ASEE Prism Magazine - October 2002
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Natural-Borne Killers

Food poisoning can make you plenty sick—and even lead to death—but help is on the way. Engineers are developing new technologies that can destroy the deadly microorganisms that cause it.

- By Alice Daniel

Think about the pressure at the deepest point in the Pacific, 36,000 feet below the water's surface. Now multiply that not once, not twice, but 10 times. It's mind-boggling to imagine, but if you're a food-borne pathogen under the watchful eyes of engineers at Washington State University, that's just the kind of stress you're under.

It's called ultra high pressure and it's one of many applications engineers are experimenting with to kill deadly microorganisms and make food safer—a task that is likely to be appreciated by anyone who has ever experienced the sheer misery of food poisoning. According to the Centers for Disease Control, 76 million Americans get sick, 325,000 are hospitalized, and 5,200 die annually from food-borne illnesses. Salmonella, Listeria, and Toxoplasma account for the majority of deaths caused by known pathogens, but it is the lethal strain of the bacteria E. coli (0157:H7) that is ingrained in the public consciousness. In 1993, one high-profile outbreak left four children dead and 700 people ill after they ate undercooked hamburgers at Jack in the Box restaurants in the Northwest.

The CDC states that the prevention of food-borne diseases is a major public health challenge, one that Gustavo V. Barbosa-Cánovas, a professor of food engineering and director of the Center for Nonthermal Processing of Food (CNPF) at Washington State, takes seriously. He is one of the engineers experimenting with such technologies as ultra high pressure, a process that relies on a pump to generate enough pressure to kill microorganisms without damaging the food. Food is placed inside a plastic bag and then immersed in water inside a cylinder. A pump pressurizes the water, which, in turn, pressurizes the food. “There's an equilibrium inside and outside the tissue of the food,” explains Barbosa-Cánovas. In fact, the difference between ultra high pressure and conventional thermal processing techniques that use high heat to destroy microorganisms is that the quality of the food is not adversely affected by the high pressure technique.

However, ultra high pressure alone is not capable of destroying spores, which evolve from bacteria and have a very thick outer layer. Spores might be found in foods that have a high pH such as canned vegetables and meats. The bacterium Clostridium botulinum is the number one enemy, says Barbosa-Cánovas, because in spore form it can cause the rare but deadly disease botulism. In such cases, heat is added to the pressure, but not enough to adversely affect food quality.

Other promising applications to kill microorganisms have evolved out of medical technologies. Ultrasound, for instance, destroys the basic functions of the microorganisms when it is applied at very high frequencies. “We're rocking them so fast and so violently, they just collapse,” says Barbosa-Cánovas. He offers an interesting analogy when explaining another process, pulsed electric-field technology: “It is like subjecting microorganisms to an electric chair with an extremely high voltage.” Ali Demirci, an assistant professor of agricultural and biological engineering at Penn State, is using pulsed ultraviolet light to kill microorganisms. By pulsing the light, the energy is intensified and, therefore, more
effective in disabling deadly pathogens by inhibiting DNA functions. “There is a big future for this technology,” says Demirci, who developed the pulsed UV system thanks to a NASA grant. “I have great confidence that this is a very powerful
system. All we need is to find the right application.”

 

Pass The Salt

The salt of the earth, literally, might prove to be one of the most useful solutions to treating food-borne pathogens when it is applied to the 17th-century principle of electrolysis. The technique, electrolyzed oxidizing (EO) water, generates both alkaline and acidic water by electrolyzing very dilute salt water into sodium and chloride. The acidic water can be used as a sanitizing solution to treat the surfaces of meats, fruits, and vegetables. It kills food-borne pathogens effectively because of the combination of a low pH, chlorine, and a high oxidation reduction potential. Microorganisms cannot grow at a low pH, and chlorine may interfere with metabolic activity, says Demirci. “Combining these produces a synergistic effect that kills microorganisms in a short time,” he says. The alkaline water, meanwhile, injures the microorganisms and also works well as a cleaning solution for food-processing equipment.

