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Scientists explore pathogen killing methods without heat

By Ahmed ElAmin , 03-Apr-2006

Scientists are studying the effectiveness of new methods -- such as ozone and electrolyzed oxidizing water -- to kill pathogens in the plant without using thermal processes.

There are good reasons for coming up with new processing technologies to increase food safety. A more effective sanitizing process without destructive chemicals or harmful heat is attractive to processors, along with the possibility of lower costs.

Heat processes can often reduce the quality of foods.

Ali Demirci, an associate professor of agricultural and biological engineering at Pennsylvania State University, is investigating the use of ozone, supercritical carbon dioxide, electrolyzed oxidizing water and pulsed UV-light to decontaminate foods and ensure products are safe.

Other emerging technologies include irradiation, high hydrostatic pressure, pulsed electric field and ohmic heating.

" Employing nonthermal ways to destroy pathogens allows us to decontaminate food without damaging the products," he stated in describing his work.

All of the methods he is testing seem promising as a way for processors to combat food-borne pathogens.

"However, more research is needed to find the best application for each technology, as well as optimising the process for a specific application," he stated. "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 stated.

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, f ruits and cheeses.

"Ozone has certain characteristics that make it attractive for use as a sanitiser in food processing," Demirci stated. "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 the laboratory, Demirci and his fellow researchers have used ozone to decontaminate alfalfa seeds and sprouts as well as small fruits, such as strawberries.

For seeds treated with ozone, a 92 per cent reduction in pathogens was achieved using a two-minute contact time, and a better than 99 per cent reduction was achieved with a 64-minute contact time with aqueous ozone.

For strawberries, a 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. The method uses 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), and the presence of chlorine and low pH, Demirci stated.

Alkaline EO water can be used as cleaning agent to remove soils.

"EO water has demonstrated strong bactericidal properties," stated 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 stated. "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 stated.

Such 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.

"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," he stated. "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.

The team 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 gave Penn State a food grant to fund part of of the study because the scientists are experimenting with a dry system of decontamination that doesn't require chemicals or water. This 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 stated.

"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 per cent 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 manufacturers don't know what to do with them, Demirci stated.

"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," he stated.

Infectious diseases are increasing throughout the world. Even though food production and storage systems are advanced, and strictly regulated in the US and Europe, millions of cases of intestinal infectious diseases occur annually. Therefore, food processors have increased their efforts to minimise foodborne infectious diseases significantly in the last decade, pushed by laws.

About 76 million cases of intestinal infectious diseases occur annually in the US.

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.

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