Optimization of citric acid production from Candida lipolytica Y-1095 using n-paraffin.

Currently, the majority of worldwide microbial production of citric acid utilizes Aspergillus niger in a carbohydrate based submerged fermentation. Due to their high carbon content, hydrocarbons also have the potential of producing high concentrations of citric acid. Initial lab experiments conducted using 1875 ml batch fermentations with n-paraffin found that Candida lipolytica NRRL-Y-1095 assimilated the feedstock and had a citric acid productivity of 47 mg l(-1) h(-1). To determine the optimum level of initial biomass concentration, n-paraffin concentration, iron concentration and temperature for the production of citric acid, a central composite design was developed using 200 ml batch fermentations. The design involved conducting 31 batch fermentations under various combinations of high and low values of these four parameters. From this investigation empirical models were developed describing the interactions between the experimental parameters and citric acid production. It was found that the maximum concentration of citric acid produced was 9.8 g l(-1) and the optimum levels of each parameter for citric acid production were, 10--12% volume for initial biomass concentration, 10--15% volume for n-paraffin concentration, 10 mg l(-1) for ferric nitrate concentration, and 26--30 degrees C for temperature.