Rheological characterization of the EPS produced by P. acidi-propionici on milk microfiltrate

The EPS produced by Propionibacterium acidi-propionici DSM 4900 has been investigated on a biochemical and a rheological basis. The EPS was mainly composed of galactose, mannose, and glucosamine, with traces of glucose, galactosamine and phosphate. It could be fractionated by anion-exchange chromatography into a major (78%) acidic fraction and a minor neutral component. Viscosity determinations in the absence and presence of salt showed a polyelectrolyte behavior and an intrinsic viscosity of 22 dl/g in 0.01 M NaCl. EPS solutions displayed a shear-thinning behavior with limiting zero-shear viscosity (η0). Variations of the specific limiting viscosity (ηsp0) as a function of concentration indicated three concentration regimes with c∗=0.2 and c∗∗=2 g/l. At relatively low concentration (4–18 g/l), G′ and G″ showed variations with limiting slopes of 2 and 1, respectively, at low frequency and a crossover of these two moduli at high frequency. Master curves of the flow curves as well as of the viscoelastic functions could be built. At the lowest concentrations, the Cox–Merz rule was obeyed while at the highest ones the superposition of |η∗(ω)| and η(γ̇) curves was obtained only at low frequencies. All these rheological determinations show that aqueous solutions of EPS behave as entangled polymer solutions. The polysaccharide does not display gelling properties and could be used as a highly viscous thickener.