Characterisation of watersoluble polysaccharides produced during prehydrolysis of pinus radiata
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 http://hdl.handle.net/10289/4310
Permanent Research Commons link: http://hdl.handle.net/10289/4310
An aqueous prehydrolysate (or prehydrolysis liquor) was produced during a mildhot-water prehydrolysis (90 minute ramp to 175 C) of commercial radiata pinewood chips. Oligosaccharide and polysaccharide material was separated from theconcentrated prehydrolysate using solvent precipitation after most of the noncarbohydratematerial was removed.These polymeric carbohydrates were fractionated based on charge and molecularweight by size-exclusion chromatography (SEC). The fractions were eachanalysed by a number of methods including MALDI-ToF mass spectrometry, andNMR. A number of different types of carbohydrate polymer structures werefound that were produced due to the partial de-polymerisation of the woodhemicelluloses 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 andaccounted for approximately 54% by mass of the polymeric carbohydrates. Mostappeared to contained between 5 and 79 hexose units with differing degrees ofacetylation. The average mol ratio of components in these polymers wascalculated 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 acetylgroups attached at C-2 and C-3 positions of some D-mannopyranosyl units. Theterminal D-galactopyranosyl units were likely to be attached at 1,4,6-linked Dmannopyranosylbranch points. Of the neutral (non-anionic) polysaccharides, thistype was most prevalent in the higher molecular weight fractions.Anionic pentose-based polymers with a backbone of β-1,4-linked D-xylopyranosylunits were also characterised. Identified as (arabino)glucuronoxylans, theyfeatured uronic acid groups consistent with 4-O-methyl-α-D-glucopyranosyluronicacids attached to the C-2 position of some D-xylopyranosyl units. Smalleramounts of terminal α-L-arabinofuranosyl units likely to be attached at β-1,3,4-linked D-xylopyranosyl branch points were also detected. These polymersappeared to mostly contain between 5 and 40 pentose units with between 1 and 4uronic acid groups attached.The anionic fractions (approximately 30% by mass) also contained large amountsof D-galactopyranosyl and L-arabinosyl units along with some D-glucuronic andD-galacturonic acid residues. This suggested the presence of carbohydratesproduced from the partial hydrolysis of arabinogalactans and pectins.The smaller molecular weight fractions of non-anionic polysaccharides wereenriched in both 1,4-linked D-galactopyranosyl units and non-acetylated hexosebasedpolymers that contained between 5 and 30 hexose units; this suggested thatsignificant amounts 1,4-galactan derived carbohydrates were present. Smallamounts of oligomers containing only pentose units were detected in these smallermolecular weight fractions along with what appeared to be other unchargedfragments of the polysaccharide-types that were present in the anionic fractions.
The University of Waikato
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