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Monday, May 26, 2014

Estimation of free fatty acids

Fatty acids are carboxylic acids with a hydrocarbon chain. They have a chain of even number of carbon atoms, generally 4-28. Fatty acids are of Two Types:

  1. Saturated Fatty acids
  2. Unsaturated Fatty acids
Saturated fatty acids have carbon - carbon single bond, whereas unsaturated fatty acids have carbon-carbon double bond.
Structure of Fatty Acid

Fatty acids are usually derived from triglycerides or phospholipids. when they are not attached to other molecules it is called as Free Fatty acids.

A small quantity of free fatty acids is usually present in oils along with the triglycerides. The free fatty acid content is known as acid number/acid value. It increases during storage. The keeping quality of oil therefore relies upon the free fatty acid content.


The free fatty acid in 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 1g of sample. However, the free fatty acid content is expressed as oleic acid equivalents.

  • 1% phenolphthalein in 95% ethanol.
  •  0.1N potassium hydroxide
  • Neutral Solvent: Mix 25mL ether, 25mL 95% alcohol and 1mL of 1% phenolphthalein solution and neutralize with N/10 alkali.
  1. Dissolve 1-10g of oil or melted fat in 50mL of the standard solvent in a 250mL conical flask.
  2. Add a few drops of phenolphthalein.
  3. Titrate the contents against 0.1N potassium hydroxide.
  4. Shake constantly until a pink color which persists for fifteen seconds is obtained.

Acid value (mg KOH/g) = (Titrate value x Normality of KOH x 56.1) / Weight of sample (g)

The free fatty acid is calculated as oleic acid using the equation
1mL N/10 KOH = 0.028g oleic acid.