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In this article we will discuss about the tests for estimation of free fatty acid.
Principle:
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The free fatty acid in an oil is estimated by titrating it against KOH in the presence of phenolphthalein indicator. The acid number is defined as the mg KOH required to neutralize the free fatty acids present in 1 g of sample. However, the free fatty acid content is expressed as oleic acid equivalents.
Materials:
i. 1% phenolphthalein in 95% ethanol
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ii. 0.1 N potassium hydroxide
iii. Neutral Solvent: Mix 25 ml ether, 25 ml 95% alcohol and 1 ml of 1% phenolphthalein solution and neutralize with N/10 alkali.
Test Procedure:
1. 1-10 g of oil or melted fat is dissolved in 50 ml of the neutral solvent in a 250 ml conical flask.
2. A few drops of phenolphthalein is added.
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3. The contents are titrated against 0.1 N potassium hydroxide.
4. Shake constantly until a pink colour — which persists for fifteen seconds — is obtained.
Calculation:
Acid value (mg KOH/g) = Titre value × Normality of KOH × 56.1/Weight of sample (g)
The free fatty acid is calculated as oleic acid using the equation
1 ml N/10 KOH = 0.028 g oleic acid
Standardization:
To find out the exact strength of KOH, prepare 0.1 N oxalic acid solution (630 mg in 100 ml water) and titrate against KOH with phenolphthalein as indicator. Calculate the strength of KOH by the formula V1N1 =V2N2.
