Modelling and Optimization of the (R)-(+)-3,4-dihydroxyphenyllactic Acid Production Catalyzed with D-lactate Dehydrogenase from Lactobacillus leishmannii Using Genetic Algorithm

Z. Findrik Blažević, M. Poljanac and Đ. Vasić-Rački

Abstract
A mathematical model for the enzymatic kinetics of the synthesis of (R)–(+)–3,4-dihydroxyphenyllactic acid (DHPL) was developed. The synthesis was catalyzed by D-lactate dehydrogenase from Lactobacillus leishmannii. Since this enzyme requires NADH as a coenzyme, formate dehydrogenase system was used for NADH regeneration. Kinetic constants of both enzymes were estimated independently from initial reaction rate experiments. The developed mathematical model was verified by the batch reactor experiment (volumetric productivity in this experiment was 4.76 g dm–3 d–1). Optimization of initial reaction conditions for DHPL synthesis was performed using the genetic algorithm (GA). The genetic algorithm as a flexible optimization tool had been used to obtain the experimental conditions where maximal volumetric productivity could be achieved. The optimal initial conditions were found in the investigated parameter area: c3,4-dihydroxyphenylpyruvic acid = 4.69 mmol dm–3, cNAD+= 4.95 mmol dm–3, cformate = 36.85 mmol dm–3, γD-lactate dehydrogenase = 3 mg cm–3, γformate dehydrogenase = 2.94mg cm–3 and the reaction time 8.5 min. At these conditions volumetric productivity of 93.06 g dm–3 d–1 can be achieved.

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Keywords
enzymatic synthesis, mathematical modelling, optimisation, genetic algorithm