Screening and functional identification of a Lactobacillus strain with high exopolysaccharide production

Abstract:

In order to enrich the microbial resources that can be used in functional foods, a Bacillus (XQ) strain with high production of extracellular polysaccharide and lactic acid was isolated from the fermented rice cake workshop in Huaiyuan, Sichuan，and it was identified as Bacillus pumilus. The lactic acid content detected by HPLC was 8 mg/mL and the concentration of crude exopolysaccharide detected by the phenol-sulfuric acid method was 7.16 mg/mL. It was determined by the filter paper method that the extracellular polysaccharides and fermentation broth had inhibitory effects on common foodborne pathogens Salmonella, Staphylococcus aureus, and Escherichia coli. The extracellular polysaccharide was further separated to obtain neutral polysaccharides E1 and acidic polysaccharides E2. When the concentration was 10 mg/mL, the scavenging activity of E1 on hydroxyl radicals was 3.24%, while the scavenging activity of hydroxyl radicals of E2 was as high as 84.58%; the scavenging activities of E1 and E2 on DPPH free radicals were 26.07% and 47.03%, respectively. E2 also had obvious anti-tumor activity. When the concentration was 4 mg/mL, the growth inhibition rate of E2 on A549 cells could reach 81.30%, and when the concentration was 6 mg/mL, the growth inhibition rate of E2 on HepG2 cells was 53.40%. In the simulated gastrointestinal tolerance experiments, it was found that XQ has a high tolerance to trypsin, pepsin and bile salts. In terms of safety, XQ has not been found to have hemolysis, is not resistant to Gram-positive antibiotics, and has good drug safety. In summary, this study indicated that XQ can be used as a potential probiotic.