Production of citric acid and single cell oil by using the yeast Yarrowia lipolytica

In this study, 12 different Yarrowia lipolytica strains, collected from different laboratories, were used to investigate microbial lipid and citric acid production using a glucose-based media under nitrogen-limited conditions in shake-flask fermentations. As a result, a domestic strain, Y. lipolytica K57, was selected. The effect of the initial glucose concentration, agitation speed and aeration rate of the bioreactor on the production of lipids and citric acid by Y. lipolytica strain K57 were investigated. The enzymatic hydrolysis of waste bread was optimized and used for the production of citric acid and lipids in a batch-type bioreactor. Fermentation kinetics, fatty acid composition and organic acids were assessed. The results show that a high citric acid yield of 0.77 (g CA/g glucose) but a low lipid yield of 0.14 (g lipid/g dry cell weight) were obtained from glucose, whereas a low citric acid yield of 0.13 g/g, a high lipid yield of 0.32 g/g and biomass of more than 60 g/L were produced from a waste bread hydrolysate by Y. lipolytica strain K57 in a bioreactor fermentation. Initial concentrations of glucose of approximately 100 g/L and dissolved oxygen of 90% generally stimulated high citric acid production, whereas initial concentrations of glucose of around 150 g/L and low levels of dissolved oxygen induced the accumulation of lipids. A high nitrogen level in the medium inhibited citric acid synthesis but enhanced biomass production.