Characterization and antioxidant activity for exopolysaccharide from submerged culture of Boletus aereus

Three polysaccharide fractions (designated as Fr-I, Fr-II and Fr-III) were successfully purified from the crude exopolysaccharide (EPS) produced from submerged culture of Boletus aereus by gel filtration chromatography on Sepharose CL-6B. The size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS) system showed that the average molecular weights (Mws) of these three fractions were 1.365 x 10(6), 1.048 x 10(5) and 2.471 x 10(4) g/mol, respectively. The SEC/MALLS also revealed that the molecular conformation of the Fr-I was a random coil, with Fr-II being a rigid rod in aqueous solution. Moreover, monosaccharide composition analysis indicated that Fr-I was mainly composed of glucose, while both of Fr-II and Fr-III were mainly composed of mannose and glucose. Then, FT-IR spectral analysis of the purified EPS revealed prominent characteristic groups. Furthermore, thermo gravimetric analysis (TGA) indicated the degradation temperature of the Fr-I (170 degrees C) was higher than those of Fr-II (156 degrees C) and Fr-III (155 degrees C). Finally, on the basis of the antioxidant activity test in vitro, Fr-I exhibited the highest antioxidant ability among these samples, which might be attributed to the monosaccharide composition and molecular weight in the EPS fraction. (C) 2014 Elsevier Ltd. All rights reserved.