What is fatty acid?
Fatty acids are monocarboxylic acids that are found in natural fats or lipids. As they are prepared from fats, they are so named. A fatty acid is one of the major components of a triglyceride, which is a form of lipid that is used in the body to stock up energy. A lipid is just a type of molecule that includes, among other things, fatty acids. Triglycerides are a secondary energy source that the body can use in the event that there is not enough sugarin the system. While fatty acids vary in terms of chemical individuality, they all have some basic qualities in common.
Types of fatty acids
According to their structure fatty acids are classified into four classes—
1) simple or straight chain fatty acids,
2) branched chain fatty acids,
3) hydroxyl fatty acids and
4) Cyclic fatty acids.
Simple or straight chain types of fatty acids
Most of the common fatty acids belong to this group in which the carbon atoms remain arranged in a single straight chain. These may be divided into two subclasses—(a) saturated and (b) unsaturated.
Saturated types of fatty acids
There is no double bond in the carbon chain of these types of fatty acids. They have the general formula CnH2nO2 or CnH2n+i COOH or CH3 (CH2)n COOH and they occur in two series- even carbon fatty acids and odd carbon fatty acids that contain even and odd number of C atoms in their molecules respectively. The former series (even carbon acids) are more plentiful in nature, ranging from C2 to C26. Among these the most common is CK, fatty acid called palmitic acid. Other common examples of even carbon fatty acids are acetic acid (C2), butyric acid (C4), stearic acid (C6) etc. Odd carbon fatty acids ranging between Ca to C25 are also found in nature, but much less frequently. A few examples of odd carbon fatty acids are propionic acid (Cs), valeric acid (Cs), heptanoic acid (Cy) etc.
Unsaturated types of fatty acids
This group is characterized by having one or more double bond(s) in their carbon chain. According to the number of double bonds present in the molecule, such types of fatty acids are grouped as monoenoic, dienoic, trienoic, tetraenoic, pentaenoic etc. However, those containing more than one of double bonds are collectively referred to as polyenoic acids. Common examples of such fatty acids are oleic acid, palmitioleic acid, linolenic acid, linoleic acid, arachidonic acid etc. Three of these namely linolenic acid, linoleic acid and arachidonic acids are called essential fatty acids because they are not synthesized in our body but are essentially required for growth and hence they must be taken through diet.
Branched chain types of fatty acids
Some even or odd carbon fatty acids have branched chains. These are less abundant in nature. The more common saturated methyl-branched fatty acids can often be identified from the mass spectra of their methyl ester derivatives, especially when spectra of model compounds are available for comparison purposes. Example of such types of fatty acids are obutyric acid, isovaleric acid etc.
Hydroxyl types of fatty acids
In some saturated or unsaturated fatty acids, one or more H atoms are substituted by hydroxyl (-OH) groups. Example of these types of fatty acids is cerebronic acid, ricinoleic acid, dihydroxystearic acid etc.
Cyclic types of fatty acids
Fatty acids containing hydrocarbon ring are of this type. Example of these types of fatty acids are, chaulmoogric acid, gorlic acid etc. Fatty acids containing up to ten carbon atoms are referred to as lower (or small chain) fatty acids where as those having more than ten carbon atoms are called higher or long chain fatty acids.