A SrTiO ₃ working electrode at 360–460 °C incorporates oxygen under UV illumination. This leads to a voltage in a solid oxide (photo-)electrochemical cell..

New approaches in process monitoring during industrial fermentations are not only limited to classical pH, dO₂ and offgas analysis, but use different in situ and online sensors based on different physical principles to determine biomass, product quality, lysis and far more. One of the very important approaches is the in situ accessibility of viable cell concentration (VCC). This knowledge provides increased efficiency in monitoring and controlling strategies during cultivations. Electrochemical impedance spectroscopy—EIS—is used to monitor biomass in a fermentation of E. coli BL21(DE3), producing a recombinant protein using a fed batch-based approach. Increases in the double layer capacitance (C_dl), determined at frequencies below 1 kHz, are proportional to the increase of biomass in the batch and fed batch phase, monitored in offline and online modes for different cultivations. A good correlation of C_dl with cell density is found and in order to get an appropriate verification of this method, different state-of-the-art biomass measurements are performed and compared. Since measurements in this frequency range are largely determined by the double layer region between the electrode and media, rather minor interferences with process parameters (aeration, stirring) are to be expected. It is shown that impedance spectroscopy at low frequencies is a powerful tool for cultivation monitoring.

Today’s yeast total biomass and viability measurements during the brewing process are dependent on offline methods such as methylene blue or florescence dye-based staining, and/or the usage of flow cytometric measurements. Additionally, microscopic cell counting methods decelerate an easy and quick prediction of yeast viability. These processes are time consuming and result in a time-delayed response signal, which not only reduces the knowledge of the performance of the yeast itself, but also impacts the quality of the final product. Novel approaches in process monitoring during the aerobic and anaerobic fermentation of Saccharomyces cerevisiae are not only limited to classical pH, dO₂ and off-gas analysis, but they also use different in situ and online sensors based on different physical principles to determine the biomass, product quality and cell death. Within this contribution, electrochemical impedance spectroscopy (EIS) was used to monitor the biomass produced in aerobic and anaerobic batch cultivation approaches, simulating the propagation and fermentation unit operation of industrial brewing processes. Increases in the double-layer capacitance (C_DL), determined at frequencies below 1 kHz, were proportional to the increase of biomass in the batch, which was monitored in the online and inline mode. A good correlation of C_DL with the cell density was found. In order to prove the robustness and flexibility of this novel method, different state-of-the-art biomass measurements (dry cell weight—DCW and optical density—OD) were performed for comparison. Because measurements in this frequency range are largely determined by the double-layer region between the electrode and media, rather minor interferences with process parameters (aeration and stirring) were to be expected. It is shown that impedance spectroscopy at low frequencies is not only a powerful tool for the monitoring of viable yeast cell concentrations during operation, but it is also perfectly suited to determining physiological states of the cells, and may facilitate biomass monitoring in the brewing and yeast-propagating industry drastically.