Saturated vs Unsaturated fatty acids- Definition, 20 Differences, Examples

Figure: Differences Between Saturated and Unsaturated fatty acids. Image Source: BioNinja.

Saturated fatty acids definition

Saturated fatty acids are the simplest form of fats that are unbranched linear chains of CH₂ groups linked together by carbon-carbon single bonds with a terminal carboxylic acid.

• The term ‘saturated’ is used to indicate that the maximum number of hydrogen atoms are bonded to each carbon atom in a molecule of fat.
• The general formula for these acids is CnH2n+1COOH.
• Fatty acids obtained from an animal source are mostly even-numbered linear chains of saturated fatty acids.
• However, lipids from all sources contain small amounts of saturated fatty acids with an odd number of carbon atoms (C₅ through C₁₇). Generally, these odd-carbon acids account for less than 1% of the total fatty acids.
• Many saturated fatty acids have a trivial name along with their scientific name, beginning with their acidic carbon.
• Most fatty acids are long-chained with 12 or more carbon atoms, but shorter fatty acids like butyric acid (C₄) and caproic acid (C₆) are important saturated fatty acids found in milk.
• The process of hydrogenation doesn’t occur in saturated fatty acids as all the carbon atoms in the chain are already saturated.
• Saturated fatty acids usually have a higher melting point than their counterparts which leads to the common understanding that saturated fatty acids remain in the solid-state at room temperatures.
• Thus, saturated fatty acids make up the fat part of all lipids and can be synthesized in the body.
• These are mostly solid and are found in animal fat like butter, meat, and whole milk. But some saturated fatty acids are also found in vegetable sources like vegetable oil, coconut oil and peanut oil.
• Because they have a high melting point, they have a higher shelf life than unsaturated fatty acids. Saturated fatty acids also have low rancidity.
• Saturated fatty makes up about 10% of all the fat required in our diet as an excess of these fats might increase the risk of heart diseases.
• Several studies have revealed that saturated fatty acids increase the Low-density Lipoproteins (LDL) cholesterol levels in the body which increase the risk of inflammation.
• Saturated fatty acids are also soluble in vitamins.
• Some examples of popularly known saturated fatty acids include stearic acid, palmitic acid, capric acid, lauric acid, myristic acids, etc.

Read Also: Fatty Acid Synthesis

Unsaturated fatty acids definition

Unsaturated fatty acids are more complex fatty acids with bent hydrocarbon chains linked together by one or more carbon-carbon double bonds with a terminal carboxylic acid group.

• The term ‘unsaturated’ indicates that the carbons atoms do not have the maximum possible hydrogen atoms bound to carbon atoms.
• As a result, unsaturated fatty acids can undergo hydrogenation, resulting in saturated fatty acids.
• Unsaturated fatty acids are divided into different groups depending on the number of double bonds present in the chain.
• Monoethenoid acids are unsaturated fatty acids containing one double bond and are represented by the general formula, CnH2n–1COOH. These are also called as monounsaturated acids.
• Diethenoid acids have two double bonds conforming to the general formula, CnH2n−3COOH. Triethenoid acids have three double bonds with the general formula, CnH2n−5COOH and so on.
• Unsaturated fatty acids with more than one double bond are termed as polyunsaturated fatty acids. These fatty acids are found in minor quantities in mammals.
• Due to the presence of double bonds, the cis and trans conformation of these molecules are important. The unsaturated fatty acids found in the human body exist in the cis conformation.
• Trans polyunsaturated fatty acids, although not produced in mammals, are produced by microorganisms in the gut of some cattle.
• Unsaturated fatty acids have a lower melting point as compared to saturated fatty acids, and thus they exist in the liquid state at room temperatures.
• These make up the oil groups within lipids. Vegetable oils contain two types of polyunsaturated fatty acids linoleic acid (lin with two double bonds) and α-linolenic acid (len with three double bonds).
• Most vegetable oils and fish oils are some of the important sources of unsaturated fatty acids.
• Because they have a lower melting point, they have a low shelf life and might spoil quickly. Chances of oxidation and rancidity are also higher in unsaturated fatty acids.
• Unsaturated fatty acids account for about 30% of all calories required for the body. Thus these are much safer and healthy compared to saturated fatty acids.
• Even though not proven, unsaturated fatty acids are assumed to decrease the low-density lipid levels in our body while reducing the chances of inflammation and heart diseases.
• Excessive consumption of unsaturated fatty acids is responsible for decreasing the cholesterol levels in the body, sometimes less than desired.
• Some examples of unsaturated fatty acids include linoleic acid, linolenic acid, oleic acid, crotonic acid, etc.

