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Controls to prevent B. cereus toxin in cup set fermented products?

B. cereus fermentation toxin ph

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#1 apmorgan

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Posted 07 May 2019 - 03:43 AM

Hi all, 

 

I'm working on a hazard analysis for a sour cream (non-dairy), and B. cereus was identified as a potential hazard introduced with ingredients. The manufacturing process is: batching > pasteurizing (pH neutral) > inoculation of LAB culture and agitation for 1 h > filling in cups > fermentation in incubator at 113F to pH of 4.4 > cold storage. 

 

Spores of B. cereus typically survive pasteurization and may germinate and grow, but they will not have much time to grow before the LAB culture grows reducing the pH. As the pH drops, vegetative cells of B. cereus will significantly decrease. If all happens quickly, B. cereus will also not produce toxins. Because of that it doesn't seem like B. cereus is of safety concern in yogurt and similar products. The combination of rapid fermentation and pH drop seems to be key to ensure safety, and this is easily achieved when you ferment the white mass inside the tank, right after pasteurization. https://www.mpi.govt...ment/14149/send

 

However, in the case I'm working on, for organoleptic reasons, the fermentation should occur inside the cups, i.e. the inoculated mass is filled in cups and taken to an incubator to ferment. The process of filling cups can take up to 8 h. It was recommended to drop the temperature of the tank to 90-100F to slow down the fermentation while the batch is filled (fermenting inside the tank defeats the purpose of the cup set product). My concern is that the inoculated mass will spend too much time (up to 8 h) in the tank at higher pH (5-7), and with less competition, since the ideal temperature for the culture to grow is ~113F. B. cereus could grow more and eventually produce toxins. 

 

Has anyone worked with cup set fermented products? What would be the maximum time at this condition (pH 5-7; temperature 90-100; less competition) to prevent B. cereus to produce toxins? Any thoughts on the validation of this preventive control?  

 

This forum has helped me so much in the past. I hope someone will be able to guide me in the right direction this time again. 

 

Thank you!


Edited by apcraig, 07 May 2019 - 03:44 AM.


#2 Tony-C

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Posted 08 May 2019 - 03:53 AM

Hi apmorgan,
 
First of all I would say that you can minimize the risks associated with B.cereus by raw material controls:
Quality of cream/milk/skim etc.
Age of above
Temperature of above
Ensuring storage tanks are not a source of contamination
Controlling any rework
 
With regards to packaging an innoculated product prior to completing fermentation in cup (cup set), Staphylococcus aureus is also a risk so hygiene is important here.

It is best to use smaller batches to ensure the time in tank is limited.
It may be that you find that an acceptable quality of product is not produced after the pH drops below 6.
You should have a profile of product that is a 'typical pH profile/acidification curve' which is time vs. pH and monitored hourly. This will be backed up by historical micro records of acceptable product.
Batches that are outside the range of this typical profile should be investigated.
 
Attached File  pH profile.pdf   122.27KB   17 downloads
 
I can send you an example of a monitoring record with pH profile if you think it will help.
 
Kind regards,
 
Tony


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#3 Charles.C

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Posted 09 May 2019 - 03:02 AM

FWIW I noted this in another text -

 

Spore germination and growth of B. cereus in fermented milks are prevented by low pH. However, growth of B. cereus has been shown in yoghurt milk at 31 °C, although, as the pH dropped, the growth rate declined, and it ceased at pH 5.7. Although  it  is  possible  that  high  levels  could  be  reached  when  initial  acid production is slow, B. cereus is not normally considered a hazard in fermented milks (22).

Kind Regards,

 

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#4 Tony-C

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Posted 09 May 2019 - 04:05 AM

Hi Charles,

 

 

I don't know where B. cereus is not normally considered a hazard in fermented milks came from but it could be out of context here.

 

I would say it is a hazard but not a probable hazard with adequate controls. Staphylococcus aureus toxin production is normally regarded as higher risk.

 

The other thing with the quote above is that this is cream and it refers to milks, creams tend to be incubated at a lower temperature (lets say around 30C) and the pH drop is much slower compared to milk yoghurt which is usually a faster fermentation at a higher temperature (about 40C).

 

Kind regards,

 

Tony

 



#5 Charles.C

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Posted 09 May 2019 - 04:28 AM

Hi Charles,

 

 

I don't know where B. cereus is not normally considered a hazard in fermented milks came from but it could be out of context here.

