Determinant of double bond in fat by Titration method

1. Estimation of Iodine Value
Jasmine Juliet .R
Teaching Assistant
Biotechnology Dept
AC&RI, Madurai.

3. Determination Of Iodine Value Of Fats
And Oil - Introduction
• Natural fats and oils are triglycerides.
• Triglycerides are formed from three fatty acids which are linked to
glycerol by fatty acyl esters.
• Fatty acids are long aliphatic chains with carboxyl groups. These are
grouped into saturated or unsaturated based on the number of double bonds
present in fatty acid.
• Unsaturated fatty acids consist of single bonds as well as double bonds
and tend to be liquids at room temperature.
• Naturally occurring unsaturated fats contain double bonds in the cis form.

4. Determination Of Iodine Value Of Fats
And Oil - Introduction
• Hydrogenation leads to the conversion of unsaturated fatty acids to saturated
fatty acids.
• The fatty acids combine with oxygen or halogens depending upon the extent of
unsaturation to form saturated fatty acids.
• So, it is significant to know the degree of unsaturation.
• There are different methods to know the level of unsaturation in fatty acids, one
among them is by determining the iodine number of fats.

5. What is iodine value?
• Iodine value, also called iodine number or iodine index, is the
mass of iodine in grams absorbed by 100 grams of oil/fat.
• It is used in the estimation of the degree of unsaturation in
fatty acids.
• The double bonds present in unsaturated fatty acids react with
the iodine;
• the more the iodine number, the more the number of C=C
bonds.

6. Principle
• The oil/fat sample taken in carbon tetrachloride is reacted with an
excess of iodine monochloride solution (Wjis solution).
• Unsaturated fatty acids undergo halogenation reaction resulting in
the addition of an iodine atom to one carbon of the double bond.
• On completion of the reaction, the remaining iodine monochloride
reacts with potassium iodide leading to the formation of molecular
iodine.
• The liberated iodine is then evaluated by titration with a standard
solution of sodium thiosulphate.

7. Materials Required
• Apparatus: Reaction flasks: Standard 250 ml iodine flasks, Erlenmeyer
flask, 500 ml capacity.
• Reagents: 1)Carbon tetrochloride, Hydrochloric acid.
2) Iodine solution: 6.5g of Iodine was dissolved in 50ml of Glacial Acetic
Acid.
3) Potassium Iodide, 10% – Dissolve 10 g of KI in 100ml purified water,
4) Potassium dichromate.
5) Sodium Thiosulphate solution, 0.1 N – Standard
6) Starch Indicator solution, 1%.

8. Erlenmeyer flasks

9. Procedure – Titration I
• The prepared sodium thio sulphate solution was standardized by taking
10ml of 10% potassium Iodide solution.
• Then added10ml of potassium dichromate (0.1N).
• Then Added 5ml of 2N Hcl diluted to 100ml with water.
• Then titrated with thiosulphate until a pale yellow colour appeared.
• Then 1 ml of starch solution was added the blue colour was produced.
• Then titrated with thiosulphate until the disappearance of blue colour..
• The titration was repeated to get the concordant value from the titrated
value.

10. Procedure – Titration I
• From Titration I, we find out the normality(strength) of Sodium
thiosulphate solution by using the following formula:
• V1N1 = V2N2
• Here, V1 = Volume of Potassium dichromate
N1 = Normality of Potassium dichromate
V2 = Volume of Sodium thiosulphate
N2 = Normality of Sodium thiosulphate

11. Procedure – Titration II
• 0.2g of Oil/fat was weighed and dissolved in 10ml of Carbon tetra
chloride.
• Then the flask was rotated gently to mix the content thoroughly.
• The flask was kept aside for about half an hour.
• Then 20 ml of 10% Potassium iodide solution was diluted by adding
200ml of water.
• The mixture was titrated with standard thio sulphate solution using
starch as an indicator.
• A blank determination was carried out without the oil then Iodine number
was calculated .

12. Calculation
• Iodine value = 12.69 (B – S) N/W
Where,
B = volume in ml of standard sodium thiosulphate solution
required for the blank.
S = volume in ml of standard sodium thiosulphate solution required
for the sample.
N = Normality of the standard sodium thiosulphate solution
(Calculated from the Titration I).
W = weight in g of the sample.

13. Uses of estimation of Iodine value
• The iodine value is a measure of the relative degree of unsaturation in oil
components, as determined by the uptake of halogen.
• Because the melting point and oxidative stability are related to the degree of
unsaturation, IV provides an estimation of these quality factors.
• The greater the iodine value, the more unsaturation and the higher the
susceptibility to oxidation.
• Peanut oil (IV 82–107) is more saturated than corn (IV 103–128), cottonseed (IV
99–113), or linseed (IV 155–205) oils;
• However, it is considerably less saturated than coconut (IV 7.7–10.5), palm (IV
44–54) or butter (IV 25–42) oils.