Optimization, partial characterization and antioxidant activity of an exopolysaccharide from Lactobacillus plantarum KX041

A novel exopolysaccharide (EPS), promisingly served as natural alternatives of commercial additives, was obtained from a culture of Lactobacillus plantarum KX041, a specie of lactic acid bacteria (LAB) regarded as Generally Recognized as Safe Foods (GRAS). However, the low yield severely hindered further study and application of the EPS. The influences of medium components and culture conditions were investigated and the optimal conditions of the EPS production were successfully obtained by response surface methodology (RSM). Maximum EPS production 599.52 mg/mL (about 3 folds than the original production) was obtained at optimal conditions of soybean peptone (20 g/L), fermentation temperature (35 °C) and initial pH (6.38). The EPS had a molecular weight of 38.67 KDa and it consisted of arabinose, mannose, glucose and galactose in a molar ratio of 0.95:12.94:7.26:3.31. A specific spectrogram of neutral polysaccharide was obtained by FT-IR analysis, and the EPS also exhibited higher thermal stability with a degradation temperature of 289.01 °C in DSC analysis. A comprehensive investigation of antioxidant activity in vitro indicated that the EPS possessed superior antioxidant activity with the EC50 value of ABTS, DPPH, hydroxyl and superoxide free radical scavenging were 0.2, 1.4, 1.7 and 5.6 mg/mL, respectively. Furthermore, combined with reducing power analysis, it suggested that the EPS not only acted as electrons donor to directly react with free radicals, but also exerted antioxidant activity with other mechanisms which need to be studied further. All these results collectively shown that as a natural compound, the EPS produced by Lactobacillus plantarum KX041 had a great potential to be developed as natural antioxidants or functional additive in food industry.