Fatty Acids and its Types

Fatty acids and its types

Fatty acids are naturally occurring non-branched aliphatic monocarboxylic acids consisting of a long saturated or unsaturated hydrocarbon chain with a terminal carboxylic group mostly obtained from hydrolysis of natural fats and oils containing even number of carbon atoms (ranges C₁₂-C₂₀).

Saturated and Unsaturated Fatty acids

The alkyl groups of saturated fatty acids contain C-C single bond.e.g.

1.	Lauric acid	(C11H23-COOH/C12H24O2)	C12H24O2
2.	Myristic acid	(C13H27-COOH/ C14H28O2)
3.	Palmitic acid	(C15H31-COOH/ C16H32O2)
4.	Stearic acid	(C17H35-COOH/ C18H36O2)

The alkyl group of unsaturated fatty acids contain at least C=C double bond. e.g

1.	Oleic acid/9-Octadecenoic acid(C17H33-COOH/ C18H34O2)	CH3(CH2)7CH=CH(CH2)7COOH
2.	Linoleic acid/ 9,12-Octadecadienoic acid(C17H31-COOH/ C18H32O2)	CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
3.	Linolenic acid/9,12,15-octadecatrienoic acid(C17H29-COOH/ C18H30O2)	CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH
4.	Arachidonic acid/5,8,11,14-Eicosatetraenoic acid	(C19H31-COOH/ C20H32O2)

Essential Fatty acids

Essential Fatty acids are those fatty acids that our body cannot synthesize so they must be taken as diet. The function of essential fatty acids is:

ii.          They prevent deposition of cholesterol in arteries and veins.

ii.          They help in reproductive functions and blood clotting.

All essential fatty acids are unsaturated i.e.:

i.          Linoleic acid           (C₁₇H₃₁-COOH)

ii.          Linolenic acid         (C₁₇H₂₉-COOH)

iii.         Arachidonic acid    (C₁₉H₃₁-COOH)

Chemical Properties of Fats and Oils

1. Saponification

The alkaline hydrolysis of fats or oils on boiling with a solution of strong alkali (NaOH or KOH) to form sodium or potassium salt of long chain fatty acid (soap) along with glycerol is called Saponification. It is the reverse process of esterification of glycerol.

                                                 

2. Rancidification

The development of disagreeable foul smell and unpleasant bad taste in a fat or oil caused by its hydrolysis or oxidation on exposure to warm, moist air for a long time is called Rancidification or Rancidity. E.g. when butter is left uncovered, the butter fat tributyrin is hydrolyzed by microorganisms in air producing butyric acid, which imparts unpleasant offensive odour and makes it off-taste. Rancidification is due to:

i.    Hydrolysis of ester linkage to give original fatty acid of sour taste.

ii.    Oxidation at double bond forming volatile aldehydes of bad odour.

3. Iodine Number

The degree of unsaturation of a fat or oil is usually measured by Iodine Number that is the number of gram of iodine consumed or absorbed by 100 gram of fat or oils. Higher the iodine number, greater would the degree of unsaturation or vice versa.

The iodine number of oils is generally higher than fats (due to higher proportion of unsaturated acids in it).

The iodine number of vegetable fats is generally higher than animal fats (except coconut and fish oil).

4. Hydrogenation of Oils

The hydrogenation of unsaturated vegetable oils such as cotton seed oil converts it into fats. Hydrogenation of vegetable oils takes place in the presence of Ni catalyst.