Water Activity - cooked meat

Do any of you have experience in water activity analysis in the cooked meat sector? I have an issue where factory cooks meat and MAP packs it under the chill chain. They have no other hurdles in place such as pH or salt content, which may act as a barrier in botulinum control.

They bought a water activity analyser which can operate at chill temperatures and with this analyser, they could obtain water activities around 0.89 at 5 degrees C - certainly below the minimum required for C. botulinum control. However, they also submitted samples to the public analyst laboratory to verify the water activity results and the public analyst results were around 0.98, certainly not low enough to rely on as a control and increase the shelf life from 10 days.

However, the public analyst lab homogenised the sample and analysed at room temperature whereas the factory determined water activity at 5 degrees C (the conditions under which the product is for sale). Factory aren't happy that the laboratory analyse for water activity under different conditions to how the product is stored and as such, provide results that do not meet the requirement to act as a barrier against C. botulinum control. 

Have the factory got any defense with their analyser? Obviously public analyst lab is UKAS accredited etc.

Pops

Dear poppysnoss,

I presume MAP implies atmospheric pressure.

I deduce from textbook the critical level C.botulinum  is 0.93

Out of curiosity how much temperature increase from 5degC  will make 0.89 > 0.93 ?

No direct experience Aw measurement but I suspect the more relevant (legal?) question may be - what is defence for the choice of 5degC ?

"Worst" case scenario issue involved maybe ?

Look forward to comments from the chilled food people here.

Rgds / Charles.C

PS - for your perusal -

The study of Koutsoumanis et al. (2010) was conducted in Greece and temperature was recorded with
miniature dataloggers (COX TRACER TM, Belmont, NC) in 60 retail cabinets from supermarkets. The
distribution  of  the  mean  temperature  for  the  tested  retail  refrigerators  is  presented  in  Figure  11.

Temperature ranged from 0° to 11.7°C, with a mean of 4.98°C and a standard deviation of 2.9°C. In
70%  of  the  tested  refrigerators  the  temperature  was  above  4°C,  while  in  6.7%  the  temperature  was
above 10°C.

Refrigerated composite products may spend the majority of their shelf-life in a domestic refrigerator,
rather  than  in  a  retail  or  industrial  chiller.  Domestic  refrigerator  temperatures  can  therefore  have  a
significant effect on the safety of these products. Once a chilled food product has left the retailer from
which it was purchased, it is beyond the reach of legislation, so correct handling and storage is entirely
down to the motivation and knowledge of the purchaser.
Data from 17 surveys of domestic refrigerator temperatures from six European countries are presented
in  Table  16.  The  data  are  presented  in  such  a  manner  as  to  facilitate  comparison  between  surveys,
although this is not always possible due to the use of different parameters and temperature ranges in
the reporting of the data. Of the ten surveys (1,856 samples) for which a mean temperature was given,
this ranged from 5° to 7.2°C. The weighted mean of the means was 6.5°C. No regional or temporal
trends are evident from these data. The weighted mean percentage of domestic refrigerators running
above the following temperatures (number of surveys in brackets) was: >4°C, 86.4% (2); >5°C, 53.9%
(11); >6°C, 58.4% (5); >7°C, 41.8% (3); >8°C, 28.7% (2); >9°C, 26.5% (3); >10°C, 5.2% (4). In the
latest survey, conducted in 100 Greek households, the mean temperature varied significantly between
refrigerators,  with  a standard  deviation  of  2.58  °C.  Another important  fact  confirmed  in  this  survey
was that, in all cases, there was major temperature variability recorded at the different locations of the
refrigerators (see Figure 12). A significantly higher mean temperature was observed in the door shelf
(8.4°C)  compared  to  the  upper  (7.6°C)  the  middle  (6.3°C)  and  the  lower  shelf  (6.7°C).  The  latter
observation is important, since some ready-to-eat foods such as pasteurized milk are usually stored in
the  door  shelf  of  the  domestic  refrigerator  (Xanthiakos  et  al.,  2006).  The  above  results  concerning
variation  of  temperature  with  time  and  location  within  the  refrigerator  are  in  agreement  with  other
survey studies on domestic refrigerators (Laguerre et al., 2002; Taoukis et al., 2005).

