The biotechnology of fermentation using yeasts, like Saccharomyces cerevisiae, has a long history in many sectors of industry from alcoholic beverages to ethanol production. A vital focus of ongoing research is the study of the key enzymes responsible for the production of the metabo­lites of interest, namely ethanol. Increasing the activity of key enzymes, like alcohol-dehydrogenase, is a primary goal of metabolic and enzyme engineering. The glucose dehydrogenase and alcohol dehydrogenase were studied in S. cerevisiae under the influence of a non-uniform pulsed mag­netic field of 30 mT for 60 minutes [34]. They found that in the presence of NAD the glucose dehydrogenase activity increased 18%, while no effect was observed in the absence of NAD or NADP. The activity of alcohol dehydrogenase in the absence of co-enzymes rose to 10.7% in the an­aerobically cultivated cells and 19.9% in those cultivated aerobically. The activity of this enzyme increased by 20.5% when NAD was added to this enzyme in the aerobic culture, while an 8.5% decrease was observed in the anaerobic culture. Thus, the non-homogenous pulsed magnetic field of 30 mT stimulated the activity of the dehydrogenases, but behaved differently in the absence or presence of NAD and NADP.

The effects on ethanol fermentation by S. cerevisiae under the in­fluence of two styles of oscillating magnetic fields were studied by Perez et al. [35]. The primary magnetic field generator was composed of several permanent magnets stacked in series, while the recirculat­ing culture broth was directed through the intervening space of the magnetic fields where spatial orientation determined the desired inten­sity of 5-20 mT for each exposure. The recirculation velocity passing through the array of static magnets modulated the frequency. The sec­ondary generator was a double layer solenoid coil that produced 8 mT. Two magnetic field generators were coupled to the bioreactor, which were operated conveniently in simple or combined ways. The overall volumetric ethanol productivity enhanced by 17% over control at an optimum magnetic field treatment of 0.9-1.2 m s-1 velocity and 20 mT plus 8 mT solenoid. These results made it possible to verify the ef­fectiveness of the dynamic magnetic treatment since the fermentations with magnetic treatment reached their final stage, 2 h earlier than the control. Perez et al. [35] postulated that membrane permeability and the redox system that are affected by the electromagnetic field might have resulted in alterations of ion transport of the substrates. As a con­sequence, the cellular metabolism was stimulated for higher ethanol production.