Evaluation of batch and semicontinuous application of high hydrostatic pressure on foodborne pathogens in salsa

The effects of high hydrostatic pressure (HPP; 545 MPa) on strains of Esche richia coli O157:H7, Listeria monocytogenes, enterotoxigenic Staphylococcus aureus, and nonpathogenic microorganisms were studied in tomato-based sals a. Products were evaluated for the survival of the inoculated pathogens fol lowing HPP treatment and after storage at 4 degreesC and 21 to 23 degreesC for up to 2 months. Inoculated samples without HPP treatment, stored under the same conditions, were also evaluated to determine the effects of the ac id environment of salsa on the survival of inoculated strains. None of the inoculated pathogens were detected in the HPP-treated samples for all treat ments throughout the storage period. Inoculated pathogens were detected in the non-HPP-treated samples stored at 4 degreesC after 1 month, with L. mon ocytogenes showing the highest level of survivors. In the non-HPP-treated s amples stored at 21 to 23 degreesC, E. coli and S. aureus were not detected after 1 week, but L. monocytogenes was detected in low levels. Studies wit h nonpathogenic strains of the pathogens were conducted at Oregon State Uni versity using HPP treatments in a semicontinuous production system. The non pathogenic microorganisms (E. coli, Listeria innocua, Listeria welshimeri, and nonenterotoxigenic S. aureus) were inoculated together into a feeder ta nk containing 100 liters of salsa. Microbiological results of samples colle cted before HPP treatment and from the aseptic filler were similar to those obtained for the pathogenic strains. No survivors were detected in any of the HPP-treated samples.