Effects of carbohydrate source on physicochemical properties of the exopolysaccharide produced by Lactobacillus fermentum TDS030603 in a chemically defined medium

A thermophilic lactic acid bacterium, Lactobacillus fermentum TDS030603, produced about 100 mg/L of EPS in purified form when grew in de Man–Rogosa–Sharpe (MRS) broth. The 1% (w/v) solution of the purified EPS was highly viscous, exhibiting an apparent viscosity (ηapp) of 0.88 Pa s at a shear rate of 10/s. To investigate the impact of carbohydrate source on the production yield and chemical structure of EPS and the viscosity of EPS solution, a chemically defined medium (CDM) has been developed. Results of TLC, HPLC, and 1H NMR spectroscopy indicated that the chemical structures of EPS released in MRS and in the CDM supplemented with glucose, galactose, lactose or sucrose were very similar. All the 1% solutions of EPSs released in CDMs were highly viscous similar to the EPS released in MRS, but their viscosities appeared to differ, presumably because of the differences in their molecular mass distributions.