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Is there a guidance somewhere for finished product micro re-testing when we get out of specification results?


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#1 DipinMaharjan

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Posted 31 January 2020 - 10:28 PM

Is there a guidance somewhere for finished product re-testing? For instance, if we have a out of specification micro results for indicator/spoilage organism, how many samples should be pull from the same lot to do the re-test? Is there a number of samples that needs to be pulled based on volume of product made to do the re-test?



#2 Charles.C

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Posted 31 January 2020 - 11:23 PM

Is there a guidance somewhere for finished product re-testing? For instance, if we have a out of specification micro results for indicator/spoilage organism, how many samples should be pull from the same lot to do the re-test? Is there a number of samples that needs to be pulled based on volume of product made to do the re-test?

 

Please clarify -

 

Product ?

RTE ?

microbial species tested for ?

specification ?

result ?


Kind Regards,

 

Charles.C


#3 Charles.C

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Posted 01 February 2020 - 08:59 AM

Is there a guidance somewhere for finished product re-testing? For instance, if we have a out of specification micro results for indicator/spoilage organism, how many samples should be pull from the same lot to do the re-test? Is there a number of samples that needs to be pulled based on volume of product made to do the re-test?

 

It  depends on the specific situation. Just as example, here are 2 possibilities -

 

(1) If the problem concerns the reliability/accuracy of an APC result, there is a simple formula which connects the number of samples, desired accuracy, variance and confidence level. (the variance can be estimated from existing data or approx. guesses). See the  procedure attached below.

(The traditional (Variable) generic sampling formulae often suggest 30 samples but this is obviously an enormous workload for micro.purposes).

 

Attached File  sample size for estimation of mean.pdf   450.24KB   39 downloads

 

(2) Many accept/reject micro. schemes use nmcM-type plans  such as the enclosed where yr situation is, say, Case 2 or 5 (similar data). You could "arbitrarily" lift the hazard level for a resampling., eg Cases 3,6 respectively.

 

Attached File  sampling plan based on hazard status.pdf   65.26KB   33 downloads

 

PS - rigorous statistical analyses of resampling procedures can be quite complex. The above are simplified suggestions.


Edited by Charles.C, 01 February 2020 - 09:50 AM.
added

Kind Regards,

 

Charles.C


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#4 DipinMaharjan

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Posted 03 February 2020 - 04:43 PM

Please clarify -

 

Product ?  Low risk chocolate inclusions, Pralines, Baked Brownies with water activity below 0.8

RTE ? YES

microbial species tested for ? Indicator Organisms - Aerobic Plate Count, Coliform, Yeast/Mold

specification ? APC <1000 cfu; Coliform <10 cfu; Yeast/mold <100 cfu

result ? Counts may vary every time

 

Thank You



#5 Hank Major

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Posted 03 February 2020 - 08:06 PM

Speaking broadly and personally, once you have a positive result, especially for Salmonella, retesting will only give you false negatives. So the best guidance I can offer is to discard the finished product unless you can irradiate it.



#6 Charles.C

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Posted 03 February 2020 - 10:04 PM

Speaking broadly and personally, once you have a positive result, especially for Salmonella, retesting will only give you false negatives. So the best guidance I can offer is to discard the finished product unless you can irradiate it.

 

Hi Hank,

The problem is non-pathogens (see OP).

 

@DM - So which results were out of spec and by how much ?

(difficult to comment without some data)


Kind Regards,

 

Charles.C


#7 DipinMaharjan

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Posted 05 February 2020 - 05:39 PM

Hi Hank,

The problem is non-pathogens (see OP).

 

@DM - So which results were out of spec and by how much ?

(difficult to comment without some data)

Hi Charles,

 

SPC counts are 20,000 and up to TNTC while Coliform counts are normally 10 cfu to 200 cfu.



#8 Charles.C

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Posted 05 February 2020 - 06:11 PM

Hi Charles,

 

SPC counts are 20,000 and up to TNTC while Coliform counts are normally 10 cfu to 200 cfu.

 

These results do seem high for baked cookies.

Do you know the Procedures used for SPC, eg time, incubation temperature ?

Similarly, are the coliform counts "MPN" or direct plate counts ?


Kind Regards,

 

Charles.C


#9 DipinMaharjan

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Posted 11 February 2020 - 04:04 PM

These results do seem high for baked cookies.

Do you know the Procedures used for SPC, eg time, incubation temperature ?

Similarly, are the coliform counts "MPN" or direct plate counts ?

Charles,

SPC - Method AOAC (3M petrifilm and Incubation temperature 35 degree for 48 hours).

Coliform - Method AOAC (3M petrifilm and Incubation temperature 35 degree for 24 hours).



#10 Charles.C

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Posted 11 February 2020 - 07:23 PM

Charles,

SPC - Method AOAC (3M petrifilm and Incubation temperature 35 degree for 48 hours).

Coliform - Method AOAC (3M petrifilm and Incubation temperature 35 degree for 24 hours).

 

Hi DipinMaharjan,

 

Thks info.

IMEX the SPC methodology quoted is usually "fairly" reliable between labs (SPC data is often variable even within same lab, eg +/- 50%).

IMEX Coliform methodology (VRB agar IIRC) can give high results for some food matrices. IMO the MPN methodology (eg BAM) is more reliable/consistent between labs.

 

I deduce the quoted data in Post 7 was for the  3 products as mentioned in Post4.

Can you post the specific results for the baked cookies ?


Kind Regards,

 

Charles.C





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