Improvement of Citric Acid Production by Gamma Irradiated Aspergillus niger Using Cane Molasses

Citric acid is in greater demand globally as a result of both population growth and industrialization. Aspergillus niger is a workhorse for the production of citric acid. Cane molasses have been chosen as a novel and economically viable substrate as a result of the rising demand for citric acid and the need for substitute materials as substrates in recent years. Therefore, the present study was conducted to improve citric acid production from A. niger using by-product of sugar (sugarcane molasses) through gamma radiation. Aspergillus niger was isolated from soil and confirmed by molecular identification based on beta tubulin gene sequencing which compared with available beta tubulin gene sequencing in the NCBI database. The NCBI database showed the highest percentage of similarity being 100 with A. niger. The fermentation process was performed in shaking flasks using sugarcane molasses. Data revealed that significantly highest production of citric acid (31.30 +/- 0.17 g/L) was obtained in a medium containing (15%) substrate level. In addition, the maximum productivity of citric acid was achieved at pH 6. Spore suspensions of A. niger were subjected to different doses of gamma radiation. Results clarified that the maximum amount (42.82 +/- 0.62 g/L) of citric acid was observed at 1.0 KGy. The amount of acid produced was increased by 1.11 fold higher than the control by the addition of 3% (v/v) ethanol after 24 hour of fermentation time. Moreover, the addition of 0.15% K4Fe (CN)6 enhanced the citric acid manufacturing. Furthermore, citric acid productivity from immobilized gamma irradiated A. niger spores was increased by 1.2 times more than that of the free ones. Citric acid was separated from the fermentation broth by precipitation method using CaCl2. In addition, FT-IR Analysis of the extracted citric acid from A. niger confirmed that there is no change in the main characteristic absorption bands of the standard citric acid.