PRODUCTION BY AND ISOLATION OF EXOPOLYSACCHARIDES FROM STREPTOCOCCUS-THERMOPHILUS GROWN IN A MILK MEDIUM AND EVIDENCE FOR THEIR GROWTH-ASSOCIATED BIOSYNTHESIS

Four Streptococcus thermophilus strains (Strep. thermophilus ETC, Stre p. thermophilus LY03, Strep. thermophilus 480 and Strep. thermophilus Sfi20) have been examined for their exopolysaccharide production capac ity. All strains produced a polymer composed of the neutral sugars glu cose and galactose, but in different ratios. It was clearly shown that the biosynthesis of exopolysaccharides from Strep. thermophilus LY03 is growth-associated and hence displays primary metabolite kinetics. T he monomer ratio of the exopolysaccharide synthesized did not vary thr oughout the fermentation cycle. The production kinetics and exopolysac charide yields were strongly dependent on the fermentation conditions. Physical factors such as temperature, pH and oxygen tension as well a s chemical factors (medium composition, initial lactose concentration, carbon/nitrogen levels) were of utmost importance.