STRUCTURAL CHARACTERIZATION OF THE EXOCELLULAR POLYSACCHARIDES PRODUCED BY STREPTOCOCCUS-THERMOPHILUS SFI39 AND SFI12

We investigated the structures of the exopolysaccharides (EPSs) produc ed by Streptococcus thermophilus SFi39 and SFi12. Both polymers were f ound to have molecular masses of greater than 2 x 10(6) Da. The SFi39 EPS consisted of D-glucose and D-galactose in a molar ratio of 1:1, wh ereas the SFi12 EPS was composed of D-galactose, L-rhamnose, and D-glu cose in a molar ratio of 3:2:1. Methylation analysis of and nuclear ma gnetic resonance spectra recorded from the native polysaccharide, as w ell as oligosaccharides released by partial acid hydrolysis, allowed t he complete structural determination of the SFi39 EPS, which consists of the following tetrasaccharide repeating unit: [GRAPHICS] Similar sp ectra recorded only from the native polysaccharide were sufficient to allow the structural determination of the SFi12 EPS, which consists of the following hexasaccharide repeating unit: [GRAPHICS] This study sh ows that the texturizing properties of different S. thermophilus ropy strains are based on the production of EPSs exhibiting chemical simila rities but structural differences.