Carboxylic acids with chain lengths in the range of 6 – 24 carbon atoms are traditionally called fatty acids.
The table below gives a summary of the fatty acid composition, their trivial names together with idoine value for some selected oils and fats.
Fatty acid composition is expressed as a weight percentage of the total amount of fatty acids measured. The weight of glycerol is neglected. The shorthand designation for fatty acids consists of two numbers, the first being the number of carbon atoms and the second being the number of double bonds in the fatty acid chain. Many natural fatty acids have trivial names applied when they were first isolated and characterised.
The iodine value indicates the degree of unsaturation of the oil but does not differentiate between monounsaturated fatty acids (eg. Oleic) and polyunsaturated fatty acids (eg. Linoleic acid), nor between cis and trans double bonds. The iodine value of natural fats and oils vary over a range.
Fatty acids can be classified according to their saturation, i.e. number of double bonds:
Saturated fatty acids (SAFAs) have no double bonds, e.g. myristic, lauric palmitic and stearic acids.
Fatty acids containing one or more double bonds are known as unsaturated.
While monounsaturated fatty acids (MUFAs) have one double bond (e.g. erucic, oleic, palmitoleic, myristoleic, gadoleic), polyunsaturated fatty acids (PUFAs) have two or more double bonds (e.g. linoleic linolenic, arachidic).
The position of the double bond can vary along the carbon chain and its position can be indicated in several ways.
Fats and oils are practically always mixtures of different fatty acids in varying proportions. Hence the degree of saturation of the different fats and oils depends upon their various fatty acids content, as you can see in the table above.