Optimization of citric acid production from glucose syrup by Yarrowia lipolytica using response surface methodology

A new criterion was proposed to evaluate the process of citric acid biosynthesis by the acetate negative mutant strain Yarrowia lipolytica AWG-7 cultivated on glucose syrup by the repeated-batch method. This criterion imparts the same weight to the overall amount of the citric acid production and to the trend in citric acid concentration. To determine the optimum levels of bacto-peptone, ammonium chloride and potassium dihydrogen phosphate which maximize the proposed objective function, a central composite design was developed using 50 ml repeated-batch fermentation. The design involved 20 processes conducted with various combinations of the five values of these three parameters. The experiments produced empirical values of the proposed criterion which were then approximated with the fourth-order polynomial. It was found that the optimal concentrations of bacto-peptone, ammonium chloride, and potassium dihydrogen phosphate equaled 8.5; 159.8 and 65 mgl-1, respectively.