Oxygen transfer rate and pH as major operating parameters of citric acid production from glycerol by Yarrowia lipolytica W29 and CBS 2073

The amount of citric acid (CA) produced by Yarrowia lipolytica is dependent on the yeast strain and growth conditions such as pH, oxygen availability and medium composition. In this work, an experimental design based on the Taguchi method was applied to evaluate the effect of parameters: pH, carbon/nitrogen (C/N) ratio in the medium, oxygen mass transfer rate (OTR) and salts concentration, on the CA production by two Y. lipolytica strains, W29 (ATCC 20460) and CBS 2073. OTR and pH showed higher influence on the CA production for both strains. The increase of OTR from air to the culture medium led to a two- and three-fold improvement of the CA production by Y. lipolytica CBS 2073 and W29, respectively. Besides the individual effects of the parameters, a significant influence of the interaction between these parameters was observed, mainly between OTR and salts. Different values of the parameters were found at the optimum conditions for each strain, but the theoretically predicted and experimentally obtained citric acid concentrations (cCA) were approximately 10 g L-1 for both strains. The optimal conditions were also validated employing crude glycerol from biodiesel industry as a substrate, and similar behaviour of the strains was observed.Acknowledgements. This work was financially supported by the Portuguese Foundation for Science Technology and the European Community Fund FEDER through Program COMPETE under the PhD grant SFRH/BD/72621/2010 provided to Patrícia Ferreira, and Post-Doctoral grant SFRH/BPD/101034/2014 provided to Marlene Lopes, also under the scope of the projects RECI/BBB-EBI/0179/2012 (FCOMP-01-0124FEDER-027462) and “BioInd - Biotechnology and Bioengineering for Improved Industrial and Agro-Food Processes”, REF. NORTE-07-0124-FEDER-000028 co-funded by the Programa Operacional Regional do Norte (ON.2 – O Novo Norte), QREN, FEDER and the strategic funding of the UID/BIO/04469/2013 unit