By Ron Long
The United States Food and Drug Administration (FDA) gave final approval for the application of ozone for disinfecting and sanitizing food and food processing environments in September 2001. Whether applied in gaseous phase in the air for storage, or dissolved in water for microbial or chemical control on food surfaces, the FDA action permits a great leap forward in making America’s foods safer with ozone. As a side benefit, ozone generally makes most foods last longer, too.
The approval accelerated what had been a simmering interest throughout the food-handling world. It would be an overstatement to say that interest in ozone treatment has come to a full boil among food processors, but as additional food/ozone related research findings come in, the industry is becoming more receptive to what, for most, is still an unfamiliar technology.
At present, the majority of ozone applications in the food industry is at larger bulk operations which use relatively high doses of disinfectant. Previously, throughout the food-handling chain, high doses of chlorine (up to 200 parts per million [ppm]) have been common. This raised concerns regarding by-product formation, such as trihalomethane (THM), a known carcinogen, formed as chlorine reacts with organic materials on food surfaces.
In certain instances (i.e., at large growers and packers who are treating tons of produce per hour straight from the field), it may be necessary to apply ozone dosages as high as 2-10 ppm in the process water. Even though the actual amount of ozone necessary to disinfect foods is low, the huge ozone demand created by high organic loads from the farm environment means systems must be designed to counter those loads with enough ozone left over to control microbes and, in some instances, to chemically destroy pesticides.
That ozone is a powerful sanitizer that is capable of remarkable microbiological control (even at low doses) is undisputed. Water treatment professionals, in particular, have become knowledgeable in the technology. Many know what ozone does and how it does it, at least with regard to water treatment applications.
Now, with the approval of ozone for food, these ozone-experienced water treatment professionals have an entirely new market for what is, essentially, an entirely new product: point of use (POU) ozone food sanitizing systems. Dealers can offer consumers and food service operators alike the ability both to serve safer food and to save money by extending the shelf life of produce, fruits, meats and fish.
The potential for the emergence of the POU ozone food sanitizer first became evident when the Electrical Power Research Institute (EPRI) successfully petitioned the FDA in the mid 90s in support of ozone in food processing. That resulted in a GRAS (Generally Regarded As Safe) status for the technology. Further work by EPRI resulted in the final FDA approval of ozone in food processing.
But testing results performed for the benefit of large food processors left a gap in validation of the process for POU customers, such as consumers and food service operators.
Soon after the original GRAS status award in 1997, this author began working with Dr. Joseph Montecalvo, Jr., professor and past chairman of the California Polytechnic University, Department of Food Science & Nutrition and a member of the Technical Advisory Panel of the US Department of Agriculture (USDA) National Organic Standards Board. The target was to develop protocols and execute testing of ozone food sanitizing systems for POU applications in the home and in the food service industry.
The peer-reviewed results of those tests have proven that small, properly designed POU ozone systems, applying dissolved ozone at very low levels and used in conjunction with safe food-handling practices, can significantly reduce risk exposure to foodborne pathogens. Research proved that a small ozone system used to rinse a variety of foods was capable of two- to four-log reduction in food pathogens on the surface of food products. Under the umbrella of a partnership among Dr. Montecalvo’s research group and the author, testing was conducted both at Cal Poly and Primus Laboratories in order to determine the sanitizing functionality of ozonated wash waters.
As background for the study, it was recognized that ozone itself is a highly reactive oxidizing agent with broad germicidal activity, used both in Europe and in the US as an alternative to chlorine for disinfecting water. Chemically, ozone is 52 percent greater in oxidation potential than chlorine, as well as 3,200 times faster. It acts over a broader spectrum of microorganisms than does chlorine and other commonly used sanitizing agents.
Next to fluorine, ozone is the most powerful oxidizing agent available. Because of its high oxidation capacity, the cell membrane of microorganisms is oxidized and ruptured, (lyced) thereby causing microbial cell destruction. This study focused upon determining the susceptibility of food pathogens to low levels of ozonated water (0.12-0.30 ppm) in an effort to determine the efficacy of ozonated water at those levels in food pathogen reduction. All microbiological food pathogen studies were conducted at the microbiological research laboratory of a leading California food safety research facility under the direct control of a registered microbiologist.
Pure cultures of E. coli, E. coli 0157:H7, Listeria monocytogenes, Staphylococcus aureus, Coliforms, Campylobacter jejuni, Shigella and Salmonella were purchased,1 grown in broth cultures and enumerated. Fresh samples of chicken, beef and lettuce were inoculated individually for each microorganism, creating two populations of 16 food samples for each food pathogen tested. A one-hour equilibration period at room temperature prior to treatment with ozonated water was maintained for all food samples. Using the small ozone system, each freshly inoculated food product was immersed in a continuously ozonated bath of municipal water (filtered through a one-micron absolute carbon filter prior to ozonation). Dissolved ozone levels reached a maximum of 0.3 ppm, as measured by the indigo thiosulfonate spectrophotometric methodology. Food products were then immersed at different immersion times (i.e., 10, 30, 60, 180 and 300 seconds) in order to determine the optimum time required for maximum microbial cell destruction.
For all experimental runs, controls were used which consisted of each inoculated food sample receiving a water wash only for the same immersion time. Following ozonation or water wash treatments, residual pathogen levels were determined by standard microbiological direct swab or Stomacher® sample preparation. Enumeration of bacterial numbers was conducted by using specific Food and Drug Administration- Association of Offical Analytical Chemists (FDA-AOAC) methods for each pathogen according to Bacteriological Analytical Manual (BAM), 8th edition published by AOAC.
