Production, purification, and structural characteristics of extracellular polysaccharides derived from Lactobacillus acidophilus

Extracellular polysaccharides (EPSs) derived from Lactobacillus acidophilus BCRC 10695 possess lots of beneficial effects to the host. In seeking to develop a fermentation process to produce EPSs, the culture medium compositions, purification, and structural analysis on EPSs were conducted. The effects of carbon sources, nitrogen sources, and surfactants on EPSs production were explored. Response surface methodology (RSM) was applied for optimizing the cultivation medium. A four-step purification approach was carried out. The gas chromatography-mass spectrometry and NMR were applied for the EPSs structural analysis. The optimal concentrations of sucrose, yeast extract and polysorbate 80 were 10.15 g/l, 25 g/l and 2 g/l respectively. The best EPS production was 923.7 mg/l in the late stationary phase of cultivation for 96 h, close to that in the experiment of 923.6 mg/l. The purification approach was able to remove 99.9% proteins and 98.5% of nucleic acid. Structural analysis showed EPSs consisted of mannose, ribose, glucose and galactose in ratios of 60.0: 22.8: 15.0: 2.2 and comprised (1→ 2) (1→6)-Mannose as backbone.