Rheological behaviour of probiotic bacteria dispersed in maltodextrin and sucrose solutions

Abstract: Probiotic bacteria are live microorganisms, which manifest health benefits in humans. The goal of this work was to characterize rheological properties of probiotic bacteria (Lactobacillus reuteri) formulation in which maltodextrin and sucrose used as excipients. To fulfil the goal, first, thermal, structural and rheological properties of maltodextrin, sucrose solutions and probiotic bacteria slurry were investigated. Probiotic bacteria formulations were prepared by adding probiotic bacteria slurry to maltodextrin and sucrose solutions at different mass fractions. Finally, rheological properties of probiotic bacteria formulations were evaluated. From TGA, the water content of PB slurry including intracellular water found 81%. In DLS, three different types of aggregations of maltodextrin were observed and characteristic size of Probiotic bacteria found 1μm. The optical microscopy results indicate that at the liquid - air interface and in dehydrated state the bacteria are birefringent and arranged in an ordered fashion resembling a nematic phase. Most of the MD, SU and MD+SU solutions show Newtonian behaviour. MD and SU solutions show strong increase of viscosity with increasing concentration. This dependence can be described by using the Spurlin–Martin–Tennent’s model. The viscosities of MD+SU solutions increase with increasing proportion of maltodextrin. The oscillation data of MD and MD+SU solutions can be described by Maxwell model. The viscosities of MD, SU, MD+SU mixed solutions decrease with increasing temperature. This temperature dependency can be described by Arrhenius model of viscosity. At very high concentrations of MD, a deviation from this behaviour is observed. The probiotic bacteria slurry shows shear thinning behaviour at low shear stress and Newtonian behaviour at higher stresses. All probiotic formulations in which probiotic bacteria dispersed in maltodextrin and sucrose solutions show Newtonian behaviour. The viscosities of maltodextrin solutions and MD+SU mixed solutions decrease by addition of probiotic bacteria whereas mixed effects of probiotic bacteria addition on the viscosity of sucrose solutions were observed. The viscosity of probiotic bacteria slurry decreases with increasing temperature, although deviations from this behavior are seen at certain conditions.