Real-time monitoring and control of the specific growth rate in yeast fed-batch cultures based on process analytical technology tools such as biocalorimetry or spectroscopy

Key features of bioprocesses, such as product quantity and quality, but also cell physiology can be related to the growth characteristics of the organism under study. The specific growth rate, a key variable, cannot be measured directly, but might be estimated and inferred from other measurable variables such as biomass, substrate or product concentrations. The present thesis reviews techniques for real-time estimation and control of the specific growth rate in microbial fed-batch cultures by focusing on its importance in the development of processes for the production of high-value products such as recombinant proteins. Existing models and monitoring techniques are discussed before comparing two particular approaches, developed within the scope of this thesis, to estimate the biomass concentration and the specific growth rate of yeast cells in real-time, based on spectroscopic methods on the one hand and on heat flow measurements on the other. Particular emphasis is given to changes that need to be undertaken when adapting the initial strategy, developed for a process with Kluyveromyces marxianus, to different type of yeast cells such as Candida utilis or Pichia pastoris or Saccharomyces cerevisiae. For both control strategies, controller errors of less than 20 % were achieved, allowing ton control the specific growth rate of the four different yeast strains at a constant setpoint