Extracellular polysaccharide with novel structure and antioxidant property produced by the deep-sea fungus Aspergillus versicolor N2bc

•Exopolysaccharide N1 was produced by deep-sea fungus Aspergillus versicolor N2bc.•Structure of N1 was elucidated by GC–MS, FTIR and NMR.•Main chain of N1 consists of glucopyranose and mannopyranose units.•The side chain contains specific galactofuranose units.•N1 possesses a high antioxidant property in vitro.

An extracellular polysaccharide, N1, was obtained from the culture medium of the deep-sea fungus Aspergillus versicolor N2bc by a combination of ethanol precipitation, ion-exchange and gel filtration chromatography. N1 was a mannoglucogalactan with molecular weight of about 20.5 kDa. Results of chemical and spectroscopic analyses, including Fourier-transform infrared, one- and two-dimensional nuclear magnetic resonance spectroscopy showed that the main chain of N1 consisted of →2)-α-d-Glcp-(1→, →2)-β-d-Glcp-(1→ and →6)-β-d-Manp-(1→ units, substituted at C-6 position of →2)-α-d-Glcp-(1→ units. The branches were composed of galactofuranose-oligosaccharides built up of →5)-β-d-Galf-(1→, →6)-β-d-Galf-(1→ and terminal β-d-Galf units. At an average, there were two branching points for every five sugar residues in the backbone. N1 possessed a high in vitro antioxidant activity as evaluated by scavenging assays involving superoxide, 1,1-diphenyl-2-picrylhydrazyl, hydroxyl radicals and reducing power. The investigation revealed that N1 was a novel antioxidant polysaccharide differing from previously described extracellular polysaccharides and could be a potential antioxidant.