Survival of bacteria in less than thorough cooked, brine-injected steaks

Bacteria that may include enteric pathogens are introduced into muscle tissues when they are injected with brine. Consequently, steaks of such non-intact, non-comminuted tissues should be cooked to temperatures sufficient to render them microbiologically safe. Studies were conducted to identify the minimum safe temperature for cooking those meats. Suspensions of Escherichia coli and Listeria innocua at numbers about 8 log cfu/ml, in broth or in brines containing 2% or 5% of each of NaCl and sodium tripolyphosphate that were not supplemented or were supplemented with 2% soy protein or 2% emulsified sunflower oil were injected into the centres of 3 cm thick steaks. Groups of four steaks injected with each type of suspension were cooked to temperatures at the centres of 50, 55, 60, 65 or 70 °C. Bacteria were recovered from samples from the centres of steaks, on agars that did or did not allow resuscitation of injured cells of each organism. The results indicated that E. coli but not L. innocua was injured by the brines; that supplementing brines with protein or oil did not protect the organisms from injury or inactivation by heating; and that cooking to a central temperature > 60 ⩽ 65 °C was sufficient to inactivate all bacteria in the meat. The centres of steaks were subsequently injected with 0.1 ml portions of five strain cocktails of E. coli O157:H7 or Listeria monocytogenes in broth containing a dye and the bacteria at numbers >8 log cfu/ml. Steaks were cooked to temperatures of 63, 64 or 65 °C, with holding for 0, 1 or 2 min after cooking before excision of all the dyed tissue from each steak and enumeration of bacteria from the tissue on resuscitating media. The results indicated that cooking to 65 °C without holding would be sufficient to reduce numbers of E. coli O157:H7 or L. monocytogenes in non-intact, non-comminuted steaks by ⩾7 log units