Kinetics and modeling of the stereoselective reduction of acetoacetic acid esters by continuously growing cultures of Saccharomyces cerevisiae

Abstract Pseudostationary experiments (chemostat cultures) revealed a decrease of D R with increasing concentration of starting material. This is interpreted as an inhibition of respiration by the starting material resulting also in a reduction of biomass concentration: glucose uptake was not affected. The products did not show any inhibitory effect. At all dilution rates > D R no reasonable steady states could be established (washout of the cultures) and the rates of reduction were negligible, as they were also in transient experiments. Maximal values of the volumetric product formation rate were approximately 1 g l −1 h −1 and found at dilution rates close to D R : obviously, the product formation is growth associated. During pulse experiments values between 1 and 2 g l −1 h −1 were measured. Product formation was found to depend strictly on oxidative glucose metabolism. A pseudomechanistic model is proposed considering regulatory effects and product formation: its sensitive parameters were estimated off- and on-line.

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