Hide decontamination technique cuts pathogen risk

The techniques include dehairing, radiation and a cattle-washing system, which has become one of the major decontamination techniques used in the meat business. The scientists also developed a test that provides a pathogen count, cutting the cost of such sampling by 98 per cent.

The developments provide an example of the successful transfer of scientific knowledge into industry practice. Over the last ten years, the beef-processing industry has spent more than $750m to increase the safety of their products, say researchers at the agriculture department's research service.

Much of the effort has focused on ways of removing contaminants from carcasses. However an Agricultural Research Service (ARS) study showed such methods are not the most efficient, as pathogens tends to gather on cattle hides, which becomes a problem they contaminate the meat during hide removal. ARS is the US Department of Agriculture's chief scientific research agency.

ARS scientist Mohammad Koohmaraie and other researchers on the project realized that removing pathogens before removing the hides would be a more effective way to reduce the risk of carcass contamination.

They worked on developing a practical, effective cattle-washing system to reduce on-hide pathogen levels.

The process involves cleaning the hide-on carcass in a high-pressure-water washing cabinet to remove excess organic matter. The carcass is then sprayed with an antibacterial compound. The scientists found several effective compounds, including sodium hydroxide, Chlorofoam, trisodium phosphate, phosphoric acid, acidified chlorine, ozonated water, electrolyzed oxidative water, and cetylpyridinium chloride.

“When companies decide which compound to use, they must also consider cost, waste disposal, and worker safety,”​ the researchers said in a release describing the project. “We tested various compounds to provide alternatives for companies to select from.”​

In field trials, subjecting live cattle to a water wash and two applications of a chemical compound reduced the number of meat samples that tested positive for O157:H7 to 3 per cent from 23 per cent.

The beef industry has since implemented chemical decontamination based on those tests and saves millions of dollars a year as a result, the ARS claims.

The scientists collaborated with several industry partners while developing and transferring the technology. They include the National Cattlemen’s Beef Association, Cargill Meat Solutions, Harris Ranch Beef, Future Beef Operations, Tyson Fresh Meats, Inc., Swift & Company, Electric Aquagenics Unlimited, Ozone International, and Safe Foods Corporation.

Koohmaraie estimates that about 40 per cent of the feedlot-raised beef harvested in the US now undergoes hide-on carcass-washing treatment, a development that benefits both beef companies and consumers.

“Cargill Meat Solutions spent millions to install hide-washing cabinets in each of the company’s six processing plants,"​ he said. "Now with fewer samples testing positive for E. coli, they save millions of dollars every year.”​

He links the method as being one of the factors that has reduced the incidence of related food borne illness. The US Department of Agriculture’s Food Safety and Inspection Service reported that the incidence of E. coli O157:H7-positive ground beef samples collected fell by 43.3 per cent after the beef industry started using the washing cabinets.

The Center for Disease Control has also noted significant reductions in illnesses caused by E. coli and the pathogens Listeria, Campylobacter, Yersinia, and Salmonella.

Before developing the washing treatment, the researchers first experimented with chemical dehairing. This process proved very effective—reducing bacterial prevalence to 1.3 per cent in one study from 50 per cent —but it was prohibitively expensive. Because it seemed to be impractical for widespread industry adoption, the researchers turned their efforts to chemical decontamination.

The researchers also examined the effectiveness of using low levels of radiation on beef carcasses to reduce pathogens before cutting and processing into ground beef.

High-penetration, high-energy radiation is a safe method of killing bacteria, but it can alter the beef’s odor and flavor. The scientists then studied low-dose, low-penetration electron beam (E-beam) irradiation—which only penetrates 15 millimeters below the surface.

They discovered that the technology does effectively reduce pathogens on the carcass surface and had little to no influence on the smell or taste of the meat when it was used to make stir fry or ground beef.

Koohmaraie and the team also developed techniques to evaluate the effectiveness of their pathogen-reduction practices. They recognized that there were no reliable methods to count pathogens within a sample, a factor they say the beef-processing industry identified as a priority.

Scientists responded by developing two methods for counting pathogen numbers — referred to as “enumeration” — on cattle hides and carcasses and in feces and ground beef.

Other tests used in the industry could spot the presence of a pathogen in a sample but not the amount of it. These tests operated through a process that causes the pathogens to grow. But because the microbes didn’t grow at a steady or predictable rate, it was impossible to tell how many had existed before the tests were run.

In addition to enabling beef processors to evaluate the effectiveness of the methods they’ve adopted to reduce pathogen levels, enumeration provides information that can be used for making risk assessments for the public, ARS stated.

One of the enumeration methods involves using a “spiral plater,” a special instrument that they compare to a petri dish on a turntable.

Spiral plating works best on samples where a high pathogen load could be expected, such as fecal matter or hides. The test uses a calibrated syringe to distribute the sample through a stylus onto an agar plate. The plate rotates as the stylus distributes the sample from the center of the plate to the edges. The movement concentrates microbes in the center.

Toward the edges, the sample gets a lot thinner, which allows counting bacteria over a very large range.

The second method uses a hydrophobic or water-repelling grid printed on a membrane filter. The method works better for carcass and ground beef samples that have low numbers of pathogens, if any, ARS stated.

First a sample is placed on the filter. Then a vacuum sucks the liquid from the sample through the filter, leaving the bacteria on the grid. Both methods enable scientists to count bacterial colonies and identify the target organisms within the sample.

The enumeration costs about $100 per sample if non-ARS methods are used. Using ARS methods, the cost drops to about $2 per sample, according to the agency.

Currently, ARS tests quantify Salmonella and E. coli O157:H7, but the researchers hope to extend the technology to other pathogens.

A highly publicized E. coli outbreak in 1993 increased consumer awareness of foodborne pathogens and prompted a spike in scientific research into pathogens and changes in food safety practices in the industry.

The Centers for Disease Control and Prevention (CDC) attributes about 73,000 illnesses and 60 deaths every year to E. coli O157:H7—one of the Shiga toxin-producing E. coli (STEC) and the variety responsible for the 1993 outbreak.

Though E. coli O157:H7 can harm humans by deactivating ribosomes and destroying kidney cells, cattle can host them without harm.

The US consumes about 27 billion pounds of beef every year and exports another 450 to 500 million pounds abroad.

Most of the research was done at the ARS Meat Animal Research Center in Clay Center, Nebraska.