Fine structures of different dextrans assessed by isolation and characterization of endo-dextranase liberated isomalto-oligosaccharides

Chromatographic analysis of endo-dextranase liberated branched oligosaccharides proved to be a valuable approach to differentiate dextrans from fermented food products or isolated lactic acid bacteria. Because these hydrolysis products also yield valuable information on the dextran fine structures, several branched isomalto-oligosaccharides were liberated from different dextrans and chromatographically purified. Mass spectrometry and two-dimensional NMR spectroscopy were used for structural characterization of the oligomers. Isomalto-oligosaccharides from L. reuteri TMW 1.106 dextrans were exclusively O4-branched. Furthermore, they contained only monomeric side chains and at least one unsubstituted backbone unit between ramified residues. In contrast, O3-branched oligosaccharides with monomeric as well as elongated side chains were isolated. The varying abundance of the O3-branched oligosaccharides suggests that side chain length is a major factor for structural differences between dextrans. Overall, we demonstrated that chromatographic analysis of endo-dextranase liberated isomalto-oligosaccharides provides valuable information on the structural properties and supplements conventional methods such as methylation analysis.