But wait - I've just realized I haven't really explained what a double bond is! EEK!
If you want a really great explanation of hydrocarbon bonding, check out this site. Mine is a simplified explanation, I admit!
Carbon has 4 electrons that want to connect with other atoms (the blue dots). Hydrogen has 1 electron that wants to connect with other atoms (the red dots). Atoms really like to have 8 electrons, so they connect with other atoms to make up 8 electrons. As you can see from this picture, carbon likes to be surrounded by 4 hydrogen atoms to make up this 8 electron configuration.
Atoms are so desperate to make up this 8 electron configuration, sometimes they will bond doubly or triply with another atom to get to that number. (Look at hydrogen cyanide to see a triple bonded nitrogen. Such a pretty molecule! I even made a bracelet based on this molecule! And yes, I am a chemistry geek, and proud of it!)
In the case of a double bond in a fatty acid, the carbon doesn't connect with a hydrogen, it connects with another carbon in a double bond, leaving the hydrogen out in the cold. Normally when we look at a fatty acid chain, we see a top row of hydrogen atoms, then a row of carbons, then a row of hydrogens. This would be a single bonded or saturated fatty acid because there are double bonds. If you look at the unsaturated fatty acid chain, there are missing hydrogen atoms where the carbon atoms are double bonded! This the double bond, and it is easily broken so something else can get in that place of the missing hydrogen. (If you recall yesterday's post, we can make the bonds break and put hydrogen in those spaces.)
All right...back to cis and trans fats!
When we have a double bond on a fatty acid, it can be in either the cis- or trans- configuration. What exactly does this mean?
In the cis configuration, the missing hydrogen atoms are on the same side of the double bond (cis means "same"). The molecules bend at the site of the double bond, giving us a kinky molecule that won't pack in nice straight, dense lines like the saturated fatty acids. Put a bunch of these together and you have a liquid oil!
In the trans configuration, the missing hydrogen atoms are on the opposite sides of the double bonds. The chain doesn't bend much, so they have a straighter shape. Meaning they can pack in more densely, resulting in an oil that behaves as a solid saturated oil instead of a liquid oil. It has a higher melting point, doesn't need refrigeration, and is cheaper than saturated oils like coconut or palm oil.
The process of partial hydrogenation can force the hydrogen atoms in a normal cis configuration to become a trans configuration. The double bonds are broken, then re-formed in the trans configuration. You are unlikely to find a trans configuration in the oils we use in bath & body products as it usually arises out of processing and would likely cost more than a regular vegetable oil.
If you're really interested in learning more about trans fats, please click here. It is a fascinating subject!
Join me tomorrow for a post on the evils of rancidity!