PLACE

University of Wisconsin - Madison

PURPOSE

1. To develop and validate sufficiently lethal processes for use by commercial jerky manufacturers in heating and drying whole-muscle beef jerky.
2. To develop a simple method for commercial processors of whole-muscle beef jerky to evaluate the lethality of new processes using a commercially available lactic acid bacterial starter culture as a surrogate for Salmonella serovars and E. coli O157:H7.

Summary

A standardized process was used to inoculate beef strips with 5-strain cocktails of either Salmonella serovars or Escherichia coli O157:H7, marinade the strips in pH 5.3 marinade for 22-24 hours at 5ْ C, and then convert the strips to jerky using various heating/drying regimes. The number of surviving organisms was determined during and after the heating/drying. In some trials a commercial lactic acid starter culture was also evaluated as a potential surrogate for the pathogens. 1. A 5-log reduction for both Salmonella and E. coli. O157:H7 was best achieved by ensuring that high wet-bulb temperatures were reached and maintained early in the process (51.7ْ C or 54.4ْ C for 60 minutes, 57.2ْ C for 30 minutes, or 60ْ C for 10 minutes) followed by drying at 76.7ْ C (dry-bulb temperature). 2. Processes that met the USDA guideline with smaller safety margins were: a) heating and drying at 76.7ْ C (dry-bulb) within 90 minutes of beginning the process, b) heating for successive hourly intervals at 48.9, 54.4, 60, and 76.7ْ C (dry-bulb), or c) heating at 51.7ْ C (dry-bulb), followed by 76.7ْ C (dry-bulb) drying started before the product water activity was < 0.86. Achieving a ≥ 3.0 log reduction in the starter culture is a possible standard for validating process lethality.

Benefits

The results of the study clearly shows the importance of wet-bulb temperature in achieving mandated lethality, thus it is strongly recommended that processors use a wet-bulb thermometer for use in processing or use a hygrometer to monitor humidity and then use a commercial available slide rule to determine wet-bulb temperature from known dry-bulb temperature and % RH values. Reductions in Salmonella serovars and E. coli O157:H7 of ≥ 5.0 log CFU can be achieved in the production of whole-muscle beef jerky by ensuring that high enough wet-bulb temperatures are reached and maintained early in the process or that high dry-bulb temperatures heating and drying is done before the beef strip water activity has fallen below 0.86. This research should help minimize their operating cost while helping them to ensure food safety and public health protection. Plants will, however, need to validate that their methodology achieves these parameters.