Inactivation of Bacillus subtilis spores by a combination of hydrostatic high-pressure and pulsed electric field treatments

Abstract

The effect of the combination of hydrostatic high-pressure (HHP) and pulsed electric field (PEF) treatments on the inactivation of Bacillus subtilis spores was investigated, using suspensions prepared by suspending the spores in various solutions at about 108 spores/ml. When the PEF and HHP treatments were successively conducted in that order, the results were compared with the case where either was conducted alone. The combined processing achieved a 7.1 log reduction in the viable spore counts at maximum. Low-temperature storage after the combined processing further led to reduced germination, and finally completes inactivation in 3 days. It was confirmed by phase-contrast microscopy that the non-treated spores gradually turned into phase-dark spores and finally germinated and changed into vegetative cells, while the spores subjected to PEF/HHP treatment did not transfer to the phase-dark stage, meaning no germination.