Optimizing the concentrations of carbon, nitrogen and phosphorus in a citric acid fermentation with response surface method

Response surface designs and analyses were used to optimize the concentrations of carbon, nitrogen and phosphorus for citric acid production by Aspergillus foetidus CCRC 30206. The citric acid production was adequately approximated with a full quadratic equation obtained from a three-factor-five-level central composite design. Analyses of the quadratic surfaces showed that in a 7-day-fermentation at 30 degrees C the maximum citric acid concentration of 43.92 g/l appeared at sucrose, NH4NO3 and KH2PO4 concentrations of 109.6, 1.83 and 0.40 g/l, respectively. The concentrations of nitrogen and phosphorus were more important than that of carbon in determining the citric acid concentration and fungal growth. Furthermore, citric acid production was more sensitive to changes in phosphorus concentrations than to changes in nitrogen concentrations in the vicinity of the optimum point of citric acid production.