title: Influence of NaCl content and cooling rate on outgrowth of Clostridium perfringens spores in cooked ham and beef.
abstract: The effect of NaCl concentration and cooling rate on the ability of Clostridium perfringens to grow from spore inocula was studied with the use of a process that simulates the industrial cooking and cooling of smoked boneless ham and beef roasts. NaCl was added to ground cooked hams A and B (which were commercially obtained) to obtain levels of 2.4, 3.1, 3.6, and 4.1% (wt/wt) and 2.8, 3.3, 3.8, and 4.3% (wt/wt), respectively, and to raw ground beef to obtain levels of 0, 1, 2, 3, and 4% (wt/wt). Ham C, a specially formulated, commercially prepared product, was supplemented with NaCl to obtain levels of 2.0, 2.5, 3.0, and 3.5%. The samples were inoculated with a three-strain mixture of C. perfringens spores to obtain concentrations of ca. 3 log10 CFU/g. Portions of meat (5 g each) were spread into thin layers (1 to 2 mm) in plastic bags, vacuum packaged, and stored at -40 degrees C. Thawed samples were heated at 75 degrees C for 20 min and subsequently cooled in a programmed water bath from 54.4 to < or = 8.5 degrees C in 15, 18, or 21 h. For the enumeration of C. perfringens, samples were plated on tryptose-sulfite-cycloserine agar and incubated in an anaerobic chamber at 37 degrees C for 48 h. Population densities for cooked ham and beef increased as cooling time increased, and NaCl exerted a strong inhibitory effect on the germination and outgrowth of C. perfringens. For beef, while 3% NaCl completely arrested growth, pathogen numbers increased by > or = 3, 5, and 5 log10 CFU/g in 15, 18, and 21 h, respectively, when the NaCl level was <2%. C. perfringens did not grow during cooling for 15, 18, or 21 h in ham samples containing > or = 3.1% NaCl. Results obtained in this study suggest that a 15-h cooling time for cooked ham, which is normally formulated to contain >2% NaCl, would yield an acceptable product (with an increase of <1 log10 CFU/g in the C. perfringens count); however, for beef containing <2% NaCl, C. perfringens populations may reach levels high enough to cause illness.
mesh_terms: D000818:Animals; D002417:Cattle; D003016:Clostridium perfringens / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D003080:Cold Temperature; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004202:Disinfectants / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D008461:Meat Products / Q000382:microbiology*; D012965:Sodium Chloride / Q000494:pharmacology*; D013171:Spores, Bacterial / Q000187:drug effects / Q000254:growth & development; D013552:Swine; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D004202:Disinfectants; D012965:Sodium Chloride