Analyses of survival data of a mixture of Salmonella spp. at fixed temperatures between 55°C (131°F) and 71.1°C (160°F) in ground beef matrices containing concentrations of salt between 0 and 4.5%, concentrations of sodium pyrophosphate (SPP) between 0 and 0.5%, and concentrations of sodium lactate (NaL) between 0 and 4.5% indicated that heat resistance of Salmonella increases with increasing levels of SPP and salt, except that, for salt, for larger lethalities close to 6.5, the effect of salt was evident only at low temperatures (<64°C). NaL did not seem to affect the heat resistance of Salmonella as much as the effects induced by the other variables studied. An omnibus model for predicting the lethality for given times and temperatures for ground beef matrices within the range studied was developed that reflects the convex survival curves that were observed. However, the standard errors of the predicted lethalities from this models are large, so consequently, a model, specific for predicting the times needed to obtained a lethality of 6.5 log 10 , was developed, using estimated results of times derived from the individual survival curves. For the latter model, the coefficient of variation (CV) of predicted times range from about 6 to 25%. For example, at 60°C, when increasing the concentration of salt from 0 to 4.5%, and assuming that the concentration of SPP is 0%, the time to reach a 6.5-log 10 relative reduction is predicted to increase from 20 min (CV ‫؍‬ 11%) to 48 min (CV ‫؍‬ 15%), a 2.4 factor (CV ‫؍‬ 19%). At 71.1°C (160°F) the model predicts that more than 0.5 min is needed to achieve a 6.5-log 10 relative reduction.

Heat-resistant spores of Clostridium perfringens may germinate and multiply in cooked meat and poultry products when the rate and extent of cooling does not occur in a timely manner. Therefore, six cooling models (PMP 7.0 broth model; PMIP uncured beef, chicken, and pork models; Smith-Schaffner version 3; and UK IFR ComBase Perfringens Predictor) were evaluated for relative performance in predicting growth of C. perfringens under dynamic temperature conditions encountered during cooling of cooked, uncured meat and poultry products. The predicted growth responses from the models were extensively compared with those observed in food. Data from 188 time-temperature cooling profiles (176 for single-rate exponential cooling and 12 for dual-rate exponential cooling) were collected from 17 independent sources (16 peer-reviewed publications and one report) for model evaluation. Data were obtained for a variety of cooked products, including meat and poultry slurries, ground meat and poultry products with and without added ingredients (e.g., potato starch, sodium triphosphate, and potassium tetrapyrophosphate), and processed products such as ham and roast beef. Performance of the models was evaluated using three sets of criteria, and accuracy was defined within a 1- to 2-log range. The percentages of accurate, fail-safe, or fail-dangerous predictions for each cooling model differed depending on which criterion was used to evaluate the data set. Nevertheless, the combined percentages of accurate and fail-safe predictions based on the three performance criteria were 34.66 to 42.61% for the PMP 7.0 beef broth model, 100% for the PMIP cooling models for uncured beef, uncured pork and uncured chicken, 80.11 to 93.18% for the Smith-Schaffner cooling model, and 74.43 to 85.23% for the UK IFR ComBase Perfringens Predictor model during single-rate exponential chilling. Except for the PMP 7.0 broth model, the other five cooling models (PMIP, Smith-Schaffner, and UK IFR ComBase) are useful and reliable tools that food processors and regulatory agencies can use to evaluate the safety of cooked or heat-treated uncured meat and poultry products exposed to cooling deviations or to develop customized cooling schedules.

Both high-fat and low-fat ground beef (percent lean:fat = ca. 70:30 and 93:7, respectively) were inoculated with a 6-strain cocktail of non-O157:H7 Shiga toxin-producing Escherichia coli (STEC) or a five-strain cocktail of E. coli O157:H7 (ca. 7.0 log CFU/g). Patties were pressed (ca. 2.54 cm thick, ca. 300 g each) and then refrigerated (4°C, 18 to 24 h), or frozen (-18°C, 3 weeks), or frozen (-18°C, 3 weeks) and then thawed (4°C for 18 h or 21°C for 10 h) before being cooked on commercial gas or electric grills to internal temperatures of 60 to 76.6°C. For E. coli O157:H7, regardless of grill type or fat level, cooking refrigerated patties to 71.1 or 76.6°C decreased E. coli O157:H7 numbers from an initial level of ca. 7.0 log CFU/g to a final level of ≤1.0 log CFU/g, whereas decreases to ca. 1.1 to 3.1 log CFU/g were observed when refrigerated patties were cooked to 60.0 or 65.5°C. For patties that were frozen or freeze-thawed and cooked to 71.1 or 76.6°C, E. coli O157:H7 numbers decreased to ca. 1.7 or ≤0.7 log CFU/g. Likewise, pathogen numbers decreased to ca. 0.7 to 3.7 log CFU/g in patties that were frozen or freeze-thawed and cooked to 60.0 or 65.5°C. For STEC, regardless of grill type or fat level, cooking refrigerated patties to 71.1 or 76.6°C decreased pathogen numbers from ca. 7.0 to ≤0.7 log CFU/g, whereas decreases to ca. 0.7 to 3.6 log CFU/g were observed when refrigerated patties were cooked to 60.0 or 65.5°C. For patties that were frozen or freeze-thawed and cooked to 71.1 or 76.6°C, STEC numbers decreased to a final level of ca. 1.5 to ≤0.7 log CFU/g. Likewise, pathogen numbers decreased from ca. 7.0 to ca. 0.8 to 4.3 log CFU/g in patties that were frozen or freeze-thawed and cooked to 60.0 or 65.5°C. Thus, cooking ground beef patties that were refrigerated, frozen, or freeze-thawed to internal temperatures of 71.1 and 76.6°C was effective for eliminating ca. 5.1 to 7.0 log CFU of E. coli O157:H7 and STEC per g.

No abstract