Bacterial resistance after pulsed electric fields depending on the treatment medium pH

Effect of temperature, pH and presence of nisin on inactivation of Salmonella Typhimurium and Escherichia coli O157:H7 by pulsed electric fields

“…The application of an external electric field causes also a sublethal injury in some of the microbial population, but it can be inactivated if recovery conditions are not suitable (García et al, 2005a;García, Somolinos, Hassani, Alvarez, & Pagán, 2009). Both lethality and the occurrence of cell damage are dependent on the microorganism and the environmental conditions (Cebrián, Sagarzazu, Pagan, Condon, & Manas, 2007;García, Gómez, Raso, & Pagán, 2005b;Lado & Yousef, 2003;Somolinos, Garcia, Manas, Condon, & Pagan, 2008). A PEF treatment of 35 kV/cm and 300 μs that inactivated 5 Log 10 cycles of Salmonella Typhimurium STCC 878 and E. coli O157:H7 in a McIlvaine buffer of pH 5.5 reduced 4 and 2 Log 10 cycles at pH 3.5, respectively (Saldaña, Puertolas, Condon, Alvarez, & Raso, 2010b).…”

“…The pH of the treatment medium is one of the most influential factors related to PEF lethality and cell damage. Generally, Gram-negative bacteria are more PEF-resistant in media of low pH (García et al, 2005b), which has been attributed to the fact that in acidic conditions, a part of the microbial population is sublethally injured rather than inactivated. The damage to the sublethally injured population can be repaired after the treatment under suitable recovery conditions, and those that survive the treatment show higher PEF resistance.…”

Acquisition of pulsed electric fields resistance in Staphylococcus aureus after exposure to heat and alkaline shocks

“…From a practical point of view it should be noted that from previously published data it can be concluded that S. aureus resistance to PEF at pH 7.0 is one of the lowest among vegetative bacteria studied so far (García et al, 2005). Furthermore, it has been demonstrated that PEF resistance barely changes among S. aureus strains (Cebrián, Sagarzazu, Pagán, Condón, & Mañas, 2007) and we previously observed that only one strain out of 15 showed a significantly higher PEF resistance (Rodríguez-Calleja, Cebrián, Condón, & Mañas, 2005).…”

“…PEF treatments were carried out in an exponential waveform pulse equipment (García, Gómez, Raso, & Pagán, 2005). High electric field pulses were produced by discharging a set of 10 capacitors via a thyristor switch (Behlke, Kronberg, Germany) in a batch treatment chamber.…”

Moderate and high intensity pulsed electric fields : Effect on microbial inactivation, shelf life and quality of fruit juices

“…Reduction of the intracellular pH thereby affects the biochemical processes in the cell including transport processes over the membrane, redox state, and enzyme activities (Cotter & Hill, 2003). Similar observations in pH difference were found for Gram-positive and Gram-negative micro-organisms in buffer solutions (Álvarez et al, 2002;García et al, 2005b;Geveke & Kozempel, 2003;Gómez et al, 2005aGómez et al, , 2005bSaldaña et al, 2010c;Wouters et al, 1999). …”