Optimization production of exopolysaccharide from Leuconostoc lactis L2 and its partial characterization.

The response surface methodology (RSM) was used to obtain a 7.6-fold increase of exopolysaccharide (EPS) 58.1 ± 0.4 g/L produced by Leuconostoc lactis L2 under the condition of sucrose 91.2 g/L, pH 5.8 and NaAc 1.2 g/L. The L2 EPS consisted of 81.2 ± 0.2% total sugar, 13.3 ± 0.4% uronic acid, 0.1 ± 0.01% protein and 0.4 ± 0.01% sulfate. As for chain conformation, congo red test testified the existence of random coil structure. Circular dichroism (CD) revealed that L2 EPS concentration closely related to its hydrogen-bond interactions and chirality. The L2 EPS exhibited moderate scavenging activities and reducing power. It had high viscosity at high concentration, low temperature and acidic to slight alkalic pH (4.0 to 8.0). The high degradation temperature (290.3 °C) implied the high thermal stability of L2 EPS. With the concentration increase (0 to 1.0 mg/mL), the absolute value of zeta potential and particle size of L2 EPS continually raised. The L2 exhibited a degree of hydrophilicity resulting from water contact angle test. Moreover, L2 EPS showed high efficiency in milk solidification. These results collectively conferred L2 EPS a promising commercial application as a safe food additive and antioxidant.