Structural characterisation of the exopolysaccharide produced by Lactobacillus delbrückii subspecies bulgaricus rr grown in skimmed milk

Abstract

The exopolysaccharide of Lactobacillus delbrückii subsp. bulgaricus rr. isolated from skimmed milk, is a heteropolymer of D-galactopyranosyl, D-glucopyranosyl, and L-rhamnopyranosyl residues in the molar ratio 5:1:1. The structure was established by linkage analysis and 1D and 2D NMR spectroscopy of the native polysaccharide, in combination with characterisation of oligosaccharide fragments, obtained by Smith degradation and partial acid hydrolysis, using methylation analysis, EIMS, and 1D and 2D 1H NMR spectroscopy. The polysaccharide has a branched heptasaccharide repeating unit with the following structure: ->2)-[beta-D-Galp-(1->3)]-alpha-D-Galp-(1->3)-beta-D-Glcp-(1->3)-beta-D-Glcp-(1->4)]-beta-D-Galp-(1->4)-[alpha-L-Rhap-(1->3)]-alpha-D-Galp-(1->