Citric acid production by Aspergillus niger ATCC 9142 from a treated ethanol fermentation co-product using solid-state fermentation.

AIMS: To investigate the ability of the citric acid-producing strain Aspergillus niger ATCC 9142 to utilize the ethanol fermentation co-product corn distillers dried grains with solubles for citric acid production following various treatments. METHODS AND
RESULTS: The ability of A. niger ATCC 9142 to produce citric acid and biomass on the grains was examined using an enzyme assay and a gravimetric method, respectively. Fungal citric acid production after 240 h was higher on untreated grains than on autoclaved grains or acid-hydrolysed grains. Fungal biomass production was enhanced after autoclaving and acid-hydrolysis of the grains. Phosphate supplementation to the grains slightly stimulated citric acid production while methanol addition decreased its synthesis. Using the phosphate-supplemented grains, the optimal incubation temperature, initial moisture content of the grains and the length of fermentation time for ATCC 9142 citric acid production were determined to be 25 degrees C, 82% and 240 h, respectively.
CONCLUSIONS: A. niger ATCC 9142 synthesized citric acid on corn distillers dried grains with solubles. The phosphate-treated grains increased citric acid production by the strain. SIGNIFICANCE AND IMPACT OF THE STUDY: The ethanol fermentation co-product corn distillers dried grains with solubles could be useful commercially as a substrate for A. niger citric acid production.