Biosynthesis of Citric Acid from Glycerol by Acetate Mutants of Yarrowia lipolytica in Fed-Batch Fermentation

Pure and crude glycerol from biodiesel production have been used as substrates for citric acid production by acetate-negative mutants of Yarrowia lipolytica in fed-batch fermentation. Both the final concentration and the yield of the product were the highest when Y. lipolytica Wratislavia AWG7 strain was used in the culture with pure or crude glycerol. With a medium containing 200 g/L of glycerol, production reached a maximum of citric acid of 139 g/L after 120 h. This high yield of the product (up to 0.69 g of citric acid per gram of glycerol consumed) was achieved with both pure and crude glycerol. Lower yield of citric acid in the culture with Y lipolytica Wratislavia K1 strain (about 0.45 g/g) resulted from increased erythritol concentrations (up to 40 g/L), accumulated simultaneously with the citric acid. The concentration of isocitric acid, a by-product in this fermentation, was very low, in the range from 2.6 to 4.6 g/L.