Modelling of aerobic growth of Saccharomyces cerevisiae in a pH-auxostat

Abstract

A model for growth and overflow metabolism of Saccharomyces cerevisiae was applied to simulate continuous cultivations in a pH-auxostat. The concentrations of glucose, biomass and ethanol are controlled by the flow ratio r between fresh medium and titrant solution, both of which are pH-regulated. A critical value of r could be derived, below which the culture becomes substrate depleted, resulting in a stop-flow condition with retained biomass but without growth. At r-values slightly above the critical value the pH-auxostat is substrate limited and unstable. Further increase of the r value results in a stable continuous culture growing at μ_max. Thus, the pH-auxostat complements the chemostat in the growth range at or close to μ_max. Even at μ_max conditions, the ethanol concentration can be controlled at a low level.