Structural characterisation of the exocellular polysaccharide produced by Streptococcus thermophilus OR 901

The exocellular polysaccharide of Streptococcus thermophilus OR 901, isolated from partially deproteinised whey, is a heteropolymer of d-galactopyranose and l-rhamnopyranose residues in the molar ratio 5:2. The structure was established by methylation analysis and 1D and 2D NMR spectroscopy of the native polysaccharide, in combination with characterisation of oligosaccharide fragments, obtained by partial acid hydrolysis, using methylation analysis and 1D 1H NMR spectroscopy. The polysaccharide has a branched heptasaccharide repeating unit with the following structure: