Killing Pathogens on Leafy Greens


A series of animations created by NMSU Media Productions
as part of the Fresh Produce Safety Initiative (FPSI)

About the FPSI

The aim of the Fresh Produce Safety Initiative is to develop and spread awareness about new processing techniques for fresh fruits and vegetables. Fresh and fresh-cut leafy vegetables, such as lettuce and spinach, have a leafy structure conducive to deep microbial penetration. Over the years, advancements in sanitizing agents and product recall strategies have increased the industry's ability to combat contamination. However, the engineering concepts behind sanitizer application techniques still have much to contribute. Combining microbiological and engineering initiatives is an important part of ensuring a safer food supply, as is distributing this information among fresh produce growers, retailers, processors, and general consumers. The Fresh Produce Safety Initiative Project is a collaborative effort between Ohio State, Iowa State, and New Mexico State University. It was funded by the USDA under their National Integrated Food Safety Initiative (NIFSI).



Using ozone during transport or cooling

Leafy greens are a leading cause of food poisoning in the United States. A new method of sanitizing greens, using gaseous ozone, kills microbes more effectively than liquid sanitizing alone. Adding an ozone generator into an existing processing chain – at the cooling or transport stages – can dramatically improve consumer safety without a big change in the production process.







Penetrating crevices with gaseous sanitizers

Crevices are a common structural feature of leafy greens, whether in the form of natural pores (stomata) or cuts and bruises from handling. Microbes, including pathogens that cause illness in humans, can hide in these crevices, When leafy greens are washed in chlorinated water, as is the common industry practice, this liquid sanitizer does not have time to penetrate crevices and kill the microbes within. This is because sanitizers in liquid solution have a fairly low diffusivity. Using a sanitizer with a higher diffusivity – such as ozone gas – makes it much more likely that microbes in crevices will be contacted and killed.







Liquid sanitizing plus gaseous sanitizing

Leafy greens are the leading cause of food poisoning in the United States. A highly effective way for commercial processors to kill microbes on leafy greens is to use a sanitizing process that combines liquid sanitizing with gaseous sanitizing, for example, washing in chlorinated water, then sanitizing with ozone gas.







How dirt impacts the sanitizing process

When produce is washed in commercial processing centers, dirt and debris in the wash water can bind up the chlorine sanitizer, reducing its effectiveness against microbes. An effective way to kill more microbes on leafy greens is to follow up this chlorine washing with a gaseous sanitizer, such as gaseous ozone, in a second step.







Why use a surfactant?

Other new methods of sanitizing greens, such as using surfactants in combination with liquid sanitizers, also can kill microbes more effectively than liquid sanitizing alone.






© 2014. Produced by New Mexico State University Media Productions as part of the Fresh Produce Safety Initiative, in cooperation with the Ohio State University and Iowa State University. The authors gratefully acknowledge support of the USDA-NIFA National Integrated Food Safety Initiative Grant No. 2009-51110-05902, titled: Pathogen inactivation in fresh produce by incorporation of sanitizers into existing operations within the produce chain.