Polysaccharides from Pleurotus eryngii var. elaeoselini, a New Potential Culinary-Medicinal Oyster Mushroom from Italy

In 2000, a new variety of P. eryngii associated with the root residues of Elaeoselinum asclepium (L.) Bertol. subsp. asclepium (Apiaceae) was described. P. eryngii var. elaeoselini Venturella, Zervakis & La Rocca is an entirely white edible mushroom distributed along the Italian territory where it grows, in autumn and spring ,from 0 to 1200 m a.s.l.. The variety was also found in Spain, on different host plants, i.e. Thapsia villosa L. and Elaeoselinum gummiferum (Desf.). Tutin. Further investigation highlighted the presence of the variety also in France, Switzerland, Malta, Slovenia, Ukraine and Romania on Laserpitium latifolium L. Preliminary investigation carried out on basidiomata of P. eryngii var. elaeoselini collected in Sicily (southern Italy) highlighted a low caloric content and interesting amount of vitamins and mineral salts. In more recent times, extracts of P. eryngii var. elaeoselini, were tested for their in vitro growth inhibitory activity against a group of bacterial reference strains of medical relevance: Staphylococcus aureus ATCC 25923, S. epidermidis RP62A, Pseudomonas aeruginosa ATCC 15442, and Escherichia coli ATCC10536. The extracts of P. eryngii var. elaeoselini inhibited the tested microorganisms in varying degrees. In this study the structural characterization of the aqueous extract obtained from P. eryngii var. elaeoselini is investigated. Different water-soluble glucans were obtained from the fruiting bodies by hot water extraction, ethanol precipitation, dialysis, DEAE cellulose ion exchange chromatography and Sephadex G-100 gel filtration. On the basis of total hydrolysis, methylation analysis and NMR experiments (1H, 13C, DQF-COSY, TOCSY, ROESY, HSQC and HMBC) different polysaccharide fractions were characterized and the structures of the repeating units of the glucan were determined. Monosaccharide composition analysis revealed that the water soluble polysaccharide fraction mainly consisted of glucose (96.3%), with a small amount of mannose (3.7%). The sequence of glycosyl residues in the polysaccharide fractions was confirmed from HMBC experiments. Long-range 13C-1H correlations were obtained from the HMBC spectrum and the cross peaks of both anomeric protons and carbons of each of the sugar moieties were examined and both inter- and intraresidual connectivities were observed. The dry fruiting bodies of P. eryngii var. elaeoselini have shown a significative antioxidant activity with the DPPH test, while the purified polysaccharides have confirmed this activity with the hydroxyl radical scavenging activity test.