A new study revealed it may be possible for a potential microwave-like device to be utilized to kill 99 percent of all bacteria on fresh produce and other foods prior to consumption. This device would not only be quick (requiring just a minute of treatment) but use very little energy.
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In a paper entitled, “Decontamination of raw produce by surface microdischarge and the evaluation of its damage to cellular components,” researchers from the University of Maryland theorized a way to decontaminate raw produce using plasma science.
Gottlieb S. Oehrlein, PhD, a professor at the University of Maryland in the Department of Materials Science and Engineering, noted the genesis of the technology was to work on an interaction of low temperature plasma operating at atmospheric pressure and interacting with model polymers and biomolecules.
For example, lipopolysaccharide provided a basic understanding of which groups are susceptible to attack by reactive species formed in low temperature plasma.
“When the opportunity arose to work on actual food items and realistic pathogens, we were able to apply the approaches evaluated before on very simple systems for these products,” he comments.
Rohan V. Tikekar, PhD, a professor at the University of Maryland in the Department of Nutrition and Food Science, was also instrumental in the study.
“As food safety professionals, we are always exploring new effective and efficient antimicrobial treatments, particularly for minimally processed products such as fruits and vegetables and meats,” he says. “When I was approached about working with Dr. Oehrlein to evaluate how well SMD can inactivate pathogens on fresh produce surface, I was quickly on board.”
The team evaluated the use of surface microdischarge (SMD)—a cold atmospheric pressure plasma (CAP) reactor with ambient air or N2/O2 mixtures as working gas—as an effective tool for the inactivation of bacteria on raw produce.
“We find that with one minute of SMD treatment, the SMD is capable of achieving over two logarithmic reduction (>99 percent) of E. coli O157:H7 inoculated on agar plates and spinach leaves,” Dr. Oehrlein says. “We further studied the effect of SMD treatments on the morphology and structural integrity of bacterium using microscopy, attenuated total reflectance-FTIR, and X-ray photoelectron spectroscopy.”
With those, the researchers found that the SMD treatments can: 1) damage the bacterial cell membrane, lead to cell expansion, and eventually cell lysis; 2) cause the oxidation of cellular components by forming carboxylic acid (COOH) and carboxylate (COO-) groups inside the bacteria and/or on the bacterial cell wall; and 3) lead to the modification of polysaccharides and phosphorus containing groups typically found in phospholipids and DNA.
“The reactive species created in the plasma change chemically the very surface and the sub-surface region of polymers and biomolecules,” Dr. Oehrlein says. “For instance, atomic oxygen can react with carbon of polymer chains and produce volatile CO and CO2, thus changing the structure of the material.”
According to Dr. Tikekar, the technology is highly flexible and simple to build and use, which means it can be utilized in food manufacturing. Eventually, restaurants and food processors could install larger devices into their production and processing lines to make things safer for all involved.
“Since the SMD reactor can be easily scaled up and integrated into existing production lines, it is highly appealing for applications in centralized large-scale raw food processing facilities,” he says. “It is also desirable for onsite treatments in homes and restaurants because it functions well with just air and electricity and produces minimal gas exhaust. Nevertheless, the reactive species created here must be treated with caution and cannot just be released in room air, since they are also the reason for the efficacy of these approaches.”
Pros and Cons
Dr. Oehrlein explains the simplest approach would be a container that houses the discharge device and contains the food items to be treated. After a given exposure, pathogens should have been eliminated, although this will depend on the types of foods to be treated. These aspects, he says, require more research.
“The potential benefits are easy scale-up and integration with current production lines or installed equipment, and a minimal need for resources since it functions based on just air and electricity,” he says. “As mentioned, the gas exhaust would have to be directed away from people, e.g. as done for the exhaust from a stove with a chimney.”
Not that there aren’t challenges. Dr. Oehrlein notes the broad spectrum of scientific questions considering the large number of different foods and pathogens, along with the engineering of the most efficient devices.
Still, it’s something both Dr. Oehrlein and Dr. Tikekar believe could be game changing in the industry in the years to come.