Structure determination of the exopolysaccharide of Lactobacillus fermentum TDS030603-a revision.

The highly viscous neutral exopolysaccharide, produced in large amounts by Lactobacillus fermentum TDS030603 in MRS broth and in a chemically defined medium supplemented with glucose, was investigated by GLC(-EIMS) monosaccharide and methylation analysis, periodate oxidation, MALDI-TOF mass spectrometry, and 1D/2D NMR spectroscopy. The GLC(-EIMS) analyses showed that the EPS contained d-glucose and d-galactose in an averaged molar ratio of 2.6:1.0, consisting of terminal d-Glcp, 3-substituted d-Glcp, 2,3-disubstituted d-Glcp, and 6-substituted d-Galp in an averaged molar ratio of 1.3:1.0:1.1:1.1, with a trace of terminal d-Galp (0.1). Combined with the NMR data of the EPS (previously reported constituent analysis: terminal Glcp, 3-substituted Glcp, 2,3-disubstituted Glcp, and 6-substituted Galp in an averaged molar ratio of 1.2:1.1:1.0:1.1) and oligosaccharides isolated after partial acid hydrolysis, a branched tetrasaccharide repeating unit, with some heterogeneity in the side chain, having the following structure is proposed: [fromula see text].