Lipids for PharmD students Lecture 2 26 Oct 2024

The properties of oils and fats vary along with the degree of unsaturation, average molecular weight and also acidity from hydrolysis.
A number of parameters are used for here analysis which are included under physical constants and chemical constants.
Physical constants include viscosity, specific gravity, refractive index, solidification point etc.
Under the group of chemical constants, conventionally the parameters like iodine value, acid value, peroxide value, saponification value, unsaponifiable matter etc.

In recent times, gas chromatographic determination of fatty acid profiles has been introduced for identification of fats and oils.
lodine value:
It is defined as the weight of iodine absorbed by 100 parts by weight of the sample of fat or oil.
lodine value is a measure of the extent of unsaturation.
Susceptibility to rancidity increases for the oil or fat having higher iodine values.
1. Addition of iodine
Iodine monochloride reacts with the unsaturated bonds in the fatty acids, adding a halogen at the C=C double bond site.


2. Determination of reacted iodine
After the reaction, potassium iodide is added to the reaction product, causing the remaining iodine monochloride to form molecular iodine.
3. Titration
The liberated iodine is titrated with a standard solution of sodium thiosulfate.
4. Use of starch as indicator
Starch is used to indicate the endpoint of the reaction, as the liberated iodine reacts with starch to produce a purple color.
Reaction with unsaturated bonds
Iodine monochloride (ICl) in glacial acetic acid reacts with unsaturated bonds in the sample, resulting in halogenation


2. Conversion to molecular iodine
Excess ICl is treated with potassium iodide (KI) and water to convert it to molecular iodine

3. Titration
The amount of iodine formed is determined by titration with sodium thiosulfate and starch as the indicator
Significance
Degree of unsaturation can be known with the help of iodine value.
Drying character of oils can be determined.
Adulterants can be recognized.
Quantity of fat or oil required for converting them into soap can be determined.
Calculate the iodine value from the expression 1.269 v/w where v is the difference, in ml, between the titrations and w is the weight, in g, of substance taken.
2. Saponification value: It is defined as the number of milligrams of potassium hydroxide required to neutralize the fatty acids resulting from complete hydrolysis of 1 g of the sample of oil or fat. Saponification value occurs in an inverse proportion to the average molecular weights of fatty acid present in the oil.
This value is normally applied for butter fat, coconut oil in which lower fatty acids glycerides occur in high content.
. Hydroxyl value: It is defined as number of milligrams of potassium hydroxide required to neutralize the acetic acid capable of combining by acetylation with 1 g sample of fat or oil.
Acetyl value: It is the number of milligrams of potassium hydroxide required to neutralize the acetic acid obtained when 1 g of sample acetylated oil is saponified. Except castor oil (acetyl value 150), most of the oils and fats have low acetyl value (3 - 15)
5. Unsaponifiable matter: It is the matter present in fats and oil, which after saponification by caustic alkali and subsequent extraction with an organic solvent, remains non-volatile on drying at 80°C. It includes sterols (phytosterol and cholesterol), oil soluble vitamins, hydrocarbons and higher alcohols. Paraffin hydrocarbons can be detected by this method as adulterants.
Acid value: It is defined as the number of milligrams of potassium hydroxide required to neutralize the free acids present in 1 g sample of fat or oil. Generally, rancidity causes free fatty acids liberation, hence acid value is used as an indication of rancid state.
Definition - It refers to the number of milliequivalents of peroxide oxygen (hydroperoxides) present in one kilogram of sample (oil or fat).
Procedure - Dissolve the weighed amount (1 kg) of fat or oil in glacial acetic acid. Add excess potassium iodide solution and titrate the resultant solution with standardized sodium thiosulphate using starch solution as indicator.