Purification and structural characterization and antioxidant activity of levan from Bacillus megaterium PFY-147

An exopolysaccharide (EPS)-producing bacterial PFY-147 was separated from Hiqiher vineyard soil and determined as Bacillus megaterium by 16S rDNA analysis and morphological. The PFY-147-EPS was purified by gel-filtration chromatography. The average molecular weight (Mw) of purified EPS was 1.878 × 10⁶ Da. The total carbohydrate contents, uronic acid and sulfated group content in PFY-147-EPS were found to be 90.37 ± 1.48%, 7.24 ± 0.36% and 2.39 ± 0.36%, respectively. The PFY-147-EPS was found to be a levan containing a backbone of 2,6-substituted β-fructoses by high performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy. The atomic force microscopy (AFM) presented that the levan formed pointed or thorny structural in aqueous solution. Scanning electron microscopy (SEM) of the levan showed compact and nonuniform block sizes morphology. Moreover, the levan exhibited higher thermal stability with a degradation temperature of 265.63 °C in DSC analysis. The levan possessed strong 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, Superoxide anion (O^2-) radical, hydroxyl (OH) radical and and2,20-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS⁺) scavenging activities and strong metal ion chelating activity. The WHC and WSI of levan were 231.29 ± 3.76% and 97.34 ± 1.72%, respectively. These might have implications in food and medicine, as well as in pharmaceutical industries.