What is Fatty Acids? Definition, Classification, Sources etc.

Fatty Acids

Fats are carboxylic acids with hydrocarbon chains (– CH2– CH2– CH2–) and represented by a chemical formula R-COOH, where R stands for hydrocarbon chain. The fatty acids are amphipathic in nature, i.e., each has hydrophilic (COOH) and hydrophobic (hydrocarbon chain) groups in the structure.

Classification of Fatty Acids

Fats are categorized into 4 significant classes:

  1. Straight chain fatty acids
  2. Branched-chain fatty acids
  3. Substituted fatty acids
  4. Cyclic fatty acids.


Straight Chain Fatty Acids

Fatty acids, in which the carbons are organized linearly,are subclassified into 2 classes:

  1. Saturated fatty acids
  2. Unsaturated fatty acids
Saturated fatty acids

There is no double bond in the hydrocarbon chain of these fatty acids. Saturated fatty acids are subclassified into two classes:

  1. Even carbon acids bring even number of carbons, e.g., palmitic acid and stearic acid.
  2. Odd carbon acids carry odd number of carbons, e.g., propionic acid.
Unsaturated fatty acids

These contain double bonds in their hydrocarbon chains. These are subclassified according to the number of double bonds present in the structure as follows:

  1. Monoenoic or monounsaturated fatty acid
  2. Polyenoic or polyunsaturated fatty acid
  • Monoenoic or monounsaturated fats carry a single double bond in the molecule, e.g., oleic acid.
  • Polyenoic or polyunsaturated fats consist of two or more double bonds; for instance:
  • Dienoic acids have two double bonds, e.g., linoleic acid present in soyabean, sunflower, saffola and groundnut oil.
  • Trienoic acids have three double bonds, e.g., Linolenic acid present in poppyseed oil, linseed oil.
  • Tetraenoic acid with four double bonds, e.g., acid present in groundnuts.
Branched Chain Fatty Acids

These are less abundant than straight chain acids in animals and plants, e.g.

  • Isovaleric acid
  • Isobutyric acid
Substituted Fatty Acids

In substituted fatty acids one or more hydrogen atoms have been changed by another group, e.g.

– Lactic acid of blood

– Cerebronic acid and oxynervonic acids of brain glycolipids

– Ricinoleic acid of castor oil.

Cyclic Fatty Acids

Fatty acids bearing cyclic groups are present in some bacteria and seed lipids, e.g., hydnocarpic acid (Chaulmoogric acid) of chaulmoogra seed.

Numbering of Fatty Acid Carbon Atoms

Fatty acids carbon atoms are numbered beginning at the carboxyl terminus.Carbon atoms 2 and 3 are frequently referred to as a and ß respectively.The methyl carbon atom at the distal end of the chain is called omega (ω) carbon.


Representation of Double Bonds of Fatty Acids

Two systems are utilized to designate the position of double bond:

  • C-system
  • ω- or n-system

In C-system (i.e., C1 being the carboxyl carbon) the position of double bond is represented by the signΔ(delta), followed by a superscript number. For instance, oleic acid is a C18 fat with one double bond in between carbon number 9 and 10 is represented as C: 18:1Δ9.

ω– or n- System

In this system, ‘ω’ or ‘n’ describes the carbon of their terminal methyl group in a fat. Inω- system or n-system, the oleic acid is denoted as C: 18:1:ω -9to indicate that:

  • ω -9 represents the double bond position which is present in between 9th and 10th carbon atoms, the first carbon atom being that of the terminal methyl group. This technique is widely utilized by nutritionists. Naturally taking place unsaturated fats belong toω -9,ω -6 andω -3 series. For instance,
  • ω -9: Oleic acid (C: 18:1:ω -9).
  • ω -6: Linoleic acid (C: 18:2:ω -6).
  • Arachidonic acid (C: 20:4:ω -6).
  • ω-3: Linolenic acid (C: 18:3:ω -3).
Sources of Fatty Acids

Almost all foods contain many different fats, consisting of saturated-, monounsaturated- and polyunsaturated omega-6 and omega-3 fatty acids. However, the amount of the various fatty acids varies from one food to another, making it possible to alter the intake of fatty acids by changing foods. These are the typical sources of fatty acids.

  • Milk and milk items; such as butter, cream, ice cream, sour cream, yoghurt, cheese and more.
  • Red meat and products made from red meat.
  • Coconut and coconut oil.
  • Avocado and products made from avocado.
  • Numerous nuts such as almonds, peanuts and brazil nuts.
  • Wheat and products made from wheat.
Functions of Fatty Acids

Fatty acids have three major physiological functions.

  1. They work as building blocks of phospholipids and glycolipids. These amphipathic molecules are essential components of biological membranes.
  2. Fat derivatives function as hormones, e.g., prostaglandins.
  3. Fats function as a significant fuel for many cells.

The industrial uses are:

  1. Fats are primarily used in the production of soap, both for cosmetic purposes and, in the case of metallic soaps, as lubricants. Fats are also converted, by means of their methyl esters, to fatty alcohols and fatty amines, which are precursors to surfactants, detergents, and lubricants.
  2. Other applications include their use as emulsifiers, texturizing agents, moistening agents, anti-foam agents, or stabilizing agents.

Carboxylic acids with hydrogen chains vital for the formation of life molecules are called fatty acids. They have amphipathic nature i.e., having both hydrophobic and hydrophilic groups.

Fatty acids without any double bond are called saturated and fatty acids having up to 6 double bonds are unsaturated fatty acids. In animals, they are mostly present in straight-chain but in plants, they form rings or are branched.

The solubility of fatty acids in organic solvents and their melting points increase with the increase in number of carbon atoms in the chain. Fats that have unsaturated fatty acids are oils and are liquid at room temperature.

Most plant fats are liquid. Those having saturated fatty acids are solid at room temperature. Animal fats are solid fats.