Monday, October 12, 2009

Fatty acids!

A triglyceride is made up of a glycerol backbone and three fatty acids. So let's take a look at fatty acids!

If you're a lotion maker, you're familiar with stearic acid as a thickener. Stearic acid is a C18 fatty acid, which means it is a long chain (C18) fatty acid without any double bonds, so it's a long chain saturated fatty acid. If we put three of these fatty acids together with a glycerol molecule, we'd have a saturated glyceride, and one with a great shelf life!

But it's fairly uncommon for an oil to have three of the same fatty acids. They tend to have at least 2 different kinds, and sometimes three, as you'll see below with sunflower and olive oil.

In the picture to the left, the three fatty acids attached to the glycerol backbone are different. One is a single bonded fatty acid, one has 1 set of double bonds, and the other has three sets of double bonds!

The fatty acids connected to the glycerol backbone determine what the kind of oil or butter. The fatty acids can have differing carbon chain lengths and different types of bonding. They can also have different configurations (trans fats - you've heard about those!) that determine if an oil is liquid or solid.

For instance, it looks like this triglyceride is composed of a C16 chain, a C18:1 chain, and a C18:3 chain. I know C16 is palmitic acid. C18:1 is called oleic acid. And C18:3 is linolenic acid. This could be a corn, cottonseed, or palm oil molecule. The polyunsaturated chain (the C18:3 or linolenic fatty acid has more than 1 double bond, which means it is unsaturated, and because there's more than 1, it's called polyunsaturated!) can go rancid quite easily!

What this means in terms of making lotions or other creations is this molecule has THREE double bonds on that last fatty acid, so it may go rancid more quickly than something like olive oil below.

Olive oil has between 55 and 85% oleic acid, 4.6% linoleic acid, 6.9% palmitic acid, and 2.3% stearic acid. In this sample molecule, we see a triglyceride with an oleic fatty acid (C18:1 - 1 double bond), linoleic acid (C18:2 - 2 double bonds), and palmitic acid (C16 - no double bonds). If oleic acid makes up the bulk of the fatty acids with its 1 double bond, we are going to see an oil that is less likely to go rancid than one that is filled with linoleic acid (2 double bonds).

(Interesting site on olive oil chemistry here!)

Okay, so this is fascinating and all, but what does this mean for bath & body makers? Olive oil is a liquid oil that is unlikely to go rancid quickly, but it will go rancid eventually, as indicated by the double bonds. It also indicates it's a liquid oil, which I'll go into tomorrow!

This is a high oleic sunflower oil molecule. I love sunflower oils in my lotions and other creations, but it tends to go rancid far too quickly for my tastes!

Normal sunflower oil will have about 25% oleic acid (C18:1), 66% linoleic (C18:2), 2% stearic (C18), and 5.6% palmitic (C16). What this means is about 91% of the sunflower oil is composed of fatty acids with 1 or 2 double bonds, so it's going to go rancid quickly. A high oleic sunflower oil is composed of 80-92% oleic acid (C18:1) and 3 to 10% linoleic acid (C18:2), with some stearic and palmitic fatty acids thrown in (less palmitic - about 5.6%).

The high oleic sunflower oil will last longer than the regular sunflower oil because there are fewer double bonds to break. It will still go rancid more quickly than a saturated oil, but fewer polyunsaturated fatty acids and more monounsaturated fatty acids (ones with 1 double bond) means you're going to have a longer shelf life oil.

The down side to the high oleic sunflower oil is you are losing the linoleic fatty acid that can be beneficial to your skin, but I'll get into that in the sunflower oil post shortly!

So what does this all mean? By looking at a oils and butter property chart, you can figure out if an oil will go rancid quickly! And you can look for specific properties the fatty acids can offer in the profile to see which one you want to add for what properties. Soapmakers have long known how to choose oils to increase or decrease certain characteristics - you can figure out which ones you want to use in your bath & body creations by looking at the oil profile as well!

Join me tomorrow for fun with molecule configurations (it really is interesting, I promise you!)


retired engineer said...

The link to the chart at Snowdrift Farms is bad. —Linda

Susan Barclay-Nichols said...

