3 replies to this topic

[carine]

hi all, 

 

my customer use cfu method to test micro on our product which is Ice  and from our site we use MPN method (where recognized and stated in the food act). both method has a comparable results where cfu method found micro lelvel ecxeed the limit, however no  micro detected by using MPN method.   Hence, what should reply to customer at this situation? 

[pHruit]

Ah, the classic "we used a different method and got a different result" conundrum...

Which limit has been exceed?

If your specification (and indeed the associated regulatory standard, since you've made reference to one) sets a limit defined against a specific method, and the results of tests using that method are within specification, then the product would appear to be within specification, at least at face value.
Of course this does assume either a homogeneous distribution of organisms within the batch, and/or a suitable statistical sampling plan to ensure that the results are genuinely representative.

The notion that both methods give similar results is perhaps questionable here given that one is showing product in spec, and one is showing it out of spec (possibly), but this could equally be reflective of variation throughout a batch - if the methods genuinely give comparable results, and have both been followed correctly, then a logically probable conclusion is that both sets of results are correct for the particular samples of material analysed and thus the material potentially is out of spec.

 

Do you have retained product samples, and if so, have you had these analysed using both methods, ideally by an accredited external lab?
Have you reviewed hygiene/process records for the batch in question?

Some more detailed information about the levels and methods might be useful for further comment from forum members, but in terms of the initial response to the customer I'd simply be saying "we are investigating this and will respond with further details in due course" (and confirming whether their results are internal or from an external accredited lab) whilst you press on with arranging analysis of retained samples, review the production process for the batch etc.

[Sam30]

Hi,

 

this is a typical situation when different methods are used which may seem to give similar results as long as everything goes fine. When it comes to choosing method of analysis always focus on Limit of Detection & Limit of Quantification should be same for both methods. Look into your methods detection & quantification limit & your customers methods limits, most likely your customer is used more accurate one. I did face a similar situation in past (CFU vs MPN) and cfu had better limit of detection & quantification (cfu -1 coliform, MPN -3 was minimum), outcome of investigation - switch or align with customers methods.  

[Charles.C]

hi all, 

 

my customer use cfu method to test micro on our product which is Ice  and from our site we use MPN method (where recognized and stated in the food act). both method has a comparable results where cfu method found micro lelvel ecxeed the limit, however no  micro detected by using MPN method.   Hence, what should reply to customer at this situation? 

 

Assuming everything else is done according to the Regulatory/textbook requirements, eg sampling, yr customer is logically using an inappropriate analytical procedure from a Regulatory POV.

 

The 2 methods discussed are fundamentally different in implementation. 2 numerical, non-negative,  identical "results" would probably be a fluke.

 

Impact-wise, need some actual numbers to give  meaningful comments, eg Number of samples?/Respective ?cfu/gram/ ?MPN/gram/ Limit?MPN/gram

 

(theoretically the MPN method was developed for/[is particularly recommended for] "low" levels of bacterial counts)