The beef industry continues to be challenged with recalls and illnesses associated with Escherichia coli O157:H7. Since 1993, beef producers and packers have spent more than $420 million dollars on beef safety research. These investments have resulted in the publication of a significant amount of research data, best practices and guidelines to assist the beef industry in assessing the overall risk of their processes and products. An additional challenge comes in finding and applying the best practices and parameters to fit such a wide range of plant sizes, products, process capabilities and yet remain cost effective. While hot water continues to be an effective antimicrobial intervention, for beef carcasses, primals and trim, whether applied alone or in combination with an organic acid, issues arise in defining how “hot is hot” and in narrowing down appropriate water versus surface temperature. In addition, questions often arise as to the minimum temperature that must be achieved for the hot water treatment to still be effective in reducing levels of the pathogens of concern for the beef industry. This also brings to bear the real world application of antimicrobial interventions and the specific ability of a processor to achieve the pressure, dwell times and temperatures such as those published in the scientific literature and as they related to different types of carcass surfaces (fat and lean). Temperatures and dwell times applied in a plant situation may vary with the facility’s in-house hot water capability (and sustainability) and worker safety, as well as with desired line speed and available space on the line for a pre-fabricated final wash cabinet.
Both Salmonella and E. coli O157:H7 are human pathogens and natural inhabitants of cattle. Although E. coli O157:H7 has been associated with fewer reported illnesses when compared to Salmonella, the severity of the illness, with the development of hemolytic uremic syndrome, and the case mortality rate, particularly for immunocompromised individuals, is significantly higher than for Salmonella. The presence of these organisms in cattle at slaughter and in associated products, poses poses a risk in raw beef products from both a public health and a regulatory perspective.
The objectives of this project were to determine the potential of hot water applied over varying exposure times and temperatures to reduce the levels of Salmonella Typhimurium, Escherichia coli O157:H7 and coliforms/Escherichia coli on beef carcass surfaces and to evaluate the effect of varying exposure times and temperatures of hot water on meat surface type (fat and lean).
Beef inside (IR) and outside rounds (OR) were obtained and subdivided into quarters for this project. Rifampicin-resistant strains of S. Typhimurium and E. coli O157:H7 were combined with bovine feces to make a fecal slurry which was then used to inoculate the meat surfaces. Uninoculated fecal slurries were spread on additional pieces in order to obtain naturally occurring coliforms and E. coli of fecal origin likely to occur on these meat surfaces. Meat samples, both lean (IR) and fat (OR), were exposed to 3 different temperatures of hot water designed to increase the meat surface temperature to 150oF, 165oF and 180oF and 3 different dwell times of 5 s, 10 s, and 15 s. Following treatment, the inoculated products and controls were analyzed for pathogen reduction, reduction in naturally occurring coliforms/E. coli and lean and fat color. The project was repeated in triplicate. Data was analyzed using PROC GLM of SAS (SAS Institute, Inc., Cary, NC). Least squares means will be generated for main effects and separated using the PDIFF option when appropriate with an alpha-level P<0.05.
There were no differences (P > 0.05) in the log reductions of S. Typhimurium and E. coli O157:H7 on the lean surfaces on the inside round for all three temperature treatments (66, 74, and 82°C). Although the 15 s treatment resulted in a numerically higher log reduction (Table 1) than the 5 and 10 s treatments, each of the times resulted in at least a 1 log reduction of both S. Typhimurium and E. coli O157:H7 for lean surfaces of inside rounds. For the fat surfaces of the beef outside round all three time treatments for the 82°C and the 10 and 15 s treatments for the 74°C resulted in the highest log reduction for S. Typhimurium. The 5 and 10 s dwell times for treatments at 66°C and the 5 s dwell time at 74°C resulted in the lowest log reduction of S. Typhimurium and E. coli O157:H7. The only time and temperature treatment for the fat surfaces of the outside round that did not result in at least a 1 log reduction for S. Typhimurium was the 66°C for 5 s treatment. For E. coli O157:H7 all temperature and time treatments resulted in at least a 1 log reduction for the fat surfaces of the outside round. These data show that as the water temperature increased the lean surfaces had a higher color recovery value; however, for all treatments the 24 h post treatment color of the lean surfaces was still acceptable. For the fat surfaces there were no differences (P > 0.05) for 24 h post treatment color recovery for any of the temperature treatments.
Based on the results of this study, time have a more significant impact on log reduction of S. Typhimurium and E. coli O157:H7 than temperature for the lean surfaces of the inside round. For outside round fat surfaces, both time and temperature play an important role. Higher temperatures resulted in greater a log reduction for both S. Typhimurium and E. coli O157:H7. For E. coli O157:H7 all temperature and time treatments resulted in at least a 1 log reduction for the fat surfaces of the outside round. On both lean and fat surfaces of beef inside and outside rounds for each of the hot water temperatures, there were no differences (P > 0.05) in log reductions of coliforms and E. coli based on time of application. However, on the fat surfaces, the 82°C treatment provided the highest log reduction for both groups of organisms. It is important that antimicrobial interventions do not create quality issues, such as discoloration, for the products. This results in additional costs to the processor in trimming and in lost yields. While there was some initial discoloration of lean and fat surfaces immediately after treatment, for all treatments the 24 h post treatment color was acceptable.