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 CaCl 2 , 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.