The researchers placed small samples of each of theSalmonella strains onto the copper alloys, and stored them at different conditions to simulate different types of food processing environments in which the bacteria might exist.

Salmonella can be a problem in dry foods and wet foods,” Ravishankar said.

Dry foods include products such as peanut butter, almond products and chocolate, while wet foods include vegetables such as tomatoes, lettuce and spinach, milk and other dairy products and anything processed in a wet environment.

Salmonella survived for longer in the simulated wet conditions than in dry conditions, Zhu said. In addition, “copper resistant strains under dry conditions only survive for about 15 minutes – just about five minutes longer than the sensitive strain.”

In dry conditions, oxidation occurs more quickly because the copper in the surface comes into contact with oxygen in the air.

The researchers further tested how well the bacteria would survive in a nutrient-rich medium versus in a non-nutrient medium. “The rich medium can protect the cells from the copper,” said Ravishankar. “We saw survival on the nutrient-rich medium initially, but soon the cells started to die off because of nutrient depletion.”

The researchers also saw that Salmonella cells on alloys with high copper concentrations began to die out much faster than those on surfaces with lower copper concentrations.

“For the highest copper concentration Salmonella cells die off in under 30 minutes,” said Zhu. “But for the other alloys containing lower copper concentrations, the bacteria can survive up to two hours.”

This is still much less than the two weeks survival achieved by Salmonella on stainless steel, leading the researchers to their conclusion: Copper alloys may be more hygienic surfaces for food processing and preparation than stainless steel.

Ravishankar said she would like to do further tests to see if organic materials on a food contact surface, such as crumbs wedged in cracks or leftover protein residues or grease from oils, could change the effectiveness of copper alloys as antimicrobial agents.

“In a food processing environment, there are going to be hard-to-reach areas where you can still have food particles,” said Ravishankar. “We want to see if the presence of food particles or some kind of organic matter on the copper surfaces changes the efficacy of the copper alloy. Does it become less effective, or is it equally effective?”

Using pure copper is not currently an option, Ravishankar said, due to the high cost of pure copper, and also due to as-yet unresolved concerns that high concentrations of copper residues could potentially have toxic effects on humans as well, if they were ingested.

In the meantime, while using copper alloys as cooking surfaces instead of stainless steel may be slightly more costly, “it will be worthwhile,” Ravishankar said. The high antimicrobial potency of copper alloys, she said, has the potential to significantly reduce cases of food poisoning.

Ravishankar’s study was funded by the International Copper Association, with preliminary research supported by Ravishankar’s start-up funds from the UA College of Agriculture and Life Sciences.