Optimization of citric acid production using a mutant strain of Aspergillus niger on cassava peel substrate

Abstract

Abstract In this study, mutation by UV-radiation and medium optimization were used to enhance production of citric acid through the screening of five local strains of Aspergillus niger using hydrolyzed cassava peel medium. Mutant strains were evaluated for citric acid production, and the physico-chemical parameters for citric acid production were further optimized using Central Composite Design (CCD) of Response Surface Methodology. Among the wild strains, a strain (FUO 2) gave highest citric acid yield of 1.93 g/l, while the mutant strain FUO 1 10 obtained after 10 min of exposure to UV-radiation yielded 9.4 g/l, an improvement of 4.87 fold. Process optimization using the mutant strain (FUO 1 10 ) on the input parameters of substrate concentration, process time, inoculum size and initial pH gave a process model with a coefficient of determination R 2 of 0.75 and a validated citric acid yield of 88.73 g/l, an improvement of 45.97 fold over the best wild strain. The response surface graphs showed significant interactive effects of input parameters on citric acid formation. This study established the usefulness of UV-mutation and medium optimization in improving the yield of citric acid. This study highlights the practicability of enhancing citric acid yield using mutant strains of A. niger on agro waste such as cassava peels, coupled with a suitable combination of optimal operational parameters. To the best of our knowledge, this work represents the first reference to the utilization of cassava peel-malted sorghum blend in submerged condition for the production of citric acid by A. niger .