Prevailing acid determines the efficiency of oleaginous fermentation from volatile fatty acids

Microbial lipids are envisaged as promising alternatives for sustainable production of chemicals and fuels. Although sugar-based substrates are the most conventional carbon sources employed for this purpose, the use of low-cost feedstock, such as organic wastes, is crucial for an economically-viable process. In this study, volatile fatty acids (VFAs) obtained during the anaerobic fermentation of food waste were used as carbon sources to produce lipids in Yarrowia lipolytica ACA DC 50109. Different total VFAs concentrations, acids profiles and carbon:nitrogen (C:N) ratios were used in both real digestates and synthetic media to establish the optimal culture conditions for lipid production. Y. lipolytica was able to grow in all cases despite of using concentrations as high as 15 g/L of total VFAs. The highest obtained lipid contents were 43.4% and 37.3% w/w using 15 g/L VFAs, 6:1 acetic:hexanoic ratio and C:N of 200:1 and 150:1, respectively. These lipids contents implied lipid yields of 0.33 g/g and 0.31 g/g, that were very close or even higher than lipid yields reported from sugars. This fact proves the suitability of using VFA derived from wastes as a low-cost carbon sources for the production of lipids and highlights the importance of paying attention to VFAs profile and C:N in the media for an efficient process.