10 replies to this topic

[gresty]

Hi All,

My first post!!

I work for a company manufacturing pickles where one of our key controls is the acid level, and I'm trying to understand the background to our acid testing procedure.

The procedure is based around a titration of the sample with Sodium Hydroxide using Phenolphthalein as the indicator and then using the equation below to calculate the acid value.

Volume of NaOH used (ml) x Acidity Factor
Weight of sample

We are currently using a factor of 0.6 for acetic acid, but the information I've found so far suggests it should be 0.06. I would also be interested to know the factors for Citric and Lactic Acids.

Does anyone know what the values should be, or can point me to a good reference source.

Thanks.

[nitac]

Hello Gresty

What is it that you are picking and is acidity a CCP? We have just revalidated our controls on pickles and have changed from acidity to pH as a CCP.

[Charles.C]

Dear gresty,

Insufficient data given. IMEX the terminology "acidity factor" is not standard textbook ?

the usual acid value equation is for KOH but easily adapted to NaOH.

assuming KOH, an example is -
text book gives, acid value = [Titration (ml of N/10) x 5.61]/ [wt of sample in gram]

def.AV = number of mg of KOH required to neutralise the free acid in 1g of sample.

Theory
1litre of N, KOH contains 56.1g KOH
1ml N, KOH contains 56.1 mg
1ml, 0.1N, KOH contains 5.61 mg (hence top line of equation)
dividing by sample wt (g) gives result per gram of sample.

If NaOH, use "40" instead of 56.1 (40= 23+16+1, approx)(no doubt you knew that already )

yr equation may involve a different "factor" logic.

Rgds / Charles.C

BTW Welcome to the forum

[faisal rafique]

Hi All,

My first post!!

I work for a company manufacturing pickles where one of our key controls is the acid level, and I'm trying to understand the background to our acid testing procedure.

The procedure is based around a titration of the sample with Sodium Hydroxide using Phenolphthalein as the indicator and then using the equation below to calculate the acid value.

Volume of NaOH used (ml) x Acidity Factor
Weight of sample

We are currently using a factor of 0.6 for acetic acid, but the information I've found so far suggests it should be 0.06. I would also be interested to know the factors for Citric and Lactic Acids.

Does anyone know what the values should be, or can point me to a good reference source.

Thanks.

Dear,

Acidity calculation is by this equation

1/10 x Equivalent weight of acid x Normality of NaOH x Titer ( Vol of NaOH used ml)
Total acid (%) = ___________________________________________________________________
10
Equivalent weight of acid: Acetic Acid= 60 g, Citirc (Mono)= 70 g etc
Equivalent weight of acid is another calculation, it all depends upon acid in fruit present ( more)
For Knowledge Equivalent weight of acid is calculated by stoichiometry of acid chosen for expresing acidity
Use this above mentioned formula and get results, any difficulty tell me, keep in mind it is %age of acid.


Faisal RAfique

Edited by faisal rafique, 02 March 2011 - 06:59 AM.

[Charles.C]

Dear faisal rafique,

Total acid (%)

This is yet another new name to me

Without going through the maths i expect it is equivalent to calculating FFA% but using acetic acid, etc instead of oleic/lauric/palmitic whatever ?. If so then the original poster can look up FFA in the textbooks.

Regardless, it was good observation to spot that equivalent weight of acetic acid is 60

Rgds / Charles.C

[gresty]

Hello Gresty

What is it that you are picking and is acidity a CCP? We have just revalidated our controls on pickles and have changed from acidity to pH as a CCP.

We make sandwich pickles, piccalilli, etc, as well as traditional ones like Pickled Onions, Red Cabbage & Beetroot. It may be that I'm trying to get too deeply into it as we also use pH as a CCP not acidity.

Thanks for the reply.

[faisal rafique]

Dear faisal rafique,



This is yet another new name to me

Without going through the maths i expect it is equivalent to calculating FFA% but using acetic acid, etc instead of oleic/lauric/palmitic whatever ?. If so then the original poster can look up FFA in the textbooks.

Regardless, it was good observation to spot that equivalent weight of acetic acid is 60

Rgds / Charles.C

FFA us related with oils while total acid (%) is related with fruit and vegetable products. It includes titratable and volatile acidity.

Faisal RAfique

[Charles.C]

Dear All,

After doing a little research into “wine” it seems that a considerable variety of terminologies / interpretations are in common use. Some examples –

1. Acid content
2. Titratable acidity (TA)
3. Total titratable acidity (TA)
4. Total acidity (TA)
5. Volatile acidity
6. Fixed acidity

Equations given for No.2 above (eg L1, L4, L6, L7 below) look operationally equivalent to that in the thread post #4 .The item “total acidity” appears to have various interpretations (eg L2, L3, L5).

Various AOAC procedures exist (eg L4 ) (from a long way back, naturally).
Here are some ilustrations of the subjectivity involved –

L1. http://www.extension...ableacidity.htm

L2. http://www.mianser.c...acidity-defined

L3. http://www.winepersp...ity_of_wine.htm


 L4. titratable acidity, AOAC 962.12.pdf   33.62KB   93 downloads

 L5. relationship between tot. acidity, tit.acidity, and pH .pdf   37.89KB   69 downloads

 L6. Analysis of TA (titratable acidity) example -1999.pdf   2.35MB   70 downloads

 L7. Measuring TA (titratable acidity) and pH.pdf   113.09KB   69 downloads

Rgds / Charles.C

PS I'm sure "total acid%" also is used somewhere, just didn't come across it yet.

PPS After all the above, i remembered that the original post was on pickles but hopefully the same basic logic applies [added - after a quick look into the pickles area, "pickles titratable activity" does seem to be popular again]

[Jules]

Pedant speaking here. Is pH a CCP? Would the CCP not be making the product to the recipe with the pH as a verification?

[Tony-C]

Pedant speaking here. Is pH a CCP? Would the CCP not be making the product to the recipe with the pH as a verification?

Thanks Jules, that makes sense, I would agree for pickled products but not for fermented.

Regards,

Tony

[Jason H.Z.C.]

Hi Jules,

Can you make sure that before pickling process the pH/acidity of each batch raw material are same?

I am not sure but how could we set a CCP(recipe) based on a changable parameter(acidity) in raw materials? However, pH is a permanent number, isn't it?

Best regards,

Jason