The study suggests that the use of cast copper alloys during food processing may help prevent cross-contamination of E. coli better than stainless steel, say researchers from the University of Southampton in the UK and the Copper Development Association in New York.
Their findings appear in the June 2006 issue of the journal Applied and Environmental Microbiology.
The study could counter a current trend in the food processing sector to use equipment made of stainless steel in their plants. Stainless steel is believed to be easier to clean and does not corrode as easily as copper under the frequent chemical cleanings needed to remove harmful pathogens.
Escherichia coli O157 is one of the most serious food-borne pathogens worldwide, causing symptoms ranging from diarrhea to hemorrhagic colitis. Cattle is a major reservoir of E. coli O157, therefore outbreaks are primarily associated with consumption of undercooked ground beef, the researchers stated.
"Cross-contamination of infected meat with points of contact during processing makes it extremely difficult to maintain," the scientists stated in a press release. "Currently, stainless steel has been the metal of choice for food preparation, however, studies have shown that even with consistent cleaning and sanitation procedures bacteria can remain viable."
In the study cast copper alloys, a mixture of metals containing varying degrees of copper, were exposed to E. coli. The same methods were used on stainless steel. Some of the copper and stainless steel samples were mixed with beef juice, some without.
The mix was incubated at either 22 degrees Celsius or four degrees Celsius for up to six hours. The results showed that three copper alloys not exposed to beef juice completely killed E. coli when stored at 22 degrees Celsius.
Only the metal alloys containing 85 per cent or more copper significantly reduced E. coli at four degrees Celsius, the scientists found.
With beef juice, alloys made up of 93 per cent or more copper greatly reduced E. coli at 4 degrees Celsius, while only one alloy (containing 95% copper) completely killed the bacterium at 22 degrees. No significant reduction in cell numbers was reported for stainless steel.
"These results clearly demonstrate the antimicrobial properties of cast copper alloys with regard to E. coli O157, and consequently these alloys have the potential to aid in food safety," say the researchers.
A similar study in 2003 by the university and the copper association found that using copper alloys for food processing surfaces holds promise for stemming Listeria contamination.
Listeria monocytogenes contamination is usually associated with the processing of ready-to-eat meat and poultry products. The study showed that the survival time of the often-deadly bacteria at room temperature is reduced to 60 minutest to 90 minutes on a copper-based surface, depending on the alloy.
During the 4.5-hour time period of the tests, there was only a minimal reduction of the bacteria on stainless steel, the scientists found.
Both studies were funded by the International Copper Association and managed by the Copper Development Association.