Chemical characterization of alkali-soluble polysaccharides isolated from a Boletus edulis (Bull.) fruiting body and their potential for heavy metal biosorption

Wild mushrooms are gathered and consumed in many regions of the world. Edible mushrooms are a good source of valuable nutritious ingredients but they also are able to accumulate heavy metals from the environment. Participation of polysaccharide components of mushroom cell walls in biosorption is poorly understood, therefore, our investigations focussed on an alkali-soluble polysaccharide derived from the cell wall of Boletus edulis. Its chemical structure is described based on chemical analysis, GPC, NMR and FT-IR and other instrumental techniques. The polysaccharide contained mainly C-3 substituted alpha-D-glucose and alpha-D-mannose. The ratio between these components was 10:4. We postulate the polymer is a (1 -> 3)-linked alpha-D-glucan decorated by alpha- (1 -> 3)-D-mannose chains. The molecular mass of the polysaccharide was estimated at about 850 kDa. Biosorption of heavy metal ions (Cd, Cu, Zn and Pb) by the tested polymer was measured using AAS techniques. The polysaccharide has a high ability to accumulate lead and cadmium.