Found in vegetable and animal oils and fats, fatty acid is among the major building blocks of fat. It’s a primary component making up triglyceride – a type of lipid that the body stores as energy and uses it when there is no primary energy source in the system. A lipid is a molecule that comprises multiple things – fatty acid is one among them. To form a triglyceride, three fatty acids bond with glycerol.

Chemical Structure

The fatty acid is a straight chain made of carbon and hydrogen atoms running along the length of the chain. However, unlike butane, octane, and propane that have the hydrogen atom at both ends of their respective chains, the fatty acid has a carboxyl group (COOH) at one of its end, which makes the fatty acid an acid. The COOH end of the fatty acid is called the alpha end.

A carboxyl group is an acid that has a carbonyl group and hydroxyl group bonding with a shared carbon atom. When the hydroxyl group (OH) is taken away from the carboxyl group of the fatty acid and it’s later attached to a compound called glycerol along with two more fatty acids without the OH, you get a triglyceride – a fat molecule. When people eat fat-rich foods, they’re consuming several such triglycerides.

Chain Length

A fatty acid can be short, medium and long. The number of carbon atoms in the chain could be 2-80; however, the common range is 12-24. The short-chain acid has 2 to 6 carbon atoms. The medium chain comprises at least 6 carbon atoms but not higher than 10 or 12 atoms. The longest ones have carbon atoms in excess of 12 and up to 24 carbon atoms.

Fatty Acid Types

Unsaturated and saturated fatty acid chemical structure. Image credit: Flickr
Unsaturated and saturated fatty acid chemical structure. Image credit: Flickr

Fatty acids can be classified based on how the whole carbon-hydrogen atoms are arranged. There are primarily two fatty acid types: saturated, and unsaturated (monounsaturated and polyunsaturated).

Saturated Fatty Acid 

In this fatty acid, every carbon atom has two hydrogen atoms attached and the bond between carbons is single. This means the fatty acid is saturated with hydrogen, making it much stable. Stearic acid is a saturated fatty acid, for example. Saturated fatty acids can withstand more heat before emitting an unpleasant smell, which makes them kitchen-friendly. Also, saturated fats stay firm at room temperature. Coconut oil and butter are saturated fats.

Monounsaturated Fatty Acid

This fatty acid has two carbon atoms bonding with each other instead of one hydrogen atom each. In other words, the bonding between the two carbon atoms are double. This bonding makes the fat unsaturated by just one double bond, meaning it’s not as stable as saturated fatty acid. Oleic acid is unsaturated fatty acid. Olive oil is a monounsaturated fatty acid. Oil present in hazelnuts, avocados and almond is monounsaturated too. When at room temperature, these fatty acids are in liquid state, but solidify upon cooling.

Polyunsaturated Fatty Acid

Instead of a single carbon pair double bonding, a polyunsaturated fatty acid has two or more such pairings. This makes the fatty acid very unstable. Linoleic acid is a polyunsaturated fatty acid. Vegetable, sunflower, flaxseed, and soybean oil are polyunsaturated. These fatty acids stay in their liquid shape, both at room temperature and when in the refrigerator.

The type of fatty acid determines how the fat looks (solid or liquid) and how healthy or unhealthy it is for consumption.

Commercial Usage and Extraction

Besides being used in several food items, fatty acid is also found in detergents, soaps, cosmetics, paints, varnishes, plastics, oil additives and lubricating oils, cleaning compounds, textile chemicals, toiletries and cosmetics, insecticides and germicides, candles, paper products, crayons and ink, etc. In fact, there are very few fields of technology or manufacturing that don’t use fatty acids in some form or the other.  

Commercially made fatty acids come from naturally occurring vegetable, animal, and marine oils and fats. Most of these raw materials happen to exist naturally as complex mixtures comprising triglycerides, alcohols and other esters. Some of the commonly used fatty acids and oils come from cottonseed, coconut, palm kernel, olive, sardine, linseed, etc.

Fatty acids are derived from these oils through a process called hydrolysis. The process makes crude fatty acids, which undergoes purification, or total distillation. The resulting fatty acids have their original fat or oil’s composition, which make them suitable for several uses. To make these mixed fatty acids more compatible for particular end-uses, further chemical and mechanical processing is required.