Comparison of the thickening properties of four Lactobacillus delbrueckii subsp. bulgaricus strains and physicochemical characterization of their exopolysaccharides.

It is now well established that physicochemical properties of exopolysaccharides (EPS) can vary between strains of a given species and according to growth conditions. The EPS production of four strains of Lactobacillus bulgaricus was monitored during growth in milk and in a chemically defined media. All strains, including the non-ropy one, produced EPS. The monosaccharide composition, molar mass (M(w)), and intrinsic viscosity of these EPS were determined and compared. Further characterization using high-performance size-exclusion chromatography revealed the presence of two fractions in all EPS: one fraction exhibited a high M(w) and a high intrinsic viscosity while the other had a low M(w) and a low intrinsic viscosity. Strikingly, the EPS synthesized by the non-ropy strain was mainly composed of the low-M(w) fraction while for the ropy strains, the fraction of high M(w) varied between 43 and 90%. According to our results, we propose that the ratio between the high-M(w) and low-M(w) fractions is critical for the texturing properties of L. bulgaricus EPS.