Application of Response Surface Methodology for Optimization of Extracellular Glucoamylase Production by Candida guilliermondii.

OBJECTIVE: Glucoamylase is among the most important enzymes in biotechnology. The present study aims to determine better conditions for growth and glucoamylase production by Candida guilliermondii and to reduce the overall cost of the medium using Box-Behnken design with one central point and response surface methodology. METHODOLOGY: Box-Behnken factorial design based on three levels was carried out to obtain optimal medium combination of five independent variables such as initial pH, soluble starch, CH4N2O, yeast extract and MgSO4. Forty one randomized mediums were incubated in flask on a rotary shaker at 105 rpm for 72 h at 30°C. RESULTS: The production of biomass was found to be pH and starch dependent, maximum production when the starch concentration was 8 g L-1 and the initial pH was 6, while maximum glucoamylase production was found at 6.5 of initial pH, 4 g L-1 yeast extract and 6 g L-1 starch, whereas yeast extract and urea were highly significant, but interacted negatively. Box-Behnken factorial design used for the analysis of treatment combinations gave a second-order polynomial regression model with R2 = 0.976 for Biomass and R2 = 0.981 for glucoamylase. CONCLUSION: The final biomass and glucoamylase activity obtained was very close to the calculated parameters according to the p-values (p<0.001), the predicted optimal parameters were confirmed and provides a basis for further studies in baking additives and in the valuation of starch waste products.

Optimization of composition of media for the production of extracellular glucoamylase by Candida guilliermendii.

The combined effects of macronutrients of media on glucoamylase production by Candida guilliermendii were studied using Design Of Experiment (DOE). A 2(P-k) factorial design was chosen to explain fifteen medium constituents: pH, Starch, Sucrose, Yeast extract, Peptone, NH4Cl (NH4)2HPO4, NH4NO3, CH4NO2 (NH4)2SO4, CaCl2, MnCl2, FeCl2, ZnCl2 and MgCl2 and analyse the results. This procedure limited the number of actual experiments performed while allowing for possible interactions between components. The p-value of the coefficient for quadratic effect of pH, starch and yeast extract concentration was < 0.001, suggesting that they were the main experimental variables having the highest effect on the production of glucoamylase. It was found that yeast extract had a great effect on glucoamylase production. The optimal combinations of media constituents for maximum which were chosen for further studies on production of glucoamylase were determined as 10 g L(-1) starch, 0.45 g L(-1) urea, 0.61 g L(-1) NH4NO3, 3 g L(-1) Yeast extract and 0.1 g L(-1) Mg SO4.