Optimization, purification and structural characterization of a dextran produced by L. mesenteroides isolated from Chinese sauerkraut

A higher yield of dextran strain Leuconstoc mesenteroides TDS2-19 was isolated from Chinese sauerkraut juice. Effects of the three main factors on exopolysaccharide (EPS) yield were investigated by central composite design (CCD) and the optimum composition was sucrose 117.48 g/L, sodium acetate 4.10 g/L, and initial pH 6.88. Optimum results showed that EPS yield was increased to 71.23 ± 2.25 g/L in 48 h fermentation, 31.24% higher than before. The molecular weight (Mw) of ESP was 8.79 × 107 Da, as determined by high-performance size-exclusion chromatography (HPSEC). Fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance spectra (NMR) showed that the polysaccharide synthesized by L. mesenteroides TDS2-19 in the MRS medium was dextran with a peak, a linear backbone composed of consecutive α-(1 → 6)-linked d-glucopyranose units. No branching was observed in the dextran structure. The present study suggested that L. mesenteroides TDS2-19 might be used for the industrial-scale production of linear dextran.