This article written by Dr. Reynold Bergen, BCRC Science Director, originally appeared in the December 2013 issue of Canadian Cattlemen magazine and is reprinted with permission.
Last month’s column discussed a Beef Science Cluster study conducted by Dr. Colin Gill, Xianqin Yang, Madhu Badoni and Mohamed Youssef of AAFC’s Lacombe Research Station. These researchers found that both large and small packing plants can produce dressed beef carcasses with very few E. coli bacteria, even though they use very different food safety interventions and strategies. But E. coli-related recalls still happen occasionally. How does beef get contaminated when the carcasses carry so few E. coli? Two papers published by this research team (Journal of Food Protection 75:144-149 and Food Control 31:166-171) help explain how this can happen.
What They Did: This research was done in a large packing plant that processed up to 280 cattle per hour, and a small packing plants that processed up to 200 cattle per week. Bacterial counts were made on carcasses leaving the cooler, then on workers hands, gloves, conveyor belts, beef trim (for grinding) and primal cuts (e.g. for steaks and roasts) as the beef moved from the chiller through the fabrication line.
What They Learned: Chilling successfully prevented microbial growth on the carcass sides in the larger plant. In the smaller plant, carcasses actually had 99% fewer viable E. coli after chilling than when they entered the cooler three days earlier. The longer cooling time used by the smaller plant allowed the carcass surface to become drier, which killed more E. coli.
Conveyor belts are a potential source of bacterial recontamination. Some conveyor belt parts (e.g. plastic slats on conveyor belt surfaces) are simple to clean routinely. Other parts (e.g. hinges between slats) are very difficult to clean thoroughly. These hard-to-clean parts may act as a hiding spot and breeding ground for microbes. More E. coli were found on conveyor belts at the smaller plant, indicating the larger plant did a better job of routinely cleaning and drying its conveyor belts and other fixed equipment.
Beef: Hamburger (ground beef trim) carries a higher risk of bacterial contamination than muscle cuts. A one inch cube of beef trim has a surface area of six square inches. If this cube is ground through a 1/8 inch die, it’s exposed surface area increases to more than 30 square inches. At the same time, any bacteria that may have been on the surface of the original cube will be mixed in, and will have a lot more meat surface area to grow and multiply on. This is why it is so important to always cook hamburger to a “well done” endpoint. Unlike trim, bacteria on the surface of steaks or roasts will remain on the surface, so they will be exposed to (and killed by) full heat for as long as the beef is cooked.
E. coli numbers were very similar on primal cuts and trim from the smaller plant and primal cuts from the larger plant. However, trim from the larger plant actually had lower E. coli numbers than primal cuts. This is probably because primal cuts are handled repeatedly as they move down the fabricating line, but trim isn’t. The larger plant may be able to control E. coli levels on primal cuts better if it changes how it manages worker’s gloves.
Gloves keep worker’s hands from contacting the meat surface. But cotton or steel mesh gloves will not prevent bacterial contamination. Bacteria are everywhere in every environment, so worker’s hands can be contaminated in a variety of ways before they put their gloves on and begin work. In fact, office staff had as much E. coli on their hands as the line workers did at the end of their shifts. At the larger plant, line workers wore cotton gloves underneath steel mesh gloves. Cotton and steel mesh gloves are porous, so they will not prevent bacterial movement from hands to meat. In fact, warm hands and wet cotton gloves may provide a good environment for bacterial growth. Line workers at the smaller plant wore rubber gloves over top of the cotton and steel mesh gloves. This may have helped reduce bacterial movement from gloves to meat. This helped the smaller plant reduce the amount of bacteria that were re-introduced to the primals as they were repeatedly handled on the fabrication line.
What it Means: Bacteria are present in both large and small beef plants. But the risk of contaminated beef can be minimized when beef processing facility management and workers understand and effectively implement known best management practices. Under the second Beef Science Cluster, this research team will help beef processing plants identify how to adjust in-plant practices to improve food safety.
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