Tuesday, December 25, 2007

Ozone Treatment to Kill Bacteria in Produce - Hope or Hype?

Every now and then, a new “breakthrough” product appears. The product, which may be anything from a sanitizer wipe to a means of detecting Salmonella instantly, is marketed as a panacea for consumers who are worried about food-borne disease. Unfortunately, these products often don’t live up to their hype.

This is the first article in my “Hope or Hype?” series. I’ll be monitoring new product releases that relate to food safety issues and, from time to time, I’ll give you my opinion, based on the available scientific information, as to whether or not the product claims are reasonable.

The Hype: The January 7, 2008 issue of Forbes magazine profiled an ozone generator, and the company that developed it, under the headline “The Ozone Solution. Purfresh aims to capitalize on E. coli scare stories by cleaning up fruits and vegetables”. The article described Purfresh’s equipment, which is used to produce ozone for produce sprayers and cold storage rooms.
The article’s headline implied that the Purfresh process is being used for both fruits and vegetables. Yet, all of the examples in the article described its use by fruit growers and packers. I wondered about this, and decided to see what studies have been carried out on the effectiveness of ozone treatment for eliminating pathogens from other produce such as lettuce or baby spinach.

I found several research articles, all of which confirmed that ozonated water is more effective than plain water. But the results were variable. A study-to-study comparison of performance was complicated by differences in the test conditions - ozone concentration, length of contact, water temperature and type and quantity of microbial contaminant - used in the various studies.

In a study of the effect of ozonated water on the bacterial levels in fresh-cut lettuce, rinsing the lettuce with ozonated water reduced the bacterial counts by roughly 95%, and extended the shelf life of the lettuce. That remaining 5% of the bacterial population, however, could still include pathogens such as Salmonella or E. coli O157:H7.

The effect of ozonated water on bacteria is very much dependent on the length of contact time. In a study of strawberries and raspberries that had been deliberately contaminated with Salmonella or E. coli O157:H7, researchers were able to kill approximately 99.9% of the bacteria. But it took more than one hour of soaking to do so.

The Bottom Line: Ozonated water was as effective as chlorinated water in most situations. And when ozone decomposes, it leaves no toxic byproducts behind in the food. But, while an ozonated water rinse can reduce overall bacterial levels and improve the shelf-life of fruits and vegetables, it cannot guarantee that the produce will be pathogen-free. Ozonation may be an improvement over chlorination, but it’s not a panacea.


  1. Hi Phyllis:

    I enjoyed your article about ozone. O3 technology has deepened with the advent of advanced oxidation and the use of UV light and catalysts. Some very interesting applications are coming forward. I have experience with O3 in water purification and I have a good understanding of the limitations in food safety, which there are. It is a poisonous gas, not particularly soluble in water and has very little residual. It is an effective oxidizer, however.

    You mentioned chlorine as a disinfectant that does maintain a residual. The problem with chlorine is that many people do not want the by-products of chlorination in their food. A technology that makes chlorination more efficient is electrolyzed water. We can get away from some of the problems of increasing Total Chlorine levels during chlorinating to achieve efficacy (breakpoint chlorination) because in the electrolytic process, pure hypochlorous acid (HOCL) creates an effective ORP at low concentrations of FAC and produces no hypochlorite. There is still contact time, Free vs. Combined chlorine, pH and temperature values affecting oxidation rates. This is where I am working on applications to enhance the technology.

    So far, neither O3 nor Electrolyzed Water is penetrating the food safety business very deeply. Both of these promising non-chemical technologies must be competitive within the very large and diverse chemical sanitizer markets. The future looks bright however for new technologies that can show high efficacy against the broad range of pathogens of concern, are safe, and cost effective.

    Please contact me to learn more about my work in sanitation and public health protection of food, water and air. rcosta1@cfl.rr.com

    Roy E Costa, R.S, M.S., M.B.A
    Public Health Sanitarian Consultant
    Environ Health Associates, Inc.

  2. Hi Mr. Costa,

    How can HClO not produce any hypochlorite (OCl-) if the ambient pH is 6-8--which is typical in these disinfectant applications? The pKa of HClO is 7.5 at 25C. This means that at a pH of 7.5 50% of the HClO will be HClO and the remaining 50%: ClO- (hypo). Can you help me understand the chemical basis of your assertion that HClO "contains no hypo". Thank you! RBG

  3. There is a lot of comment on ozonated water, but what about air-borne ozone that kills bacteria and pathogens? That is not even mentioned here and is the best way to circulate the oxidizer, thinner than water that is for sure, and easier to apply killing more pathogens than water?


Note: Only a member of this blog may post a comment.