Speaker
Description
Living yeast cells in the brewery industry are active cells. They have different responses to AC electric field if they possess different dielectric properties. Electrical parameters which are used to determine health of yeast cells are the conductivities of the cytoplasm (CC), the cell membrane (MC), dielectric constant of the membrane and the cytoplasm, respectively. These parameters affect cell translational speeds of positive dielectrophoresis. We measured yeast velocities during their movement towards the electrode tips, under various AC field frequencies. The value of LCF, where yeast cells were repelled (i.e. negative force) from the tip after being attracted, was recorded against the conductivity of the solution (SC). It was observed that as the SC was increased the LCF was shifted towards a higher frequency value. Yeast velocity spectra were reduced significantly under greater SC value. When the increased SC reached a critical value the attractive force became negligible, implying equivalence to the cytoplasmic conductivity. Our experiments showed that yeast cells of 1.15 x 10$^5$ cell/ml displayed the initial positive dielectrophoresis at LCF of 60-90 kHz, when using SC of 6 microS/m. The velocity spectrum of yeast suspensions were affected by SC of which the cells were suspending during the experimentation. An abrupt change in the velocity pattern was explained in terms of the dielectric properties of cell membrane and cytoplasm of yeast cells which reflect their metabolic health status. By iterative curve-fitting methods, we achieved to determine the health of yeast suspensions expressed in terms of the cytoplasmic and the membrane conductivity values.