 

I would say it is a hazard but not a probable hazard with adequate controls. Staphylococcus aureus toxin production is normally regarded as higher risk.

 

The other thing with the quote above is that this is cream and it refers to milks, creams tend to be incubated at a lower temperature (lets say around 30C) and the pH drop is much slower compared to milk yoghurt which is usually a faster fermentation at a higher temperature (about 40C).

 

Kind regards,

 

Tony

 Hi Tony,

 

Yes, I realised conditions not identical.

 

From cream section -

 

B. cereus is common in milk, and its endospores are able to survive pasteurisation. Some strains are also psychrotrophic, and capable of growth in refrigerated dairy products. Nevertheless, there are very few reports of B. cereus food poisoning associated  with  dairy  products.  There  have  been  a  small  number  of  outbreaks associated with the consumption of pasteurised cream. In 1975 cream found to contain 5xl06 cfu B. cereus caused illness in several people. In 1989, two members of the same family became ill after consuming fresh single cream that was later found to contain B. cereus at levels of 3x107 /g .

(Microbiology Handbook, Dairy Products/Fernandes,2008)


Kind Regards,

 

Charles.C


#6 Tony-C

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Posted 09 May 2019 - 05:03 AM

Thank you Charles.

 

That makes sense, IME cream is more likely to be grossly contaminated with B.cereus than milk and fresh cream a more likely source of B.cereus than cultured creams. Shelf life may also be a factor in fresh products with fresh cream having a slightly longer 'life'.

 

Kind regards,

 

Tony



#7 apmorgan

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Posted 10 May 2019 - 04:12 PM

Thank you Tony and Charles. This is very helpful. 

 

It seems like germination and growth of B. cereus could easily happen; but vegetative cells will decrease to safe levels once the competition grows and the pH drops, in this case to 4.4. This study indicates at least a 4-log reduction once pH reaches 5: https://www.ncbi.nlm...pubmed/16084267

 

Do you know how high the population of B. cereus must be before it starts producing toxin? 10^5, 10^4? 

 

Thank you again!



#8 Charles.C

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Posted 10 May 2019 - 10:24 PM

Thank you Tony and Charles. This is very helpful. 

 

It seems like germination and growth of B. cereus could easily happen; but vegetative cells will decrease to safe levels once the competition grows and the pH drops, in this case to 4.4. This study indicates at least a 4-log reduction once pH reaches 5: https://www.ncbi.nlm...pubmed/16084267

 

Do you know how high the population of B. cereus must be before it starts producing toxin? 10^5, 10^4? 

 

Thank you again!

 

It might depend on the specifics, ie  "sour cream (non dairy) = more precisely ?

 

For "dairy products" / general public (not infant) B.cereus bacterial limits typically seem in range  103 - 104 cfu/gram


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Charles.C


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#9 Tony-C

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Posted 11 May 2019 - 04:56 AM

I would also consider the guidance on infective dose.

 

 

Infective dose
Illness is commonly associated with the consumption of 105-108 organisms. The infective dose can vary depending on the amount of enterotoxin produced.
https://www.thermofi...acillus-cereus/
 
Infective dose:  The presence of large numbers of B. cereus (greater than 106 organisms/g) in a food is indicative of active growth and proliferation of the organism and is consistent with a potential human health hazard. The number of organisms most often associated with human illness is 105 to 108; however, the pathogenicity arises from preformed toxin.
https://www.mb-labs....llus-cereus.pdf
 
My thinking here is that in defining your levels a bolt and braces approach would be to also consider portion size. So let's say a portion size is 100g. Then we are talking about a maximum limit of 103/g (although realistically I would be wanting to see much less or not detected in a g).
 
Going forward I would spend a period sampling the base before and after pasteurization then after inoculation throughout incubation to get an idea if present and the numbers.
 
Kind regards,
 
Tony


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#10 apmorgan

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Posted 14 May 2019 - 12:28 AM

Thanks for sharing Tony, these are excellent references! 



#11 Charles.C

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Posted 14 May 2019 - 11:58 PM

Some further directed  info, possibly slightly  more recent (2016) than the FDA material in previous post albeit quoting similar data regarding basic cell number danger levels.

 

Attached File  Bacillus-cereus-in-Milk-and-Dairy-Products.pdf   914.57KB   8 downloads


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