Optimized Production of L-phenylalanine by Fermentation Using Crude Glycerol

Abstract

Crude glycerol, a by-product of the commercial production of biodiesel, was used directly as the carbon source to produce the essential amino acid L-phenylalanine in an optimized fermentation process involving the novel recombinant bacterium Escherichia coli BL21(DE3). In developing the
optimal process, a Plackett-Burman experimental design was used to identify the components of the medium that most affected the production of the cell mass and L-phenylalanine. For the specified carbon source and with ammonium sulfate as the nitrogen source, the media components that were the most influential were: KH₂PO₄, K₂HPO₄, NaCl, MgCl₂, CaCl₂, CoCl₂, CuSO₄, Na₂MoO₄, ZnSO₄ and yeast extract. A three-level and five-factor central composite experimental design was then used to identify the optimal concentrations of the most influential components of the medium and the optimal duration of the fermentation. Under the optimal combination of conditions for biomass production, a biomass concentration of 1.23 g/L was achieved in 32.43 h. Similarly, under the optimal conditions for production of L-phenylalanine, a metabolite concentration of 1.03 g/L was achieved in 30.29 h. A high correlation between the models’ predicted responses and the actual responses achieved in independent validation
experiments confirmed the validity of the models.