The Chemistry of Shea Butter.
Ok so after writing the back story of Shea Butter yesterday, today I thought I’d focus on its chemistry and particularly to the bit that is said to give Shea its sun protection qualities. So, here we go!
Butters by definition melt at somewhere around 40C and in Shea Butter, the chemical that help keep what would otherwise be an oil buttery is Stearic acid.
Stearic Acid has a melting point of 69.3C, it is a fatty acid and as such is oil soluble and has no pH.
The Stearic Acid content of Shea Butter naturally ranges from 26-48% depending on growing conditions, climate and botanical variant. In some parts of Africa the shea butter is more liquid than others due to lower levels of stearic. This is important as while stearic acid is essential for forming the structure of shea butter and its butteriness it isn’t such a big deal biologically or in terms of the products moisturising capacity.
The gritty bits that develop in Shea butter products over time are due to the stearic acid beading together. They tend to do this in reaction to both the effects of gravity and of time. The more variable the storage temperature, the more likely the product will become gritty. The lower the viscosity and yield value of the formula, the more it is affected by gravitational forces.
As an aside I’ve just made a low viscosity water-in-oil moisturiser with shea and after standing for a week it too has developed this grittiness so I’ll need to address that! The gritty bits rub-in very easily but look unsightly. They are an issue in this formula because the oil phase predominates (it is the external phase) and is therefore more mobile than it otherwise would be. Also there is a lot of shea in this formula.
As another aside, you can reduce the likelihood of shea butter becoming gritty by tempering it. I carried out a range of experiments a few years ago and found that heating shea to 80-90C and then flash freezing it was best for reducing the potential for grit formation as it acted to smash the stearic beads up so small that it was energetically unfavourable for them to form beads again. As that isn’t practical for large-scale manufacturing I also tried a homogenise while cooling method which worked very well too. So heat to 80-90C then homogenise until it reaches around 45C, just before it starts to set, then cool it quickly but not necessarily by freezing it.
Some of my results can be seen here. This is when I was experimenting with different heat-and-hold times. I found it didn’t make much difference how long you held it at high temperature for, what mattered most was how it cooled as you can see from the grittiness in the room temperature samples.
Like any fatty product Shea butter will go rancid over time as the fatty acids react with oxygen in the air or impurities in the butter and break down. That said Shea Butter is pretty robust, its biggest problem is that in being a solid (rather than an oil), it is often stored in packaging that allows oxygen to get onto many of its sides – in a bucket for example. So shea butter suffers for its high surface area possibly more than it suffers from its chemistry.
Shea Butter is actually quite robust chemically because it is almost entirely devoid of polyunsaturated fats (unlike oils such as Rosehip or Evening Primrose). In fact the majority of its fats are triglycerides of C16:0 (palmitic) with only a few C18:1 (Oleic) and a small amount of C18:2 (linoleic or Linolenic depending on bonding). The butters relative stability is confirmed by its subsequent low Vitamin E content – plants make the vitamin E to protect their oil and they will only make as much as they need.
On the point of rancidity I will say that the shea butter does contain a very high level of oleic acid bound as part of a triglyceride. The rancid smell that develops in a fat or oil usually stems from the breakdown of Oleic Acid and Oleic is usually the first thing to break down because it has two double bonds – easy sites of access for oxygen attack (free radical). However, the smell of Shea is not just down to Oleic Acid. A study carried out in 2009 (Volatile compounds of shea butter samples made under different production conditions in western, central and eastern Africa. Bail, Stefanie; Krist, Sabine; Masters, Eliot; Unterweger, Heidrun; Buchbauer, Gerhard. Journal of Food Composition and Analysis, Vol 22 (7) – Nov 1, 2009) found a good fifty or more aromatic compounds in Shea butter including some that might have got their during processing – tobacco notes, metallic notes, earthy, mouldy, balsamic, mossy, waxy etc.
Shea butter typically contains around 100ppm Vitamin E and the vast majority of that is in the alpha form (which is biologically active), by comparison Rosehip oil can contain around 1000ppm – 10 times more.
