What is the Unsaponifiable Fraction of a vegetable oil?
Chemically speaking, the bulk of your vegetable oil is what we would call a triglyceride - Tri = three, glyceride = related to glycerin. In short vegetable oils are mixtures of three fatty acids that are bound to one glycerine backbone. When we are soaping (saponification) those fatty chains break and the hand that they were holding onto glycerin with lets go and forms a soap - a soap is literally a fatty acid plus an ionic head group - Sodium and Potassium (from the lye) are the most common but Triethanolamine soaps are also well-known. But the saponification reaction doesn't work on EVERYTHING contained within that vegetable oil. The bit that resists this chemical breakdown is the unsaponifiable fraction and that's what we are going to talk about here.
Vegetable oils will almost always contain a proportion of 'stuff' that won't saponify. Jojoba oil is particularly resistant to saponification and will only form soaps in very harsh conditions - much harsher than your typical hand-made soaper can manage. That is one reason why Jojoba doesn't make a good soaping oil on its own - it simply doesn't turn into soap. But it can make a very good super-fat / moisturising bar if that's more your thing.
This 'stuff' that doesn't want to play with the lye and become soap is called the 'unsaponifiables' and each oil has its own unsaponifiable footprint.
So which oils contain an Unsaponifiable Fraction?
For many cosmetic chemists or cosmetic chemistry enthusiasts, our first experience with an unsaponifiable fraction is when we look to use Squalane, which more often than not is sourced from Olive Oil. Squalane is one of the most 'famous' unsaponifiables but it isn't the only one! It turns out that oils such as Rice Bran, Walnut and Wheat germ have much higher unsaponifiable fractions than Olive Oil and that their unsaponifiable fraction contains a few other useful bits and pieces that affect how it soaps (if you are a soaper) and how it feels and acts on the skin (for emulsions and oil blends).
How much Unsaponifiable Fraction is contained in each oil?
In general the unsaponifiable percentage of a vegetable oil will account for only between 0.5-6% of the total volume of oil. Amaranth Co2 Oil, Sunflower and Rice Bran are common exceptions to that having between 7-12%, up to 15% and up to 7% respectively.The overall percentage of the unsaponifiable fraction does contribute to how the oil will feel and behave during soaping but more important than the percentage is the actual chemical composition of this fraction.
Taking a closer look at the Unsaponifiable Fraction of several oils.
The chemistry of the unsaponifiable fraction is interesting. It is here that we find many of the antioxidants, some anti-inflammatories and some anti-microbial chemicals that give particular oil or butter its specialised functions. In addition, the unsaponifiable fraction may contain some of the oils UV protective qualities. Indeed some oils are harvested specifically for this unsaponifiable fraction, which is separated off and sold separately to the main oil as more money can be made that way. Olive squalane and natural vitamin E are two examples. The financial value of this unsaponifiable fraction and the fact that it can be affected by how the oil is extracted has meant that it has been widely studied for some oils, especially in the food industry where many of the health claims for particular oil are dependent on this unsaponifiable fraction being present and in a reasonable quantity.
Looking at the table we see that the unsaponifiable fraction may be rich in Squalene, Tocopherols (vitamin E), Phenolics or Sterols. These chemical families bring their own features and benefits to the oil.
Squalene is found naturally in sebum at a concentration of around 12%. It is a potential free radical scavenger and is able to inhibit lipoperoxidation induced by UVA radiation. Our sebum production can vary during our lifetime as it is linked to our hormones, at times when hormonal production is very low, oils rich in Squalene might be highly beneficial.
Squalene is a precursor in the biosynthesis of cholesterol.
Cinnamic Acid, Vanillic Acid, Ferulic Acid, Ellagic Acid, Gallic Acid.
The phenolic content of an oil can contribute so much in terms of an oils skin care benefits. However, non-immunological contact urticarial has been known to be caused by cinnamic acid, benzoic acid, sorbic acid and essential oils so this could potentially make some oils unsuitable for those with very sensitive skin or those with a known reactivity.
Ellagic acid has been studied in relation to melanoma cells. It has also been studied in relation to skin brightening where it has a huge potential.
A mixture containing Ferulic acid and vitamin C was found to protect the skin from the harmful effects of UV irradiation. Another study attributed the control of erythema to caffeic and ferulic acid present in the plant extract of interest.
Y-Oryzanol is a triterpineol ester with ferulic acid that is found mainly in rice bran oil. Its molecular formula is C40HH58O4. Research has found that this chemical increases peripheral blood flow of the skin and increases sebaceous secretions when applied topically Sebum production and pore size is influenced by the action of testosterone and it has been found that the y-Oryzanol has growth promoting action and gonadotropic action through pituitary stimulation. Y-Oryzanol has only been known since 1953 when it was successfully extracted by Tsuchiya and Kaneko.
Gallic Acid is a powerful antioxidant and is readily bioavailable due to its lipophilic chemistry.
Phenolic Tick List.
One of the best-known sterols is cholesterol. According to a paper published in 1975 the skin produces between 59 and 113 mg per day or 1.5-9% of total surface lipids. At least a part of that originates from the epidermis and the sebaceous glands. Other secretions come through the skin.
In Olive oil a phytosterol - Beta Sitosterol has an action similar to azelaic acid. When ingested it can help to regulate sebum production. This molecule has also been studied in treatments for androgenic alopecia, a condition that causes hair loss in both men and women. This sterol was found to posse's hair growth promoting activity due to its inhibitory effect on 5-alpha reductase. Beta Sitosterol is also found in Black Seed Oil (Nigella Sativa), Pumpkin Seed Oil, Black Cumin Seed, Avocado, Rice Bran, Wheat Germ, Corn Oils, Soybean and Sea buckthorn.
|Oil||Unsaponifiable %||Squalene mg/100g approximation||Tocopherols mg/100g Oil approximation||Phenolic Compounds mg/Kg Oil||Sterols mg/Kg||y-oryzanol mg/100g|
|Vanillic acid, Cinnamic Acid, Ferulic acid, Ellagic Acid, Gallic Acid etc|
|Olive||1-2%||300-12000 (depending on cultivar)||Up to 1900||500||800-2600|
|Soybean Crude||1-2%||125 +-||Up to 14000||<10||3440|
|Soybean Refined||0.8-1%||18||up to 11000||<10||2590|
|Canola||0.5-1.2%||26.2||up to 100||82-122||8500|
|Avocado Flesh (fresh)||1-2%||370||up to 1500||11 to 13||3500-4800|
|Pumpkin||0.7||80-350||50||12 to 16||2940|
|Amaranth (CO2)||7 to 12||up to 300||317||34|
References: Bioactive compounds in unsaponifiable fraction of oils from unconventional sources. Sylwester Czapliciki, Dorota Ogrodowska, Dorota Derewiaka, Malgorzata Tanska & Ryszard Zadernowski. European Journal of Lipid Science and technology 211, 113, 1456-1464. Antioxidant activity of sesame, rice bran and bene hull oils and their unsaponifiable matters. Farhoosh, Reza, Tavassoli-Kafrani, Mohammad Hossein, Sharif, Ali. European Journal of Lipid Science and Technology, Volume 113 (4)-April 1, 2011. FA and Unsaponifiable Compositiion of Amazonian Palm Kernel oils. Bereau, Didier, Benjeloun-Mlaya, Bouchra, Banoub, Joseph, Bravo, rene. Jounrnal of the American Oil Chemists Society, Vol 80 (1)-Jan 1, 2003. Influence of avocado oil processing on the nature of some unsaponifiable constituents. Fariness M, Soulier J, Rancurel A, Montaudoin M, Leborgne L. Journal of the American Oil Chemists Society, Vol 72, (4) - April 1, 1995. Influence of avocado oil processing on the nature of some unsaponifiable constituents. Journay of the American Oil Chemists Society, Vol 72, (4) April 1, 1995. Crude Palm Oil from Interspecific hybrid Elaeis Oleifera X E.guineensis: Alcoholic constituents of Unsaponifiable Matter. Journay of the American Oil Chemists Society, Vol 92, May 1 2015. Protective effects of unsaponifiable matter from rice bran on oxidative damage by modulating antioxidant enzyme activities in HepG2 cells . LWT- Food Science and Technology, Vol 61(2) - May 1 2015. Quantitative Changes in some UNsaponifiable Components of Soya Bean Oil due to Refining. Department of Food Engineering and Biotechnology, Technion- Israel Institute of Technology, Haifa, Israel 1974 1143-1147. A new method for simultaneous estimation of unsaponifiable constituents of rice bran oil using HPTLC. Journal of Separation Science, Vol 30 (16) - Nov 1, 2007. Tocopherols in the unsaponifiable fraction of cocoa lipids. Division of Food Science, Pensylvania State University, 1973. Unsaponifiable matter, total sterol and tocopherol content of avocado oil varieties. Journal of the American Oil Chemists Society, 1 June 1993. Phenolic compounds in seed oils. Vera VAn Hoed, Ghent UNiversity, Lipid technology Nov 2010. Endogenous biophenol, fatty acid and volatile profiles of selected oils. School of science and technology, Charles Sturt University. Food Chemistry 100 (2007) 1544-1551. Tocopherol, tocotrienol and plant sterol contents of vegetable oils and industrial fats. Journal of food composition and analysis 21 (2008) 152-161.
Processing methods, natural variation, ageing and unsaponifiable concentration.
As you can no doubt appreciate from reading the above, the unsaponifiable fraction of a vegetable oil is highly valuable and to be protected. Because of that much research has gone on into the best way to process oils so as to maintain the integrity and ensure a high yield of unsaponifiable matter in is retained. A study looking at traditional production of Shea butter found that the boiled kernels produced Butter quality oil in terms of overall unsaponifiable content, vitamin E content and texture than the smoked kernels. Boiling and smoking prior to extraction are both traditional processing methods that heat the kernel and soften the kernel content.
Typically after preparing the seeds or kernels for oil extraction, the next step in is to mechanically crush them. Whether the unsaponifiables can be extracted mechanically like this (cold pressed) depends on whether they are bound to the membrane or not - the stronger they are bound, the easier they will be to extract. Sometimes, like with Shea, the first step is to soften the kernel or seed with heat and that can increase the extractability of the unsaponifiable method but in other cases the seeds or kernels move straight to the screw press. The most important thing to note here is that a pre-treatment involving heat might increase oil yield and quality over a totally cold-pressed extraction. Different methods of heating have been tested to work out the best way to treat a particular oil, methods such as microwave heating (not the type you have at home) or other vibrational processes have yielded varying results with one study showing microwave processed rapeseed oil to have a better oxidative stability than oil extracted with no heat pre-treatment. There are many times when customers take the cold-pressing process to be as it sounds, completely cold and then assume that any heating of the oil will be detrimental to its quality. This is an incorrect way to interpret the situation although it is true that excessive heat can be a factor in reducing oil quality. We will pick that up again later.
Another extraction method and one that doesn't use heat as such is enzymatic extraction. This extraction method also has its roots in folk medicine; traditionally prepared coconut oil is one example of oil produced this way. One study comparing sunflower oils extracted mechanically vs. enzymatically found the crude and refined oil concentration to be quite similar in all respects except one. The enzymatic extraction gave ten times more polyphenols in the crude oil than the mechanical method. However, upon refining the enzyme extracted oil the polyphenol concentration dropped to the same level as the other methods. While it is tempting to say 'let's just use the crude oil' that would be largely unattractive as the crude oil would typically be murky, potentially gritty and contain a sediment.
The final step in oil extraction may be a solvent wash, especially for low oil-yield crops or where the oil is very valuable or difficult to fully extract due to being unbound. Soybean oil is an example of an oil that is often solvent extracted due to its low oil content.
The solvent used is usually food grade hexane, which is a petrochemical that is pretty much fully recovered after processing. There are food standards that govern how much hexane is allowed to be left as residue in the oil and this is set at around 10 parts per million - around the same level that you would find trace metal impurities such as lead and cadmium. IT is likely that as oil cleaning and recovery processes improve over time that this allowable limit will reduce although it is unlikely to ever be set at zero due to the impossibility of proving a negative.
In one study rapeseed oil that was solvent extracted was compared to oil that had been pressed as the only extraction step. A higher phytosterol content was found in the solvent-extracted oil - around 23% more. The conclusion here is that solvent extraction should not be discounted out of hand and that in some cases it can produce an oil with more of the good stuff still in it than cold pressing alone.
An alternative solvent that is used is CO2 extraction. Supercritical CO2 is becoming more viable a way of extracting seed and kernel oils although it is not without its problems and in some cases the oxygen that the CO2 extraction delivers to the oil can cause oil instability, a situation that can be remedied when the extraction is done with ascorbic acid added to the oil (vitamin C) but it is clear that while CO2 extraction has its benefits, it is not without a down-side. That said, a solvent extraction process is often used for Rice Bran Oil, as that is a difficult oil to process. Several studies have found that a CO2 extraction of Rice Bran produced an oil richer in Essential Fatty Acids and Oryzanol than was possible with hexane.
The bleaching and deodorizing steps were found to be the most destructive steps on the phytosterol content of rapeseed and Soybean oils. During the refining process in one evaluation the loss of sterols in soybean oil reached 18% and in rapeseed 52%. This is largely due to the phytosterol content being water-soluble. Bleaching is still largely done physically rather than chemically and is often less of an issue than the deodorizing step, which involves heat of between 220-260°C. At 240°C the tocopherol level in Soybean and Rapeseed oil was found to be reduced by 25% and that at 260°C and above more than 84% of vitamin E was lost. Note that these temperatures are way in excess of those experienced during cosmetic manufacture so vitamin E is largely heat-stable for the purposes of cosmetic science.
In oils that need de-gumming phenolic actives may be dramatically reduced in this step. A study reported losses of around 66% in rapeseed oil. These phenolics can be recovered in the gum fraction though and research into their recovery is storming ahead - it is likely that the recovered actives could be re-added to the oil post-processing, either that or they could be sold on as a separate ingredient.
Vitamin E - How much is enough and can you have too much?
Nearly all vegetable oils contain vitamin E, tocopherol as part of their unsaponifiable fraction as it is this, which maintains the oxidative stability of the oil during the plants life - oils that were originally present to feed the growing plant! Studies have shown that it is the Y-Tocopherol that best protects the oil from oxidation while the a-tocopherol best interacts with our biological membranes (the skin). This is important to note as too much vitamin E can be both irritating and act as a pro-oxidant - something that actually speeds up oxidation. The exact conditions required for pro-oxidation are complex and somewhat unknown but suffice to say buying mixed tocopherols to add to an oil blend to prevent oxidation is a better plan than buying alpha tocopherol and expecting it to do the same job. We recommend no more than 2% vitamin E in a cosmetic product and between 0.1-1% as an anti-oxidant.
Choosing a good oil from an unsaponifiable perspective.
So how do you go about choosing a good oil in terms of its unsaponifiable content? Well that depends on what you are after. If you are looking for moisturisation and barrier protection the Squalene might be useful, especially in post-menopausal women whose natural oil production from the pores is likely to be diminished. This makes Rice bran, Sunflower, Pumpkin and Olive oil highly desirable. If you are after an antioxidant rich oil for skin protection again the Olive is a good choice but so is Sunflower or Wheat germ. With regards to phenolics don't overlook Sunflower seed oil - a very cheap oil but one whose process has been researched intensely due to this oils popularity as a health food. Remember that it is your phenolics that give you that second, more complex range of antioxidants for skin protection - ideal for helping to prevent sun and other environmental damage. In terms of sterols you can't go past wheat germ, the perfect oil for eczema or psoriasis prone skin that fails to secrete enough natural protection and for the y-orzanol it has to be rice bran.
In terms of knowing whether to go with a refined, organic, cold-pressed or Co2 extracted oil the best advice I can give here is to ask for more details. There is no single answer as to which process is best for all oils as all oils are different so the best way to know if you are getting what you want is to check the specification and compare. New Directions can help you with that.
I hope you have enjoyed looking more deeply into this unsaponifiable fraction with me and wish you all the best with your formulating work.
20 June 2017