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

Goh KK, Hemar Y, Singh H

Institute of Food, Nutrition, and Human Health, Massey University, Private Bag 11 222, Palmerston North, New Zealand. K.T.Goh@massey.ac.nz

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 approximately 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 x 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 (approximately 1.15) and adopt a random coil conformation.

Published 19 January 2005 in Biopolymers, 77(2): 98-106.
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