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Effect of prior sublethal heat shock on survival of Salmonella spp. during isothermal cooking. 2010.

A. Vasan, S. Ingham, B. Ingham. Poster presented at the annual meeting of the Institute of Food Technologists. Chicago, IL. July 2010.


Exposure of Salmonella to sublethal stress reportedly increases the thermo-tolerance of the pathogen on subsequent heating. This is of importance in slow cooking of meats when pathogens may be exposed to sublethal temperatures for varying periods of time, thereby increasing the likelihood of pathogen survival. This enhanced thermotolerance may make it difficult for processors to meet target pathogen lethality outlined in USDA guidance (Appendix A).

We studied the effect of sublethal heat shock treatment on subsequent thermotolerance of Salmonella during isothermal cooking (54.4°C) of lean ground beef (6-9% fat). Six different heat shock treatment combinations of time (5 or 30 min) and temperature (47.2, 48.3, 49.4°C) were evaluated. D-values at 54.4°C ranged from 36.5 (control) to 58.6 min, indicating a heat-shock effect and suggesting an increase in Salmonella thermal tolerance during slow cooking. Previous work indicated a D-value for E. coli O157:H7 ranging from 25.4 to 48.6 min under similar experimental conditions (Wiegand et al. 2009. J. Food Prot. 72:1727-1731). The higher D-values seen with Salmonella support use of this pathogen as the target microorganism when validating cooking treatments. For a copy of this poster, click HERE.

Use of Lactic Acid Bacteria as Pathogen Surrogates to Validate Commercial Whole-Muscle Beef Jerky Process Lethality against Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, and Staphylococcus aureus. 2010.

Sarah E. Dierschke, Barbara H. Ingham, Steven C. Ingham. Poster presented at the annual meeting of the Institute of Food Technologists. Chicago, IL. July 2010.  


Beef jerky is often processed at low temperature and/or low humidity to attain desired quality.  The low-humidity heating reduces process lethality due to enhanced heat-resistance in pathogens such as Salmonella.  Additionally, evaporative cooling occurs on the surface of the strips, reducing the temperature to which pathogens are exposed.

The USDA/FSIS has identified Salmonella, E. coli O157:H7, L. monocytogenes, and S. aureus as pathogens of concern in beef jerky (5).  Because Salmonella is considered the most heat resistant, destruction of Salmonella is believed to ensure the destruction of the other pathogens (5).  In response to several illness outbreaks linked back to beef jerky over the last 40 years, the USDA/FSIS requires processors to validate a 5-log reduction in Salmonella during the manufacture of jerky in order to ensure the safety of the finished product (5).  Validation can be costly and time consuming for small processors.  Most available research validates specific processes or additional chemical treatments (2, 3, 4,); thereby limiting process options and making it difficult  for processors to continue using their unique processes (2, 3, 4).   

Lactic acid bacteria (LAB), particularly Pediococcus spp., have been shown to be effective pathogen surrogates in the validation of ground-and-formed beef jerky processes (1).  Using LAB as surrogates is a safe way to perform challenge studies specific to unique processes. For a copy of this poster, click HERE.

Lethality of Small-Scale Commercial Dehydrator and Smokehouse/Oven Drying Processes Against Escherichia coli O157:H7-, Salmonella spp.-, Listeria monocytogenes-, and Staphylococcus aureus-inoculated Turkey Jerkyand the Ability of a Lactic Acid Bacterium to Serve as a Pathogen Surrogate. 2010.

Paul Williams, Wan Mei Leong, Barbara H. Ingham, Steven C. Ingham. Poster presented at the annual meeting of the Institute of Food Technologists. Chicago, IL. July 2010.


Only one published study (5) has explored the lethality of commercial turkey jerky processes against Salmonella and other pathogens. Processors, therefore, are limited in their ability to comply with USDA guidance requiring use of jerky-making processes validated for lethality. Our laboratory strives to provide the industry with novel in-plant process validation methods using GRAS lactic acid bacteria (LAB) starter cultures as pathogen surrogates; here this concept is applied to whole-muscle turkey jerky.

Whole muscle turkey strips (5.08cm x 15.24cm x 0.6cm) were inoculated with Listeria monocytogenes, Staphylococcus aureus, Saga 200 (LAB –Pediococcus acidilactici), or a mixed inoculum of Escherichia coli O157:H7 and Salmonella. After allowing for bacterial attachment, strips were marinated in Barbeque or Teriyaki spice mixes, hand tumbled, marinated 12 to 24 h (4 °C) and processed in a small commercial dehydrator or a large commercial smokehouse/oven.

Sufficient pathogen lethality was achieved using a commercial smokehouse process with high wet-bulb temperature, or when drying in a small commercial dehydrator (6 h) was followed by  heating for 10 min in a 133° oven. Across all processes and spices, survival of Saga 200, E. coli O157:H7, and Salmonella spp. was not significantly different (p<0.05). Saga 200 could serve as an effective pathogen surrogate for in-plant validation of turkey jerky processing. For a copy of this poster, click HERE.