Pressurized water extraction of polysaccharides as secondary metabolites from Lentinula edodes

The suitability of pressurized water extraction (PWE) of crude polysaccharides as secondary metabolites from Lentinula edodes was investigated. A series of experiments were carried out to examine the effects of extraction times and pressures. The results indicated that the maximum recovery of polysaccharides was about 90% of the crude polysaccharides from mycelia pellets when the pressure was at 10.1 MPa for 70 min (28 degrees C). This was a drastic improvement over that of boiling water extraction (BWE) at 0.1 MPa for 40 min, which gave only 27.9% recovery. A nitroblue tetrazolium (NBT) reduction assay was used to examine the macrophage stimulating activities (MSA), and it was found that the PWE polysaccharides retained the MSA. The morphology of the macrophage cells treated by PWE polysaccharides was also examined and found to be similar to that of the positive control lipopolysaccharides treated. Finally, gel chromatographic and NMR experiments revealed that both PWE and BWE polysaccharides showed the presence of four similar molecular mass components and the alpha-(1-->4)-D-Glcp and beta-(1-->6)-D-Glcp linkage residues. The improved PWE efficiency is probably due to the possibility that under high pressure, the solid polysaccharide's hydrogen bonding is partially destroyed to increase structure elasticity and water solubility.