UV method rids leafy vegetables of pathogens
can dramatically reduce the risk of contamination, according to a
Canadian research study.
The new way of cleaning produce will not only make food safer to consume, but it should also extend the shelf life of products because vegetables are often spoiled by microbial action.
At least 19 food-borne illness outbreaks have been linked to leafy greens since 1995, resulting in two deaths and 425 people becoming seriously ill, according to figures from the US Food and Drug Administration.
Problems with contaminated vegetables getting to the market can occur when pathogens actually get into the internal tissue of such greens as lettuce, said Keith Warriner, a professor at the University of Guelph's department of food science.
When lettuce is harvested for bagged salads it is normally kept cool in containers of water and then washed again at the processing plant, he said. If the water is contaminated, which it sometimes is, bacteria will be passed onto the lettuce.
"You can wash it for as long as you like, but you're not going to remove all the pathogens because they can hide in cut edges and the pores of the lettuce leaves," he said.
To find a way to eliminate pathogens in vegetables, Warriner, along with researcher Christina Hajdok, decided to apply the same method used to decontaminate food cartons.
Like fresh produce, the surface of carton packaging material is full of crevices that can provide protective sites for microbes.
The method involves sterilizing milk, juice and soup cartons with a spray of hydrogen peroxide at the same time they are illuminated with UV light.
The UV light converts the hydrogen peroxide into antimicrobial free radicals that penetrate into the packaging material to inactivate microbes.
To test the method on produce, Warriner artificially contaminated tomatoes, cauliflower, iceberg lettuce, romaine lettuce, Spanish onions and broccoli with Salmonella. After "cleaning" the vegetables using the hydrogen peroxide and UV method, he managed to achieve almost complete inactivation of the pathogen.
"The good thing about hydrogen peroxide and UV is that they make free radicals that can penetrate right into the subsurface of vegetables so we can ensure the pathogens in the lettuce leaf can be inactivated, something that washing cannot do," said Warriner.
Consumers would not actually be consuming any hydrogen peroxide by eating vegetables that have been cleaned by the method, said Warriner.
Plants contain enzymes called catalase that degrade hydrogen peroxide into water. The free radicals are so short-lived that within seconds they do their job and are converted to water as the by product.
Warriner said he has determined the optimal levels of hydrogen peroxide and exposure time. Next, he will test his decontamination method on produce contaminated with E. coli O157:H7 and other viruses to show the true potential of the system.
In October last year, 23 people in three states became sick from eating lettuce contaminated with E. coli O157:H7. Most people aren't aware that, next to ground beef, fresh produce is the most common culprit in food-borne illness, Warriner said.
At least 19 food-borne illness outbreaks have been linked to leafy greens since 1995, resulting in two deaths and 425 people becoming seriously ill, according to the US Food and Drug Administration.
