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Free fatty acids in milks - Potentiometric method?


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#1 poppysnoss

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Posted 22 February 2009 - 11:07 PM

Hello All.

I have recently inherited an autotitrator which seems to have the ability to measure free fatty acids in milk/cream samples amongst others. However, I have no solid knowledge of these machines and there are no instruction booklets etc with the kit.

A bit of a long shot, but I wondered if anyone had any knowledge or experience of potentiometric analysis of FFA? I've had a quick look online but can't find anything substantial. :dunno:

I would be extremely grateful if anyone had any information.

Many thanks in advance

Poppy


Edited by poppysnoss, 22 February 2009 - 11:07 PM.

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#2 AS NUR

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Posted 23 February 2009 - 01:43 AM

Dear Poppy..

I use manual method to measure FFA in Non dairy creamer product .. in this procedure we use alcohol neutral to disolve the sample, and we doing titration, Acid base titration, using Phenolptalein as Indicator...

So. with this information.. IMO.. you have to know about the end point of your titration ( Potential electrical ) of your system, you can find that "end point" by using manual titration, at " the end pount", the solution give Pink colour if you using PP indicator, you have to measure the potential electric. after that you can put the potential electrical number to your equipment ( autotitrator) as "the end point" set....

And verify ..you have to compare the data between manual and autitrator..to make sure that your autotitrator is run well...

Hope can help you...

rgds

AS Nur


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#3 SaRaRa

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Posted 25 February 2009 - 12:38 AM

Hello poppysnoss!

Well... I am not sure if I will be much of a help but I 've looked a lil bit in my notes and I found the following:

The acidity of the cream of the milk is usually expressed in Soxhlet-Henkel degrees. The method is the same with the one used in milk. Soxhlet Henckel (S.H.) degrees express the quantity of N/4 NaOH that are required to neutralise the acidity of 100 ml of milk.
Normal milk has an acidity that has a range of 6-7,5 S.H. High acidity (>7.5 S.H.) is due to the growth of organisms in the milk that ferment part of the lactose into lactic acid that raises the acidity. Low acidity (<6 S.H.) is due to the contamination of animals from mastitis (a disease... I am not sure if I translate it correctly) or due to the addition of water and alcalic substances in milk.

Another way of expressing milk acidity is using Dornic degrees (neutralising the sample with N/9 of NaOH) and also % lactic acid.
The relationship between the different units is the following:

1 S.H. = 2,25 Dornic units = 0,0225% lactic acid

Method:

25 ml of milk + 1 ml phenolophthalein in a glass. Sample is being titrated with N/4 NaOH until the white colour of milk turns into pink. S.H. is being calculated according to:

S.H. = a x 100 / b where

a = ml N/4 NaOH that was used for the neutralization of 25 ml of milk
b = ml of sample

Other methods of measuring acidity:

1. Boiling test

Milk with an acidity over 11 S.H. is being coagulated during boiling when compared to the "normal" milk that doesnt coagulate. The coagulation of milk by heating is promoted with the increase of acidity:

Acidity S.H. / Coagulation temperature
15,5 / 66
17,7 / 28,44
22,2 / 24,27
25,3 / 16-18

According to the above, milk quanity in a tube is heated until boiling. If the milk is coagulated this means that the acidity is higher than 10 S.H. and its not usable for further treatment.

2. Alcohol test

This test is used usually in milk industries when they receive the raw milk. The method is based in the fact that milk with an acidity of >9,8 S.H. is coagulated when it is mixed with equal amount of alcohol 68%. This test is better than the boiling test because it can track smaller amounts of acidity and it gives information about other anomalies of the milk beng tested. With this test even milk with "normal" acidity coagulates if it has "firstmilk" (the first milk that comes from the animal... dunno how to translate it in English) or animals that are infected with mastitis (a disease). This test cannot be used for goat milk.

Method:

5 ml milk + 5 ml alcohol 68% are mixed in a tube. If the milk is coagulated (this can be clarified by noticing small agglomerated units in the sides of the tube) it means that the acidity is >9.8 S.H. and that means that the milk is not considered OK for pasteurisation.

3. Measuring pH

pH is another method of expressing acidity of milk. "Normal" milk has a pH of 6,5-6,7 with most normal 6,65. Milk with pH < 6,5 is considered acidified and its usually not accepted by milk industries. Milk with pH > 6,8 shows that the animal that produced the milk is sick.


Cheers!


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#4 SaRaRa

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Posted 25 February 2009 - 12:37 PM

Hmm I think the following link is more useful and acurate from my previous post.

DAIRY CHEMISTRY: A Practical Hanbbook for dairy chemists and others having control of dairies.

This link might not have to do with dairy products but it has to do with automated techniques for continuous titration. Check it out:

Implementation of Online Instrumentation in a Vegetable Oil Refinery


Edited by SaRaRa, 26 February 2009 - 12:49 PM.

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#5 poppysnoss

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Posted 26 February 2009 - 09:12 PM

:thumbup: Thanks for the link, Sa Ra Ra! Am off to check them out now.
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#6 poppysnoss

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Posted 01 March 2009 - 10:19 PM

Does anyone know a manual titration method for FFA analysis on fresh milk? Not sure whether you can analyse milk in its straight form or whether the fat needs to be extracted first.


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#7 Charles.C

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Posted 02 March 2009 - 04:57 AM

Dear poppysnoss,

Here is AOAC reference for coconut milk (google). Bit old (1984) so most recent AOAC version should be checked but the classic methods are usually maintained. Possible dependency on type of milk also ?

2.3 Free Fatty Acids
The FFA content was determined as recommended by the standard Association of
Official Analytical Chemists method (AOAC, 1984). 25ml of 95% alcohol was
neutralized using standardized 0.0598M NaOH using Phenolphthalein as the indicator.
The solution was added to 25ml of coconut milk and mixed well. 25ml of diethyl ether
was added to the resulting solution and mixed well. The solution was titrated with
0.0598N NaOH with Phenolphthalein as the indicator, till the pink color persisted. The
FFA was calculated in terms of percentage of Lauric acid per 100ml of coconut milk.
http://www3.ntu.edu...... Yashasvi.pdf.

Rgds / Charles.C


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Kind Regards,

 

Charles.C


#8 poppysnoss

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Posted 02 March 2009 - 04:13 PM

Thankyou for that, Charles - that's brilliant. :smile:

I have just ordered a copy of the 16th edition AOAC methods from my uni library so will see if there's anything more in there.


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