Read Also: Beta-oxidation of Fatty Acid

Key Differences (Saturated fatty acids vs Unsaturated fatty acids)

Read Also: Omega oxidation (ω-oxidation) of fatty acid

Examples of saturated fatty acids

Stearic acid

• Stearic acid is an example of long-chained saturated fatty acids with a hydrocarbon bone of 18 carbon atoms. The scientific name of this acid is octadecanoic
• These are mostly found in animals (30%), and plant (5%) fats and are an important component of shea butter and cocoa butter.
• It is white in color with a mild odor and has a melting point in the range of 68-70°C.
• Stearic acid is produced by the saponification of triglycerides in fats and oil with boiling water.
• Stearic acid might be used as a food additive in some foods, but more important use of this fatty acid is as a lubricant or softening agent.
• It is also highly used in industries to make soaps, and detergents are other cleaning agents.
• In humans, dietary stearic acid is oxidatively saturated to oleic acid, and it also is associated with lower LDL levels than other saturated fatty acids.

Palmitic acid

• Palmitic acid is an example of long-chained saturated fatty acids with a hydrocarbon bone of 16 carbon atoms. The scientific name of this acid is hexadecanoic
• It is naturally found in palm oil and palm kernel oil, along with other sources like butter, cheese, milk, and meat.
• It is white in color with greasy consistency and has a melting point of 63°C.
• Palmitic acid is produced by the process of saponification of palm oil in the presence of higher temperature water.
• It is used in industries for the production of detergents, soaps, and other lubricants. Besides, it is also added as a food additive as it adds texture to processed foods.

Examples of unsaturated fatty acids

Linoleic acid

• Linoleic acid is an example of polyunsaturated fatty acids that is one of the two essential fatty acids in humans.
• It is an 18-carbon fatty acid mostly found in plant oils.
• It is a doubly unsaturated fatty acid, also known as an omega-6 fatty acid, found mostly in plant glycosides.
• It exists as colorless or white oil that is virtually insoluble in water.
• It is not synthesized within the body of mammals and thus has to be taken in through diet sources.
• Linoleic acid is used in the biosynthesis of arachidonic acid, along with prostaglandins, and also forms the lipid layer in the cell membrane.
• The consumption of linoleic acid is essential for health, and its deficiency might result in hair loss and skin scalding.

Oleic acid

• Oleic acid is an example of monounsaturated fatty acid naturally found in vegetable fats and oils.
• Naturally, it is colorless and odorless, but the commercially made oleic acid might appear yellow.
• Oleic acid is the most common monounsaturated fatty acid in nature, but it exists as esters instead of fatty acids or their salts.
• It is found in high concentrations in body fats and phospholipids of the cell membrane. It is the most abundant fatty acid in the adipose tissues in humans.
• Biosynthesis of oleic acid occurs within the body by dehydrogenation of stearic acid in the presence of the enzyme stearoyl-CoA 9-desaturase.

References

1. Jain JL, Jain S, and Jain N (2005). Fundamentals of Biochemistry. S. Chand and Company.
2. National Center for Biotechnology Information. PubChem Compound Summary for CID 5281, Stearic acid. https://pubchem.ncbi.nlm.nih.gov/compound/Stearic-acid. Accessed July 29, 2020.
3. National Center for Biotechnology Information. PubChem Compound Summary for CID 985, Palmitic acid. https://pubchem.ncbi.nlm.nih.gov/compound/Palmitic-acid. Accessed July 29, 2020.
4. National Center for Biotechnology Information. PubChem Compound Summary for CID 5280450, Linoleic acid. https://pubchem.ncbi.nlm.nih.gov/compound/Linoleic-acid. Accessed July 29, 2020.
5. National Center for Biotechnology Information. PubChem Compound Summary for CID 445639, Oleic acid. https://pubchem.ncbi.nlm.nih.gov/compound/Oleic-acid. Accessed July 29, 2020.

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