WHAT IS OZONE AND WHERE CAN IT BE FOUND?
Ozone is a highly reactive form of oxygen, consisting of three oxygen atoms (O3). It is a potent oxidant/disinfectant that quickly decomposes to diatomic oxygen (O2), while reacting with targeted organic matter or microorganisms. Ozone is naturally generated in the stratosphere, the upper atmosphere layer that protects us from harmful radiations. Gaseous ozone is formed also in the atmosphere during lightning, and on earth surface by photochemical reactions, UV sterilization lamps, and high voltage electric arcs.
SIGNIFICANCE OF OZONE IN FOOD PROCESSING
Ozone is a potent antimicrobial agent. It can effectively kill viruses, bacteria, fungi, and parasites, including those causing food spoilage or human diseases. Efficacy of ozone, however, depends on the target microorganism and the treatment condition. Commercial applications of ozone include purification of drinking water, sterilization of containers for aseptic packaging, decontamination of fresh produce, and food preservation in cold storage. Ozone also is useful in deodorizing air and water.
HOW IS OZONE GENERATED INDUSTRIALLY?
Ozone is commonly generated by electrical discharge. In this method, dry air or oxygen is passed between two parallel or concentric electrodes that are coated with a dielectric material. Oxygen molecules are broken down to charged oxygen atoms, which recombine to form ozone molecules. Depending on the feed gas, ozone production rate varies from 1-3% (w/w) to 6-16% (w/w) for air and pure oxygen, respectively.
HOW DOES OZONE KILL MICROBES?
Ozone destroys microorganisms by reacting with oxidizeable cellular components, particularly those containing double bonds, sulfhydryl groups, and phenolic rings. Therefore, membrane phospholipids, intracellular enzymes and genomic material are targeted by ozone; these reactions result in cell damage and death of microorganisms.
HOW IS OZONE DIFFERENT FROM OTHER CHEMICAL TREATMENTS?
The strong antimicrobial properties of ozone is partially related to its oxidation-reduction potential (2.07 V), which is higher than that of chlorine (1.36 V). Ozone has many advantages over chlorine and other antimicrobials. Ozone destroys microorganisms instantly and effectively, without leaving harmful residues in treated food or processing water. Therefore, ozone is safer and environmentally friendlier than most other antimicrobials. Ozone gas should be produced on-site and it cannot be stored or transported. Although this may be considered a disadvantage, it is meritorious that only air or oxygen is needed to produce the sanitizer.
IS OZONE SAFE TO USE IN FOOD PROCESSING?
Ozone is a colorless gas at ambient conditions, and it is readily detectable by the human nose at 0.01-0.05 ppm. At low concentrations, ozone has a characteristic pleasant odor, similar to that of fresh air after a thunderstorm. High concentration of ozone gas in air is objectionable and could pose health risks. According to OSHA regulations, the permissible level of exposure to ozone in the workplace environment is 0.1 ppm, during a normal 8- hour day (40-hour workweek). The shortterm exposure limit is 0.3 ppm for exposure of less than 15 min (4 times per day). Therefore, the production and use of ozone in food processing should be controlled and monitored, and excess ozone should be removed by a commercial „ozone destruct” unit.
CURRENT AND POTENTIAL APPLICATIONS OF OZONE IN THE FOOD INDUSTRY
Ozone can be applied, in its aqueous or gaseous phase, to decontaminate foodcontact surfaces, sanitize equipment, recycle wastewater, and decrease the pesticide levels on fresh produce. The microbiological quality and shelf-life of vegetables, fruits, cheeses, eggs, nuts, and meats can be improved when these products are directly treated with ozone, or stored in ozonecontaining environment. For fresh-produce processing, ozone can be used to sanitize processing water, or to decontaminate the product itself. The use of ozone in the gaseous phase helps in controlling mold and bacteria, both, in the air and on the surface of the product.
COMMERCIAL OZONE-GENERATION SYSTEMS
Gaseous or aqueous ozone generators are commercially available and relatively inexpensive instruments. Generators vary in production capacity from a few pounds to hundreds of pounds of ozone per day. It should be cautioned, however, that suitable treatment chambers, monitoring devices, and excess gas destruction units, should be designed and integrated with the ozone generators to produce functional food treatment systems.
IS THE APPLICATION OF OZONE APPROVED BY REGULATORY AGENCIES?
In 1982, ozone was declared GRAS for treatment of bottled water, and since 2001, FDA approved its use as an antimicrobial agent in foods. Depending of the application, ozone use may fall under the guidelines of the federal insecticide, fungicide, and rodenticide act (FIFRA), thus entering the jurisdiction of the Environmental Protection Agency (EPA).
Food processors should confirm with ozone equipment suppliers or directly with the EPA to determine if a particular ozone application will require a special pesticide registration under FIFRA. Ozone is also listed in the national organic program (NOP) final rule, which permits its use in processed products labeled as “organic” or “made with organic”. There are no special labeling requirements for ozone-treated products.