Exopolysaccharide production by three different strains of Streptococcus thermophilus and its effect on physical properties of acidified milk

Physical and rheological properties of commercial low-fat yogurt and of skim milk acidified with single strains of Streptococcus thermophilus were evaluated. Concentration of exopolysaccharides (EPS) varied from 40 to 168 mg glucose equivalents per liter, and EPS showed different degrees of ropiness. Further characterization of nonropy and ropy EPS from three S. thermophilus strains revealed intrinsic viscosity of 0.130.66 mL/mg, respectively, which had a significant impact on apparent viscosity and the ability of regaining structure after shearing. Compared with regular milk acidification, batch fermentation with supplemented skim milk at constant pH resulted in a strain-dependent increase of EPS yield by a factor of 47.