Parametric characterization of the initial pH effect on the polysaccharides production by Lentinula edodes in submerged culture

Edible fungus Lentinula edodes (L. edodes) produces exo-polysaccharides (EPS), which have been obtained from submerged mycelia cultures. EPS are bioactive products which can be obtained more efficiently from submerged cultures compared to regular production methods from endo-polyssacharides from the fruiting bodies of fungus cultured on solid medium. A common manner to characterize the production ability of L. edodes is using the kinetic parameters evaluation of a suitable mathematical model which takes into account the effects of diverse experimental conditions. The aim of this study is characterize the production of exo-polysaccharide extracts from submerged cultures of three strains of L. edodes (commercial, L5 and L9) using the estimated parameters of the proposed model. The submerged mycelia cultures have fixed initial pH of 6.5, 4.5 and 3.5. Submerged cultures at an initial pH of 4.5 had maximum amounts of biomass of 10.0–15.4 g L⁻¹. The exo-polysaccharide extracts concentrations are in the range of 0.44–0.97 g L⁻¹. The strain L9 obtained a higher yield biomass-substrate (Y_X/S = 1.62). At pH 4.5, the commercial strain obtained a higher yield of product-substrate (Y_P/S = 0.147). If the initial pH is 3.5, the lowest Y_X/S is obtained in values ranging from 0.85 to 1.21. The maximum growth rate was higher for strain L9 at pH 4.5 with μ_max values. The obtained exo-polysaccharide extracts from the three strains have the maximum total carbohydrate amounts of 0.5–0.93 g L⁻¹. A soluble proteins percentage range of 0.16–0.39% is obtained. From the hydrolyzed exo-polysaccharide extracts, glucose, mannose, galactose and arabinose can be identified as the main mono-saccharides. O[sbnd]H bonds, ether bonds, C[sbnd]N bonds and carboxyl bonds are the identified functional groups of the exo-polysaccharides.