Fate of Escherichia coli O157:H7 in ground beef following high-pressure processing and freezing

Aims: 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. Methods and Results: 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 106 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 102 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. Conclusions: 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. Significance and Impact of the Study: 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.