Optimization and characterization of exopolysaccharides with a highly branched structure extracted from Leuconostoc citreum B-2.

The fermentation conditions for exopolysaccharides (EPS) with a highly branched structure extracted from Leuconostoc citreum B-2 were optimized by response surface methodology (RSM). The results showed that under the optimal fermentation conditions of sucrose, yeast extract and pH of 99.80 g/L, 5.94 g/L and 6.12, respectively, the B-2 EPS yield was 59.33 ± 1.34 g/L, which was 5.93 times greater than that from the initial nonoptimized conditions. Chemical composition analysis showed that the carbon, hydrogen, nitrogen and sulfur contents of the B-2 pure EPS (P-EPS) were 39.05 ± 0.25%, 7.19 ± 0.08%, 0.72 ± 0.03% and 0%, respectively. The content of uronic acid was high, reaching 20.94 ± 6.30%. B-2 EPS had certain 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl (·OH), superoxide anion (O2-), hydrogen peroxide (H2O2), nitroso radical (NO2-) scavenging abilities and reducing power. The degradation temperature of the B-2 EPS was 313 °C, indicating that B-2 EPS have high thermal stability. The emulsification effect on vegetable oils was better than that of hydrocarbons. The EPS produced by Leu. citreum B-2 was activated in different concentrations of sucrose-supplemented skimmed milk, which caused the skimmed milk to have different degrees of solidification. Moreover, B-2 EPS promoted the growth of probiotic bacteria, especially Lactobacillus delbrueckii.