Ozone Re-Emerges as an Economical and Green Safety Tool

Because ozone is effective against all known bacteria and their spores, it can readily control ubiquitous pathogens like Listeria and Campylobacter. In some applications, such as produce, seafood, poultry, and ready-to-eat foods, ozone spray is applied directly to the product, resulting in longer shelf life or increased yield.

Many failures in the earlier use of ozone occurred because people in the industry failed to recognize its limitations. Because it is applied at much more dilute concentrations than conventional sanitizers, it is less likely to work with heavy soil (BOD) loads. Dissolved ozone is applied at anywhere from 1/10th to 1/50th the concentration normally used for chlorine sanitizers. Ozone is used at 2 to 5 parts per million (PPM), compared to 50 to 200 PPM for chlorine-based sanitizers.

Early use in poultry chiller applications, for example, failed miserably because a heavy BOD load overwhelmed the limited amount of ozone. A heavy BOD load must first be reduced. On hard surfaces, the ozone spray can be coupled with a high-pressure water stream. Heavy aqueous BOD loads can be addressed with pre-filtration followed by ozonation. While the practice of treating equipment with additional chlorine-based sanitizers does reduce surface bacteria, it does not remove the maturing soils that can develop into a biofilm, providing a receptive medium for rapid new colonization. Continuous ozone sprays prevent these biofilms from forming.

The concept of altering an innocuous oxygen molecule to make it into a potent cleaning and sanitizing agent that then reverts back to simple oxygen is difficult to imagine and has been greeted by a great deal of skepticism. The suggestion that it also has some capacity to degrease, lengthen shelf life, and increase yield turns skepticism into disbelief. The industry hopes education and word of mouth will be the driving force behind a new awareness of ozone’s benefits.

Kryptonite for E. coli?

Despite all this hope, questions remain. How large a role will ozone-based systems play in the future? Will ozone be able to replace chlorine and other chemicals? Real-life experience and research have provided some answers. In response to the Escherichia coli spinach outbreak in the spring of 2007, Fresh Express, a division of Chiquita, awarded $2 million for research on the possible causes and prevention of future E. coli outbreaks.

The results of those studies were released at a seminar held last September in Monterey, Calif. The headline in the San Jose Mercury News the next day read “Ozone Gas May Be E. coli Kryptonite.” According to the article, the research studies found that “ozone gas is faster and more effective than chlorinated water at sanitizing greens.” Seafood.com ran a story the same month reporting that Beaver Street Fisheries had upgraded its sanitation system at Tropic Seafoods, one of the largest lobster plants in the Caribbean, choosing a 100% ozone system and eliminating the use of all chlorine.

Robbins and colleagues at the University of Illinois evaluated ozone’s high degree of effectiveness against Listeria monocytogenes. The study, published in the March 2005 issue of the Journal of Food Protection, showed the wide disparity between the efficacy of ozone and that of chlorine in eliminating Listeria. An ozone concentration of 1 PPM produced an 8.16-log reduction in planktonic cells; a chlorine concentration of 100 PPM produced a 6.49-log reduction after 10 minutes of exposure.

Chlorine-based sanitizers are attractive because they are relatively inexpensive, a quality which will continue to make them valuable in our fight against various pathogens. At the levels allowed during production, however, the cleaning abilities of chlorine sanitizers are significantly limited. The control of ubiquitous agents like Listeria is better achieved through the continuous application of a more powerful sanitizing solution. The application of ozone, with an aqueous concentration that is not regulated because it simply breaks down into pure oxygen, can maintain an almost pre-production level of sanitation throughout the production day. This quality is what makes it so attractive from a food safety standpoint.

A Wake-Up Call

It’s about time for the ozone industry to wake up and develop the science and engineering necessary to make this technology the gold standard for food safety; the food industry must become familiar with ozone’s benefits. The Food and Drug Administration (FDA) approved ozone in June 2001 as an antimicrobial agent on food. According to Seafood.com, “This eliminates a problem with chlorine, the sanitizer still used in most of the food industry, but which can react with organic matter found in water to produce unwanted compounds.”