Parametric Optimization of Citric Acid Production from Apple Pomace and Corn Steep Liquor by a Wild Type Strain of Aspergillus niger: A Response Surface Methodology Approach

In this work, parametric optimization of citric acid production (yield) from six process variables: apple pomace (AP) concentration, volume of corn steep liquor (CSL), pH, temperature, methanol concentration, and methanol addition time is reported. Fifty-four experiments were performed according to the Box-Behnken design method. A polynomial regression model was developed from the experimental data and effects of the variables were explained using response surface methodology approach. A coefficient of determination (R2) of 0.92 indicated the significance of the model. The optimum conditions for citric acid yield obtained from the model were 33.81 g/L of AP, 42.5 g/L of CSL, 2.05% (v/v) of methanol concentration, methanol addition time of 33 h, pH 4.54, and temperature of 32.88 °C with a corresponding yield of 62.00 g/L. Conducting an experiment using the optimum conditions gave citric acid yield of 68.26 g/L, a 10% increase over the model results.