Tuesday, April 21, 2015

Fatty acids: What's up with them? Part two

Yesterday we took a look at a question Erika posted in the fatty acids post on the blog. Let's take a look at more of that fantastic question!

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? 

Although I don't think you can judge the nature of an oil by the fatty acid composition alone, I think it will give you some valuable information. For instance, if you see that there are loads of oleic acid and linoleic acid, you can guess that it's probably a more liquid oil than one filled with stearic acid or myristic acid, both of which are solid at room temperature. If you see that the oil has more cis bonds than trans bonds, you can guess that the one with more cis bonds will be more liquid than those with the trans bonds.

The top molecule is oleic acid with the kink in the middle thanks to the cis bond. The bottom molecule is stearic acid without a kink in the middle. The lack of kinks makes it easier for the molecules to lie closer to the other ones, which makes it more solid at room temperature. (This is why we see trans fats in our foods. They are meant to replicate solid fats like butters.)

Want to know more about cis and trans fats? Check out this post! Curious about how to figure out the melting point of butters? Check out this post! 

There are more features to oils than the fatty acids, though. There are phytosterols, polyphenols, vitamins, tocopherols, and more. So when you consider something like hazelnut oil, you can consider the fatty acids, but also take a look at the tannins, which will make it feel drier than something like olive oil.

I think you also need to consider personal interpretation for skin feel. For instance, you say you think sunflower feels rough and dry, while I feel it feels very slick and greasy.

As an aside, fatty acids that are not part of a triglyceride are called free fatty acids, and there is some indication free fatty oleic acids might be disruptive to the skin's barrier and increase transepidermal water loss. (Take a look at this post to learn more.) This is one reason to consider the greater picture when looking at the fatty acids of oils. 

So, as you can probably tell, I don't think that you can judge an oil by its fatty acid profile alone because there are just too many variables that go into how an oil will feel, what its melting point will be, what it offers to our skin, and so on.

Join me tomorrow as we continue our look at fatty acids!


Anonymous said...

Another couple of long time questions I had answered! Thank you for this awesome post!

Tammy Locgaz said...

great info, thanks heaps for the question and the answers from the "Guru Susan."

Elisabeth said...

Bravissima! Everything I never knew I needed to know about oil molecules. Thank you, Susan, for taking the time to go deep into the subject. Thank you also, Erika, for posing such intelligent questions.
*will go to bed a lot wiser*