Viscometric and static light scattering studies on an exopolysaccharide produced by Lactobacillus delbrueckii subspecies bulgaricus NCFB 2483

The rheological properties and molecular parameters of a purified exopolysaccharide (EPS) produced by a ropy strain of Lactobacillus delbrueckii subsp. bulgaricus NCFB 2483 were investigated. Using capillary viscometry, an intrinsic viscosity of 2,013 mL/g was obtained. The flow curves were fitted by both the Carreau and the Cross equations for shear‐thinning fluids, with the Carreau equation giving a better fit. The Cross equation fitted fairly well the plot of reduced viscosity as a function of reduced shear rate with an exponent value (1 − n ) of ∼ 0.76, typical of random coil polymers. Furthermore, the concentration dependence of the viscosity plot showed a gradient of approximately 1.1 in the dilute regime and 3.3 in the semidilute regime. Molecular parameters were obtained using a multiangle laser light scattering technique. The 2483 EPS molecules had a weight‐average molar mass of approximately 2 × 10 6 Da and a z ‐average root mean square radius (RMS) of approximately 151 nm. From the light scattering data, the bacterial EPS was also found to have a low polydispersity index (∼ 1.15) and adopt a random coil conformation. © 2004 Wiley Periodicals, Inc. Biopolymers, 2005