The results of this study show that a four-log reduction (measured in colony forming units [cfu] per gram of food tested) in E. coli on the surface of fresh chicken from 5.1 x 108 cfu/gm to 1.65 x 104 cfu/gm. For total coliforms, a four-log reduction (from 3.5 x 107 to 1.7 x 103) was observed on fresh romaine lettuce after 180 seconds of immersion in ozonated tap water. A two- to three-log reduction in Listeria monocyto genes (from 8.5 x 10 cfu/gm to 2.2 x 105 cfu/gm) was found after 180 seconds of immersion in ozonated water. Little changes were observed in all cases for the control water wash; generally less than 0.5-log reduction.
A consistent three-log reduction in Staphylococcus aureus was observed on beef (sirloin steak) after 180 seconds of ozonated water immersion. A four-log reduction was found with E. coli 0157:H7 on romaine lettuce after 180 seconds of ozonated water immersion treatment. Additionally, a four-log reduction was observed for Campylobacter jejuni on chicken (i.e., 1 x 108 cfu/gm to 1.25 x 104 cfu/gm). A slightly less than four-log reduction was found after 180 seconds of immersion for Shigella on romaine lettuce and a four-log reduction in Salmonella was observed (3.9 x107 cfu/gm to 4.1 x 103 cfu/gm).
The results show that at dissolved ozone levels of 0.3 ppm and immersion times of 180 seconds, major reductions in surface food pathogens were consistently observed.
The results from this study allow for the following conclusions:
- se of the small POU system, as designed, confidently reduced foodborne pathogens from the surfaces of fresh food products tested.
- Overall, two- to four-log reductions were found for all eight food pathogens tested.
- To achieve optimum results, the immersion time of the food product with hand massaging (vigorous rubbing of the food surface to assure contact) in the ozonated water was found to be three to five minutes for dissolved ozone levels of up to 0.3 ppm, even though ozone levels as low as 0.12 and immersion times as brief as 10 seconds produced significant results on some pathogen species.
- The results further indicate that increasing the dissolved ozone levels results in greater reduction in bacterial numbers. Therefore, this may suggest that increasing the ozone levels above 0.3 ppm may reduce the contact time of the food product in the ozonated water. Further studies will be conducted in order to prove this concept.
- In all cases, water washing of the food products tested did not significantly contribute to food pathogen reduction. In nearly all cases, less than a one-log cycle reduction was observed.
- Use of a properly designed small ozone system may offer both the consumer and the food service operator an effective means of reducing the risk of foodborne pathogen levels in foods when coupled with safe food handling and application of Good Manufacturing Practices (GMP).
In a recent second groundbreaking study, Dr. Montecalvo’s team, together with the author, produced the first-ever microscopic video capture of the real-time destruction of the dangerous foodborne pathogen E. coli 0157:H7 utilizing POU ozone food sanitation technology. The new video shows the actual instantaneous cellular disruption of the bacteria with the addition of low levels of ozone gas dissolved in water.
“Food safety at the home level and in restaurants has become a national priority,” Montecalvo continued. “That’s why visually proving the effects of ozone on pathogens that make people sick is so significant. To our knowledge it’s never been done before in real time.
“The numbers of E. coli colonies utilized in the research were nearly one hundred million times greater than would typically be found on contaminated foods,” Dr. Montecalvo stated. “The recently completed video documentation agrees directly with our previous studies which show greater than four-log (99.99 percent) inactivation of bacteria such as E. coli 0157:H7, Salmonella, Listeria, Staphylococcus and Campylobacter on surfaces of lettuce, meat and poultry with low level ozone technology.”
As in the previous studies, the cellular disruption of the pathogen using 0.3 ppm low level ozone technology was accomplished.
Testing of the process for controlling dangerous foodborne pathogens has confirmed that low-levels of ozone applied to food surfaces can significantly reduce the risk of illness caused by bacteria on produce, fruit, meats, fish and poultry.
With a powerful, proven tool such as properly designed POU ozone systems, water treatment professionals now have new benefits to offer their customers and ozone’s list of applications continues to grow.
- From the American Type Culture Collection, www.atcc.org.
The University-level testing and video capture of the pathogen destruction utilized an Olympus IX51 Inverted Microscope donated exclusively for the study by Olympus America, Inc.
Although most strains of E. coli are harmless, occurring in the intestines of healthy humans and animals, this strain produces a powerful toxin and can cause severe illness. Animals, including birds, dogs and cows tolerate 0157:H7 far better than people and often shed the bacteria in their feces. The bacterium can be spread to foods in the field from fecal contamination by workers, by contact with bird or animal feces and by contact with water contaminated by such sources. The bacteria can then infect crops such as lettuce, spinach, onions or even apples when contaminated manure is used as fertilizer or when contaminated water is used to irrigate fields. Most recently, E. coli 0157 found in bagged salads packaged by Dole sickened over two dozen people in 2005.
About the author
Ron Long is President/CEO of Purity International, LLC, a manufacturer and marketer of ozone generators, ozone systems and ozone components. The company also manufactures the Behrick Air Dryer series. Long has been designing and manufacturing ozone systems since 1985. He was co-founder of Ozotech, Inc. and founder of Longmark Ozone Industries, Inc. He has produced ozone systems for major organizations and entities, including NASA’s Space Shuttle Program, Disneyworld, Robert Bosch, Inc., major beverage and water bottlers and many others. In addition to research with Cal Poly, he has assisted in ozone research with Clemson University, the US EPA and several private laboratories. He received his Bachelors degree from California State University, Fresno and has been awarded several ozone technology-related patents. He can be reached at Purity International, LLC; 3550 Sabin Brown Rd., Wickenburg, AZ 85390. Phone: (928) 684-2705. email: [email protected] or on the internet at www.purityintl.com