Steam pasteurization to reduce bacterial populations on commercially slaughtered beef carcasses

A steam pasteurization system (SPS) has been shown in laboratory and commercial evaluations to effectively reduce bacterial populations on freshly slaughtered beef. Our study evaluate d the bactericidal uniformity of SPS. Samples were collected from the five anatomical locations, one per carcass, 40 samples per location , so that 200 carcasses were evaluated before and 200 after pasteurization. Each carcass was sampled by wiping a 300 c m2 area of the specified location with a moist, sterile sponge. For all locations, the total aerobic plate count (APC) after pasteurization was lower (P#.01). Before pasteurization, the midline was contaminate d most heavily (2.5 log10 cfu/cm2 ). After pasteurization, the neck and midline had the highest residual APCs (1.3 and 1.1 log 10 cfu/cm2, respectively). For all anatomical locations, the enteric bacteria (E. coli, total coliform, an d Enterobacteriaceae ) were lower (P#.01) after than before pasteurization. Only two of 200 pasteurized carcasses ha d E. coli populations greater than 1 cfu/cm2. During pasteurization, steam blankets the carcasses, theoretically providing uniform bacterial destruction. This study demonstrated the effectiveness of SPS for reducing total aerobic and enteric bacterial populations uniformly over five anatomical locations on commercially processed carcasses.


Summary
A steam pasteurization system (SPS) has been shown in laboratory and commercial evaluations to effectivel y reduce bacterial populations on freshly slaughtered beef.Our study evaluate d the bactericidal uniformity of SPS.Samples were collected from the five anatomical locations, one per carcass, 40 samples per location , so that 200 carcasses were evaluated before and 200 after pasteurization.Each carcass was sampled by wiping a 300 c m area 2 of the specified location with a moist, sterile sponge.For all locati ons, the total aerobic plate count (APC) after pasteurization was lower (P#.01).Before pasteuri zation, the midline was contaminate d most heavil y (2.5 log cfu/cm ). 10 2 After pasteurization, the neck and midline had the highest residual APCs (1.3 and 1.1 log 10 cfu/cm , respectively).For all anatomical 2 locations, the enteric bacteria (E.coli, total coliform, an d Enterobacteriaceae ) were lower (P#.01) after than before pasteurization.Only two of 200 pasteurized carcasses ha d E. coli populations greater than 1 cfu/cm .During pas-2 teurization , steam blankets the carcasses, theoreticall y providing uniform bacterial destruction .This study demonstrated the effectiveness of SPS for reducing total aerobic and enteric bacterial populatio ns uniformly over five anatomical locations on commerc i ally processed carcasses.

Introduction
The microbiological safety o f meat products has received increased attention in recent years.The potential for bacteria in meat products to cause illness and death has pushed this issue to the forefront for consumers, regulators, researchers, and the industry.
In July 1996, th e USDA-FSIS issued a final rule on "Pathogen Reduction ; Hazard Analysis and Critical Control Point (HACCP) Systems".The regulations require changes in the way industr y produces meat and meat products.Foremos t is the requirement that all slaughter facilities deve lop HACCP systems.In addition, facilities will be required to implement sanitation standard operating procedures and microbiologica l testing of carcasses, with standards for generi c E. coli and Salmonella being defined.Antimicrobial treatments during slaughter will l i kely be necessary to consistently meet these USDA microbial standards.In previous studies, steam pasteurization (Frigoscand ia Food Process Systems, Bellevue, WA) effectively reduced both pathogen (laboratory eval uations) and naturally occurring bacteria l population s (evaluations on commercial beef carcasses).The current study was designed to verify, in a commercial slaughter facility , the uniformity of bacterial destruction over the entire carcass surface.

Experimental Procedures
A commercial-s cale SPS was used after the final carcass wash in a beef slaughter facility.Sample s were collected during 2 processing days from randomly s elected carcasses immediately before and immediately after pasteurization.Samples were collected from inside round , loin, midline, brisket, and neck.One location was sampled per carcass and 40 carcasses were sampled per location before and after pasteurization (200 carcasses before and 200 othe rs after pasteurization).Samples were collected using the sponge technique required under the new USDA-FSIS regulations for carcass microbial sampling.Both sides of a single sterile sponge are passed over a 300 cm 2 area.The sponge is premoistened in a sterile stomacher bag cont aining 30 ml of diluent (.1% peptone diluent with .1% Tween 20) and, after sampling the specified area, is returned to the same diluent.Dilutions were plated on Petrifilm ™ plates to enumerate APCs, enteric bacteria E. coli (generic), total coliforms, and Enterobacteriaceae .Counts were made according to manufacturer's instructions.The minimum detectable count for Petrifilm™ plates was .1 cfu/c m .All data were converted 2 to log cfu/cm .The significance level was set 10 2 at P#.01.

Results and Discussion
For all carcass sites, the APC was lower (P#.01) after than before pasteurization (Table 1).Before pasteurization, the midline had the highest APCs; the loin had the lowest; and the inside round, brisket, and neck were intermediate.After pasteurization, the neck and midline had the highest APCs, approximately 1.2 log 10 cfu/cm .The inside roun d, loin, and brisket had 2 similar APCs, approximately .6 log cfu/cm .10 2 Pasteurizatio n reduced bacteria by 65% for inside round, 84% for loin, 96% for midline, 92% for brisket, and 60% for neck.
E. coli was present at low levels before pasteurization and wa s decreased ( P#.01) at all sites after pasteurization .E. coli populations on 189 of 200 carcasses fel l within the range <.1 to 1.0 cfu/cm before pasteurization .Some sam-2 ple counts were as high as 5 cfu/c m.After 2 pasteurization, 198 of 200 carcasses fell within the <.1 to 1.0 cfu/cm range, with only two 2 carcasse s having E. coli populations greater than 1 cfu/c m .Very similar results were found 2 for coliform an d Enterobacteriaceae populations.
In previous steam pasteurization evaluations, samples were collected from one carcass location .Those evaluations demonstrated effective bacterial destruction, but questions remained about the uniformity of bacterial destruction over th e entire carcass surface.Our study demonstrated that steam pasteurization reduces bacterial populations uniformly.A large surface area was sa mpled at each location, and the locatio ns represented the entire carcass.Steam pasteurization can reduce the risk of pathogenic bacterial contamination in beef, but is not a replacement for good sanitation standards, clean and carefu l slaughter operations, or Good Manufacturin g Practices.Steam pasteurization can serve as a critical control point for pathogens during slaughte r .Current technology allows automatic tracking of individual carcasses.Additionally, SP S provides assurance to processor s that USDA-FSIS microbiological standards will be met continuously.
immediately b efore steam pasteurization treatment; After = population immediately 1 after steam pasteurization treatment.Mean bacterial populations are averages of 40 replicates.SEM=standard error of mean. 2 Means with different superscripts are different (P #.01).a,b,c,d