Evaluation of peroxyacetic acid as a post-chilling intervention for control of Escherichia coli O157:H7 and Salmonella Typhimurium on beef carcass surfaces.

Four experiments were conducted to test the efficacy of peroxyacetic acid as a microbial intervention on beef carcass surfaces. In these experiments, beef carcass surfaces were inoculated with fecal material (no pathogens) or fecal material containing rifampicin-resistant Escherichia coli O157:H7 and Salmonella Typhimurium. Inoculated surfaces were subjected to a simulated carcass wash with and without 2% l-lactic acid treatment before chilling. In Experiments 1 and 2, the chilled carcass surfaces were sprayed with peroxyacetic acid (200 ppm; 43°) for 15 s. Peroxyacetic acid had no effect on microbial counts of any organism measured on these carcass surfaces. However, lactic acid reduced counts of E. coli Type I (1.9log(10) CFU/cm(2)), coliforms (3.0log(10) CFU/cm(2)), E. coli O157:H7 (2.7log(10) CFU/cm(2)), and S. Typhimurium (2.8log(10) CFU/cm(2)) entering the chilling cooler and prevented growth during the chilling period. In Experiment 3, peroxyacetic acid at different concentrations (200, 600, and 1000 ppm) and application temperatures (45 and 55 °C) were used to investigate its effectiveness in killing E. coli O157:H7 and S. Typhimurium compared to 4% l-lactic acid (55 °C). Application temperature did not affect the counts of either microorganism. Peroxyacetic acid concentrations up to 600 ppm had no effect on these microorganisms. Concentrations of 1000 ppm reduced E. coli O157:H7 and S. Typhimurium by up to 1.7 and 1.3log(10) CFU/cm(2), respectively. However, 4% lactic acid reduced these organisms by 2.7 and 3.4log(10) CFU/cm(2), respectively. In Experiment 4, peroxyacetic acid (200 ppm; 43 °C) was applied to hot carcass surfaces. This treatment caused a 0.7log(10) CFU/cm(2) reduction in both E. coli O157:H7 and S. Typhimurium. The collective results from these experiments indicate that peroxyacetic acid was not an effective intervention when applied to chilled inoculated carcass piece surfaces.