The acid value is a measure of free fatty acids in oils and fats, indicating hydrolysis of triglycerides. It is determined by titrating a sample dissolved in ethanol and ether against potassium hydroxide. A higher acid value means more free fatty acids have formed due to rancidity caused by chemical and enzymatic hydrolysis over time and poor storage conditions. The acid value gives an indication of a fat or oil's age and extent of deterioration.

1. Acid value

2. Introduction
Free fatty acids are a source of flavors and
aromas.
short chain of free fatty acids tend to be water
soluble and volatile with characteristic smell.
Long chain saturated and unsaturated fatty acids
are more prone to oxidation in their free form .
The breakdown products are aldehydes, ketones,
alcohols, and organic acids which provide
characteristic flavors and aromas

3. • Different fat samples may contain
varying amount of fatty acids.
• In addition, the fats often become rancid
during storage.
• Rancidity is caused by chemical and
enzymatic hydrolysis of fats into free
acids and glycerol
Introduction

4. Acid value
• It is the number which expresses in milligrams
the amount of KOH necessary to neutralise
the free acid present in 1 g of the substance.

5. Principle
RCOOH + KOH → ROO- K+ + H2O
AV is also known as
neutralization number or acid number or
acidity
The acid value is determined by directly
titrating the oil/fat in an alcoholic medium
against standard potassium
hydroxide/sodium hydroxide solution.

6. Ip procedure
• Dissolve about 10 g of substance [ weight
mentioned in the individual monograph ] being
examined accurately weighed, in a 50 ml of
mixture of equal volumes of ethanol 95 % and
ether, previously neutralised with 0.1 m KOH to
phenolphthalein solution.
• If the sample does not dissolve in the cold
solvent, connect the flask with a reflux condenser
and warm slowly with a frequent shaking until
the sample dissolves.

7. • Add 1 ml of phenolphthalein solution titrate
against 0.1 M KOH until the solution remains
faintly pink after shaking for 30 seconds.

8. Ethanol-ether solution
Prepare a mixture of ethanol and
diethyl ether (1:1, v/v). Neutralize with
sodium hydroxide titrant and add 1.0
mL of phenolphthalein indicator until
pink colouration is observed. Freshly
prepare the solution.

9. Phenolphthalein indicator
Dissolve 1 g of phenolphthaein in 100
ml of rectified spirit.

10. 0.1M KOH
• Dissolve about 6 g of KOH in distilled water to
produce 1000 ml

11. 95% ethanol
• 95ml of ethanol to 100 ml with water.

12. calculation
• Acid value = 5.61 n/w
• N= the number of ml of 0.1 M KOH required.
• W= the weight in g of the substance.

13. Note
• If the oil purpose of preservation has been
saturated with carbon dioxide for the purpose
of preservation, gently reflux the solution of
the oil in ethanol 95 % and ether for 10
minutes before titration.
• The oil may be freed from the CO2 by
exposing it in a shallow dish in a vacuum
desiccator for 24 hours before weighing the
sample.

14. Significance and application of Acid
value
• It gives how much generation of
free fatty acid has taken place
which leads to rancidity.
• It gives an indication about the
age and extent of its
deterioration.

15. Significance and application of Acid
value
• To Find rancid state, triglycerides are
converted into fatty acids and glycerol,
causing an increase in acid number.
• It is a measure of the free fatty acids
(FFA) in a sample of oil or fat indicates
hydrolysis of triglycerides. Such reaction
occurs by the action of lipase enzyme

16. Significance and application of Acid
value
• it is an indicator of inadequate
processing and storage conditions (i.e.
high temperature, and relative humidity,
tissue damage)
• The acid number is a measure of the
amount of carboxylic acid groups in a
chemical compound, such as a fatty acid,
or in a mixture of compounds

17. Drawbacks of non-aqueous solvents in
determination of acid value
• Currently used non-aqueous solvents are
toxic, such as ethanol or isopropanol
heated up to 60ºC or higher or diethyl
ether-ethanol solvent.
• Incomplete solubility of test oil portion in
alcohol (even under heating) caused by
the formation of a dispersed system.

18. • Conditions for accurate acid-base titration in hot
amphoteric solvents might deteriorate due to the
increase of the solvolysis constant for anion
titrable weak acids with an increase in
temperature. This conclusion follows from the
fact that the solvent auto-protolysis constant
increases, and the acid dissociation constant
decreases with increased temperature.
• Need to previously neutralize the solvents