Exopolysaccharide produced by Streptococcus thermophiles S-3: Molecular, partial structural and rheological properties.

Yogurt fermented by Streptococcus thermophiles S-3 strain showed higher viscosity and thicker mouth feel than the ones using other lactic acid bacteria strains, which was due to the higher yield of exopolysaccharide (EPS-3) produced during fermentation process. In the present study, molecular characteristics, partial structural features and rheological properties of EPS-3 were studied using triple-detector HPSEC, NMR and steady & dynamic rheological testing, respectively. EPS-3 showed relatively high molecular weight (574 kDa) and narrow polydispersity Index (1.27). Monosaccharides composition analysis indicated that EPS-3 was composed of N-Acetyl-galactosamine, galactose and glucose in the molar ratio of 1:2:1. Conformational parameters from Mark-Houwink equation (0.68) and Rg & Mw relationships (0.56) both indicated a random coil conformation of EPS-3. Results from steady flow tests showed an obvious shear thinning behavior, which was enhanced with the increased concentrations and decreased temperatures. Dynamic rheology indicated that EPS-3 was reluctant to form gel in water solution (G" > G'). EPS-3 demonstrated compatible interaction with milk protein with less syneresis in comparison to the yogurts adding agar and/or pectin. With all the information provided, this study could help promote the application of both EPS-3 and S. thermophiles S-3 strain in different dairy products.