Structural elucidation of an extracellular polysaccharide produced by Lactobacillus helveticus

An extracellular polysaccharide produced by a strain of Lactobacillus helveticus isolated from cheese milk has been investigated. Sugar and methylation analysis together with 1H and 13C NMR spectroscopy revealed that the polysaccharide is composed of hexasaccharide repeating units. The sequence of sugar residues was determined by use of two-dimensional nuclear Overhauser effect spectroscopy and heteronuclear multiple-bond correlation experiments. The structure of the repeating unit of the exopolysaccharide from L. helveticus is as follows: