Penn State Researcher Developing Nonthermal Ways to Kill Food Pathogens

Penn State researcher developing nonthermal ways to kill food pathogens
Friday, March 31, 2006

University Park, Pa. -- Soft-spoken and mild-mannered, Ali Demirci doesn't seem like a natural born killer. The associate professor of agricultural and biological engineering in Penn State's College of Agricultural Sciences has a decidedly unthreatening appearance. But make no mistake -- he's every germ's worst nightmare. "I don't like pathogens," he says simply. "My work is all about finding novel ways to kill them without using heat. Employing nonthermal ways to destroy pathogens allows us to decontaminate food without damaging the products." There are good reasons for coming up with new processing technologies to increase food safety, according to Demirci. "Infectious diseases are increasing throughout the world," he says. "Even though food production and storage systems are advanced, and strictly regulated in the United States, about 76 million cases of intestinal infectious diseases occur annually. Therefore, efforts to minimize foodborne infectious diseases have increased significantly in the last decade." Foodborne pathogens, including E. coli O157:H7, Salmonella and Listeria monocytogenes, cause serious outbreaks in this country and all over the world due to consumption of contaminated meat, poultry, eggs, milk, fruits and vegetables, Demirci points out. To produce safe foods, novel technologies are being investigated for various applications. "Emerging technologies include irradiation, high hydrostatic pressure, pulsed electric field and ohmic heating," he says. "I have been investigating the use of ozone, supercritical carbon dioxide, electrolyzed oxidizing water and pulsed UV-light. "They all seem promising to combat food-borne pathogens," Demirci adds. "However, more research is needed to find the best application for each technology, as well as optimizing the process for a specific application. We hope the efforts will pay off by reducing outbreaks due to consumption of minimally processed foods." Ozone has been proven to be a more effective antimicrobial than the most commonly used disinfectant, chlorine, against a wide range of microorganisms, Demirci explains. It has been used safely in water treatment plants for decades. In 2001, the FDA approved using ozone to treat raw commodities and decontaminate minimally processed fruits and vegetables. "In Europe and Japan, ozone is used to increase shelf life of foods such as meats, fruits and cheeses," he says. "Ozone has certain characteristics that make it attractive for use as a sanitizer in food processing. It is a strong antimicrobial agent with high reactivity and spontaneous decomposition to a nontoxic product -- oxygen. "Ozone decays quickly in water, thus, its use may be considered as a process rather than a food additive, with no safety concerns about consumption of residual ozone in food products," he says. "Ozone has been used with varied success to inactivate microflora on meat, poultry, eggs, fish, fruits, vegetables and dry fruits." In his laboratory, Demirci and his associates have used ozone to decontaminate alfalfa seeds and sprouts as well as small fruits, such as strawberries. For seeds treated with ozone, a 92 percent reduction in pathogens was achieved using a two-minute contact time, and a better than 99 percent reduction was achieved with a 64-minute contact time with aqueous ozone. For strawberries, 99.9 percent reduction was obtained using pressured gaseous ozone after 64 minutes of contact time. Electrolyzed oxidizing (EO) water is another novel disinfecting and cleaning agent, which is produced by electrolysis of a very dilute saltwater solution in an electrolysis chamber. The generation of EO water involves subjecting the saltwater to direct current voltage, creating two types of water possessing different characteristics. One is a dilute sodium hydroxide solution (alkaline EO water), the other a mild hypochlorous acid solution (acidic EO water). "The antimicrobial activity of acidic EO water appears to be due to the combination of high oxidation-reduction potential (ORP), presence of chlorine and low pH. On the other hand, alkaline EO water can be used as cleaning agent to remove soils. "EO water has demonstrated strong bactericidal properties," says Demirci. "Our studies also suggest that EO water can be used instead of expensive cleaning and sanitizing products for clean-in-place cleaning of certain food-processing systems, such as dairies." As a pathogen killer, pulsed ultraviolet light also has a lot of potential. Ultraviolet light, an electromagnetic radiation in the spectral region, possesses germicidal properties, according to Demirci. It deactivates the DNA of microorganisms and thus destroys their ability to multiply and cause disease. "Ultraviolet technology is a nonchemical approach to disinfection," he says. "In this method, nothing is added, which makes this process simple, inexpensive and very low-maintenance." The key to making this technology affordable is that the ultraviolet light is pulsed. "Many researchers have demonstrated the effectiveness of UV-light for reduction of microbial loads on food surfaces by inactivating the bacterial components and DNA of microorganisms without adversely affecting the quality of the food," he says. "These studies involve continuous UV-light applications. "The conventional systems produce continuous UV-light with a power dissipation in the range of 100 to 1,000 watts," Demirci continues. "Generating these high-intensity, energy-density levels with continuous UV-light can be costly to the user, which demands that systems be designed for the maximum conversion and collection efficiency of UV radiation. However, pulsed UV systems can dissipate many megawatts of electrical power in the light source. "Therefore, a modest energy input can yield high peak power dissipation. The pulsed light flashes are created by compressing electrical energy into short pulses and using these pulses to energize an inert gas lamp. The lamp emits an intense flash of light for a duration of a few hundred microseconds. Because the lamp can be flashed many times per second, only few flashes are required to produce a high level of microbial kill," Demirci explains. "We have evaluated pulsed UV technology for decontamination of alfalfa seeds, corn meal, fish, honey, milk and water." Penn State got its experimental system through a NASA grant. "NASA is interested in our research and gave Penn State a food grant to fund part of it because we are experimenting with a dry system of decontamination that doesn't require chemicals or water and would be a useful process on a space station or shuttle because it requires only electricity." Documenting that these novel technologies are effective in killing pathogens in a controlled setting is just part of the challenge, Demirci points out. "In the laboratory environment over the last six years, we have proved that they work," he says. "But now, we have to figure out how to make them work on the production line. It is a huge challenge to boost these technologies' ability to kill pathogens to near 100 percent at production line speeds and transfer the technology to the commercial arena." The equipment to accomplish these novel technologies is all commercially available to food-processing companies, "but they don't know what to do with them," Demirci says. "We are focused right now on trying to determine what we need to do to make these cutting-edge concepts work commercially to reduce food-borne illness." What makes Demirci's research especially promising, he believes, is that it has applications to homeland security. "If a terrorist would contaminate the food supply or the water supply, these novel food-safety technologies, if perfected, could be used to decontaminate food and water supplies," he says. "We are investigating funding sources for our work with the defense and homeland security departments."

Contact Jeff Mulhollem jjm29@psu.edu 814-863-2719

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