Physicochemical properties of a water soluble extracellular homopolysaccharide from Lactobacillus reuteri SK24.003

A water soluble exopolysaccharide was obtained from Lactobacillus reuteri SK24.003 and its rheological and structural properties were investigated. The polysaccharide yield reached around 40.8 g/L for 48 h of fermentation. The purified exopolysaccharide was an α-d-glucan with the molecular weight of 2.50 × 107 g/mol. Thermal analysis showed the exopolysaccharide broke down above 200 °C, the weight dramatically lost (around 53.0%) from 230 to 340 °C and the melting point was 147.7 °C with the enthalpy value of 78.4 J/g. The glucan solution (3.0-9.0%, v/w) has an opalescent, milky-white color and the concentration affected the depth of color. The viscosity increased rapidly with concentration in the range of 3.0-20% (w/v) with relatively high viscosity as well as poor solubility at a concentration higher than 20% (w/v). The solution also exhibited the non-Newtonian pseudoplastic behavior with increasing shear rate from 0.01 to 100 l/s. This glucan had a high viscosity in solution and this could make it suitable for usage as gum substitute in some processing food.