Butter behaviour is more about triglycerides than fatty acids.
In 2016 I wrote two articles about Shea Butter and felt that I’d totally aced the subject! There was this one on the role of women in the Shea story and this one about its chemistry. While I still look back at these articles and think they are pretty OK, I’m now kicking myself that I let another, bleedingly obvious fact about the chemistry of Shea (and other butters) slide right through my fingers.
The value of viewing butters by their triglycerides rather than fatty acids has only just become apparent to me after I’ve sat here for a few weeks evaluating different butters, oils and waxes under the microscope and comparing that to their usual, eyeballed selves. Even in writing this I’m cringing at how little attention I paid to this, mostly likely because I have a tendency to dive deep and miss the shallow water until I’m done down there and am on the way back up. Anyway, let’s have a look.
We (meaning the royal ‘everyone and their mother ‘we’) tend to talk about oils in terms of their fatty acid chemistry. An oil, butter or wax is said to contain lots of oleic, palmitic or stearic acid and that’s why it feels like this, looks like that or behaves how it does. The only trouble is, for the most part these fatty acids are not floating around behaving in their fatty acid way. They are bonded to glycerin and exist in gangs. We call these gangs triglycerides as I’ve mentioned before no doubt and as you probably already know by your internet reading.
Triglycerides have their own ways of occupying space and time and while they do relate to their component fatty acids in many ways, viewing them only as that misses something interesting.
Let’s explore this first by focusing on three fatty acids that are commonly found in butters as examples: Stearic, Oleic, Palmitic.
As, out of those three, I only have stearic acid as a stand-alone ingredient in my lab at this point in time I can only show you this but I’ll do my best to describe the others with the data I can find. I’ll then share with you some information about triglycerides of these three fatty acids and the experimental data I’m gathering.
Stearic is a C18:0 fatty acid so saturated (no double bonds). On its own it has a melting point of 69.3C
Oleic Acid is a C18:1 fatty acid that has one double bond. It has a melting point of 13-14C
Palmitic Acid is a C16:0 fatty acid (no double bounds) that has a melting point of 62.9C
When I melt Stearic Acid onto a microscope slide and magnify it to 800x I see a jagged, dense crystalline structure which look all sharp and pointy:
Stearic Acid 800x Magnification
Combining 20% Stearic Acid with 80% Caprylic Capric Triglyceride creates a pot-set balm with buttery, snowflake-like texture with a frosted, icy appearance. While it feels quite nice it’s not got enough structural integrity to be useful like this. I chose this as it was the simplest and purest triglyceride I had to hand to use as a model oil phase for these binary systems. It is a C8, C10 saturated triglyceride of known structure. If I was to use a whole vegetable oil as my model oil phase the triglyceride composition would be more variable and there would be other chemicals present (free acids, unsaponifiable fraction including vitamins and maybe plant pigments such as carotenoids). This is what that combination looks like under the microscope:
Stearic Acid thickened Caprylic Capric Triglyceride at 800x magnification
This is what MCT and Stearic Look like in the sample:
My un-tested assumption or hypothesis would be had I swapped Stearic for Palmitic I would have achieved a very similar outcome albeit a little softer and less formed perhapse. This guess takes into consideration the lower melting point of palmitic and my prediction that its shorter chain length (but same orientation) may potentially pack even more tightly than the stearic which is a little bulkier.
As for Oleic with its very low melting point, I’d expect that to remain fluid, potentially even when frozen upon which I’d expect at least some of the oleic to wax-out to the bottom of the sample.
Next we should move onto triglycerides as chemical entities and explore those.
Triglycerides of Stearic, Palmitic and Oleic.
My first step was to hunt down some science papers that already appreciated the glory of the triglyceride and found this paper on cardiovascular disease which, I must say doesn’t sound relevant at first glance.
Berry, Sarah. (2009). Triacylglycerol structure and interesterification of palmitic and stearic acid-rich fats: An overview and implications for cardiovascular disease. Nutrition research reviews. 22. 3-17. 10.1017/S0954422409369267.
What I appreciated about this article was its triglyceride information table which you can see for yourself here: https://www.researchgate.net/figure/Melting-temperatures-of-some-TAG-molecular-species-of-different-polymorphic-forms_tbl1_24427412
This table showed me two things:
- That triglycerides containing the same fatty acids could have very different physical properties and
- That the triglycerides could exist in different crystal shapes and forms.
I feel the need to interject here and state (for my own vanity I presume) that while neither of these things were surprising in and of themselves, my aha moment came from finally seeing this data in front of me and having it clear away my assumptions once and for all. This is why the cooling and setting process for butters matters, this is where the many crystaline forms of chocolate originates from, this is why butters often have a wide rather than narrow melting range, this is why some are prone to grittiness while others are crumbly. This is more important than the individual fatty acid chemistry OR the unsaponifiable fraction data, both of which matter but neither of which matter more than this!
Triglyceride Short-Hand.
Rather than write out the name in full, the nutrition and food industries (which appear to have more data on triglycerides than any others I’ve yet found) use shorthand which I’m finding as amusing as I am helpful.
