7 replies to this topic

[SaniS]

Can I have some pathogenic/spoilage microbes multiply below zero degree ??

Why there is critical limit 5 degree for chilled foods?

What will grow if the temp is -14 frozen food?

Love to hear your reasons on safety aspect rather than a quality point of view

[shea quay]

Most bacteria I've encountered have a minimum growth temperature of 0-10'C, with Listeria and Yersinia having a rate at 0'C. I think 5 was traditionally picked as it was below the minimum for Staph Aureus (which is 7'C). Their may be some bacteria that grow below 0'C. I don't think so myself due to the unavailability of water, but may leave that one to more learned posters. Bacteria can survive freezing, however. The lower the temperature you freeze products to, the greater the probability you will kill them, if not through the freezing process, then by making them not viable during the thawing process. "Managing Frozen Foods" by Chris Kennedy was my particular book which I found useful during my time in the frozen foods side of things, but I left it with the company.

Just used the edit function to chance the word "bible" to "particular book which I found useful" as part of the new and PC approved shea quay.

Edited by shea quay, 24 May 2012 - 05:01 PM.

[Charles.C]

Dear SaniS,

Presume you mean degC.

Can I have some pathogenic/spoilage microbes multiply below zero degree ??
Apparently yes, eg L.mono. down to -0.4degC, Y.enterocolitica down to -1.3degC
 ECFF_Recommendations_2nd_ed_18_12_06.pdf   402.26KB   69 downloads

Why there is critical limit 5 degree for chilled foods?
In fact required max. temperatures depend on where you are, eg UK (+EC?) max 8degC, USA max 5degC (41degF) and also maybe on the situation, eg static storage/display, transport/distribution etc.
The reason – rather simplistically – “Bacteria thrive in a temperature range from 41 degrees F to 140 degrees F.” (http://www.myflorida...y/food/temp.htm ). The UK also (effectively) take refrigerator capabilities into account (I think).
Industries also offer their own (optimistic) variations, eg I hv seen - seafood pathogens do not grow above 4.4degC (obviously L.mono. is a popular exception, albeit probably not from the sea ).

What will grow if the temp is -14 frozen food?
Apparently nothing if you refer to micro-organisms on Earth, eg
“Frozen products do not require any added preservatives because microorganisms do not grow when the temperature of the food is below -9.5°C”, http://en.wikipedia....iki/Frozen_food

Rgds / Charles.C

PS Much more elaborate statements (with exceptions) can be found also, eg

In England, Wales and Northern Ireland food that is likely to support the growth of pathogenic micro-organisms or the formation of toxins must be kept at a temperature of 8°C or below. The requirement applies to the temperature of the food, not the surrounding air. The requirement applies to foods, including raw materials and ingredients, at all stages of preparation, processing, transport, storage and display for sale within the manufacture, retail and catering sectors. Schedule 4 provides exemptions from the chill holding requirement in defined circumstances for some foods even though they are inherently likely to support the growth of pathogenic micro-organisms or the formation of toxins.

In Scotland the requirements are different. Any person in respect of any commercial operation or food premises who keeps food without a refrigerator, a refrigerated chamber or a cool ventilated place is guilty of an offence unless the food is held at over 63ºC. As there is no specific temperature mentioned for the chilling of foods that are likely to support bacterial growth it is recommended that if the food storage place chosen exceeds 8°C then the shelf life of the foodstuff may need to be reduced. Food should be kept at ambient temperature for the shortest time possible. Schedule 4 of the Scottish Regulation does however contain a number of specific exemptions for chill holding.

From a manufacturing perspective the performance of the proposed distribution chain should be validated and monitored by the responsible party and taken into account when specifying shelf life.

Chilled food temperature labelling:

> Store at 5degC max, eat within x days of opening
> Keep refrigerated (taken to mean 8ºC max - legal basis).

http://www.chilledfood.org/MEDIA/POSITION+STATEMENTS/temperature.htm

[shea quay]

SaniS, please meet my learned poster, Mr.C; Charles, this is SaniS!