Another thing that I’ve found interesting in my reading is the heat stability of the vitamin E in the butter. While shea butter may be cold-pressed, pre-processing of the kernels is anything but! The kernels are usually boiled up to soften them before being laid out either in the sun or in a dryer to dry out before extraction. The heat treatment has been found to reduce the level of vitamin E slightly but not enough for it to be a real problem. So if you are wondering if your vitamin E content in the shea buter will deminish if you heat it then I’d say probably not!
Unsaponifiables – Sun Protection Factor.
It is this bit of Shea Butter that makes it more tricky for soapers to use but that also makes it insanely interesting for Cosmetic Chemists as it is within this portion that we find our anti-inflammatories!
Most other oils and butters have a unsaponifiable content of less than 1%, Shea Butter has up to 11%. This fraction contains the prized and much talked about Cinnamic Acid Esters, the stuff that is supposed to give Shea Butter its SPF. Well let’s talk about that now….
So the cinnamic acid esters are part of a family of chemicals called Triterpenes and these make up around 65% of the total unsaponifiable content. So to put that more simply somewhere between 1.3- 7.5% of the Shea Butter is this.
There are a handful of different triterpenes to investigate but of those, the Lupeol Acetate and Amyrin Cinnamate seem to have the highest potential to act as anti-inflammatories in and on humans.
An interesting paper on this is here (Anti-inflammatory and chemopreventive effects of triterpene cinnamates and acetates from shea fat. Toshihiro Akihisa, Nobuo Kojima, Takashi Kikuchi, Ken Yasukawa, Harukuni Tokuda, Eliot T Masters, Aranya Manosroi, Jiradej Manosroi)
These chemicals are also pretty robust in terms of their heat stability so I wouldn’t worry about damaging them by heating your shea butter when making your product.
These chemicals work by reducing inflammation which is quite possibly where the SPF stories have come from. Using anti-inflammatories as sunscreens might seem like a good idea and indeed it is quite a convenient idea (you are likely to look less red and feel less irritated) but is it actually a smart plan? Well I’d use the analogy here of the anti-histamine and hay fever. An anti-histamine won’t cure your hay fever but it will take the edge off (or stop) your over-reaction to what is otherwise a harmless natural stimuli. So people don’t generally get cancer from hay fever although being a fellow sufferer I do understand how disabling hay fever can be and I’m sure it isn’t harmless. However, we do know that too much sun IS harmful and that our body alerts us to those signs by turning the skin pink then red, having it feel prickly, itchy or sore and burned. If we use anti-inflammatories to by-pass our natural warning mechanisms are we really doing ourselves any favours given that we are still exposing ourselves to a carcinogen? I’d logically sum this up in the same way that I’ve summed this sort of thing up before by saying that the job of anti-inflammatories is to clean up damage from any source and not to prevent it. Oh and before I get people writing in telling me that sun is good I am aware of that. The skin tells us when we have had enough, we ignore our skin at our peril.
As for the sterols (which include cholesterol, ceramides and squalane) well these are likely to help with moisture retention and barrier functioning if anything. It is highly unlikely that the <1% of sterols in shea butter would be able to penetrate through the skin and raise blood cholesterol levels so any benefit would be entirely limited to the skin barrier.
While I was aware of the basic chemistry of Shea Butter before writing and researching this I hadn’t gone into any detail and had grown to regard Shea as simply another butter. However, that is simply not the case. The anti-inflammatory potential of Shea is remarkable as is its relative stability and because of that I think I’ll start valuing it a little more highly than before.
Just one last thing, I have seen a number of websites trying to promote their Shea as a higher quality, containing vitamin A, being more potent etc. This ALWAYS happens with ingredients, people trying to push their product over another but in my experience they do this often without any real data to back it up. What I will say is that in my reading (and I’ve read at least 20 papers in order to write this) I didn’t find one mentioning that vitamin A was present in Shea Butter, all I found was one study (the cinnamate one) that used vitamin A as a control substance from which to validate their results on. I would also urge you all to question (politely) any seller that promotes their product as superior in terms of quality to ‘the rest of the market’ and ask them for some data to support that as data is available and all of what I’ve mentioned above can be tested. If a supplier can’t give you an in-depth chemical analysis of their product that doesn’t mean they are trying to con you, it probably just means they don’t have the data which is fine but then they can’t bang on about how much better than the others their product is. See what I’m saying?
In a (shea) nut shell, Shea is good.
Go get some on you