9 replies to this topic

[DipinMaharjan]

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?

[Charles.C]

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 ?

[Charles.C]

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).

 

 sample size for estimation of mean.pdf   450.24KB   46 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.

 

 sampling plan based on hazard status.pdf   65.26KB   42 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

[DipinMaharjan]

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. 

[Hank Major]

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.

[Charles.C]

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)

[DipinMaharjan]

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.

[Charles.C]

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 ?

[DipinMaharjan]

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).

[Charles.C]

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 ?