Automated fed-batch culture of Kluyveromyces fragilis based on a novel method for on-line estimation of cell specific growth rate

Abstract

A corrected feed-forward control strategy was developed for automated substrate feeding in aerobic fed-batch cultures. The control strategy incorporates a novel method for on-line estimation of specific growth rate as a performance indicator of the fed-batch culture. The estimation is based on the measurement of the maximum substrate uptake rate (MSUR) using on-line dissolved oxygen (DO) concentration data and mass balances. It allows the controller to track changes in the specific growth rate to compensate for process disturbances. The control strategy was applied to fed-batch culture of Kluyveromyces fragilis to maximize the volumetric productivity of lactase. A maximum volumetric lactase productivity of 2.98 U/ml h was achieved. The control was shown to be stable throughout the culture period even at the highest cell density of 69 g/l. This technique is applicable to various aerobic systems, especially for microbial cultures showing high specific oxygen uptake rates, since it only requires on-line measurement of DO concentration without the need for off-gas analysis. In a comparison carried out with three other fed-batch control strategies (DO-stat, exponential feeding and exponential feeding with manual feedback control), the corrected feed-forward control strategy exhibited the best performance by achieving the highest volumetric lactase and biomass productivity.