Purification of polysaccharide from Lentinus edodes water extract by membrane separation and its chemical composition and structure characterization

Currently, most of the polysaccharide fractions are purified using the methods usually limited to the laboratory scale or easily raising question of residual reagent, which may obstruct the future application of polysaccharide. In our study, we employed sequential ultrafiltration with different membranes combined with HPGPC to purify polysaccharide fractions from the water extract of Lentinus edodes directly. The chemical composition, morphology and structure characteristic were analyzed by chemical methods and instrumental analysis including automatic amino acid analyzer, Elemental Analyzer, SEM, HPGPC, HPAEC-PAD, FT-IR and NMR. Results indicated that three polysaccharide fractions named as LE-UF-1, LE-UF-2 and LE-UF-3 were successfully purified using ultrafiltration membranes with MWCO of 2.5, 5 and 10 kDa in sequence. Mw and polysaccharide content of LE-UF-1 (~136 kDa, 86.11%) were the highest, followed by LE-UF-2 (14–61 kDa, 49.82%) and LE-UF-3 (14–35 kDa, 22.44%). Surprisingly, LE-UF-2 had 11.73% amino acid, and LE-UF-3 had 19.64% amino acid. The polysaccharide in all the three fractions was heteropolysaccharide that mainly consisted of Glc, Gal and Man. There might be more β-sugar residues in LE-UF-1 and LE-UF-2, while more α-sugar residues in LE-UF-3. Our study provides a greener and more efficient potential procedure for large-scale polysaccharide purification, and is able to prepare the polysaccharide fractions from Lentinus edodes that may be used for food or drug development.