ARS | Publication request: Thermal inactivation of Bacillus anthracis Sterne in irradiated ground beef heated in a water bath or cooked on commercial grills

Submitted to: Innovative Food Science and Emerging Technologies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 17, 2009
Publication Date: January 1, 2010
Citation: Juneja, V.K., Porto Fett, A.C., Call, J.E., Marks, H., Tamplin, M., Luchansky, J.B. 2010. Thermal inactivation of Bacillus anthracis Sterne in irradiated ground beef heated in a water bath or cooked on commercial grills. Innovative Food Science and Emerging Technologies. 11:123-129.

Interpretive Summary: Bacillus anthracis has been identified as a potential biological weapon. An intentional contamination of meat with B. anthracis spores could result in massive fatalities and large economic losses. This emphasizes the need to better define and quantify the heat treatment given to raw meat to provide an adequate degree of protection against survival of B. anthracis. The results suggest that relatively low levels of spores of B. anthracis do not possess any unique characteristics which would predispose them to survival under normal cooking parameters used for ground beef patties. We developed times and temperature regimens for predicting the destruction of this pathogen in beef. This information will be of immediate use to consumers and to the food industry and regulatory agencies to guard against this pathogen in foods.

Technical Abstract: The thermal stability of heat-shocked and non heat-shocked spores of the virulence-attenuated Sterne strain of Bacillus anthracis was evaluated at select temperatures in irradiated, raw ground beef (25% fat) heated in a water bath or cooked using two different commercial grills. For the former, 3-g portions of inoculated ground beef were packaged in bags that were completely immersed in a temperature-controlled circulating water bath held at 65 degree C (149 degree F), 70 degree C (158 degree F), 75 degree (167 degree F), and 80 degree C (176 degree F) for a predetermined length of time. For the latter, formed ground beef patties (95-g each) were inoculated with spore preparations A or B of the Sterne strain and then cooked on a commercial open flame gas grill or on a commercial clam-shell electric grill to achieve target internal temperatures of either 71.1 degree C (160 degree F), 82.2 degree C (180'F), or 93.3 degree C (200 degree F). For ground beef heated in a water bath, there was an observed reduction of ca. 2.5 to 3.0-log10 spores/g within 30 sec at 65 degree C (149 degree F) to 80 degree C (176 degree F). The calculated D-values were 0.09, 0.06, 0.06, and 0.03 min at 65 degree C (149 degree F), 70 degree C (158 degree F), 75 degree (167 degree F), and 80 degree C (176 degree F), respectively, for the steepest portion of the observed concave survival curves, and the corresponding z-value was 30.12 degree C. For ground beef patties that were inoculated with spore preparation A, cooking the patties on either grill resulted in a reduction of ca. 2.0 to 3.5 log10 CFU/g. Using spore preparation B, cooking the patties on the gas grill resulted in a reduction of ca. 0.8 to 2.9 log10 CFU/g, whereas cooking the patties using the clam-shell grill resulted in a reduction of ca. 1.0 to 1.9 log10 CFU/g for all temperatures tested. Thus, our data validated that heating ground beef in a water bath or cooking ground beef patties on commercial grills under conditions that may be typically used by consumers and/or retail establishments is effective at killing spores of B. anthracis Sterne.