Tuesday, February 4, 2014

Oil chemistry review: Triglycerides and fatty acids

What do we find in our oils? We find triglycerides, polyphenols, phytosterols, vitamins, minerals, and more! Let's take a look at these things one by one...

What are triglycerides? This beautiful molecule to the left is a triglyceride (castor oil to be exact). It is a molecule with a glycerol (or glycerine) backbone and three fatty acids attached to it. If you look at this molecule - around the middle, before the OH bonds - you'll see a double line. This is a double bond, which means this is an unsaturated molecule.

In a saturated triglyceride, the carbons are single bonded, which are hard to break. They are stable over long periods of time because there isn't going to be oxidation. Most of these are buttery fats like coconut oil, babassu oil, palm oil, and animal oils. Oils like beeswax and candelilla wax are also saturated (yep, I don't think of beeswax as an oil either, but it fits the description!) Jojoba is another saturated triglyceride, which explains its long shelf life.

In an unsaturated triglyceride, these double bonds can be broken easily and oxidation occurs. The more double bonds, the more potential for oxidation. This explains the shelf life of something like grapeseed oil. It has 3 double bonds in the chain (it is a C18:3 triglyceride, meaning is has 18 carbon bonds and 3 double bonds), which means it has three places where the bonds can be broken and the oxidation can occur!

Attached to that glycerol/glycerin backbone you see the fatty acids.

Which fatty acids might we find in our oils? When you look at the code after the name of the fatty acid, this is how to translate it...The C means the number of carbons in the chain, the number is the number of carbons and the number after the colon - if there is one - is the number of double bonds in the chain. If there is no colon, it means there are no double bonds, and that indicates a saturated fatty acid. If there is a number after the colon, it means this is an unsaturated fatty acid with 1 or 2 or 3 or 4 double bonds, depending on the number. So oleic acid (C18:1) is an unsaturated fatty acid that has one double bond.
  • caprylic acid (C8)
  • capric acid (C10)
  • lauric acid (C12)
  • myristic acid (C14)
  • palmitic acid (C16)
  • stearic acid (C18:0)
  • oleic acid (C18:1)
  • linoleic acid (C18:2)
  • linolenic acid (C18:3)
  • arachadonic (C20:4)
Those interesting shapes are due to the double bonds. Fatty acids that contain no double bonds are found in a straight chain. Those with a double bond will have a kink or a bend, and the more double bonds, the more kinks or bends.

So an saturated fatty acid is one that has no double bonds and lies straight. It should have a longer shelf life than an unsaturated fatty acid with double bonds that doesn't lie straight. The more saturated the fatty acids, the stiffer the product tends to be. For instance, coconut oil is filled with saturated fatty acids while olive oil has really low levels. We'd expect the coconut oil to be a stiffer or more solid product than the olive oil (which it is).

Related posts (and I really encourage you to check these out for this series...)
Fatty acids
Hydrogenation and fatty acid shapes
Cis and trans fats

Join me tomorrow as we review polyphenols and phytosterols!


Simona said...

Love this article - the more chemistry lessons, the better! Thank you, Susan!

Just one question: why do we write C18:0 when we talk about Stearic Acid? Is it the same as C18 and this was an example that we can read it this way too? This is how I read this, but I just wanted to have a confirmation. It sounds like writing 1.00 instead of 1 to me.

Jennifer said...

Great review! I had that same question about stearic acid. What's with the zero? Note, I think arachadonic is actually spelled arachidonic (I make soap, and googled it b/c I wasn't familiar with that one). When I was taking chemistry in college, way back in the dark ages, they talked about how saturated fats, with their straight fatty acid chains, were able to pack in tighter together, and so tended to be solid at room temp. Unsaturated fatty acids, because of the kinky chain/double bonds, tended to not pack as tightly together and so stayed liquid at room temp. Helpful from a nutrition standpoint, back when everyone was avoiding saturated fats.

melian1 said...

"The lipids are arranged in a highly organized lamellar arrangement (fine layers alternating between different materials) with small amounts of water present. This is considered to be a very effective barrier to trans-epidermal water loss (TEWL)." --so would an emulsifier that created a lamellar structure (olivem, olivoil glutamate, etc) actually be better for helping slow tewl? does using an emulsifier of that nature change the penetration of the oils?

Susan Barclay-Nichols said...

Hi Simona. I don't know why, that's just how I see it all the time. Perhaps because there are so many variations on the C18 chain and it's a way of not mixing it up with something else?

Hi Jennifer. Thanks for catching the typo!

Hi melian! You're jumping ahead a few weeks here, but it appears that liquid crystal emulsifiers would be a good choice for reducing TEWL further! And I'm still looking into how it affects the penetration of the oils. It's interesting how much of the information about the liquid crystal emulsifiers is "it is known" or "it would seem"!