Optimization of citric acid production by Aspergillus niger in the presence and absence of SR63

Citric acid is one of the most important organic acid, which is used wildly in different industries, and this demand has been growing every year. This study was aimed to investigate the optimal conditions for the production of citric acid by Aspergillus niger in the presence and absence of SR63. In this study, we used different environmental samples such as air, soil, water and leaves to isolate the fungus. Colonies with the ability to growth on czapek dox agar medium were screened. To increase the production efficiency, SR63 was added to fermentation liquid medium. Also, optimising of fermentation condition, temperature of medium and time of fermentation were examined. Overall, 10 colonies were isolated from different environment, which one of them had the best citric acid production ability in compare to the others. The best result was achieved in 30°c for 6 days into a medium with 0.0125g/L SR63 at pH 5. Regarding the results, SR63 could increase the production of citric acid by inhibition of overgrowth of A. niger fungal thread.