Assessing the side chain architecture of dextrans by quantifying enzymatically liberated oligosaccharides

Dextran is a water-soluble α-glucan that can be produced from sucrose using dextransucrases from lactic acid bacteria. Numerous studies have investigated fermentatively and enzymatically produced dextrans and their structure. However, the fine structure of dextrans, particularly their side-chain architecture, was rarely characterized. In this study, a quantitative approach for fine structural characterization of dextrans was developed and applied to ten structurally diverse dextrans. The method was based on endo-dextranase hydrolysis and HPAEC-PAD quantification of the liberated mono-, di-, and oligosaccharides (branched at position O2, O3, and O4) by using their relative response factors (RRFs). The developed method yielded detailed information on the occurrence of different structural elements. To obtain more reliable and quantitative information on side-chain length, TEMPO oxidation was used to selectively oxidize the terminal glucose units in the dextrans. This pretreatment in combination with a subsequent analysis of the enzymatically liberated oligosaccharides allowed for the differentiation between mono-, di-, and trimeric side chains and elongated side chains (> 3 glucose units). The application of the method showed clear differences between the side chain architectures of different O3-branched as well as O4-branched dextrans. Overall, the developed analytical approach provides detailed, unprecedented insights into the fine structure of dextrans.