Enhanced Production of Citric Acid by Mutant PN12 of Aspergillus fumigatus Using Statistical Design

Distillery spent wash is an unwanted residual liquid waste generated during alcohol production. It is a potential source for production of different industrially important products. Distillery spent wash is dark colored and has many organic compounds as a waste. In this experiment, removal of color and organic compounds was carried out by anaerobic treatment. The treated spent wash was utilized for citric acid production with the help of microorganisms. The current study was performed with the treated spent wash which was applied for high level of citric acid production by a mutant strain of Aspergillus fumigatus PN12. The parent strain Aspergillus fumigatus PN12 was mutagenized by UV exposure to enhance citric acid production. After UV exposure investigation, mutant strain was selected for optimization and statistical method. The best citric acid production obtained was, 26.45 g/L at 30 ℃ with pH 6.0, 0.1 g/L of KH2PO4 and (NH4)2SO4 under OFAT. Under RSM optimization, maximum citric acid production was achieved as 30.89 g/L. Thus, the process optimization through the statistical approach resulted in a 1.16-fold enhancement in citric acid production as compared to that of the OFAT parametric conditions. Citric acid producing enzymes such as aconitase, NAD+-isocitrate dehydrogenase and NADP+ isocitrate dehydrogenase was studied. Maximum activity (U/mg) of aconitase (3.19±0.023), NAD+-isocitrate dehydrogenase (3.0±0.15) and NADP+ isocitrate dehydrogenase (2.91±0.17) was observed at 96 h. The present study can conclude that spent wash is potential source for citric acid production. Utilization of mutant strain of Aspergillus fumigatus PN12 is beneficiary for large scale industrial fermentation and citric acid production.