| Research Abstract |
A dielectric technique has been developed, which can monitor cell concentration and electrical properties of cells in fermentation. Since biological cells show high apparent dielectric constant, which is due to interfacial polarization caused at the interfaces between the plasma membrane and the cytoplasm, the capacitance of the cell suspension placed between a pair of electrodes is directly proportional to cell concentration in principle. In order to apply this principle to monitoring of the cell concentration in fermenting broth, we have examined the following practical problems: determination of the optimum probe frequency of the applied ac field, correction for the residual inductance arising around electrodes and leads, reducing the artifactual capacitance due to electrode polarization, and design of electrodes. As a result of this examination, we found that this medhod is applicable to on-line monitoring of the cell concentration in fermenting broth. In addition, it was confirmed that this method is applicable to a wide range of culture systems, i.e., suspension culture of yeast, animal and plant cells, microcarrier culture of animal cells, and culture of yeast cells immobilized in alginate beads. Dead biological cells show low dielectric constant compared with alive cells because interfacial polarization is extremely reduced with the dead cell plasma membranes that are freely permeable to ions. When dead cells increase in the latter half of the stationaly state, the capacitance of the fermenting broth, therefore, decreases with increasing the concentration of dead cells. The decrement of the capacitance was found to be proportional to the ratio of the methylene bule stained cells. This result suggests that the dielectric technique can also measure the concentration ratio of dead cells to alive cells.
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