ONLINE MONITORING OF CELL CONCENTRATIONS DURING YEAST CULTIVATION BY DIELECTRIC MEASUREMENTS

To elucidate the possibility of measuring on-line cell concentrations in bioreactors by dielectric measurement, we designed two prototypes of sensors, an immersed type sensor and an installed one, and developed a new practical correction method for excluding the influence of conductance changes in a medium during cultivation. A typical growth curve consisting of a lag, logarithmic and death phases was monitored on-line by the value of capacitance even in a medium with higher salt concentrations. Until the early stage of death phase, growth features were coincident with those measured by colony counting and dry cell weight. However, during the death phase, cell concentrations monitored by dielectric measurement agreed with that of colony counting, rather than that by dry cell weight. It was shown that the influences of intensities of aeration and agitation in the fermentor on the dielectric measurements were little when the gas hold-up phenomenon in the fermentor was not large.