Ozone inactivation of norovirus surrogates on fresh produce.

Preharvest contamination of produce by foodborne viruses can occur through a variety of agents, including animal feces/manures, soil, irrigation water, animals, and human handling. Problems of contamination are magnified by potential countrywide distribution. Postharvest processing of produce can involve spraying, washing, or immersion into water with disinfectants; however, disinfectants, including chlorine, have varying effects on viruses and harmful by-products pose a concern. The use of ozone as a disinfectant in produce washes has shown great promise for bacterial pathogens, but limited research exists on its efficacy on viruses. This study compares ozone inactivation of human norovirus surrogates (feline calicivirus [FCV] and murine norovirus [MNV]) on produce (green onions and lettuce) and in sterile water. Green onions and lettuce inoculated with FCV or MNV were treated with ozone (6.25 ppm) for 0.5- to 10-min time intervals. Infectivity was determined by 50% tissue culture infectious dose (TCID(50)) and plaque assay for FCV and MNV, respectively. After 5 min of ozone treatment, >6 log TCID(50)/ml of FCV was inactivated in water and ∼2-log TCID(50)/ml on lettuce and green onions. MNV inoculated onto green onions and lettuce showed a >2-log reduction after 1 min of ozone treatment. The food matrix played the largest role in protection against ozone inactivation. These results indicate that ozone is an alternative method to reduce viral contamination on the surface of fresh produce.

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 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. 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.