 

The  above  data  clearly  show  that  storage  temperature  at  both  retail  and  domestic  level  can  vary
significantly between refrigerators. This variability should be taken into account in the evaluation of
the safety risks of refrigerated composite products.

 

This isn't something they can simply control with oxygen headspace in the MAP gas mixture?

The C. botulinum controls are pH <5, water activity <or= 0.97, minimum aqueous phase salt of 3.5%.

See attached FSA guide.

Dear poppysnoss,

It's an interesting problem. :smile:

I think you are correct re 0.97, my textbook probably quoted for the combined  proteolytic/non-proteolytic possibilities, eg  –

cb1 - C.botulinum, NZFA.pdf   87.56KB   21 downloads

Here is an illustration of  non-proteolytic, C.botulinum,  growth patterns –

cb2 - non-proteolytic C.botulinum,boundary for growth-no growth.png   104.92KB   3 downloads(Stringer,2005)

Thks for the FSA attachment which I guess is a  précis of –

cb3 - vacpacguide (details),FSA,2008.pdf   268.49KB   22 downloads

As an aside - from my experience within commercial analytical services, the most simple / quickest / reliable route might be to contact the public analyst and ask as to their basis for choosing measurement temperature in such  cases ?.  :smile:

Regarding temperature/salt/pH etc, I appreciate you are obliged to follow UK legal requirements to the letter however in truth the (scientific ) devil is somewhat, as usual, in the details. If you have a look at the discussion documents  prior issue of the (2008) vacpac  “recipe” you will get the idea –

cb4 - C.botulinum, FSA, vacuum pack-MAP,2006, Final report.pdf   1.22MB   21 downloads

The very elegant  training program on FSA site mentions a few of the caveats, eg see NaCl, Aw entries.

http://vacuumpacking...dule1/section1/

I noticed these comments within cb3 attachment -  

5. Chilled storage and handling of foods

The maximum temperature specified in legislation for retail of chilled food is 8°C in England, Wales and Northern Ireland. The Food Hygiene (Scotland) Regulations specify chilled food to be stored in a refrigerator, refrigerating chamber, or a cool ventilated place. Neither is there a harmonised approach to legislated temperature rules within the EU, with temperatures of 0°C to 8°C specified in different countries. There are also different requirements for different food groups.Within the UK, when held and distributed by the manufacturer, it is likely that chilled food is maintained at no more 5°C, and probably lower. Indeed, agreed retailer own label chilled prepared food temperature on delivery to retailers’ Regional Distribution Centres is commonly

set at 5ºC maximum, through commercial agreements.

In practice, surveys of all chilled food outlets (including major multiples, farmers markets, small stores and other outlets) indicated that in the UK, the average temperature at retail was 4°C-6°C, with 6% of samples at >8°C. The position appears similar in many other European countries.

>>>>>>>> 

(my words – “In the absence of any other limiting factors”) >>>>>>>>>>>>

 

This study noted a dramatic effect of storage temperature on toxin formation by non-proteolytic C. botulinum. For example from the model in ComBase Predictor, time to toxin is predicted as 3 days at 10°C, 6 days at 8°C, 12 days at 6°C, 16 days at 5°C, and 24 days at 4°C. Thus, if all chilled food could be maintained at 4°C/5°C (for example) throughout the chill chain (including inthe home), the safety margin would be extended further. It is likely that there will also be a benefit with other psychrotrophic pathogens and shelf-life extension may also be possible. In order to further extend the margins of safety of chilled foods with respect to psychrotrophic foodborne pathogens, it is suggested the UK continues to strive for better temperature control throughout the chill chain (including domestic storage), and that 5°C is adopted as a target for best practice. It should be noted that this comment is not based on any particular outbreak of food poisoning. This suggestion re-iterates various recommendations made by Richmond in 1991.

 

The overall consequences with respect to deviations from the “ideal” level of < 3degC seem to remain a topic for debate. I still suspect that this may be the primary cause of yr present conundrum assuming pH, salt data is in compliance and shelf life > 10 days.

Rgds / Charles.C

PS – In all the above docs, I saw no comment regarding operational measurement temp.for  Aw. You might consider a further check at, say 10degC as well ?