Process control, microbial sensors

Riedel, K., Renneberg, R., Wolienberger, U., Kaiser, G., Scheller, F., Microbial Sensors. Fundamentals and Applications for Process Control , J. Chem. Tkch. Biotechnol. 44 (1989) 85-106. 

Despite these potential problems, many microbial biocatalysts have been identified with sufficient selectivity and sensitivity to allow their use in single analyte determination. The low cost, stability, and ease of use makes such analyses attractive. The most commonly reported application for such sensors is process control, both in fermentation and downstream monitoring. A wide range of fermentation products have been monitored by microbial biosensors including alcohols, amino acids, antibiotics, organic acids, peptides, and vitamins. 

Riedel K, Renneberg R, Wollenberger U, Kaiser G, and Scheller FW (1989) Microbial sensors fundamentals and applications for process control. Journal of Chemical Technology and Biotechnology 44 85-106. 

There are several barriers to the successful control of bioprocesses due to particular circumstances that are related to their characteristics the complexities of microbial metabolisms, the nonlinearity of microbial reactions, the frequent use of batch and fed-batch operations, and the limited availability of sterihzable online sensors for important process variables such as cell and product concentrations. Furthermore, it is difficult to construct mathematical models that can predict the entire range of batch or fed-batch operations that many fermentation processes require. 

A process variable is a parameter of the current status of a process under operation, and, therefore, the measurement of process variables is a key to understanding what is happening in a bioreactor and to being able to control the process. Most of the sensors used for the measurements of process variables are inserted into the culture broth of a bioreactor. These must have qualities that will allow them to be repeatedly sterihzed (autoclavable) in order to prevent microbial contamination in bioreactors. Naturally, all the sensors must be calibrated before sterihzation. 

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