[Physicochemical property and antioxidant activity of exopolysaccharide produced by endophytic fungal Fusarium redolens 6WBY3 isolated from Fritillaria unibracteata var. wabuensis].

Objective: To study the exopolysaccharide (EPS) of endophytic fungal Fusarium redolens 6WBY3 isolated from Fritillaria unibracteata var. wabuensis (FUW) including its antioxidant activities.

Methods: We isolated the EPS from the culture medium of strain 6WBY3 using the methods of degreasing with organic solvent, precipitation with ethanol, decoloration with macroporous resins, deproteinization with protease in combination with sevag reagent, desalination with dialysis and separation with DEAE-cellulose ion exchange chromatography. Then, we analyzed the EPS fractions using high-performance gel-permeation chromatography with evaporative light scattering detector (HPGPC-ELSD), ultra violet (UV) spectra, scanning electron microscope (SEM), PMP precolumn derivatization with high performance liquid chromatography (PMP-HPLC), fourier transform infrared (FT-IR) spectroscopy and 1H-nuclear magnetic resonance (1H NMR) methods. We evaluated the antioxidant activity of the EPS using DPPH and ABTS radical scavenging activities and iron ion chelating ability methods.

Results: We obtained two homogeneous EPSs, namely 6WBY3EPS-3 and 6WBY3EPS-4, with the molecular weight (Mw) of 17.41×106 and 8.84×105 Da, respectively. 6WBY3EPS-3 was composed of mannose, glucose and galactose in a molar ratio of 8.16:4.96:10.00, while 6WBY3EPS-4 was composed of mannose, rhamnose, glucose and galactose in a molar ratio of 8.08:1.71:6.32:10.00. The results of SEM showed that 6WBY3EPS-3 was the irregular multilateral body, and 6WBY3EPS-4 was rules of quadrilateral body. The results of FT-IR and 1H NMR analysis exhibited that 6WBY3EPS-3 was acidic polysaccharose with abundant galactofuranose, mannofuranose and a few α-D-glucopyranose, while 6WBY3EPS-4 possessed pyranose ring mainly. Those two EPSs had anomeric hydrogen with α-(main) and β-glycosidic configuration. Furthermore, the results of antioxidant activity suggested that both 6WBY3EPS-3 and 6WBY3EPS-4 had a weak DPPH radical scavenging ability, a moderate ABTS radical scavenging activity and a moderate iron ion chelating effect.

Conclusion: The two EPSs from the endophytic fungus 6WBY3 were firstly obtained and investigated. Our investigation indicated that the EPS from 6WBY3 had the application potential as an antioxidant in medicine and food industries. In addition, this work can also provide theory reference for improving development of EPS from other endophytic fungi.