Abstract
The secretion of exopolysaccharides and oxalic acid in cultures of a white rot Ganoderma applanatum strain and a brown rot Tyromyces palustris strain were tested in terms of culture time, pH range, and temperature. The high yield of exopolysaccharides (EPS) required a moderate temperature of 28 °C for G. applanatum and 20 °C for T. palustris. G. applanatum and T. palustris accumulated more EPS when the concentration of the carbon source (maltose for G. applanatum and fructose for T. palustris) was 30 g/L. The results indicate that the production of oxalic acid by G. applanatum is correlated with the initial pH value of the culture medium and the concentration of oxalic acid increased to 1.66 ± 0.2 mM at the initial pH of 6.5 during the fungal growth. During the growth of T. palustris, the reduction of the initial pH value of the growing medium lowered the oxalic acid concentration from 7.7 ± 0.6 mM at pH 6.0 to 1.99 ± 0.2 mM at pH 3.5. T. palustris accumulated considerably more oxalic acid than G. applanatum and its presence did not affect significantly the production of exopolysaccharides. We also observed that the maximum amounts of exopolysaccharides secreted during cultivation of G. applanatum and T. palustris were 45.8 ± 1.2 and 19.1 ± 1.2 g/L, respectively.
Highlights
IntroductionMushrooms have been valued as edible and medicinal resources
For thousands of years, mushrooms have been valued as edible and medicinal resources
The results indicate that the production of oxalic acid by G. applanatum is correlated with the initial pH value of the culture medium and the concentration of oxalic acid increased to 1.66 ± 0.2 mM at the initial pH of 6.5 during the fungal growth
Summary
Mushrooms have been valued as edible and medicinal resources. Fungal submerged cultivations carried out to obtain extracellular active compounds have received great interest. This type of cultures may be affected by many parameters such as the initial medium pH, growing temperature, medium composition which can regulate fungal morphology and structure, the uptake of various nutrients, and the biosynthesis of the active product. Tyromyces palustris belongs to the ecological group of brown rot fungi accumulating organic acid, mainly oxalic acid, in its surroundings, causing a rapid decrease in pH values (Sakai et al 2006). White rot fungi do not accumulate the acid to such a great extent as brown rot fungal strains, but
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