Sublethal injury and recovery of Escherichia coli O157:H7 after ohmic heating

Abstract

This study investigated the inactivation, sublethal injury, and recovery of Escherichia coli O157:H7 cells induced by ohmic heating (OH) in phosphate buffer saline (PBS) using thin agar layer (TAL) method. The voltage gradients of OH were 10 V/cm and 5 V/cm, which required 3 min and 13 min to reach the center temperature of 72 °C, respectively. The results indicated that OH at 10 V/cm voltage gradient had a comparable inactivation effect to 5 V/cm at the end of heating process. The proportion of sublethally injured cells in the survivors increased with increasing heating time and temperature and reached a maximum (>97%) at the end of both treatments. When different liquid media, temperature, pH, and sodium chloride (NaCl) concentrations were used to study the recovery process of sublethally injured cells, limited nutrition, low temperature (4 °C), lower pH (4.0), and higher NaCl concentrations (more than 3%) significantly inhibited the recovery process. These results could provide the potential possibility to explore the combination of OH with other technologies (e.g. low temperature, low pH, and high salt) to inactivate targeted pathogens in foods.