Does salmonella die off in low moisture product?

Hi,

We are having a discussion at our company: we produce a dry powder with a low Aw-value.

Occasionally we are facing a contamination with salmonella in our finished product. We are working very hard to get this under control.

The manager now has heard salmonella will die off in low moisture product after about six months of storage and is convinced this also counts for our product. I have some correspondence from an external microbiological expert who is stating this indeed will occur in some occasions, and could be the case for our product. However, in mij previous work experience I have seen salmonella surviving in a product which was even more dry for a much more longer period (and even after a heating step). 

We (the QA department) will not accept "storage >6mnd" as a reliable killing method for pathogens and I have found some articles which confirm the survival of salmonella i low moisture-foods, but I am quite curious to hear your opinions on this! Is it common for salmonella to die off in low moisture products?

You have a great point here Pat.  All of the research that I have done, and I have seen done by some of my peers, shows that dry-storage is in no way exempt from salmonella and that one of the biggest problems is that people believe that it will die off in all cases given time and temp.  Long-life, temperature resistant salmonella can be found in a lot of ingredients and finished product.  Whereas you might be safer with a low-moisture product, the chances for contamination are still prevalent.  It is no wonder that you cant find a lot of info on this, there have not been a lot of studies conducted on low-moisture foods.  Long story short, storage > 6mnd is not an empirically evidence-based kill step, do not assume that it will die off given time, keep good GMPs and PRPs in place. 

Hi,

 

We are having a discussion at our company: we produce a dry powder with a low Aw-value.

 

Occasionally we are facing a contamination with salmonella in our finished product. We are working very hard to get this under control.

 

The manager now has heard salmonella will die off in low moisture product after about six months of storage and is convinced this also counts for our product. I have some correspondence from an external microbiological expert who is stating this indeed will occur in some occasions, and could be the case for our product. However, in mij previous work experience I have seen salmonella surviving in a product which was even more dry for a much more longer period (and even after a heating step). 

 

We (the QA department) will not accept "storage >6mnd" as a reliable killing method for pathogens and I have found some articles which confirm the survival of salmonella i low moisture-foods, but I am quite curious to hear your opinions on this! Is it common for salmonella to die off in low moisture products?

Hi Pat,

Some evidence for Longevity -

Salmonella, survival in low moisture Foods, 2010.pdf   396.4KB   46 downloads
Survival, responses, and sources of Salmonella in low-moisture environments,2013.pdf   579.57KB   41 downloads

Finding ways to release Salmonella positive RTE foods is a great way to kill people and go to jail.

https://www.justice....11426350488.pdf

Will not even go discussion with the manager on the storage, but anyway, have you done serotyping on your finished product sample? Also sampling on the environment and serotyping for whichever turned positive?

Finding ways to release Salmonella positive RTE foods is a great way to kill people and go to jail.

 

https://www.justice....11426350488.pdf

Agree on that! We do not produce RTE foods, but it still is not even legal to release positive tested product even if later samples might come out negative. 

For me it is not the question if we can release it or not, we will not. But I would like to have some information on this "I heard salmonella will just dissapear after a certain time"-thing ;-)

Charles, thank you for the information!

Will not even go discussion with the manager on the storage, but anyway, have you done serotyping on your finished product sample? Also sampling on the environment and serotyping for whichever turned positive?

Believe me we are sampling to the moon and back ;-)

Everyone who wants to do something they know they should not can always find "science" to back it up (i'm thinking anti-vaccers and the fraudulent research linking MMR to autism) 

Even if there is one paper that showed a die off, you'd have to be able to duplicate the conditions EXACTLY.....same subtype, same aW, same room temp, micro load in the air, same storage unit, same sampling plan, same swab type, same incubator,same person counting colonies..............I think you get the picture

http://www.jfoodprot...028X-73.10.1919

https://www.frontier...2013.00331/full

http://aem.asm.org/c...69/7/3687.short

the list of research is long and I did not look at the above

So unless you're manager has a PHD in microbiology and did her thesis on salmonella and nonone in the world knows more than she does, she shouldn't be even entertaining this notion

Sheesh and the GFSIs wonder why recall #'s aren't going down???????

just googles salmonella survival in dry environments then the link for scholarly research papers

Thank you for your input! Also a good argument to have (repreduction of tests) 

I am wondering why this expert (quite experienced company) came up with the possibility, it probably has happened somewhere, but my experiences have been different so I was a bit confused on this subject. (Not anymore ;-))

There is some evidence that in certain circumstances there may be a decline in count during storage of dry products (see e.g. https://www.scienced...022030270863111), there are a lot of caveats in this and "possibility" is probably the key word to take away here, i.e. a long long way from anything close to a reliable mechanism for a food safety control!

In case you needed further ammunition to help with the internal discussion, you may also want to have a look at the troubles Lactalis has had with Salmonella in milk power over the last few years - quite a lot of info on google.

Everyone who wants to do something they know they should not can always find "science" to back it up (i'm thinking anti-vaccers and the fraudulent research linking MMR to autism) 

Is it overly contentious to also add the hyperactivity and the "Southampton Colours" to this list ;)

pHruit...........i hadn't had instant mac n cheese in a very long time.........fd&c yellow #7 (or some such yellow colour) had been removed and replaced with tumeric............it did not taste the same as i remembered lol but I would imagine the removal came from the same public outcry as you've mentioned regarding the southhampton 6 (i had to look that one up!)

Agree on that! We do not produce RTE foods, but it still is not even legal to release positive tested product even if later samples might come out negative. 

 

For me it is not the question if we can release it or not, we will not. But I would like to have some information on this "I heard salmonella will just dissapear after a certain time"-thing ;-)

 

Charles, thank you for the information!

 

 

 

 

Believe me we are sampling to the moon and back ;-)

I trust that it is :) What I am only implying if you consider serotyping. It is not mandatory but it will help to establish the possible cause :) Anyway, I hope that everything turns ok and normal soon :)

When you are reviewing your CCPs for any function the key is being able to back the decision that you have made with some sort of peer reviewed scientific evidence.  For those that are not familiar with the site:

https://scholar.google.com/

This is a great place to search for the scientific articles and evidence that are either going to make or break some of the decisions we make about food safety.  I would check this for temperature resistant salmonella and salmonella survival in dry storage.  Don't back up your decisions with google articles.  Use legitimate, peer reviewed journal articles or thesis.

Cheers!

Thanks I was indeed not familiar with this site :-) 

Also Pat, since your company hired an "expert" I would be wary of future decisions they make and don't take those "experts" at face value

Here's another example

let's assume your dry powder tests neg for salmonella, but your sample wasn't randomized or large enough do not really indicative of the powder (and let's face it, you need to sample 25 times from a 1000 kg unit to really come close to know if there is salmonella or not) so the product is released

Your customer is making, yogurt that needs a fermentation stage...........oh look there is salmonella in your powder ingredient...........wow the salmonella explodes..............your customer doesn't test for it because you've given them a CoA that says negative

Bamo, you're both in a recall

You need to first figure out where it's coming from and then look at strategies for eradication