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      Characterisation of watersoluble polysaccharides produced during prehydrolysis of pinus radiata

      McDonald-Wharry, John
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      McDonald-Wharry, J. (2010). Characterisation of watersoluble polysaccharides produced during prehydrolysis of pinus radiata (Thesis, Master of Science (MSc)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/4310
      Permanent Research Commons link: https://hdl.handle.net/10289/4310
      Abstract
      An aqueous prehydrolysate (or prehydrolysis liquor) was produced during a mild

      hot-water prehydrolysis (90 minute ramp to 175 C) of commercial radiata pine

      wood chips. Oligosaccharide and polysaccharide material was separated from the

      concentrated prehydrolysate using solvent precipitation after most of the noncarbohydrate

      material was removed.

      These polymeric carbohydrates were fractionated based on charge and molecular

      weight by size-exclusion chromatography (SEC). The fractions were each

      analysed by a number of methods including MALDI-ToF mass spectrometry, and

      NMR. A number of different types of carbohydrate polymer structures were

      found that were produced due to the partial de-polymerisation of the wood

      hemicelluloses during the prehydrolysis process.

      The O-acetylated (galacto)glucomannans were the most extensively characterised.

      These partially-acetylated hexose-based polymers were the main type found and

      accounted for approximately 54% by mass of the polymeric carbohydrates. Most

      appeared to contained between 5 and 79 hexose units with differing degrees of

      acetylation. The average mol ratio of components in these polymers was

      calculated to be approximately 3.7 : 1.3 : 1 : 0.2 (D-mannosyl : acetyl : D-glucosyl

      : D-galactosyl). They had a structure consistent with a linear backbone of β-1,4-

      linked D-mannopyranosyl and β-1,4-linked D-glucopyranosyl units with acetyl

      groups attached at C-2 and C-3 positions of some D-mannopyranosyl units. The

      terminal D-galactopyranosyl units were likely to be attached at 1,4,6-linked Dmannopyranosyl

      branch points. Of the neutral (non-anionic) polysaccharides, this

      type was most prevalent in the higher molecular weight fractions.

      Anionic pentose-based polymers with a backbone of β-1,4-linked D-xylopyranosyl

      units were also characterised. Identified as (arabino)glucuronoxylans, they

      featured uronic acid groups consistent with 4-O-methyl-α-D-glucopyranosyluronic

      acids attached to the C-2 position of some D-xylopyranosyl units. Smaller

      amounts of terminal α-L-arabinofuranosyl units likely to be attached at β-1,3,4-

      linked D-xylopyranosyl branch points were also detected. These polymers

      appeared to mostly contain between 5 and 40 pentose units with between 1 and 4

      uronic acid groups attached.

      The anionic fractions (approximately 30% by mass) also contained large amounts

      of D-galactopyranosyl and L-arabinosyl units along with some D-glucuronic and

      D-galacturonic acid residues. This suggested the presence of carbohydrates

      produced from the partial hydrolysis of arabinogalactans and pectins.

      The smaller molecular weight fractions of non-anionic polysaccharides were

      enriched in both 1,4-linked D-galactopyranosyl units and non-acetylated hexosebased

      polymers that contained between 5 and 30 hexose units; this suggested that

      significant amounts 1,4-galactan derived carbohydrates were present. Small

      amounts of oligomers containing only pentose units were detected in these smaller

      molecular weight fractions along with what appeared to be other uncharged

      fragments of the polysaccharide-types that were present in the anionic fractions.
      Date
      2010
      Type
      Thesis
      Degree Name
      Master of Science (MSc)
      Supervisors
      Manley-Harris, Merilyn
      Publisher
      The University of Waikato
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