Structure characterization, modification through carboxymethylation and sulfation, and in vitro antioxidant and hypoglycemic activities of a polysaccharide from Lachnum sp.

An exopolysaccharide (LEP) was isolated from the fermented broth of Lachnum YM240. The structure of LEP was analyzed by fourier transform infrared spectrometry (FT-IR), high performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GCMS), and 1D and 2D-nuclear magnetic resonance spectroscopy (NMR). The carboxymethylated and sulfated derivatives of LEP was difined as CLEP and SLEP which with molecular weight (Mw) of 3.64 × 104 and 2.17 × 104 g/mol respectively. The yield of CLEP and SLEP were 60.27 ± 3.04% and 42.88 ± 2.16%, with degree of substitution (DS) values of 0.36 and 0.14 respectively. The result of antioxidant activity and hypoglycemic activity showed that CLEP with higher (DS) and (Mw) exhibited stronger antioxidant abilities on scavenging DPPH radical and hydroxyl radical compared with SLEP and LEP, with EC50 value of 1.05 and 0.80 mg/mL respectively. The reducing power of CLEP (0.533) and SLEP (0.428) was greater than LEP (0.353). In addition, CLEP and SLEP showed higher alpha-glucosidase inhibitory and alpha-amylase inhibition activities and exhibited significant inhibitory effects against the diffusion of glucose compared to LEP. Furthermore, CLEP and SLEP showed more significant effects than LEP at the same dosage, indicating that carboxymethylation and sulfation modifications were effective ways to enhance antioxidant and hypoglycemic activities of the polysaccharide.