[Media optimization for exopolysaccharide by Pholiota squarrosa (Pers. ex Fr.) Quel. AS 5.245 on submerged...

Our previous work has indicated that mycelium growth and exopolysaccharide accumulation in submerged fermentation by Pholiota squarrosa (Pers. ex Fr.) Quel. AS 5.245 are strongly affected by many internal and external factors, including medium constituents and fermentation conditions. In this study, we use an effective two-phase statistical approach to enhance exopolysaccharide production. In the first phase, Plackett-Burman design was undertaken to evaluate the effects of the twenty factors, i.e., glucose, fructose, maltose, yeast extract, tryptone, K2HPO4, KH2PO4, (NH4)2SO4, NaNO3, FeSO4, MgSO4, MnCl2, ZnCl2, FeCl3, CuSO4.5H2O, vitamin B1, initial pH, the temperature, the medium volume and the duration, to the fermentation. By regression analysis, yeast extract, tryptone, fructose, MgSO4, MnCl2, initial pH and temperature were found to be important for exopolysaccharide production, while glucose, maltose, NaNO3, ZnCl2, vitamin B1, the duration and the volume are important to the mycelium biomass. In the second phase of the optimization process, a response surface methodology (RSM) was used to optimize the above critical internal factors, and to find out the optimal concentration levels and the relationships between these factors. Based on the results of the first phase, a five-level six-factor (yeast extract, fructose, MgSO4, maltose, ZnCl2 and initial pH) central composite rotatable design (CCRD) was employed. By solving the quadratic regression model equation using appropriate statistic methods, the optimal concentrations for obtaining 876.32 microg exopolysaccharide per milliliter of fermentation liquor were calculated as: 6.0g/L yeast extract, 11.5g/L fructose, 0.5g/L MgSO4, 9.6g/L maltose, 38.6mg/L ZnCl2 and with the initial pH 5.3. The experimental data under various conditions have validated the theoretical values.