Kinetics of continuous whey fermentation by Kluyveromyces fragilis

Continuous whey fermentation by Kluyveromyces fragilis was studied in a 30-dm3 stirred fermenter as a function of the dilution rate (D) and feed concentration of lactose (So). By using the concept of material and energy balances, it was possible not only to check the consistency of the experimental steady-state responses, but also to develop an unstructured model based on a Monod-type kinetic equation for cell growth and two independent linear equations for the consumption rates of lactose and oxygen. Moreover, a typical Lineweaver—Burk plot enabled the yeast specific growth rate to be described as that of an enzyme-catalysed reaction in the presence of an unknown noncompetitive inhibitor (that was identified with a reference intermediate compound produced by the microorganism itself under partially anaerobic conditions and expressed in terms of ethanol equivalent). In this way, the experimental cell concentrations were reconstructed with a mean standard error of about 10%, thus confirming the capability of this model to provide a reliable basis for further scale-up of this fermentation process.