[F1ANNEX II U.K. DETERMINATION OF FREE FATTY ACIDS, COLD METHOD
Textual Amendments
1. SCOPE AND FIELD OF APPLICATION U.K.
This method describes the determination of free fatty acids in olive oils and olive pomace oils. The content of free fatty acids is expressed as acidity calculated as the percentage of oleic acid.
2. PRINCIPLE U.K.
A sample is dissolved in a mixture of solvents and the free fatty acids present titrated using a potassium hydroxide or sodium hydroxide solution.
3. REAGENTS U.K.
All the reagents should be of recognized analytical quality and the water used either distilled or of equivalent purity.
3.1 Diethyl ether; 95 % ethanol (v/v), mixture of equal parts by volume. U.K.
Neutralize precisely at the moment of use with the potassium hydroxide solution (3.2), with the addition of 0,3 ml of the phenolphthalein solution (3.3) per 100 ml of mixture.
Note 1: Diethyl ether is highly inflammable and may form explosive peroxides. Special care should be taken in its use. U.K.
Note 2: If it is not possible to use diethyl ether, a mixture of solvents containing ethanol and toluene may be used. If necessary, ethanol may be replaced by propanol-2. U.K.
3.2 Potassium hydroxide or sodium hydroxide, titrated ethanolic or aqueous solution, c(KOH) [or c(NaOH)] about 0,1 mol/l or, if necessary, c(KOH) [or c(NaOH)] about 0,5 mol/l. Commercial solutions are available. U.K.
The exact concentration of potassium hydroxide solution (or sodium hydroxide solution) must be known and checked prior to use. Use a solution prepared at least five days before use and decanted into a brown glass bottle with a rubber stopper. The solution should be colourless or straw coloured.
If phase separation is observed when using aqueous solution of potassium hydroxide (or sodium hydroxide), replace the aqueous solution by an ethanolic solution.
Note 3: A stable colourless solution of potassium hydroxide (or sodium hydroxide) may be prepared as follows. Bring to the boil 1 000 ml of ethanol or water with 8 g of potassium hydroxide (or sodium hydroxide) and 0,5 g of aluminium shavings and continue boiling under reflux for one hour. Distil immediately. Dissolve in the distillate the required quantity of potassium hydroxide (or sodium hydroxide). Leave for several days and decant the clear supernatant liquid from the precipitate of potassium carbonate (or sodium carbonate). U.K.
The solution may also be prepared without distillation as follows: to 1 000 ml of ethanol (or water) add 4 ml of aluminium butylate and leave the mixture for several days. Decant the supernatant liquid and dissolve the required quantity of potassium hydroxide (or sodium hydroxide). The solution is ready for use.
3.3 Phenolphthalein, 10 g/l solution in 95 to 96 % ethanol (v/v) or alkali blue 6B or thymolphthalein, 20 g/l solution in 95 to 96 % ethanol (v/v). In the case of strongly coloured oils, alkali blue or thymolphthalein shall be used. U.K.
4. APPARATUS U.K.
Usual laboratory equipment including:
Analytical balance;
250 ml conical flask;
10 ml burette class A, graduated in 0,05 ml, or equivalent automatic burette.
5. PROCEDURE U.K.
5.1 Preparation of the test sample U.K.
When the sample is cloudy, it should be filtered.
5.2 Test portion U.K.
Take a sample depending on the presumed acidity in accordance with the following table:
| Expected acidity (oleic acidity g/100 g) | Mass of sample (g) | Weighing accuracy (g) |
|---|---|---|
| 0 to 2 | 10 | 0,02 |
| > 2 to 7,5 | 2,5 | 0,01 |
| > 7,5 | 0,5 | 0,001 |
Weigh the sample in the conical flask (4.2).
5.3 Determination U.K.
Dissolve the sample (5.2) in 50 to 100 ml of the previously neutralized mixture of diethyl ether and ethanol (3.1).
Titrate while stirring with the 0,1 mol/l solution of potassium hydroxide (or sodium hydroxide) (3.2) (see Note 4) until the indicator changes (the colour of the coloured indicator persists for at least 10 seconds).
Note 4: If the quantity of 0,1 mol/l potassium hydroxide (or sodium hydroxide) solution required exceeds 10 ml, use the 0,5 mol/l solution or change the sample mass according to the expected free acidity and the proposed table. U.K.
Note 5: If the solution becomes cloudy during titration, add enough of the solvents (3.1) to give a clear solution. U.K.
Carry out a second determination only if the first result is higher than the specified limit for the category of the oil.
6. EXPRESSION OF RESULTS U.K.
Acidity as a percentage of oleic acid by weight is equal to:
where:
=
the volume of titrated potassium hydroxide solution (or sodium hydroxide) used, in millilitres;
=
the exact concentration in moles per litre of the titrated solution of potassium hydroxide (or sodium hydroxide) used;
=
282 g/mol, the molar mass in grams per mole of oleic acid;
=
the mass of the sample, in grams.
Oleic acidity is reported as follows:
to two decimal places for values from 0 up to and including 1;
to one decimal place for values from 1 up to and including 100.]