Isolation, purification and characterization of exopolysaccharide produced by Leuconostoc pseudomesenteroides YF32 from soybean paste.

A water-soluble exopolysaccharide (EPS)-producing strain YF32 was isolated from soybean paste, which was then identified as Leuconostoc pseudomesenteroides. After culturing the strain in Man-Rogosa-Sharpe (MRS) medium containing 5% sucrose at 30°C for 48h, the EPS was purified, and a yield of 12.5g/L was achieved. The weight-average molecular weight (Mw) was 5.54×106Da by high-performance size-exclusion chromatography (HPSEC). The structural characterization of the purified EPS was determined by gas chromatography (GC), Fourier transform infrared (FT-IR), 1H, 13C nuclear magnetic resonance (NMR) spectroscopy. The results demonstrated that the exopolysaccharide was glucan 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 degradation temperature (Td) of EPS was 307.62°C, which suggested that dextran exhibited high thermal stability. YF32 dextran also showed high water solubility and emulsibility. All results suggested that dextran has the potential to be applied in food fields as a food additive.