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3.2.1.1. Saturated and unsaturated fatty acids

Saturated and unsaturated fatty acids

Fatty acids are classified into two groups:


Saturated fatty acids

In saturated fatty acids, all of their covalent bonds between carbon atoms are single bonds, so their hydrocarbon chains are linear. They are solid at room temperature.

El ácido palmítico es un ácido graso saturada de 16 carbonos.By BruceBlaus. When using this image in external sources it can be cited as:Blausen.com staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762. (Own work) [CC BY 3.0], via Wikimedia Commons

They are found in animal fats, and in coconut, palm, and peanut oils.

Examples of saturated fatty acids are myristic, palmitic, and stearic.

Saturated fatty acids

Melting point (ºC)

Myristic CH 3 - (CH 2 ) 12 - COOH

53.9

Palmitic CH 3 - (CH 2 ) 14 - COOH

63.1

Stearic CH 3 - (CH 2 ) 16 - COOH

69.6

Lignoceric CH 3 - (CH 2 ) 22 - COOH

86.0

The chains of the saturated fatty acids can be packed by Van der Waals bonds between the atoms of the neighboring chains. The longer the chain (more carbons), the greater the possibility of formation of these weak interactions. Therefore, at room temperature, saturated fatty acids are usually in the solid state.

Animated image: Saturated fatty acids .

Unsaturated fatty acids

The unsaturated fatty acids have one or more double bonds in the carbon chain. The distance between the atoms of these carbons is not the same as with the others, nor the bond angles, so unsaturated fatty acids present elbows, with changes of direction, in the places where a double bond appears between carbon atoms.

This causes that the molecules have more problems to form bonds by means of Van der Waals forces between them. Therefore, at room temperature, unsaturated fatty acids are usually in a liquid state, having a lower melting point.

By OpenStax College [CC BY 3.0], via Wikimedia Commons

Unsaturated fatty acids are present in vegetable oils and oily fish oils.

An example of an unsaturated fatty acid that has only one double bond (monounsaturated) is oleic acid. Among the polyunsaturated, the most important are linoleic (C18 and two unsaturations), linolenic (C18 and three unsaturations) and arachidonic (C20 and four unsaturations).

Unsaturated fatty acids

CH 3 - (CH 2 ) 7 -CH = CH - (CH 2 ) 7 -COOH

Oleic acid. Melting point = 13.4 ºC

CH 3 - (CH 2 ) 4 -CH = CH-CH 2 -CH = CH - (CH 2 ) 7 -COOH

Linoleic acid. Melting point = -5 ºC

Animated image: Unsaturated fatty acids.

Saturated and unsaturated fats

The saturated fat containing fatty acids that have no double bonds between carbons of the hydrocarbon chain.

The saturated fat found in foods of animal origin such as meat, sausages, milk, dairy products, etc., and are solid at room temperature. Although there are also some of vegetable origin, such as coconut and palm oil, very common in industrial pastries.

The consumption of saturated fat increases the level of cholesterol in the blood, being one of the main risk factors for heart disease.

The unsaturated fats contain fatty acids with a double bond. They are found in foods of plant origin, such as in oil (olive, sunflower, corn, ...), in nuts and in seeds (sunflower, flax, sesame, etc.).

The monounsaturated fats contain fatty acids with a double bond. For example, they are found in oleic acid in olive oil and other seed oils (sunflower, rapeseed, etc.), and in nuts. They are liquid at room temperature.

The polyunsaturated fats contain fatty acids with several double bonds between the carbon atoms of the hydrocarbon chain. They are more solidified than monounsaturated fats but less than saturated fats, so they are also liquid at room temperature. Some polyunsaturated fats contain, for example, acids omega 3 and omega 6, which are not produced by the organism and must incorporate through food.

Fundamental Ideas on Fatty Acid Classification

There are two types of fatty acids:

  • Saturated fatty acids .
    • All of its covalent bonds are simple.
    • Its hydrocarbon chains are linear, allowing more Van der Waals bonds to be packed up and established between atoms in neighboring chains.
    • The longer the chain, the more likely there are these weak interactions with neighboring chains.
    • Due to the large number of these interactions, they are in a solid state at room temperature. High melting point.
  • Unsaturated fatty acids .
    • They have one or more double bonds in the hydrocarbon chain, which causes elbows or angles to form in their chain.
    • These angles prevent many weak interactions between neighboring chains, reducing packing and increasing the mobility of the molecules.
    • They are in a liquid state at room temperature. Low melting point.