Citric acid production by Yarrowia lipolytica SWJ-1b using corn steep liquor as a source of organic nitrogen and vitamins

In this study, Yarrowia lipolytica SWJ-1b was cultivated in the medium containing corn steep liquor (CSL) to replace yeast extract. In the medium containing 1.0 g/L of CSL, 27.5 g/L of citric acid (CA) was produced by Y. lipolytica SWJ-1b, with a 1.24-fold increase compare to the control medium containing yeast extract. It was showed that the addition of CSL could obviously influence the metabolism of Y. lipolytica SWJ-1b. The improved activity of the key intracellular enzymes indicated that the pyruvate carboxylation pathway was enhanced, which suggested carbon flux to CA in was redistributed in Y. lipolytica. During the fermentation in a 5 L fermenter, 52.3 g/L of CA was obtained from 60.0 g/L of glucose, with a productivity of 0.22 g/L/h. Only 5.5 g/L of isocitric acid was produced during the process, and 96.7% of glucose was consumed at the end of the fermentation. Results suggest that CSL could be used as an alternate source of organic nitrogen to replace the more expensive yeast extract in CA production by Y. lipolytica SWJ-1b. Furthermore, CSL could stimulate the rates of substrate uptake and improve CA yield. These results indicate the potential application of CSL for low-cost CA production on a commercial scale.