Statistical study on fermentation conditions in the optimization of exopolysaccharide production by Lactobacillus rhamnosus 519 in skimmed milk base media

•The chemical and physical factors in exoploysaccharide production were optimized.•The kinetic of growth and exopolysaccharide production was followed.•The exopolysaccharide/cell ratio was compared in Suc-MRS and Suc-SM.•A polynomial model for exopolysachcaride production was proposed.

To optimize the exopolysaccharide (EPS) production by Lactobacillus rhamnosus 519, fermentation experiments using response surface methodology (RSM) were carried out. Studying the effect of different carbon and nitrogen sources on EPS production in skimmed milk (SM) resulted in selecting of sucrose and yeast nitrogen base (YNB) for the optimization experiments. The effect of pH, incubation time, YNB concentration and sucrose concentration on EPS production in SM was studied. The results showed that pH, incubation time and sucrose concentration have significant effect on EPS production (P≤0.05). Maximum EPS production was 256 mg/L and the optimum pH, incubation time, YNB concentration and sucrose concentration for EPS production were found to be 5.7, 49 h, 9.8 g/L and 25.8 g/L, respectively.