The impact of Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes preparation methods on high-pressure processing efficacy in apple and orange juices.

The use of high-pressure processing (HPP) to inactivate foodborne pathogens within fruit- and vegetable-based juices is well understood; however, less is known regarding HPP-induced sublethal injury of bacterial cells and potential detection of stress-adapted bacterial cells during post-HPP cold storage. FDA Juice HACCP requires HPP-treated juice manufacturers to demonstrate a 5-log reduction of the pertinent microorganism and maintain the 5-log reduction throughout the product's shelf-life. A barotolerant, or tolerant of high pressure, and a barosensitive, easily damaged by high pressure, strain of Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes were prepared in three growth conditions (neutral, cold-adapted, or acid-adapted) and used to evaluate HPP inactivation with increasing pressure levels (200-600 MPa) in two juice matrices (apple and orange). A 75-day shelf-life analysis was conducted on HPP-treated juices inoculated with acid-adapted, barotolerant strains for each pathogen and assessed for inactivation and detection. Acid-adapted cells provided the most conservative results for inactivation studies, and E. coli O157:H7 was the most barotolerant of the three microorganisms. Under the conditions tested, a 5-log reduction of L. monocytogenes MAD328 was achieved immediately following pressure treatment, S. Cubana required 24 h, and E. coli O157:H7 TW14359 required 4 days of post-HPP cold storage to attain a 5-log reduction. Positive enrichments of L. monocytogenes in orange juice were observed during cold storage while maintaining the 5-log reduction. These results suggest, under the conditions tested, the preferred inoculum preparation for HPP validation studies is the use of acid-adapted, barotolerant strains. At 586-600 MPa (180 s, 4 °C), a 5-log reduction was achieved during post-HPP cold storage, suggesting sufficient HPP lethality is reached at elevated pressure levels combined with a subsequent cold holding duration.