Occurrence of sublethal injury after pulsed electric fields depending on the micro-organism, the treatment medium ph and the intensity of the treatment investigated.
OBJECTIVE
The objective was to investigate the occurrence of sublethal injury after pulsed electric field (PEF) depending on the treatment time, the electric field strength and the pH of the treatment media in two Gram-positive (Bacillus subtilis ssp. niger, Listeria monocytogenes) and six Gram-negative (Escherichia coli, Escherichia coli O157:H7, Pseudomonas aeruginosa, Salmonella serotype Senftenberg 775W, Salmonella serotype Typhimurium, Yersinia enterocolitica) bacterial strains.


RESULTS
A characteristic behaviour was observed for the Gram-positive and Gram-negative bacteria studied. Whereas Gram-positive bacteria showed a higher PEF resistance at pH 7.0, the Gram-negative were more resistant at pH 4.0. In these conditions, in which bacteria showed their maximum resistance, a large proportion of sublethally injured cells were detected. In most cases, the longer the treatment time and the higher the electric field applied, the greater the proportion of sublethally injured cells that were detected. No sublethal injury was detected when Gram-positive bacteria were treated at pH 4.0 and Gram-negative at pH 7.0.


CONCLUSIONS
Sublethal injury was detected after PEF so, bacterial inactivation by PEF is not an 'all or nothing' event.


CONCLUSIONS
This work could be useful for improving food preservation by PEF.
García
D
D
Departamento de Producción Animal y Ciencia de los Alimentos, Facultad de Veterinaria, Universidad de Zaragoza, Zaragoza, Spain.
Gómez
N
N
Mañas
P
P
Condón
S
S
Raso
J
J
Pagán
R
R
D001412:Bacillus subtilis / Q000502:physiology; D015169:Colony Count, Microbial / Q000379:methods; D003470:Culture Media; D004558:Electric Stimulation / Q000379:methods; D004926:Escherichia coli / Q000502:physiology; D019453:Escherichia coli O157 / Q000502:physiology; D006090:Gram-Negative Bacteria / Q000502:physiology*; D006094:Gram-Positive Bacteria / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008089:Listeria monocytogenes / Q000502:physiology; D011550:Pseudomonas aeruginosa / Q000502:physiology; D012475:Salmonella / Q000502:physiology; D013997:Time Factors; D015008:Yersinia enterocolitica / Q000502:physiology
D003470:Culture Media