Antioxidant and antimicrobial activities of exopolysaccharides produced by a novel Aspergillus sp. DHE6 under optimized submerged fermentation conditions

Abstract

Microbial exopolysaccharides are biomacromolecules that are known for their significant importance. Fungal exopolysaccharides are widely utilized in different biotechnological applications such as pharmaceuticals, medicine, cosmetics and food. In this study, fifty fungal isolates were screened for their exopolysaccharides production under submerged fermentation. A novel Aspergillus sp. DHE6 was found to be the best exopolysaccharides producer, with a yield of 7.2 ± 0.24 g/L. Optimization of culture conditions increased exopolysaccharides yield by 3.6-fold (26.1 ± 0.42 g/L). The optimal incubation temperature, initial medium pH, incubation period and the rate of agitation were 30 °C, 6.0, ten days and 150 rpm, respectively. The best carbon and nitrogen sources were glucose at 40 g/L and yeast extract at 1.5 g/L, respectively. Exopolysaccharides were partially purified from Aspergillus sp. DHE6 and characterized using FT-IR-spectrum. Major functional groups were –OH, –CH, –C C, and C– O –C. The partially purified Aspergillus sp. DHE6 exopolysaccharides exhibited excellent antioxidant activity with median effective concentration (EC 50 ) of 573.6 μg/mL using DPPH radical scavenging assay. Agar diffusion assay showed that exopolysaccharide exhibited strong antibacterial activity against the tested hazardous human pathogens ( Staphylococcus aureus , Bacillus subti lis, Bordetella pertussis and Pseudomonas aeruginosa ). Therefore, these results suggest the suitabilility of Aspergillus sp. DHE6 exopolysaccharides for medical purposes and food industry. • Hyper production of exopolysaccharides from a novel terrestrial fungus Aspergillus sp. DHE6. • Optimization of culture conditions increased exopolysaccharides yield by 3.6-fold. • Exopolysaccharides were partially purified and characterized using FTIR-spectrum. • The major functional groups were –OH, –CH, –C C, and C– O –C. • Exopolysaccharides exhibited excellent antioxidant and antibacterial activities.