Summary: Food Ingredient Functionality: Polysaccharides

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  • 1 Physicochemical properties of polysaccharides

  • 1.1 Polysaccharide building blocks

  • What are different properties of alpha and beta linked sugars?

    Alpha --> highly soluble, flexible and easy to degrade by humans (e.g. starch)
    Beta --> highly crystalline, insoluble and non-degradable by humans (e.g. Cellulose)
  • 1.2 Molecular weight

  • What is the difference between poly- or mono-dispersed?

    Polydispersed --> molecules that have a range of different Mw
    Monodispersed --> molecules that all have the same size
  • 2 Analytical techniques

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  • How can the molecular weight distribution be determined?

    By HPSEC (High Performance Size Exclusion Chromatography), where larger molecules are less retained by the column compared to small molecules.
  • How can the monosaccharide composition be determined?

    Hydrolising the polymer to its monomeric building blocks. Analysis of these mono-sugars by HPLC (High Performance Liquid Chromatography) or GC (Gas Chromatography).
  • Only neutral sugars can be analysed by GC and HPLC? Which method can you use to also analyse uronic acids?

    High Performance Ion Exchange Chromatography
  • How can the degree of methylation and acetylation be determined?

    The ester level of polysaccharides can easily be performed after saponification of the ester groups (e.g. Methyl esters, acetyl groups) under alkaline conditions. 
    • Methylation --> methanol is quantified using GC or a spectrophotometric colour assay. 
    • Acetylation --> acetic acid can be quantified using an enzymatic colour assay using spectrometry or by HPLC or GC as well
  • How is the level of methyl esterification quantified, and acetylation?

    Methyl esterification --> mole methanol per 100 moles of galacturonic acid
    Acetylation --> mole acetic acid per 100 moles of sugar residues 
  • How can the level of admiration be determined?

    Complex, but for pure pectins, simply the presence and level of nitrogen is taken as measure for the level of amide groups present.
  • How can the presence of anionic hydrocolloids be determined?

    The presence of negatively charged polysaccharides can be recognised by their complex formation with methylene blue. Can be used to distinguish neutral and charged polysaccharides. The type of polymer cannot be revealed in this way.
  • How can different anionic hydrocolloids be distinguished?

    • (Time consuming) sugar composition analysis
    • Quick methods
      • gel formation upon the addition of calcium --> pectin or alginate
      • pectins --> presence of (esterified) methanol by GC analysis
      • carrageenan --> rhodizonate colour assay --> after acid hydrolysis, the carrageenan bound sulphate can be complexed with rhodizonate and the resulting colour can be measured at 520 nm

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