1. Characters of naturally present fatty acids
They are usually monocarboxylic acids, R-COOH.
The number of carbon atoms is even (4-28).
Hydrocarbon chain is not straight but zigzag.
They are either saturated or unsaturated (up to 6 double bonds).
Naturally present fatty acids are cis non-conjugated.
The main functional group is COOH, sometimes fatty acids contain additional functional group other than COOH e.g. OH in hydroxy acids.

2. Nomenclature and abbreviation of fatty acids
The name of fatty acid is derived from the number of carbon atoms.
Number + noic (saturated fatty acids).
Number + enoic (unsaturated fatty acids with one double bond).
Number + dienoic (unsaturated fatty acids with two double bonds).
Number + trienoic (unsaturated fatty acids with three double bonds).

3. Nomenclature and abbreviation of fatty acids
Name
IUPAC name
Abbreviation
Stearic acid
octadecanoic
C18:0
Oleic acid
octadecaenoic
C18:1C9
Linoleic acid
octadecadienoic
C18:2C9,12
linolenic acid
octadecatrienoic
C18:3C9,12,15
12-hydroxyoleic acid
(Ricinoleic acid)
12-hydroxy- octadecaenoic
C18:1C9 , 12-OH

4. Common fatty acids
I. Saturated Fatty Acids (General Formula : CnH2nO2)
Number of
carbon
Name
Formula
Occurance
C4:0
Tetranoic
Butyric
C3H7COOH
Butter fat
C6:0
Hexanoie
Caproic
C5H11COOH
Butter fat & coconut
C8:0
Octanoic
Caprylic
C7H15COOH
C10:0
Decanoic
Capric
C9H19COOH
Cl2:0
Dodecanoic
lauric
C11H23COOH
Palm oil
Cl4:0
Tetradecanoic
myristic
C13H27COOH
Palm oil, nutmeg & butter
Cl6:0
Hexadecanoic
palmitic
C15H31COOH
Palm oil, c.s.o, olive oil & butter fat
Cl8:0
Octadecanoic
stearic
C17H35COOH
milk & animal fats.
C20:0
Eicosanoic
Arachidic
C19H39COOH
Arachis oil.

5. Common fatty acids
II- Unsaturated fatty acids [General formula: CnH2n-xO2 (x = d.b x 2)]
Number of carbon
Name
Formula
Occurance
C18:1C9
Octadecaenoic
Oleic
C17H33COOH
Most oils
C18:2c9,12
Octadecadienoic
Linoleic
C17H31COOH
Cotton seed oil & sesame oil
C18:3c9,12, 15
Octadecatrienoic
Linolenic
C17H29COOH
Drying oils,
e.g. linseed oil

6. Cyclic Fatty Acids:-
Fatty acids containing a carbocyclic unit are most commonly cyclopropene or cyclopentene compounds.
The most known cyclopropenyl fatty acids are malvalic and sterculic which are present in high levels in sterculia oils and at lower levels in cottonseed oil.
The most common Cyclopentenyl fatty Acids are hydnocarpic acid (16:1), chaulmoogric acid (18:1), and gorlic acid (18:2) which are present in Chaulmoogra oil.

7. Hydroxy Fatty acids :-
These contain hydroxyl groups in their hydrocarbon chains.
12-hydroxyoleic acid or ricinoleic acid, present in castor oil.
Essential fatty acids:-
They are required for maintenance of normal growth, reproduction and skin permeability. They cannot be synthesized by the cell of the body and must be obtained from external sources, e.g linoleic, linolenic acid.

8. Physical Examination of oils & fats
Melting point
The melting point of fat is determined by heating. The fat starts to melt (incipient fusion) & finally become liquid (complete fusion).
The difference between incipient and complete fusion is characteristic for individual lipid.
Factors affecting melting point
1. The proportion of saturated to unsaturated fatty acids.
Saturated fatty acids have a higher melting point.
2. The length of the fatty acid chains.
The longer the fatty acid chains, the higher the melting point.

9. Physical Examination of oils & fats
Melting point
3. The geometry of carbon double bonds.
Trans fatty acids melt at higher temperatures than cis configuration. 
4. The position of the double bonds.
The melting point (not greatly) depends on where the double bond is located on the chain.

10. Physical Examination of oils & fats
Titer Test
The titer of an oil or fat is the solidifying point of the mixed fatty acid.
The titer temperature is characteristic for individual lipid and for assessing the hardness.
The lipid is saponified by alcoholic KOH then acidified by HCl to liberate the free F.A.
The melted fatty acids are allowed to cool. After the solid begins to separate, the temp rises to certain extent due to the latent heat liberated during solidification.
The highest temperature is taken as the titer value.

11. Physical Examination of oils & fats
Maumene test (thermal test)
It depends on recording rise in temperature on addition of 1 ml Br2 to 10 ml 10% solution of oil in chloroform (interaction with double bonds).
Thermal test gives indication about degree of unsaturation of lipid.
Determination of water
The moisture content is determined by Karl-Fischer reagent.
The reagent consists of I2 + SO2 + anhydrous methanol + anhydrous pyridine.
Determination of water content by evaporation is not accurate due to loss of some volatile substances.

12. Physical Examination of oils & fats
Specific gravity
Specific gravity (at 25oC) = weight of certain volume of oil weight of the same volume of water
The sp. gravity of oils & fats is always less than one.
It’s increased by hydrogenation & rancidity due to saturation of the double bonds, in the fatty acids of the oils.
It’s measured by pycnometer or westphal balance.
Pycnometer
Westphal balance

13. Physical Examination of oils & fats
Refractive index (R.I.)
Refractive index (at 25oC) = sine the angle of incident light sine the angle of refraction light
There are two types of refractometers which are, Abbe refractometer (which reads the true refractive index directly) and Butyro (Bu) refractometer (Which reads arbitrary refractive index).
R.I increases with the increase in length of hydrocarbon chain & the number of double bonds.

14. Physical Examination of oils & fats
Viscosity
Viscosity is the resistance due to friction between particles.
It can be measured by the use of viscometer.
Color
The color of oil can be measured using lovibond tintometer or the optical density at specified max using spectrophotometer.
Color is due to Carotenoids