Pre-Cut, Bagged Salad May Actually Contribute To Growth Of Salmonella

And I'm cooking pre-trimmed french beans right now for supper. <groan>

... we’ve repeatedly seen how pre-cut, bagged salad products can harbor ugly pathogens like listeria or salmonella. A new scientific study finds that pre-cutting these leafy vegetables may actually be contributing to the growth of salmonella.

... juices released from cut and damaged leaves can not only significantly encourage the growth of Salmonella enterica, but also enhance the pathogen’s ability to attach to the leaves of the salad and to the salad’s plastic bag container.

In short: The juices released from cut salad leaves may help grow more salmonella that is more difficult to get rid of — to the point where washing the salad will not remove the pathogens.

... exposure to the salad liquids aids in the forming of a biofilm that allows the salmonella to cling more durably to surfaces.

... salad leaf juices can also help to grow pathogenic E. coli bacteria. Before that, a 2012 review found that pathogens are particularly difficult to get rid of on fresh produce. [emphasis mine]

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Replies to This Discussion

If only I was better at growing my own leaves, then maybe I wouldn't have to worry about stuff like this...and should I expect it to happen more often if trump diminishes the FDA?

Interesting information.  I would not worry about the beans if you are cooking them.  As an added precaution, you could put them into a colander and rinse thoroughly.  But cooking should kill off any pathogens on your food.

On the other hand, salad is not cooked, although I used to know someone who stir-fried her lettuce.

What bothers me about the article is how incomplete it is.  It appears designed to instill fear, rather than empower the reader.  The authors did not say how much it takes to cause an infection.  Salmonella and E. coli can require an infectious dose of 10,000 organisms to infect a person.  If the study found 100 bacteria, that's not zero, but also not harmful for most people.  With many bacteria, it can require a dose of thousands of bacteria before a person's defenses are breached.  Stomach acid kills most, unless you take an acid-suppressing medication for reflux.  They also don't give advice, such as, if you put the lettuce into a salad spinner, rinse water over it and spin, does that remove most of those bacteria?  Probably, and it would be reasonable advice. 

Another option, since the bag seems to be an issue, is maybe when one gets the salad home, transfer it to one of those silver-impregnated produce bags before refrigerating.   It might be even better to add a 1/4 cup of vinegar to a quart of water in a bowl, place the salad into that, then rinse it off and spin.  I don't know if that will work, but it's a reasonable precaution for the careful eater. 

The authors don't seem to go so far as to recommend not eating packaged salad.  Why don't they make a recommendation, rather than just instill fear?

The Consumer Reports article  linked in the Consumerist article does give numbers, and the did find some that were about the 10,000 organism range.  They also make recommendations, and stop short of saying not to buy those products.:

"What you can do

Buy packages as far from their use-by date as you can find.
Even if the bag says "prewashed" or "triple-washed," wash the greens yourself. Rinsing won't remove all bacteria but may remove residual soil.
Prevent cross contamination by keeping greens away from raw meat."

I had cholera when I was in Turkey at 20 years old.  I could have died, but I didn't.  I certainly would not eat food from street vendors in Istanbul again.

Is it so difficult with you to buy the greens separately? Here that is cheaper and healthier. 

That is what I do.  They are in the same store, a few feet from packaged greens.

I've been too lazy to cut-up my own greens most of the time, but will try it again.

I've also been too lazy to wash and spin my greens very often, but from what I've read, a good pathogen-reducing procedure for all fruits & veggies is to spray them with vinegar, then spray with Hydrogen Peroxide, then rinse with water.  I read this method years ago, but it was only from one researcher, but a few months ago, I read a statement from what I think is a reliable source, that agreed with the first researcher, that it was very good at killing pathogens.

Spud, after my kidney transplant when I was on very high doses of immunosuppressive drugs, my mother experimented with the vinegar method on some red grapes for me (she didn't use Hydrogen Peroxide, though.)  To my taste buds, I thought the grapes tasted awful.  They had a strange taste.  She didn't think so, however.  So there's two opinions right there.  One yay, one nay.

Perhaps I don't know what I'm talking about, but I can't imagine what a vinegar and Hydrogen Peroxide wash would do to delicate leafy greens.  I make a habit of washing all my fruits and vegetables thoroughly, but just in water.  

I totally understand the convenience of prepacked salad mixes.  I've used them in the past.  I'll be on immunosuppressive drugs the remainder of my life, so it's been recommended I avoid any fresh fruits and veggies that are pre-sliced and packaged.  The more these items have gone through the chain of being handled and processed, the odds gets higher for contamination to occur along the way.  At home, all the sanitary controls are in your hands.    

Carl, I've used Vinegar and Hydrogen Peroxide on delicate leafy greens quite often without any noticeable effects.  Of course I rinse well with water right after.

I've used those two chemicals on all fruits & veggies I eat for years and never noticed an off taste, but again,  I rinse well with water right after.

Here's a good article on this technique: http://www.michaelandjudystouffer.com/judy/articles/vinegar.htm

Spud, perhaps my mother overdid the vinegar wash.  But I'm glad this process has been working for you. In the article you posted it states to use spray bottles.  I know for fact that my mother didn't use a spray, and I'm not sure what her method was.  Perhaps that was the problem.

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