The response surface optimization of exopolysaccharide produced by XG-3 and its rheological property.

The response surface methodology (RSM) was used to optimize the exopolysaccharide (EPS) production by a lactic acid bacteria (LAB) XG-3. Two-level factorial design screened three significantly influencing factors sucrose, initial pH and sodium acetate. Central composite design (CCD) predicted under the condition of sucrose 80.1 g L, initial pH 5.8 and sodium acetate 3.7 g L, the maximal EPS yield obtained a 2.9-fold increase, reaching 97.5 ± 1.1 g L. This maximal value was far exceeding EPS production by other species strains reported so far. The results suggested that XG-3 had a potential for large-scale EPS production. The rheological properties of XG-3 EPS was further investigated. It was a typical non-Newtonian fluid, exhibiting pseudo-plastic behavior. The EPS concentration and temperature exerted positive and negative impact on apparent viscosity, respectively. The XG-3 EPS maintained relatively higher viscosity at moderate pH (6-8). The intrinsic viscosity [] was 409.7 (25 °C) and 201.7 (35 °C), which was relevant to temperature but irrelevant to EPS concentration. This EPS efficiently coagulated sucrose-supplemented milk in a concentration-dependent manner. These results indicated that XG-3 EPS had an applicable potential in food processing fields especially dairy products.