Effect of oxygen concentration and redox potential on recovery of sublethally heat-damaged cells of Escherichia coli O157:H7, Salmonella enteritidis and Listeria monocytogenes.

The measured heat resistance of cells of Escherichia coli O157:H7, Salmonella enteritidis and Listeria monocytogenes was up to eightfold greater when they were grown, heated and recovered anaerobically rather than aerobically. Measured heat resistance was highest when anaerobic gas mixtures were used (time at 59 degrees C for a 6-decimal (6-D) reduction of E. coli O157:H7, 19-24 min); moderate when low concentrations of oxygen (0.5-1%) were included (time for a 6-D reduction, 5-17 min); and lowest when higher concentrations of oxygen (2-40%) were used (time for a 6-D reduction, 3 min). This effect was principally attributed to the recovery conditions, and a greater effect was noted at lower heating temperatures. The use of reduced oxygen concentration (< 2% O2), e.g. packing under an anaerobic gas mixture or a vacuum, might therefore increase the risk of these pathogens surviving heat treatments applied to food. It is also possible that foods that are packed in air but with a low redox potential might allow the survival of heated cells, and thus the anticipated level of safety might not be achieved.