Structural analysis and molecular characterization of exopolysaccharides produced by submerged mycelial culture of Collybia maculata TG-1

Two different exopolysaccharides (EPSs) were obtained by submerged mycelial culture of an edible mushroom, Collybia maculata TG-1, and their chemical structures were studied by gas chromatography (GC), Fourier transform-infrared (FT-IR) spectroscopy, methylation analysis, and NMR spectroscopy. A compositional analysis result by GC indicated that both EPSs (designated as Fr-I and Fr-II) were galactomannans consisting of mainly mannose and galactose. FT-IR spectroscopy was used for obtaining vibrational spectra of the EPSs. In the anomeric region (950-700 cm−1), both EPSs exhibited the characteristic absorption at 810 cm−1 corresponding to the existence of mannose. The obvious absorption peaks at 910 and 880 cm−1 in both EPSs revealed the co-existence of α and β configurations. In a 13C NMR analysis, two anomeric peaks appeared at 102.0 and 99.6 ppm, which were assigned to the mannose (C-1) and galactose (C-1) residues, respectively. In a GC-MS analysis, the methlylation data confirmed the presence of a (1→3)-linked β-d-mannopyranosyl backbone mainly substituted O-6 by galactopyranosyl residues. The size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS) system showed that the weight-average molecular mass of the Fr-I and Fr-II were 7.95×104 and 2.09×104 g/mol, respectively. Moreover, the SEC/MALLS revealed that the molecular conformation of the Fr-I was a random coil, with Fr-II being a rigid rod in aqueous solution.