|Kuo, Tsung Min|
Submitted to: Enzyme and Microbial Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 13, 2007
Publication Date: March 15, 2007
Citation: Levinson, W.E., Kurtzman, C.P., Kuo, T. 2007. Characterization of Yarrowia lipolytica and related species for citric acid production from glycerol. Enzyme and Microbial Technology. 41:292-295. Interpretive Summary: The American Jobs Creation Act of 2004 provides new tax incentives for using the alternative fuel known as biodiesel that is produced from renewable agriculture materials such as soybean oil. The rapid growth of biodiesel production has led to anticipated overabundance of the major processing byproduct glycerol. We are exploring new microbial processes for using glycerol to produce value-added chemicals. In this study, a number of microbial species were examined for their ability of using glycerol under various reaction conditions to produce new compounds. We found several fungal strains that could use glycerol effectively for producing an organic acid called citric acid, an important industrial compound widely used in foods, beverages, confectionery, medicinal applications, toxic waste treatments, and blue prints, and also used as plasticizer and foam inhibitor. The impact of this study provides basic information for scientists to develop bioprocesses for producing value-added compounds indirectly from low cost vegetable oils.
Technical Abstract: Twenty-seven Yarrowia lipolytica strains as well as five strains from three other species of the Yarrowia clade (Aciculoconidium aculeatum, Candida hispaniensis and Candida bentonensis) were screened for citric acid production with pure glycerol as the carbon source. The cultures were grown under nitrogen-limited conditions. None of the non-Yarrowia strains produced citric acid, although they were able to grow on glycerol. All of the Y. lipolytica strains were able to produce citric acid in varying concentrations. The highest yielding strain in the initial screen, Y. lipolytica NRRL YB-423, produced 21.6 g/L citric acid from 40 g/L glycerol (54% yield). The citric acid to isocitric acid ratio of this strain was 11.3, while most of the strains produced ratios of between 2 and 6. Further work with this strain showed that the optimum carbon to nitrogen ratio for the rate of citric acid production was 172 while the best combination of rate and yield was obtained at a C/N ratio of 343. In addition, this strain was able to produce citric acid from crude glycerol obtained as a biodiesel production byproduct at a rate and yield comparable to that obtained with pure glycerol.