In the last 20 to 30 years, advancements have been made in the small-scale production of EO water so that it now can be generated on site. But the challenge of this technique is in making sure the solution comes into contact with the entire surface area of the food, especially the tiny crevices where microorganisms hide. It is a matter of experimenting with the parameters of the process—such as contact time, temperature, and even voltage and amperage applied to the machine to get better quality EO water—to make sure it is effective, says Demirci.

Today, many dairy farms go through a multi-step cleaning process on their milking systems that involves the storage and transportation of concentrated alkaline and acidic chemicals. But with a machine that generates EO water, farmers would be able to make the two solutions on site when needed. “If we prove that this works, farmers would only need to buy table salt, water, and electricity,” says Demirci. At the research and development level, EO water is proving to be highly effective, he says. It removes almost all of the milk solids from the pipes and it kills all of the microorganisms if given the proper treatment time and temperature. EO water may eventually save dairy farmers both money and storage space.

Yen-Con Hung, a professor of food engineering at the University of Georgia, is also working on various applications of EO water. “We think this technology has a lot of potential for the food processing industry and also for the consumer at home to wash fresh fruits and vegetables and to wash the cutting board,” says Hung. He stresses the importance of developing a smart machine—one that attaches to kitchen sinks and adapts to various needs. For instance, the water for washing a cutting board might have different properties than the water used for washing produce. “We want to achieve the maximum effectiveness without damaging the product or surface contact. You don't want residue on food. But when you're washing a counter top, you might want that water to have a residual effect,” says Hung, who is also working on enhancing the properties of EO water so that it will be less corrosive when used on food processing equipment. In Japan, a washing machine was recently introduced that uses EO water instead of detergent.

Demirci is also exploring an emerging technology—ozonation—that destroys microorganisms but leaves no residue behind. “Ozonation is a process, not an additive,” says Demirci. “After the treatment, the ozone is converted back into oxygen.” The challenge, once again, has to do with contacting the entire food surface. Demirci is experimenting with slight hydrostatic pressures and food-grade surfactants that break the surface tension of the water, allowing the ozone to make contact. “We haven't reached the point where we can kill all of the pathogens,” says Dermirci. “We can kill 99.9 percent of E. coli 0157:H7 on alfalfa seeds, but unless it's at least 99.999 percent, we don't call it a successful process.”

Even as engineers are applying technologies to kill food-borne pathogens, they also are adjusting the parameters of the very equipment needed to study those pathogens. When scientists at the USDA Eastern Regional Research Center in Wyndmoor, Penn., wanted to use a pilot plant setting to study the effectiveness of controlling food-borne pathogens in commercial fruit-processing equipment, they called on Paul Walker, a professor of agricultural and biological engineering at Penn State. “It's hard to study pathogens in a commercial setting,” says Walker. “The splashes, spills, and mists of the processing equipment would very quickly spread the contaminants all over the place. The first time that happens is the last time I want to enter that facility.”

Walker is developing a large containment chamber that both holds and decontaminates commercial-style fruit processing equipment. That way, researchers can determine the best strategies for controlling pathogens on a pilot plant scale, including the speed and firmness of the brushes, the length of the washing cycle, the water temperature, and the types of anti-microbial agents to be used. During processing, the chamber is held under negative pressure so no bacteria can escape. Once the processing cycles are complete, the chamber is filled with steam to decontaminate the entire system.

According to the Centers for Disease Control, food-borne illnesses can also be caused by manmade chemicals. North Carolina-based Triangle Laboratories, Inc. is marketing a new screen that reduces the cost and turnaround time for detecting contaminants such as dioxins in food. RapidScreen can be read by a layperson, guarantees no false positives, and takes three days, instead of the traditional 25 days, says Chad Roper, director of Business Development. RapidScreen's design evolved out of standard EPA methods—high resolution gas chromatography/mass spectrometry and isotopic dilution—but is tailored to the food industry. That's what engineers do, says Roper. “They take the proven technology and apply it to a very specific circumstance. They take science and modify the parameters to make it meet a real human need.”

 


Alice Daniel is a freelance writer based in Fresno, Calif.
She can be reached at adaniel@asee.org.