Structural characterisation of the exopolysaccharide produced by Streptococcus thermophilus EU20

Streptococcus thermophiha EU20 when grown on skimmed milk secretes a high-m olecular-weight exopolysaccharide that is composed of glucose, galactose an d rhamnose in a molar ratio of 2:3:2. Using chemical techniques and 1D and 2D-NMR spectroscopy (H-1 and C-13) the polysaccharide has been shown to pos sess a heptasaccharide repeating unit having the following structure: [GRAPHICS] Treatment of the polysaccharide with mild acid (0.5 M TFA, 100 degreesC for 1 h) liberates two oligosaccharides; the components correspond to the repe ating unit and a hexasaccharide equivalent to the repeating unit minus the terminal alpha -L-Rhap. (C) 2001 Elsevier Science Ltd. All rights reserved.