Effect of growth phase and inoculum size on the inactivation of Saccharomyces cerevisiae in fruit juices, by pulsed electric fields

Inactivation of three Saccharomyces cerevisiae strains by PEF treatment, at different growth phases and initial inoculum sizes was investigated. The conditions of the PEF treatment were: electric field level of 8–11 kV/cm, 3 pulses, 50 μF capacitance or 12.5 kV/cm, 40 pulses, 1 μF capacitance. The inactivation of yeasts ranged from 2 to 5.8 log cycles when the inoculum size increased from 5 × 10 5 to 1 × 10 11 CFU/ml, respectively. In all the experiments, the reduction of yeasts population was linearly enhanced by increasing the inoculum size, independently of the growth phase. Different experiments were designed to explain the observed behavior. By increasing yeasts concentration the probability of formation of pearl chains would increase. As a consequence of the large volume of these “equivalent cells” the PEF treatment efficiency would increase.