Microbial sensors fermentation processes

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. 

Acetic Acid. On-line measurement of acetic acid concentrations is required in fermentation processes. The microbial sensor for ethyl alcohol described above could be used for the determination of acetic acid(8). 

Extensive research and development of microbial sensors has been carried out by Suzuki et al. (89-94) and Rechnitz et al. (95-97) (see Table III). Microbial sensors consisting of membrane-bound whole cells and an oxygen electrode were constructed for the determination of substrates such as assimilable sugars, acetic acid, alcohols and ammonia, and for the estimation of biochemical oxygen demand (BOD) (98-104). Glutamic acid was determined with a microbial sensor which consists of membrane-bound whole cells containing glutamate decarboxylase and a carbon dioxide gas electrode. These microbial sensors have been applied and evaluated for on-line measurements in fermentation processes (105,106). 

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. 

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