Extraction, characterization, antioxidant activity and rheological behavior of a polysaccharide produced by the extremely salt tolerant Bacillus subtilis LR-1

Fermented meat possesses plenty of microbial resources. In this study, a novel exopolysaccharide (EPS) secreted by the extreme salt-tolerant Bacillus subtilis LR-1 was researched. The optimal extraction conditions of EPS in fermentation broth (4 °C precipitation temperature, 80 mL/dL ethanol concentration, and 12 h precipitation time for maximum yield of 53.43 g/L) were determined through response surface methodology. The structural component of BL-P1, a purified polysaccharide, was glucose (82.95%) and mannose (13.58%), with an average molecular weight of 41.11 kDa by HPLC and HPGPC analysis. Congo red assay, FT-IR and NMR suggested that BL-P1 was a multi-branched hexasaccharide repeating unit with a tertiary helical structure. BL-P1 was mainly composed of 1,4,6-α-D-Glcp, 1,4-β-D-Glcp, 1,2-α-D-Manp, 1,3-β-D-Glcp, and T-α-D-Glcp at different locations, and contained a backbone fragment of →4,6)-α-D-Glcp-(1→4)-β-D-Glcp-(1→. The result of antioxidant activity showed that BL-P1 displayed strong quenching capacities on DPPH (77.65%) and hydroxyl radicals (93.23%). Additionally, the rheological behavior of BL-P1 showed thermal stability both during heating and subsequent cooling process and under the conditions of high concentration of NaCl and CaCl2, and had good synergistic thickening performance with gellan gum. In general, BL-P1 screened from the extreme salt-tolerant Bacillus subtilis LR-1 exhibited the potential application as a natural antioxidant and additive in functional food and related industries.