Controls to prevent B. cereus toxin in cup set fermented products?
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!
Quality of cream/milk/skim etc.
Age of above
Temperature of above
Ensuring storage tanks are not a source of contamination
Controlling any rework
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.
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).
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 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)
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
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!
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
I would also consider the guidance on 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/
https://www.mb-labs....llus-cereus.pdf
Thanks for sharing Tony, these are excellent references!
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.
Bacillus-cereus-in-Milk-and-Dairy-Products.pdf 914.57KB 9 downloads