Viability of Clostridium perfringens, Escherichia coli, and listeria monocytogenes surviving mild heat or aqueous ozone treatment on beef followed by heat, alkali, or salt stress

The threat of pathogen survival following ozone treatment of meat necessitates careful evaluation of the microorganisms surviving under such circumstances. The objective of this study was to determine whether sublethal aqueous ozone treatment (3 ppm of O-3 for 5 min) of microorganisms on beef surfaces would result in increased or decreased survival with respect to subsequent heat, alkali, or NaCl stress. A mild heat treatment (55degreesC for 30 min) was used for comparison. Reductions in three-strain cocktails of Clostridium perfringens, Escherichia coli O157:H7, and Listeria monocytogenes on beef following the heat treatment were 0.14, 0.77, and 1.47 log(10) CFU/g, respectively, whereas reductions following ozone treatment were 1.28, 0.85, and 1.09 log(10) CFU/g, respectively. C perfringens cells exhibited elevated heat resistance at 60degreesC (D-60 [time at 60degreesC required to reduce the viable cell population by 1 log(10) units or 90%] = 17.76 min) following heat treatment of beef (55degreesC for 30 min) but exhibited reduced viability at 60degreesC following ozone treatment (D-60 = 7.64 min) compared with the viability of untreated control cells (D-60 = 13.84 min). The D-60-values for L. monocytogenes and E. coli O157:H7 following heat and ozone exposures were not significantly different (P > 0.05). C. perfringens cells that survived ozone treatment did not exhibit increased resistance to pH (pH 6 to 12) relative to non-ozone-treated cells when grown at 37degreesC for 24 h. The heat treatment also resulted in decreased numbers of surviving cells above and below neutral pH values for both E. coli O157:H7 and L. monocytogenes relative to those of non-heat-treated cells grown at 37degreesC for 24 h. There were significant differences (P < 0.05) in C. perfringens reductions with increasing NaCl concentrations. The effects of NaCl were less apparent for E. coli and L. monocytogenes survivors. It is concluded that pathogens surviving ozone treatment of beef are less likely to endanger food safety than are those surviving sublethal heat treatments.