Ozone use for the inactivation of listeria
Listeria is a common term to refer to a specific strain of bacteria species. There are seven (7) known species of Listeria. The specific species L. monocytogenes is the cause of Listeriosis, a serious infection caused by eating food contaminated with this strain of bacteria. This disease can be deadly and will pose a greater risk to those with weakened immune system. Both L. monocytogenes, and Liseteriosis, are commonly known only as Listeria, and Listeria illness.
Listeria is found in soils, this can lead to fruit and vegetable contamination. Listeria can also be found in all types of meat products, milk, and eggs. Higher risk foods are any uncooked or undercooked foods, unpasteurized milk, raw vegetables, and some ready-to-eat foods.
Click here to learn more about Listeria from the CDC (Center for Disease Control and Prevention).
Ozone can be used for the reduction, or elimination of L. monocytogenes on food products. Since achieving GRAS approval for the use of ozone for direct contact with food in 2001 the use of ozone for the elimination of L. monocytogenes has increased significantly.
To eliminate Listeria or any other bacteria with ozone successful implementation of ozone is necessary. While every application is different, there are a few fundamentals that will apply in most applications.
Implementation of Ozone
The most common method of using ozone for pathogen reduction is by dissolving ozone into water. Aqueous ozone is very stable, safe, and easy to manage. Typically, ozone is dissolved into water using an Ozone Injection System and then sprayed onto the surface requiring disinfection. This surface may be a hard equipment surface, or the surface of a food product.
In 2000, the Journal of Food Science published a paper by Kim & Yousef showing the effect of dissolved ozone in a batch reactor on Listeria monocytogenes. Dissolved ozone at 0.4 and 0.8 ppm inactivated 4.6 and 5.7 log CFU/ml within 30 seconds. Additional tests were run at higher dissolved ozone levels. Higher dissolved ozone levels did show faster (immediate) inactivation of Listeria monocytogenes.
Dissolved ozone can be sprayed on food and produce using spray bars, or other spraying methods. Conveyers work well to allow the sufficient contact time, and offer full coverage of the aqueous ozone. It is important that all of the produce is contacted by the aqueous ozone to achieve desired antimicrobial intervention. Contact times can be varied by altering conveyer speeds, spray tip design, and spray bar design/quantity. If water is already used in an application to wash produce it is very simple to add ozone to this water and achieve an antimicrobial intervention step without any major changes to the current processes.
The use of gaseous ozone for the elimination of pathogens is less common. There is less research showing the effects of gaseous ozone on bacteria. The application of gaseous ozone is dependent upon the temperature, humidity, contact time, and ozone levels. Research has been conducted to determine that gaseous ozone will reduce and inactivate L. monocytogenes; however, more research is necessary to determine the effectiveness of ozone within different variables.
Produce in need of disinfection can be placed in chambers, rooms, or even cargo containers for ozone treatment. A sealed area that can contain the produce and ozone gas while maintaining human safety will work. It is necessary to assure sufficient air movement past each piece of produce. Ozone levels from 1.0 — 100 ppm are used in this application with contact times from 20 minutes to 10 hours. For more information on the potential of using gaseous ozone in your application contact our application engineers today.
Click here for more information and to view ozone research papers on this topic