Thanks! It was time I put a link to my own oil & butter comparison chart there!

Erika F said...

I'm so confused!! I'm going in circles and about to pull my hair out! I'm trying to understand fatty acid profiles. I get double bonds and saturated versus unsaturated in terms of a fatty acid chain. And, I understand what fatty acid profile tells us in terms of shelf life of an oil. But, I'm confused about what else it tells me.

For example, oleic acid (monounsaturated - omega 9 - C18:1) - not an EFA, helps with cell regeneration and provides skin softening properties, and is also moisturizing. My question is how does it do that? What's the mechanism? Is it related to fatty acid synthesis and the pathway in metabolism? And why is oleic acid regenerative as opposed to linoleic acid which is said to restore barrier function.

Linoleic acid (duo-unsaturated - omega 6 - C18:2), an EFA, helps restore barrier function and acts as anti-inflammatory that can help with dry and itchy skin; can reduce TEW. How does LA work as an anti-inflammatory? Is it because it has 2 double bonds? Is it related to the conversion of linoleic acid to GLA and AA?

What differentiates the two in terms of how they work? Is it because one has only one double bond and the other has 2? They're the same chain length. So, I don't understand what makes one provide cell regeneration and the other restore barrier function?

Then, I look at fatty acid profiles of oils high in oleic acid I find...

olive oil (78%)
high oleic sunflower oil (74%)
hazelnut oil (66 to 85%)
avocado oil (75 to 80%)

Avocado oil feels soft, spreads long, and seems to absorb at a medium rate. Olive oil seems about the same.

Sunflower oil, on the other hand, feels rough and dry.

And, hazelnut oil feels a dryness somewhere between avocado and sunflower.

Why is that? Is it related to other fatty acids in each oil?

Then, I look at other fatty acids in each of the oils and additional confusion sets in, with the function, or mechanism of other fatty acids contained in those oils.

Another example, coconut oil. It contains a lot of lauric acid (47.5%) But, so what? (not to sound cheeky) What does that mean other than the fact that lauric acid is a saturated fatty acid, C12, so it's a medium chain fatty acid, no double bonds, which offers a long shelf life.

What is the effect, or benefit of lauric acid? What can I expect from the lauric acid in coconut oil?

And, coconut oil also contains unsaturated fats with "18.1% myristic acid (C14), 8.8% palmitic acid (C16), and a titch of stearic, oleic, linoleic, and arachidic acids. Because of this saturation, this is a very long lasting oil."

C16 palmitic acid and C18 stearic acid are also saturated fatty acids, as well as myristic acid (C14)

I also found...

Stearic acid - helps with moisture retention, flexibility of skin and skin repair (saturated C18), it also provides thickening properties - how? why? is it because it's a saturated fat?

And myristic acid (C14), which is much like stearic acid, but it's considered a penetration enhancer - why is this considered a penetration enhancer when it's similar to stearic acid which works as a co-emulsifier and thickener.

GLA - helps with inflamed skin, and helps restore barrier function (polyunsaturated - omega 6 - C18:3)


I'm not trying to be a chemist. I just would like some basic understanding so that when I look at the fatty acid profile of an oil I can say, oh, hey, this has lots of myristic acid, so I can expect __________ from this oil because myristic acid does __________________ by way of __________________ (in an easy to understand way) :-)

Am I missing something obvious somewhere? I just can't seem to wrap my head around it.

Any clarification or direction is greatly appreciated.

Thank you,

Anonymous said...

Haha Erika, we have a lot of questions in common here. I hope we'll get some answers at some point :)

Susan Barclay-Nichols said...

Hi Erika. I've been researching your question for quite some time, and the answer has turned into a three day post about fatty acids. You can read part one here.. The short answer is that it's hard to get good information on some of these fatty acids - oleic and linoleic are fine, but not much on palmitic or lauric, as examples. The short answer on skin feel of oils is that you can't really determine them on fatty acids alone. And the short answer on what you can say about the oils is...well, it's not short. Check that post out on Wednesday.

I've done what I can to answer your question! Thanks for a great question, and let me know if you have more!