Survival of heat-shocked Yersinia enterocolitica after irradiation in ground pork

Earlier studies conducted in our laboratory showed that heat-shocked Yersinia enterocolitica (45°C for 60 min) are more resistant to a subsequent heat treatment of 55 or 60°C in ground pork than cells not previously heat-shocked. The increased thermotolerance was partly attributed to the production of stress proteins. The present study was performed to determine if the stress proteins produced by heating could also afford protection to the cells to irradiation. As part of the study, the effect of air versus vacuum packaging on survival of Yersinia to irradiation was also examined. Irradiating the inoculated pork at 1.0 kGy was sufficient to completely eliminate this pathogen. The irradiation D value for both heat-shocked and non-heat-shocked cells was statistically the same (0.15 kGy). Neither heat-shocking Yersinia nor packaging under vacuum resulted in increased resistance of this organism to irradiation. In addition, no effect was seen in virulence of the cells after these treatments, when compared with controls.