Optimization of the fermentation process, characterization and antioxidant activity of exopolysaccharides produced from Azotobacter As101

Abstract

Azotobacter was selectively isolated and purified from the soil samples of Xinjiang Salt Lake Scenic spot, the fermentation technology of exopolysaccharides (EPS) by Azotobacter was optimized, and the antioxidant activity of exopolysaccharides (EPS) was studied. The bacteria were isolated and purified from the soil samples by the scribing method and the 16SrRNA gene was used for molecular identification. The carbon source, fermentation time, inoculation amount and pH of target bacteria in the exopolysaccharides (EPS) fermentation process were optimized through single-factor experiments and their antioxidant activity was measured. Eight types of Azotobacter were isolated and purified from the soil samples of Salt Lake scenic spot. Among them, As101, which showed 99.58% homology with Azotobacter salinestris, was selected as the target strain. Through single-factor experiments which used exopolysaccharides (EPS) yield and exopolysaccharides content as indexes, the optimal conditions for the As101 fermentation process were determined as follows: fermentation temperature 35, fermentation time 96h, pH 7 and mannitol as carbon source. Exopolysaccharides content from Azotobacter salinestris was 61.35% and the yield was 6.34 g/L. The results of the exopolysaccharides (EPS) antioxidant activity experiment under optimal conditions showed that As101 EPS had excellent scavenging ability against DPPH free radical, ABTS free radical and hydroxyl free radical, with IC50 values of 6.11 mg/ml, 2.42 mg/ml and 9.57 mg/ml, respectively. As101 with high yield and high exopolysaccharides content was isolated from saline soil in a special environment of Xinjiang, and the EPS obtained showed excellent antioxidant activity. The Azotobacter found in this study would provide the material basis for further opening up the adsorption of exopolysaccharides on heavy metals and the improvement of saline-alkali soil and contribute to further understanding of the structure and other activities of exopolysaccharides derived from Azotobacter.