Approaches for molecular characterization of modified biopolymers

• Main Author: ter Haar, R.
• Other Authors: Gruppen, Harry, Schols, Henk
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2011
• Subjects: analytical methods; biopolymers; modification; analytische methoden; biopolymeren; modificatie; Antarc*; Antarctica
• Online Access: https://research.wur.nl/en/publications/approaches-for-molecular-characterization-of-modified-biopolymers

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 ...