Produzione in fed-batch ripetuto di acido citrico da Yarrowia lipolytica con riciclo di biomassa per microfiltrazione tangenziale

In this work, citric acid production by Yarrowia lipolytica ATCC 20346 was studied in a laboratory-scale Membrane Recycle Bioreactor composed of a stirred fermenter coupled to a flat-membrane cross-flow microfiltration (CFMF) unit. By increasing the number of production cycles, citrate productivity (R-p) tended to reduce in spite of the fact that the production medium had been integrated with vitamins, whereas the yield factor for citric acid production on glucose was found to be approximately constant. By operating with partial cell discharge (when using either the production media enriched with amounts of nitrogen and essential nutrients equivalent to the mass of cells disposed of, or the growth medium), it was possible to obtain the expected microbial biomass with no or very limited citrate excretion. To minimise the contribution of the cell growth phase to the overall citrate productivity and yield on glucose, it would be convenient to subdivide the process into the following stages: growth phase, yeast recovery by CFMF; Ist prolunged fed-batch production using a pi-I-controller as an indirect feedback of simultaneous substrate and alkaline reagent feeding; yeast recovery by CFMF; 2nd prolunged fed-batch production.