Partially Hydrogenated Fats: Definition & Examples

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, we will learn about hydrogenation, what it is, and how the chemical reaction occurs. Then we will look at how this process affects fats, why hydrogenation of fats began, and why it is now banned.

Hydrogenation History

Look at a stick of butter, a tub of shortening, and a jog of vegetable oil. These are all fats, but why are they each so different? One of the main differences between each of these kinds of fats is if they are saturated or unsaturated. If a fat is saturated then it is typically a solid at room temperature (like butter) and are very useful in baked goods. But saturated fats are not as healthy as unsaturated fats. So in the early 1900's a technique was developed to make unsaturated fats solid, this technique was hydrogenation.

The process of hydrogenating fats creates trans fats, which you have probably heard about and know they are not healthy for you at all and have been linked to cardiovascular disease. Today many countries, including the United States, have banned the process of hydrogenating fats due to the health risks posed from trans fats.

Hydrogenation Chemistry

Hydrogenation is the process of providing a bunch of hydrogen atoms to a carbon chain with a double bond in order to break the double bond and create single bonds. When fats are hydrogenated they go from being unsaturated to saturated.

Hydrogenation bombards a double bond with a bunch of hydrogen atoms until the double bond breaks adding hydrogen to the carbon
Hydrogenation reaction

Typically fats are bombarded with hydrogens on a metal catalyst such as nickel. With so many hydrogen atoms being bombarded at the double bond some of the hydrogen atoms are able to attach to the carbon atom, breaking the double bond, allowing another hydrogen atom to attach.

Partially Hydrogenated Fats

Typically when food industries hydrogenate fats they don't completely hydrogenate the fat. This way they can get some qualities of a saturated fat and some qualities of an unsaturated fat. In this case, the fat is bombarded with the hydrogen atoms as with hydrogenation. Yet there is a lower ratio of hydrogen atoms. So when some of the double bonds broke, they weren't able to fully become hydrogenated, so they revert back to a double bond. Yet when the bond reforms into a double bond, it forms a trans double bond in a process called isomerization.

Most unsaturated fats naturally form a cis double bond. A cis double bond is when both carbon atoms are on the same side of the double bond, making the bond bulky. A trans bond puts the carbon atoms on opposite sides of the double bond, making it easy to stack just like an unsaturated fat.

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