Bioethanol production in bioreactor assisted by magnetic field: Correlation between S. cerevisiae H⁺ effluxes and fermentative efficiency

This study simultaneously evaluated fermentation kinetics and H+ fluxes during fermentation by Saccharomyces cerevisiae in order to elucidate the biochemical mechanisms behind bioethanol production induced by ELF magnetic fields. Fermentation kinetics were monitored by glucose uptake, ethanol production, secondary products (glycerol), pH, biomass, and biochemical characterization of ATPase activity through proton efflux density measurements.A face-centered central composite design 2(2) was performed, considering independent variables such as recycling arrangements (bioreactor with a spiral-shaped tube, whole bioreactor, and bioreactor with a U-shaped tube) and magnetic flux density (5, 10, and 15 mT), while alcoholic fermentation efficiency and H+ efflux density of the P-ATPase were the response variables.ELF magnetic fields induced substrate consumption and bioethanol formation in all experimental configurations when compared to fermentations without the field. However, the whole bioreactor exposed to 10 mT was the most attractive condition, resulting in an average increase of approximately 40 % and 18 % in the overall volumetric productivity of glucose consumption and ethanol production, respectively, compared to the control experiment. The effect of magnetic flux density on fermentative efficiency and H+ efflux density was statistically significant (p < 0.1). A direct correlation between H+ efflux and yeast performance during fermentation under magnetic fields was found through the application of a method for simultaneous optimization of the experimental results. The data are discussed in relation to the biological mechanism of action involved and the potential applications of this technology at an industrial scale are envisioned.