Experimental Procedure
Ground beef, 85%-lean was purchased at a local retail supermarket and was allowed to remain on the counter in the microbiology laboratory for 24 hours at room temperature. At the end of this time, the aerobic plate count (APC) of the ground beef was determined to be approximately 12,000,000 colony forming units (CFU) per gram.
Three food contact surfaces were evaluated in these experiments.
A commercial hard maple cutting board, 12"x18"x11/2", Pro-Chef, from Boos Company, Effingham, IL
Plastic cutting board, 12"x18"x11/2", Plasti-Tuff, from Teknor Apex, Pawtucket, RI
Stainless steel surface in the form of the outside bottom of a stainless steel 12"x20"x4" pan, from Volwrath, Sheboygan, WI
These surfaces were marked off in squares equivalent to 8 square inches (2.8"x2.8"). To simulate contaminated surfaces, approximately 1 ounce of ground beef was smeared, using a paper towel, over the surfaces for approximately 2 minutes until there was a maximum saturation of ground beef adhering to the surfaces.
Each surface was then sampled using dacron-tipped swabs that were rinsed in letheen broth. Each swab was wetted, rubbed across the surface in one direction, rinsed in 10 ml letheen broth, rubbed in the opposite direction, and rinsed a second time. Appropriate dilutions were made and plated on aerobic count PetrifilmTM. The PetrifilmTM was incubated at 35ºC for 48 hours.
In Experiment 1, the contaminated surfaces were simply wiped with home-style dish cloths that had been rinsed in 3 solutions:
Tap water
1 part 5% white vinegar (H.J. Heinz, Pittsburgh, PA) combined with 4 parts water
A 200-PPM quaternary ammonium compound sanitizer (Red Sink Sanitizer, Jefco Laboratories / SMS Technologies, Chicago, IL)
In Experiment 2, the conventional 3-step wash-rinse-sanitize procedure was used. A Viking #43 brush (Sparta Brush Company, Sparta, WI) was used to scrub the 3 surfaces in 4 gallons of detergent solution (Yellow Dishsoap, Jefco Laboratories / SMS Technologies, Chicago, IL). The surfaces were rinsed in flowing water. Then, a 200-PPM quaternary ammonium compound (Red Sink Sanitizer, Jefco Laboratories / SMS Technologies, Chicago, IL) was squirted from a bottle onto each surface.
In Experiment 3, each of the 3 surfaces was sampled before and after scrubbing under flowing, 100-110ºF water for 30 seconds using a Viking #43 scrub brush.
xperiment 1 demonstrated that rinsing a cutting board with a solution of 1 part 5% vinegar to 4 parts water was a more effective sanitizer than using a quaternary ammonium compound solution for removing aerobic bacteria from a food contact surface. Assuming that there are not more than 1,000 Salmonella per 8 square inches (which is a high estimate), vinegar would be effective in reducing the numbers of this pathogen on surfaces to a safe level with no other treatment. Using only water and using a quaternary ammonium compound solution were quite similar in their sanitizing performance, but not as effective as the vinegar solution. The data indicate that a lower population of bacteria was present on the stainless steel surface. This is an indication that bacteria do not adhere to stainless steel as easily as to plastic and wood surfaces. The data also indicate that bacterial contamination is much easier removed from a stainless steel surface.
In Experiment 2, it is evident that the rinsing-after-washing process does little to reduce bacterial counts, even though the surfaces were rinsed with flowing water. Applying the quaternary ammonium compound solution had essentially no value. This has been apparent in practical sampling of food contact surfaces in retail food operations. The data indicate that washing surfaces with the detergent solution was the critical step for removing aerobic bacterial contamination from food contact surfaces.
Experiment 3 shows the practical value of the pre-wash, rinse, and scrub before putting the cutting board into the detergent-and-water sink. Simply scrubbing the cutting board in flowing water, without the use of a detergent reduced the bacteria enough that even if there were a heavy load of Salmonella, Campylobacter jejuni, or other pathogens, there would be so few pathogens remaining that the surface would be considered safe. Putting a cutting board containing pathogens into a clean detergent solution in a sink merely contaminates the wash water.
Conclusions
The FDA code and health departments across the United States have emphasized the use of sanitizing chemicals as the critical point for making food contact surfaces safe. These data show that this assumption is not always accurate. Wiping the surface with a clean cloth soaked in vinegar appears to be a very effective sanitizer, based on the data. Simply rinsing and scrubbing a dirty surface with flowing water seems to be more effective than cleaning and sanitizing food contact surfaces with a cloth dipped in a quaternary ammonium compound solution. It is also known that when a quaternary ammonium compound solution becomes dirty in an open bucket into which dirty cloths are dipped, the solution becomes susceptible to degradation by filth, dirt, and other debris. As a result, the solution does not remain at its beginning strength over a period of 2 hours that the solution is used. The quaternary ammonium compound solution used in this experiment was dispensed from a squirt bottle to maintain its effectiveness and prevent degradation.