Lentinula boryana, commonly known as Shiitake of the Americas, is found in subtropical and tropical regions of the American continent. The b-D-glucan-(1→3)-type polysaccharides from mushrooms show activity against several diseases. More specifically, polysaccharides from the fruiting body and mycelium of the related mushroom Lentinula edodes (Shiitake) have very interesting chemical and biological properties. In the present work, three submerged fermentations of mycelia of Lentinula boryana were performed, using a medium containing glucose, peptone and malt extract. During the culture parameters such as mycelial growth, glucose consumption, pH and exopolysaccharide (EPS) production were followed. In the first fermentation the pH decreased during the fermentation (6.0 to 3.5), glucose consumption started after the fourteenth day and EPS were produced during the stationary phase of the culture. In the second fermentation the influence of the glucose was tested. In the absence of glucose, mycelial growth and EPS production were lower than in the culture with glucose. In the culture in which glucose was added on the twenty-second day, all parameters quickly changed, rapidly becoming similar to those of the culture that had received glucose at the beginning. In the third fermentation the influence of the aeration was analyzed by growing the flasks with and without shaking. Shaking was very important for good development of the mycelium and EPS production. The EPS obtained from the fermentations were analyzed and were composed mainly of glucose (71-77%), galactose (1-3.7 %) and mannose (16-20%). A new fermentation was performed in which the mycelium were removed by filtration and then the exopolysaccharides were precipitated from the filtrate by freeze-thawing. The precipitate had a similar monosaccharide composition to the other fermentations. The ¹³C-NMR spectrum had C-1 signals at d 102.8, indicating anomeric carbons in the b configuration. An O-substituted C-3 signal appeared at d 86.2, a substituted C-6 signal was observed at d 68.5 and free C-6 at d 60.9. These results suggest the presence of a b-D-glucan-(1→3) and C-6 substituted glucose units from a branched or linear glucan. Methylation analysis and other purification steps will be carried out to furnish more information about the exopolysaccharide structure.
Supported by CNPQ, Fundação Araucária and Pronex–Carboidratos