Behavior of the rheological parameters of exopolysaccharides synthesized by three lactic acid bacteria

Exopolysaccharides (EPS) from Lactobacillus delbrueckii subsp delbrueckii (L. delbrueckii), Bifidobacterium infantis ATCC 15697 (B. infantis) and Streptococcus thermophilus Th4 (S. thermophilus) were produced and isolated form whey fermentations. A central composition rotatable design was employed to study the effects of EPS concentration, pH and ionic strength on the parameters in the Power Law. EPS and NaCl concentrations of 10.25 g/L and 0.08 M, respectively, and pH 5 were considered at the central point. Quadratic models for explaining the observed responses were determined using the surface response methodology. The three EPS presented a shear – thinning behavior. At the highest EPS concentration (20 g/L) consistencies of solutions of EPS from B. infantis, L. delbrueckii and S. thermophilus were 9.518, 17.706 and 13.136 mPa s, respectively. Contour plots, generated from the fitted models, were used to define the pH–ionic strength regions for higher consistencies and lower flow behavior index. Results suggested that EPS synthesized by B. infantis and S. thermophilus are polyelectrolytes while those produced by L. delbrueckii are neutral polysaccharides.