Fate of Escherichia coli O157:H7 in ground beef following high-pressure processing and freezing.
The purposes of this study were to evaluate the efficacy of high pressure to inactivate Escherichia coli O157:H7 in ground beef at ambient and subzero treatment temperatures and to study the fate of surviving bacteria postprocess and during frozen storage. Fresh ground beef was inoculated with a five-strain cocktail of E. coli O157:H7 vacuum-packaged, pressure-treated at 400 MPa for 10 min at -5 or 20 degrees C and stored at -20 or 4 degrees C for 5-30 days. A 3-log CFU g(-1) reduction of E. coli O157:H7 in the initial inoculum of 1 x 10(6) CFU g(-1) was observed immediately after pressure treatment at 20 degrees C. During frozen storage, levels of E. coli O157:H7 declined to <1 x 10(2) CFU g(-1) after 5 days. The physiological status of the surviving E. coli was affected by high pressure, sensitizing the cells to pH levels 3 and 4, bile salts at 5% and 10% and mild cooking temperatures of 55-65 degrees C. High-pressure processing (HPP) reduced E. coli O157:H7 in ground beef by 3 log CFU g(-1) and caused substantial sublethal injury resulting in further log reductions of bacteria during frozen storage. HPP treatment of packaged ground beef has potential in the meat industry for postprocess control of pathogens such as E. coli O157:H7 with enhanced safety of the product.