The estimation of the yeast growth phase by nonlinear dielectric properties of the measured electric current

We measured the activity of yeast in each growth phase by using nonlinear dielectric properties. In this paper, we used a 2-electrode system, rather than the previous 4-electrode system, to measure the current waves for the analysis of the phase angle of response waves and the facilitation of the measurements. As a result, in the exciting frequency and field, 14 Hz and 0.75 V cm or 1.25 V cm−1, the 2nd harmonic of the response wave for cell suspensions showed a significant difference between the induction phase and the others. However, for the supernatant of suspensions, there was no difference in the power spectrum of the even-numbered harmonics. With the phase angle, the same tendency was observed in the power spectrum. When another combination of field and frequency (0.25 or 1.75 V cm−1 and 7, 28, 35 or 42 Hz) was applied, there were no significant differences in either the power spectrum or the phase angle. These results were different from those measured by a 4-electrode system, although the range of frequency and field are almost the same. However, we found that the 2nd harmonics in the induction phase were different from those in the other phases. We can say that this 2-electrode system is applicable for the estimation of the growth of yeast cells.