Approaches for molecular characterization of modified biopolymers

R. ter Haar

Research output: Thesisinternal PhD, WU

Abstract

In this thesis, research on the molecular characterization of products obtained after structure modification of oligosaccharides, starch, model peptides, and bovine α-lactalbumin is described. The research goals comprised the development of analytical tools as well as the elucidation of molecular structures by using these tools.

The structure of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized gelatinized potato starch was analyzed after degrading it to fragments, using acid hydrolysis and methanolysis. Mass spectrometric analysis of the resulting oligomers revealed that the TEMPO oxidation proceeds in a block-wise manner. Also, a high acid-resistance of especially the α(1à4) glucuronic acid-glucuronic acid glycosidic linkage was observed, making oxidized starch a possible dietary fiber. The structure of epoxidized granular 1-allyloxy-2-hydroxypropyl-waxy maize starch was characterized by a similar approach using enzymatic hydrolysis. This showed that the created epoxy groups took part in subsequent reactions to form cross links and/or diols.

Discrepancies in literature concerning the specificity of immobilized Candida antarctica lipase B in the acylation of oligosaccharides were explained. Molecular sieves, used to remove free water from the organic reaction medium, were found to be responsible for the catalysis of side-reactions. Next, hydroxy-aryl esters of various oligosaccharides were chemically produced. Via a peroxidase-mediated reaction, these esters could subsequently be coupled to the model peptide Gly-Tyr-Gly, as a proof-of-principle for enzymatic protein glycosylation.

In addition, α-lactalbumin was glycated with various saccharides via the Maillard reaction. Products were studied using UPLC-ESI-TOF MS and size exclusion chromatography. A detailed view on the extent of glycation and the dispersity of the products was obtained. The glycation rate, extent of protein cross-linking, and the foam stability of the glycated α-lactalbumin depended on the type of saccharide used. Similar saccharide structures led to similar behavior. The glycation rate and the extent of protein cross-linking decreased when the degree of polymerization of the saccharide increased. Dehydrated Amadori products, as identified by UPLC ESI-TOF MS, were found to be an indicator of the formation of cross-linked protein.

  

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Gruppen, Harry, Promotor
  • Schols, Henk, Co-promotor
Award date28 Oct 2011
Place of Publication[S.l.]
Print ISBNs9789461730503
Publication statusPublished - 2011

Keywords

  • biopolymers
  • modification
  • analytical methods

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  • Projects

    Novel carbohydrate-protein conjugates through enzymatic synthesis

    ter Haar, R., Gruppen, H. & Schols, H.

    15/09/0728/10/11

    Project: PhD

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