8 replies to this topic

[Andy_Yellows]

Hi all,

 

Bit confused by the whole 'acceptable levels of contamination' subject with regards to lab testing. I've looked at various sampling plans and the stated acceptable levels and keep finding figures such as 10³cfu/g. What I don't really get is the necessity of the indices and what it actually means. If someone has the time to explain this to me that'd be great as I'm blagging bits of my sampling plan to a certain extant at the moment. 

As well as this I've had some lab results back and they state things like >3.00x10⁵ (as a result of a tvc test). This just doesn't make a lot of sense to me as this really isn't my area of expertise.

 

Any help would be much appreciated.

 

Regards,

 

Andy

[Charles.C]

Hi all,

 

Bit confused by the whole 'acceptable levels of contamination' subject with regards to lab testing. I've looked at various sampling plans and the stated acceptable levels and keep finding figures such as 10³cfu/g. What I don't really get is the necessity of the indices and what it actually means. If someone has the time to explain this to me that'd be great as I'm blagging bits of my sampling plan to a certain extant at the moment. 

As well as this I've had some lab results back and they state things like >3.00x10⁵ (as a result of a tvc test). This just doesn't make a lot of sense to me as this really isn't my area of expertise.

 

Any help would be much appreciated.

 

Regards,

 

Andy

 

Hi Andy,

 

Don’t worry, you are far from alone as demonstrated below.

 

Very briefly, the 2 numbers in yr post translate to 1000 cfu/gram and 300,000 (units missing, probably again cfu/gram) respectively.  i hope you are familiar with.these formats.

 

TBH, “Indices” sounds like you are well on  the way to becoming a mathematician as well as a microbiologist.

 

"Indices" is the plural of "index"

 

From a Maths POV,  Index = Power = Exponent = Superscript (x) in numbers like a^x , eg  the  "4" in the number 10⁴

 

https://www.mathsisf...dex-power-.html

 

For example,  in the following thread, wherever you see the words "exponent" or "power", translate as index (or indices if plural)  -

 

http://www.ifsqn.com...how-many-zeros/

 

I suspect you will soon be encountering "Logs" as well, so maybe this "aps" special will be of pre-emptive interest -

 

http://www.ifsqn.com...interpretation/

[Andy_Yellows]

Thanks Charles, just wondered if it all meant something slightly different to the mathematical way of putting it but it sounds like its just a shortened version. 

 

The whole micro area really isn't my thing, it's something I'm trying to learn myself but it is a struggle. I'm sure we all have fields where we're not too strong though!

 

Regards

 

Andy

[GMO]

I'm no microbiologist either but learning.

 

TVC = Total viable count.  It's basically a crude measure of the total number of cfu (colony forming units, i.e. stuff which grows on a plate) from a gram of your foodstuff.  You may also use TVC swabs which will then be taken from a 10 x 10cm square.  TVC is therefore measuring what is alive on your surfaces or in your food.  Cleaning well will reduce this loading.  Cooking foods well and treating them hygienically e.g. effective cooling, good GMP will reduce TVC loading on foods. 

 

Why use TVC and not pathogens?  Well if you wait till pathogens are in your food, it's too late.  TVC is an indicator that things are going ok or not.  From experience working in lots of factories if you fail to control TVCs (or enteros in some factories are used as indicators) you will have a pathogen issue later as it's your early warning system that summit ain't right!

[Charles.C]

TVC is a complicated item. Opinions on the value of TVC (food samples)  as a safety  indicator vary.

 

Currently, for RTE foods, seems to be regarded in UK as primarily a quality indicator.

 

 HPA, 2010, rte micro. guidelines.pdf   998.98KB   192 downloads

 

 

 

.

 

 

[gud2ya]

Usually the standard values gives something like "it should not exceed 10³ cfu/g of a specific type of microorganism..."

 

Use that as your max value to determine if your results are acceptable or not.

[GMO]

TVC is a complicated item. Opinions on the value of TVC (food samples)  as a safety  indicator vary.

 

Currently, for RTE foods, seems to be regarded in UK as primarily a quality indicator.

 

HPA, 2010, rte micro. guidelines.pdf

 

 

 

.

Retailers often use it as a hygiene indicator which is what I meant, it's not a safety indicator of course because in the absence of pathogens there is no risk.  What I'm trying to say is it's a verification tool not an absolute.

[Charles.C]

Retailers often use it as a hygiene indicator which is what I meant, it's not a safety indicator of course because in the absence of pathogens there is no risk.  What I'm trying to say is it's a verification tool not an absolute.

 

Indeed as you say. Textbooks have also been arguing over this for several decades. IIRC the EC avoided the issue by using  E.coli (and maybe Enterobacteriaceae ?).

 

It's also enticingly logical  to predict that the probability of a pathogen existing must increase with the TVC.

[Dr.Des]

If you're going to be interpreting results it's always worthwhile doing a 'microbiology for non-microbiologists' type course (pretty sure Leatherhead do one) as they cover all this area regarding how numbers are reported, units used etc.