I want to see the certified calibration certs for that research though!

[Charles.C]

SaniS, please meet my learned poster, Mr.C; Charles, this is SaniS!

I want to see the certified calibration certs for that research though!

Dear shea quay,

Thanks again.

To be honest i hv just located one more nice link (US oriented i suppose) which further clarifies some of the storage numbers, etc previously given. Hopefully most people will see this post before my earlier thesis (too lazy to [slightly] edit). eg -
 

The suggested temperature specification for refrigeration of foods has been revisited from time to time as knowledge and technology have advanced. Initially 7°C (45°F) was considered the optimal temperature; however, technological improvements have made it economical to have domestic refrigeration units working at a temperature of 4-5°C (40-41°F). For perishable products ≤4.4°C (40°F) is considered a desirable refrigeration temperature.

http://www.foodsafet...p?id=7&sub=sub1
(maybe US refrigerators are more efficient/reliable than European ones).

 

Above Link now Broken, replaced by pdf below (added by CharlesC,,280120)

 time and temperature abuse of refrigerated foods,2006.pdf   685.19KB   33 downloads

PS your memory of S.aureus might still hv inspired the first effort of course.

Rgds / Charles.C

[shea quay]

I can neither find fault with your logic, scientific evidence nor musical tastes on this topic, Charles!

[Cranberry]

Good research Charles.

However, laboratory studies are all well and good but they can have varying degrees of relevance to industry depending on the conditions used in the study. Yes L. mono and Y. entero may technically be able to grow below zero with otherwise optimum conditions in someone's lab but the chances of them being are able to do it in a frozen food product after being stressed out by whatever processes the product has gone through are debateable. I can run a marathon in X time if I train properly, have the right food and get a good nights sleep. If get called into work the day before and the hotel fire alarm goes off at 3am the night before (thank you Llanelli marathon) then my performance is considerably worse.

Personally, after a few pints of Guinness I'll eat pretty much anything, regardless of the ins and outs of the temperature it has been stored at. If I worried too much about all the bacterial badness I’d seen in my previous life, I would be very hungry most of the time.

[Charles.C]

However, laboratory studies are all well and good but they can have varying degrees of relevance to industry depending on the conditions used in the study. Yes L. mono and Y. entero may technically be able to grow below zero with otherwise optimum conditions in someone's lab but the chances of them being are able to do it in a frozen food product after being stressed out by whatever processes the product has gone through are debateable. I can run a marathon in X time if I train properly, have the right food and get a good nights sleep. If get called into work the day before and the hotel fire alarm goes off at 3am the night before (thank you Llanelli marathon) then my performance is considerably worse.

Personally, after a few pints of Guinness I'll eat pretty much anything, regardless of the ins and outs of the temperature it has been stored at. If I worried too much about all the bacterial badness I’d seen in my previous life, I would be very hungry most of the time.

Dear Cranberry,

If you replace Guinness with Newcastle Brown I can happily acquiesce.

Actually the existence of microorganisms showing low temperature microbiological activity in food is a well-documented real world phenomenon, eg

 ts6 - chilling and freeezing.pdf   1.79MB   61 downloads

You are correct that the processes are slow since metabolic reactions of microorganisms are enzyme catalyzed and the rate of such reactions is dependent on temperature. In addition a variety of other intrinsic/extrinsic factors are also related to growth capabilities, eg Aw, pH.

Such metabolic activity may have implications with respect to safety or spoilage of foods as illustrated in the attachments enclosed

 ts4 - microorganism activity, temperature-line.png   54.12KB   7 downloads
 ts2 - L.mono., Y.enterocolitica, growth-control - food-path-summ.pdf   266.22KB   34 downloads
 ts3 - poultry spoilage.png   274.42KB   6 downloads
 ts1 - extended shelf life - refrigerated foods - microbio_0298.pdf   79.58KB   46 downloads

Rgds / Charles.C