5) and galacturonic acid residues substituted by pentose residues (GalA3Pentn, n=1-2). Surprisingly, it was also observed the occurrence of galacturonic acid residues substituted by hexose residues (GalAnHexm, n=2-5, m=1-2). The fragmentation of the observed [M+Na]+ ions, obtained under ESI-MS/MS and MSn allowed to confirm the proposed structures constituent of these pectic oligosaccharides. Furthermore, the ESI-MSn spectra of the ions that could be identified as GalAnHexm (n=2-5, m=1-2) confirmed the presence of Hex or Hex2 residues linked to a GalA residue. Methylation analysis showed the presence, in all EPG treated samples, of terminally-linked arabinose, terminally- and 4-linked xylose, and terminally- and 4-linked glucose. The occurrence of GalA substituted by Glc, and Glc--(1→4)-Glc are structural features that, as far as we know, have never been reported to occur in pectic polysaccharides.
Description
Keywords
Galacturonic acid Pectin Structure Tandem mass spectrometry Electrospray
Citation
Nunes C, Silva L, Fernandes AP, Guiné RPF, Domingues MRM, Coimbra MA. (2012) Occurrence of cellobiose residues directly linked to galacturonic acid in pectic polysaccharides. Carbohydrate Polymers, 87(1), 620-626