Glucoamylase is among the most important enzymes in biotechnology. The present study aims to determine better conditions for growth and glucoamylase productivity by Candida famata and to reduce the overall cost of the medium using central composite design (CCD) with one central point and response surface methodology. A three-level central composite design (CCD) factorial design based was employed to obtain optimal medium combination of four independent variables such as soluble starch, (NH4)2HPO4, yeast extract, and MgSO4. 25 randomized mediums were incubated in flask on a rotary shaker at 105 rpm for 72 h at 30°C. The production of biomass was found to be starch, (NH4)2HPO4 and yeast extract dependent; maximum production was obtained when the starch concentration was 5 g/L, yeast extract, 5 g/L and (NH4)2HPO4 2 g/L. Positive interaction was observed between (NH4)2HPO4 and both starch and yeast extract. All the variables were highly significant for glucoamylase production according to their p values; maximum production was found at 5 g/L of yeast extract, 7 g/L of starch and 3 g/L of (NH4)2HPO4; furthermore, yeast extract and (NH4)2HPO4 interacted positively. Central composite design used for the analysis of treatment combinations gave a second-order polynomial regression model with R2 = 0.99 for biomass and R2 = 0.98 for glucoamylase. The final biomass and glucoamylase activity obtained was very close to the calculated parameters; the predicted optimal parameters were confirmed and provide a basis for further studies in the valuation of starch waste products.
Key words: Candida famata, glucoamylase, fermentation, central composite design, RSM correlation coefficient, analysis of variance (ANOVA).
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