Are margarine and shortening prepared by hydrogenating vegetable oils? Why?

1 Answer
Mar 21, 2015

Yes they are.

Many oils are unsaturated, that means they have double bonds in the chain structure of their fatty acids. Double bonds tend to make the chains less flexible, so they can't fit together nicely and attract each other less well by London forces.

In short: unsaturated fats tend to have a lower melting point, and are usually called oils (the difference between oil and fat is not really chemical, it's just the state they're in at room temperature).

By hydrogenation, we add a hydrogen atom at both sides of a double bond:

#-CH=CH- +H_2->-CH_2-CH_2-#

So it becomes a single bond, and heightens the melting point. This is not only done to vegetable oil, but to any oil that needs to "harden" (like fish oil).
Below is an example of a fat (or oil) with the usual three fatty acid chains: one saturated (blue) one unsaturated (green) and one poly-unsaturated (red). The black part in the middle is the glyceride-group that holds the lot together.

enter image source here