Characterization of the exopolysaccharide produced by Streptococcus thermophilus 8S containing an open chain nononic acid

The exopolysaccharide produced by Streptococcus thermophilus 8S in reconstituted skimmed milk is a heteropolysaccharide containing D-galactose, D-glucose, D-ribose, and N-acetyl-D-galactosamne in a molar ratio of 2 : 1 : 1 : 1. Furthermore, the polysaccharide contains one equivalent of a novel open chain nononic acid constituent, 3,9-dideoxy-D-threo-D-altro-nononic acid, ether-linked via C-2 to C-6 of an additional D-glucose per repeating unit. Methylation analysis and 1D/2D NMR studies (H-1 and C-13) performed on the native polysaccharide, and mass spectrometric and NMR analyses of the oligosaccharide obtained from the polysaccharide by de-N-acetylation followed by deamination and reduction demonstrated the hepta saccharide repeating unit to be: -->)-alpha-D-Galp-(1-->2)-beta-D-Ribf-(1-->4)-beta-D-Galp-(1-->4)-beta-D-Glcp-(1-->7')-Sug-(1-->4)-beta-D-GalpNAc-(1--> in which Sug is 6-O-(3',9'-dideoxy-D-threo-D-altro-nononic acid-2'-yl)-alpha-D-glucopyranose.