The effect of the electric field on lag-phase, ethanol and β-galactosidase production of a recombinant S. cerevisiae growing on lactose

Abstract

The production of ethanol and β-galactosidase from cheese whey and other sub-products from industries can be a good way of minimizing environmental problems and producing valuable products from low-cost raw materials. A recombinant S. cerevisiae NCYC869-A3/pVK1.1 flocculent strain expressing the lacA gene (coding for β-galactosidase) of Aspergillus niger under ADHI promotor and terminator was used in the experiments, once this strains has higher ethanol and β-galactosidase productivities. Batch culture experiments were performed in SSlactose medium with 50 g/L lactose. A 2 dm3 bioreactor with agitation, temperature and pH measurement and control, was used. The experiments were conducted under aerobic and anaerobic conditions. The temperature was maintained at 30 ◦C and the pH at 4.0. Moreover, electrodes were placed inside the bioreactor and experiments were conducted at three different electric fields, ranging from 0.5 to 2.0 V.cmˉ¹ to determine the effect of the electric field in the fermentation profile. For all the experiments the biomass, protein, β-galactosidase activity, lactose, glucose, galactose and ethanol were measured. Finally, the lag phase and specific growth rate were calculated. Significant changes in lag phase and biomass yields were found when using 2.0V.cmˉ¹. The results show that ohmic heating enhances early stages of the fermentation, indicating that ohmically heated fermentations may be extremely useful in food industry.