CONICET | Buscador de Institutos y Recursos Humanos

In order to obtain maximum performance during industrial fermentation processes, it is important to know the metabolic state of microorganisms involved. In particular, the nonlinear-dielectric spectroscopy is a technique to monitor in-vivo and in-situ membrane proteins of microorganisms in cell suspensions. It is is based on the interaction between membrane proteins and an applied electric field between electrodes immersed in the cell suspensión. Previous work from our group showed changes in the module of the third harmonic of a suspension of Saccharomyces cerevisiae when glucose was added. However this technique is complex and does not allow continuous monitoring of the current. In addition the method not measured phase, nor were there other harmonics with significant information. In this work we present a simple methodology for monitoring the metabolic activity of a yeast suspension. We use a tripolar cell, with a gold electrode, a Ag/AgCl reference electrode and a spherical stainless steel counter-electrode. 3.5 g of S. cerevisiae was suspended in 75 ml of a saline solution. Room temperature was maintained during all measurements. A sinusoidal overpotential of 50 mV and 700 hz was applied, and the real and imaginary current of the fundamental and 2nd to 6th harmonics was measured. Glucose 100 mM was added after 40 min. Enormous changes were observed in the parallel resistive component at the fundamental frequency, and in the parallel capacitive component at fundamental and 5th harmonic after addition of glucose. These changes are simultaneous with the production of CO2 and disappear when fermentation ends. The sensing of CO2 was discarded by bubbling gas on the electrode. In this way, a reproducible method to monitor the metabolic activity in suspensions of S. cerevisae was obtained.

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