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Interpretation of "log" in total plate count

calculation of log

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#1 Ulysses

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Posted 08 February 2018 - 06:53 PM

Hi,

 

Im working on on our shelf life test for our fresh meat. My question is on how to determine the "log" or how to calculate it base on my TPC (total platye counts). see below the part of email I received regarding for the requirement that we need to meet for japanese standard.

 

TPC Standards (Japan):

Greater than Log 8 = Spoiled

Greater than Log 7 = initial stage of spoilage

Log 6 or less = General standard for non-processed food (meat, fish etc.) at the point of sale

Log 5 or less = General standard for processed food at the point of sales

 

Thanks,

 

Ulysses


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#2 gagansaini1

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Posted 08 February 2018 - 07:16 PM

Hi

 

First thing we need to know is the Dilution Factor, or how much the original sample is diluted:
here Initially 5mL in 45mL = Final Volume / Sample volume = 50/5 = 10.
Then two serial dilutions of 1/100.
Total Dilution Factor = 10 * 100 *100 = 10^5 (10 raise to the power 5)
CFU/mL = cfu/ml = (no. of colonies x dilution factor) / volume of culture plate
= (137 * 10^5)/0.1
=1.37*10^8
So Total colony forming units = 1.37*10^8 CFU/mL
Converting CFU/mL to Log value
For example,
Total colony forming units = 1.37*10^8 CFU/mL and you want to convert it into Log value,
Just take Log(CFU/mL)
Here, log (1.37*10^8) = 8.13924922.
 
Hope this help.......

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#3 Charles.C

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Posted 09 February 2018 - 03:48 AM

Hi,

 

Im working on on our shelf life test for our fresh meat. My question is on how to determine the "log" or how to calculate it base on my TPC (total platye counts). see below the part of email I received regarding for the requirement that we need to meet for japanese standard.

 

TPC Standards (Japan):

Greater than Log 8 = Spoiled

Greater than Log 7 = initial stage of spoilage

Log 6 or less = General standard for non-processed food (meat, fish etc.) at the point of sale

Log 5 or less = General standard for processed food at the point of sales

 

Thanks,

 

Ulysses

 

It's easy although yr email is in Japanese maths.  By "Log 8" the sender actually meant the number 8.00000. Etc.

 

By common convention you will need a result for product "APC"/"TPC"/"TVC"/ whatever in units of cfu/gram (or maybe cfu/ml). Call it X cfu/gram

 

Then you need a scientific calculator with a "log" function/button. (NOT a "ln" button !)

 

Then, as per calculator manual for using log function, enter X and click "log" (sometimes the reverse, follow the manual)

 

Now compare the result to the values in yr email.

 

As a test check, if X = 1000 cfu/gram, the answer in calculator should be 3.000000etc

Similarly, if X = 100,000 cfu/gram, the calculator should show 5.000000etc

 

PS - Unfortunately the procedures/interpretations for measuring X in Canada and Japan may be different so yr data may actually be OK but not necessarily match their opinions.


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Kind Regards,

 

Charles.C





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