Enhancing Microbial Lipids Synthesis for Biodiesel Production by <i>Y. lipolytica</i> W29 from Volatile Fatty Acids: Two-Stage Batch Strategies

Microbial lipids produced by Y. lipolytica have the potential to be used as feedstock for the biodiesel industry, but the high costs of pure substrates used for its production are limiting the potential of this application. Volatile fatty acids (VFAs), obtained in anaerobic fermentation of organic wastes, are inexpensive carbon sources for the cost-effective production of microbial lipids. In this work, two-stage batch cultures were tested as a strategy to improve lipids production by Y. lipolytica W29. The process consists of a first growth phase in glucose or glycerol, followed by a lipogenic phase in VFAs medium composed of a mixture of acetate, propionate, and butyrate. The addition of three pulses of 6 g·L−1 VFAs mixture, or a single pulse of 18 g·L−1 VFAs mixture, in the lipogenic phase boosted microbial lipids production (23–25%, w/w) and prevented lipids mobilization. Microbial lipids synthesized in such conditions are mainly composed of oleic acid (54%) with an unsaturated/saturated fraction above 78%. The main properties of biodiesel produced from Y. lipolytica W29 lipids are within the ranges of the EU biodiesel standard EN 14214