Speaker
Sakshin Bunthawin
(Biotechnology of Electromechanics Research Unit, Science of Physics, Faculty of Technology and Environment, Prince of Songkla University, Kathu, Phuket 83120, Thailand)
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 ($\sigma_c$), the cell membrane ($\sigma_m$), dielectric constant of the membrane ($\varepsilon_m$) and the cytoplasm ($\varepsilon_c$), respectively. These parameters affect cell translational speeds of positive dielectrophoresis. We measured yeast velocities during their moving towards the electrode tips, under various AC field frequencies. Lower critical frequency (LF), where yeast cells were repelled (i.e. negative force) from the tip after being attracted, was recorded against the conductivity of cell suspension medium ($\sigma_s$). It was observed that as the $\sigma_s$ was increased the LF was shifted towards a higher frequency value. Yeast velocity spectra were reduced significantly under greater $\sigma_s$ value. When the increased $\sigma_s$ reached a critical value the attractive force became negligible, implying equivalence to the cytoplasmic conductivity. Our experiments showed that yeast cells of 1.15 $\times$ 10$^5$ cell.ml${}^{-1}$ displayed the initial positive dielectrophoresis at LF of 60-80 kHz, when using $\sigma_s$ of 6 $\mu$S.m$^{-1}$. The velocity spectrum of yeast suspensions were affected by $\sigma_s$ of which the cells were suspending during the experimentation. An abrupt change in the velocity pattern explained dielectric properties of cell membrane and cytoplasm of yeast cells which reflect their health. By curve-fitting method, we achieved to determine health of yeast suspensions
through the cytoplasmic and the membrane conductivity values.
Author
Sakshin Bunthawin
(Biotechnology of Electromechanics Research Unit, Science of Physics, Faculty of Technology and Environment, Prince of Songkla University, Kathu, Phuket 83120, Thailand)
Co-author
Dr
Raymond Ritchie
(Biotechnology of Electromechanics Research Unit, Science of Physics, Faculty of Technology and Environment, Prince of Songkla University, Kathu, Phuket 83120, Thailand)
