Aims: The objective was to investigate the occurrence of sublethal injury in Escherichia coli by pulsed electric fields (PEF) at different pH values.
Methods and results: The occurrence of sublethal injury in PEF-treated E. coli cells depended on the pH of the treatment medium. Whereas a slight sublethal injury was detected at pH 7, 99.95% of survivors were injured when cells were treated at pH 4 for 400 micros at 19 kV. The PEF-injured cells were progressively inactivated by a subsequent holding at pH 4.
Conclusions: PEF cause sublethal injury in E. coli. The measurement of sublethal injury using a selective medium plating technique allowed prediction of the number of cells that would be inactivated by subsequent storage in acidic conditions.
Significance and impact of the study: This work could be useful for improving food preservation by PEF technology and contributes to the knowledge of the mechanism of microbial inactivation by PEF.