5 replies to this topic

[matthewcc]

Hello all,

 

We do proficiency testing for water activity and moisture percentage (loss on drying). For moisture analysis, for example, we have some results that are somewhat different between ours and the third-party lab, around 6 1/2% and 9%, respectively. How close do they need to be, and what is a scientifically justified way of defining an acceptable range?

 

We are certified with NSF GMP and SQF for food safety in the United States and manufacture dietary supplements under 21 CFR Part 111 regulations.

 

Thank you,

Matthew

[GMO]

That sounds like a significant difference.  It's difficult to know if it's a food safety risk but the proficiency and calibration of what methods you are using should be baked into your HACCP plan (if you excuse the pun).  If you have an error in your measurement or could have one, you need to make your targets more stringent to accommodate.  Or you may realise that your controls are so tight that kind of variation wouldn't have an impact on food safety or quality.  

 

Apart from working out if the error is one you can live with, I'd also be keen to work out the calibration and proficiency.  Your scales used for the moisture loss should be calibrated to national standards and you'd need pretty accurate ones for that activity (I remember doing it in labs at school and being crap at it!)

 

The next bit I'd look at is if you can get signed up to a proficiency scheme.  They exist for chemical and micro testing in general so I'm sure one will exist for water activity and moisture by drying.  That way you can periodically test your staff and find out if everyone is capable of producing an accurate result.  I'd certainly do this if my measurements were part of testing for food safety reasons.

 

If you are a member of a group representing your industry they may already have some proficiency schemes out there or alternatively, ask the lab you sent it for testing to as they certainly will.

[Brothbro]

What instruments do you use for Moisture and aW? Especially for aW, these instruments are usually pretty user friendly (just pop a sample in the chamber and go). It makes me wonder if you should look into whether the lab is using a different instrument than you are, if yours is properly calibrated/maintained, and the manufacturer's claim on how precise/accurate the instrument should be.

 

As for whether your result difference is significant, have you tried asking the third-party lab? If you've organized this proficiency testing with them they could have some insights into what results are considered acceptable. Third party labs run tons of proficiency tests all the time, they should have some knowledge on this.

[matthewcc]

We have a Decagon pawkit for water activity and an AND MF-50 Moisture Analyzer. We run the water activity meter calibration control samples once a day before the first sample is tested when the device will be used, and we check the moisture analyzer's calibration daily using a single weight. We have an annual calibration service for the moisture analyzer. (The water activity meter manufacturer recommends annual factory calibration to maintain optimal performance, but we haven't been doing that.)

 

What instruments do you use for Moisture and aW? Especially for aW, these instruments are usually pretty user friendly (just pop a sample in the chamber and go). It makes me wonder if you should look into whether the lab is using a different instrument than you are, if yours is properly calibrated/maintained, and the manufacturer's claim on how precise/accurate the instrument should be.

 

As for whether your result difference is significant, have you tried asking the third-party lab? If you've organized this proficiency testing with them they could have some insights into what results are considered acceptable. Third party labs run tons of proficiency tests all the time, they should have some knowledge on this.

[matthewcc]

I forgot to mention I think the third-party lab used a slightly different method for moisture analysis, heating in an oven, but I will have to confirm.

[Brothbro]

You may want to check in with the manufacturer or the manual on how accurate their device is compared to the traditional method (oven drying). Ideally your acceptable range for proficiency testing results would take the device's error into account. I don't have a good answer for how close your result needs to be, but it typically involves some statistics that take into account the total spread of results among the tested group. If you organized this testing through the 3rd party lab they may have some insight for you. If not, then you could define your own based on some research and the risk this testing addresses in your process. 

 

That said creating your own scheme can be hard, and even then proficiency testing is often not very insightful/useful if it's conducted with a small group in one facility. Part of the point to this type of testing is checking results across multiple labs, so GMO makes a good point that signing up for a testing service could be worthwhile if aW is key to the safety of your product.