These are my favourites although I’m willing to accept that I’m probably writing them in the wrong order just so they look funnier and are more memorable to me:
POP = Palmitic-Oleic-Palmitic
POO = Palmitic-Oleic-Oleic
SOS = Stearic-Oleic-Stearic
Many more orientations exist and while Oleic is commonly found in position two, it isn’t always. Physical property wise, the exact position of the fatty acids in relation to each other matters as this determines the shape of the triglyceride and, subsequently, how close (or far away) it can get to other chemicals when present in a formula or even when in the stand-alone raw material. Again, what this means is you don’t know everything about a fat just by knowing its fatty acids, further, that you don’t know everything about a triglyceride just by knowing the names of the fatty acids it contains. Oooohhhh I’m excited now!
Applying this view to cosmetic butters:
I put this table together using information I found across a number of scientific publications outlining the structure, typical composition and melting points of the triglyerides. Referencing more than one paper gave me a higher level of confidence that the information I was finding was typical rather than a one-off. Presenting the data this way was something I decided to do in order to help in me work through how the internal triglyceride structure influences the external appearance and performance of the butters in question.
Looking at this I can see why Shea is such a bugger to work with at times.
I can also get an inkling as to why cocoa butter is smoother than shea and mango and more likely to feel dry over oily.
As for mango, this table seems to provide evidence as to why this tends to be harder and feel less greasy than shea.
The analysis as I see it so far.
Shea is the only butter of the three to have a significant proportion of triglycerides present in a permanent liquid state. It is also the butter with the largest range in triglyceride melting point. Taking it further we can see it has big chunks of triglycerides existing as high, medium and low melting point chemistry at room temperature. If you are thinking that these different triglycerides will bond together and form a new homogenous blend, that’s not the case. Sure they might tangle up together a little but it’s more likely they just swim (swim being the operative word thanks to that liquid) around in their oily pool prefering their own company to that of ‘others’, just waiting for the temperature to change a little so they can melt or solidify some more and cause more chaos.
In terms of crystal chaos I’m not entirely sure how to read this in terms of relating it to what happens in real life but it looks like Shea has the least choices when it comes to crystal structures. It contains 52% of its triglycerides in orientations that can take on three crystaline forms and 27% or nearly 1/3 that exists as just one. Compared to Cocoa which has 3 triglycerides each capable of 3 different crystal structures accounting for 80% of its chemistry it seems quite tame. Mango reads similarly to Shea but we must keep in mind that mango is less likely than Shea to have some liquid fats at room temp so while the potential for crystal morphing is there, the opportunity is more limited given the lack of room to ‘swim’.
NOTE: The greater the potential for movement in a chemical blend, the more opportunity there is for chaos. That’s one of the reasons thickening a product helps to keep its form stable.
Symetry
The potential for symetry to play a role in butter properties is one of the things that becomes clearer once you look at the triglycerides.
POP and SOS are symmetrical, POS is so close to being it can almost be thought of as so.
OOO is, of course symmtrical but it’s also liquid so it can’t play this game.
OOS is, quite frankly a mess.
I’ve still got more to research in this regard but the physics around it intrigue me and others by the looks of it. There have been several papers published that evaluate the crystalline behaviour of fats and lipids, linking them to their triglyceride symetry or otherwise. Here’s one.
The fact that 80% of the triglycerides in cocoa butter are symmetrical or close enough to it is most likely the reason it can be so smooth. That they are comprised of mainly saturated fats is likely the reason they feel dry rather than greasy.
In terms of butters, Cocoa wins the symetry wars, not because it has the most symetrical triglycerides- these three are actually very similar in proportion that way – but because it doesn’t contain the unsymmetrical or low melting point chaos that the other two butters do. So, it can let its symmetry shine un-interrupted.
So can we see this under the microscope?
Above are pictures taken at 800x magnification of pure butters. While it can be hard to work out what we can see here, it’s easy to see the three butters have their own unique structural arrangement.
Mango butter forms little flower-shaped crystals, cocoa is dominated by long curly swirls which I think is beautifully fitting given its African heratige and then there’s shea. Shea also has a curly structure but it’s fibers appear shorter and more C than U shaped. They are also interrupted by crystals every-so-often.
I would be lying if I tried to make out I can tell you exactly what we are seeing yet but feel confident enough to suggest these slides demonstrate perfectly how three simple fatty acids: Stearic, Oleic and Palmitic can come together to form triglycerides with their own unique characters which go on to create butters with their own unique internal structural richness and complexity. One that goes way beyond that of the individual fatty acids.
And with that I’ll leave this article.
This little piece of butter loving is part of my humungous Oleogel project. A project that is keeping me engrossed while I remain mostly working at home thanks to the COVID outbreak. I can’t say I’ve minded that at all and have instead felt transported to so many places both microscopically and real-worldly thanks to the threads of imagination this project has twanged.
I hope you’ve found that both interesting and helpful and that like me, you are sciencing the shit out of this pandemic (reference from The Martian BTW).
Amanda x
Realize Beauty 