Fatty Acids: Meaning and Types

In this article we will discuss about the Meaning and Types of Fatty Acids.

Meaning of Fatty Acids:

Fatty acids are organic acids having hydrocarbon chains that end in a carboxylic group (—COOH). Hydrocarbon chains may be straight or have ring structure. Some fatty acids also possess hydroxyl groups. Length is 4-24 carbons. The common fatty acids have 16 or 18 carbons. Plants have the biosynthetic machinery to manufacture all types of fatty acids.

Animals also have this machinery but many animals lack the mechanism to synthesise three fatty acids— linoleic, linolenic and arachidonic acids. They are called es­sential fatty acids (EFA; Burr and Burr, 1930). They must be present in the animal diet. Essential fatty acids occur in most edible oils like those of Sunflower, Groundnut, Cotton­seed, Coconut, etc. Their deficiency produces phrenoderma or follicular hyperkeratosis.

Types of Fatty Acids:

Fatty acids are of two main types— saturated and unsaturated.

I. Saturated Fatty Acid:

Saturated fatty acids do not possess double bonds in their carbon chains. They have a general formula of C_nH_2nO₂, e.g., C₁₆H₃₂O₂ (palmitic acid), C₁₈H₃₆O₂ (stearic acid).

II. Unsaturated Fatty Acids:

Unsaturated fatty acids possess one or more double bonds in their carbon chains. The general formula is C_nH_{2n- 2x}O₂ e.g., oleic acid (with one double bond, monoene, C₁₈H₃₄O₂), linoleic acid (with two double bonds, diene, C₁₈H₃₂O₂), linolenic acid (with three double bonds, triene, C₁₈H₃₀O₂), arachidonic add (with four double bonds, tetraene, C₂₀H₃₂O₂).

Unsaturated fatty acids have lower melting point than the saturated fatty acids. Most plant lipids have unsaturated fatty acids while most animal lipids have saturated fatty acids. Aquatic animals of colder waters, however, possess unsaturated fatty acids. Carboxylic group of a fatty acid is hydrophilic, polar or water soluble while the rest of the hydro­carbon chain is nonpolar, lipophilic, hydrophobic or water insoluble.

Polar end sticks to water so that fatty acids form a monomolecular layer over it. The water soluble end of fatty acid also reduces surface tension and increases the wetting or cleaning power of water. Soap action is actually the action of fatty acids contained in it.