Author
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Zaika, Laura |
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Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/23/2003 Publication Date: 9/1/2003 Citation: ZAIKA, L.L. INFLUENCE OF NAC1 CONTENT AND COOLING RATE ON OUTGROWTH OF CLOSTRIDIUM PERFRINGENS SPORES IN COOKED HAM AND BEEF. JOURNAL OF FOOD PROTECTION. 2003. v 66(9). pg. 1599-1603. Interpretive Summary: One of the most common types of food poisoning in the United States is caused by the bacterium Clostridium perfringens. Illnesses have been traditionally associated with inadequate cooling practices in retail food service operations. Thus, there was a need to determine the time and temperature for cooked cured meat products to remain pathogen-free and provide vital data for performing risk assessment on cooked meat. We demonstrated that ham containing >2% NaCl will restrict the growth of this deadly pathogen even when the rate and extent of cooling is extended to 15 hours. Similar results were obtained with beef containing >2% NaCl. However, C. perfringens can grow to dangerously high levels in beef containing <2% NaCl. These findings will be of immediate use to retail food service operations and regulatory agencies to aid with the disposition of products subject to cooling deviations and, therefore, will enhance the safety of the cooked foods. Technical Abstract: The effect of NaCl concentration and cooling rate on the ability of Clostridium perfringens to grow from spore inocula was studied using a process that simulates the industrial cooking and cooling of smoked boneless ham and beef roast. Sufficient NaCl was added to 2 different ground commercially-obtained cooked hams (designated ham A and ham B)to contain 2.4, 3.1, 3.6 and 4.1% (w/w) and 2.8, 3.3, 3.8 and 4.3% (w/w), respectively, and to raw ground beef to contain 0, 1, 2, 3 and 4% (w/w). Ham C, a specially-formulated and commercially-prepared product, was supplemented with NaCl to contain 2.0, 2.5, 3.0 and 3.5%. The samples were inoculated with a three-strain mixture of C. perfringens spores to obtain about 3 log10 CFU/g. Portions, 5 g, of meat were spread into thin layers, 1-2 mm, in plastic bags, vacuum-packaged and stored at -40oC. Thawed samples were heated at 75oC for 20 min and subsequently cooled in a programmed water bath from 54.4oC to < 8.5oC in 15, 18, or 21 h. C. perfringens was enumerated by plating on tryptose-sulfite-cycloserine agar and incubating in an anaerobic chamber at 37oC for 48 h. Population densities in cooked ham and beef increased with increasing cooling time, and NaCl exerted a strong inhibitory effect on germination and outgrowth of C. perfringens. In beef, while 3% NaCl completely arrested growth, pathogen numbers increased by >3, 5 and 5 log10 CFU/g in 15, 18 and 21h, respectively, when the NaCl content was <2%. C. perfringens did not grow during cooling for 15, 18 or 21 h in ham samples containing >3.1% NaCl. Results suggest that a 15-h cooling of cooked ham, normally formulated to contain > 2% NaCl, would yield an acceptable product (<1 log10 CFU/g increase in C. perfringens population); however, in beef containing <2% NaCl, C. perfringens populations may reach levels high enough to cause illness. |