A viscous extracellular polysaccharide produced by Lactobacillus helveticus K16 has been investigated. Sugar and methylation analysis, 1 H and 13 C NMR spectroscopy revealed that the polysaccharide is composed of a hexasaccharide repeating unit. The sequence of sugar residues was determined by use of two-dimensional nuclear Overhauser effect spectroscopy and heteronuclear multiple bond connectivity experiments. The structure of the repeating unit of the exopolysaccharide from L. helveticus K16 is as follows: Download full-size image