Effect of moderate electric field on the metabolic activity and growth kinetics of Lactobacillus acidophilus

Moderate electric fields (MEF), applied across microbial growth media may potentially affect the permeability of cell membranes. We investigated the effects of MEF on bacteriocin (lacidin A) production during fermentation and on microbial growth kinetics of Lactobacillus acidophilus OSU 133. We comparatively investigated the following treatments: conventional, MEF (1 V/cm, 60 Hz, for 40 h), combinations of MEF (1 V/cm, 60 Hz, for the first 5 h) and conventional fermentation (for 35 h), and discrete MEF (I V/cm, 2 min on and off, for 40 h). In all treatments, except as noted below, temperature was set at 30 degrees C. The two exceptions were control (conventional) and discrete MEF treatment, which were conducted both at 30 and 37 degrees C. MEF treatments at the early stage of fermentation at 30 degrees C showed the maximum bacteriocin activity. Minimum bacteriocin production was observed under conventional fermentation at 37 degrees C. A mathematical model based on Monod growth kinetics was used to predict bacteriocin production and showed results consistent with conventional treatment data. MEF did not have a significant effect on the lag time, maximum specific growth rate, biomass production and pH change under the different experimental conditions at each specific temperature. Based on the observations, bacteriocin activity under the presence of MEF at the early stage of fermentation increased without significant change in the final biomass.