Each year a tiny, rod-shaped species of bacteria with a fondness for proliferating on human food causes numerous cases of food poisoning around the world, sometimes leading to severe illness and even death.
prepare food on surfaces made with materials that contain some amount of the element copper, known as copper alloys.
Ravishankar¹s lab collaborated with Chris Rensing, formerly an associate professor in the UA department of soil, water and environmental sciences and now at Research Triangle Institute International, for the study, which was published recently in the journal Food Microbiology.
³Chris Rensing had already done some research with copper, and he knew that copper surfaces have antimicrobial activity,² said Ravishankar. The International Copper Association donated six samples of copper alloys for the study, including samples of copper mixed with metals such as nickel, iron, chromium, phosphorous and tin that varied in their copper concentration from 60 to 99.9 percent.
Copper is harmful to bacteria because it reacts with oxygen in the atmosphere over time in a process called oxidation, which produces a residue that is toxic to some bacteria. Oxidation is what makes pure copper change in color over time from a rusty gold to a watery green.
³We decided to see the antimicrobial effect of all these copper alloy surfaces on Salmonella,² said Ravishankar. Salmonella was selected as the microbial guinea pig for the study because of its prevalence and the significant harm it causes worldwide because of diarrheal disease.
³Salmonella has caused outbreaks from eating a broad range of different types of foods, including meats and poultry, dairy products, peanut products, ice creams and even chocolate,² said Ravishankar.
She found that because of oxidation, food contact surfaces made of materials containing copper are far less habitable for bacteria than stainless steel, which showed no antimicrobial properties at all.
³Right now, food industries use stainless steel,² said Ravishankar, ³and stainless steel does not seem to have any antimicrobial activity.²
If there are bacteria on a stainless steel surface, she said: ³They will survive for a long time.²
One test by Ravishankar¹s lab manager, Libin Zhu, showed that Salmonella can survive for longer than two weeks on stainless steel surfaces.By contrast, the bacteria showed significant reductions on copper alloys.
³We tested three copper-resistant strains and one copper-sensitive strain,² said Zhu.
Copper-resistant strains are lineages of bacteria that have been exposed to copper for several generations, long enough for the cells to develop genetic resistance to its antimicrobial effects.
Copper-sensitive strains, by contrast, have never been exposed to copper and are much more susceptible to the toxicity of oxidation.
The researchers placed small samples of each of the Salmonella 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.
³Salmonella can be a problem in dry foods and wet foods,² 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, ³copper resistant strains under dry conditions only survive for about 15 minutes just about five minutes longer than the sensitive strain.²
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.³The rich medium can protect the cells from the copper,² said Ravishankar.
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,² said Zhu. ³But for the other alloys containing lower copper concentrations, the bacteria can survive up to two hours.²
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.
³In a food processing environment, there are going to be hard-to-reach areas where you can still have food particles,² said Ravishankar. ³We 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?²
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, ³it will be worthwhile,² Ravishankar said.
The high antimicrobial potency of copper alloys, she said, has the potential to significantly reduce cases of food poisoning.
Ravishankar¹s study was funded by the International Copper Association, with preliminary research supported by Ravishankar¹s start-up funds from the UA College of Agriculture and Life Sciences.
Research study report: http://www.ncbi.nlm.nih.gov/pubmed/22265316UA Department of Veterinary Science and Microbiology:
Daniel Stolte | University of Arizona
Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute
Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy