The Science of Shea butter

Shea butter (Butyrospermum parkii) is a complex vegetable fat (Triglyceride) derived from the African Shea nut tree Vitellaria paradoxa (C. F. Gaertn, Sapotaceae, family) (Fig 1.) and Vitellaria Nilotica spp.unique across Western and Eastern Africa respectively [1, 2]. Abundance of the shea nut tree is observed in the Savannah Belt across West African countries such as: Benin; Burkina Faso; Cameroon; Central African Republic; Guinea Bissau; Ivory Coast; Nigeria; Ghana; Senegal, Sierra Leone [2]. Diversity of the shea nut tree has been attributed to genetic composition and dependent on variation in different climatic conditions such as temperature, rainfall, and humidity [3], consequently able to invariably affect the variety and health of the nut tree and the quality of Shea butter extraction.
 
Fig 1. African Shea nut tree. 
Origins:  Our unrefined Sheabutter is sourced from two regions in West Africa – Northern Ghana and Western Nigeria due to the abundance of the stearic and oleic rich triglyceride fraction [4]. Compared with its Eastern African counterpart, the sheabutter from West Africa has been shown to have moderately higher levels of triglycerides and polycyclic triterpenes [5].High variability in anti-oxidants-tocopherols and phenols across several regions in Africa are shown with higher tocopherols from hot drier climates for example in West Africa, Chad being the highest concentration [6].This shows that topical application of sheabutter can introduce vitamins and antioxidants which can protect the skin. Tocopherols for example, is known to make up 96% of our skin’s natural antioxidant defense system. Therefore topping up with natural occurring tocopherols in sheabutter can have the immense benefits including acting as an anti-inflammatory agent, absorbing UV rays, and preventing the free radical damage introduced externally from sun UV rays and environmental pollution.
To extract the butter, healthy shea nuts are roasted and pound into a paste (manually) from which the shea butter (lipid fraction) is removed through a process known as “kneading”. An admixture of cold and warm water is added to separate the fractions according to local tradition [7, 8]. The sheabutter is then poured into a clean filter cloth, left to cool, solidify and stored appropriately for use. Raw unprocessed / unrefined shea butter colour ranges from golden yellow (Ghana) to grayish yellow (Nigeria) and feels like whipped butter with a nutty aroma and woody smell. Chemically refined shea butter on the other hand is white in colour and has no smell. On an industrial scale, chemical solvents such as n-Hexane is used for optimisation of shea butter from its kernels. However, when compared to the extraction of shea butter using the traditional methods, potency of the healing and anti-inflammatory properties of sheabutter is lost [11] even though it may still retain its moisturising properties [3].
Fatty acids are important for human metabolic needs, with carboxylic acids (R-COOH) on one end of their structure and the R, the long unbranched carbon chain. We can get some from our diets, e.g nuts and oils, while some can be synthesised within the body e.g stearic acid. Essential fatty acids are stored in plants from triglycerides (3 fatty acids) and glycerol. It is an essential constituent of the shea butter that plays an important role in its widespread application in nutrition, cosmetic and the confectionery industry. (See table below on EFA composition). Oleic Acid (structure, Fig 2.) and stearic acid rich triacylglycerol (TAGs) fatty acids are the most abundant EFAs in Sheabutter averaging (ca. 41%) and (ca. 46%) respectively, but  dependent on regional variability. Other fatty acids present in smaller amounts are linoleic acid, palmitic acid, linolenic acid, arachidic acid and paulinic acid. We discuss the main components below:
 
Table 1. Composition of Essential Fatty Acids and physical melting and boiling point. [7]
 
Oleic Acid: Oleic acid is a mono-unsaturated omega-9 fatty acid found in various animal and vegetable sources [9] (highly derived from olive oil hence the name). With its cis double bonds in the methyl group, the cis configuration is the most abundant in nature, with extra virgin olive oil containing ca. 70g/100g per edible amount. Oleic Acid is not specific to olive oil alone. Shea butter is being recognised now as a great source of oleic acid [8]. Naturally occurring oleic acid is predominant in edible grade A ( USA Food Grade Classification) shea butter from the West African region: Nigeria, Ghana and Gambia [7]. In particular, it is known for anti-repellent properties when used as a mosquito repellent. It has been tested for reducing oxidation stress and acts as a barrier for free radicals when added topically on to the skin and for reducing signs of premature ageing.
Fig 2. 3D Structure of Oleic Acid  [12].
Stearic Acid: In nature, stearic acid (Fig 3a,b.) is saturated , with no double bond and consist of three stearic acid molecules joined together by one glycerol molecule. Stearic acid provides the structural hold of natural unrefined shea butter. Its waxy solid properties and bi functional character makes it useful for many applications: soap making; cosmetic; detergents; and as a lubricant. Stearic acid is responsible for the emollient and emulsifying properties of sheabutter. The triglyceride derived from three molecules of stearic acid is called stearin which is the hard fraction utilised by the food industry [4]. Interestingly, archaeological studies analysed the structure of stearic acid on ancient Egyptian mummies was used as hair gel, inferring that this has been used for centuries[12]. The source of the hair gel is not conclusive though but as the shea nut tree has been indigenous to Africa, it could be likely that sheabutter was applied. 
Fig 3a: 2D structure (note the position of the carboxylic group compared to Fig 3b). 
 
Fig 3b. 3D structure of Stearic Acid [13].

Linoleic Acid: Linoleic Acid (Fig 4.) is a poly unsaturated omega 6 fatty acid with anti-inflammatory, acne reductive, skin-brightening and moisture retentive properties when applied topically on to the skin [10]. It is abundant in many nuts and plant seeds. It cannot be synthesised by the human body, so must be derived from external sources- plants and plant oils. Shea butter applied topically on the skin or ingested can aid in the regeneration of human cells, and helps with secondary biosynthesis of arachidonic acid which has a function to promote growth in healthy humans.
 
Fig 4. 2D Structure of Linoleic Acid. 
Concerning the science of shea butter, several studies detailed here and in literature suggest the immense benefits of this plant butter indigenous to Africa.In order to present the hidden secrets of shea butter, our business aims to understand the science as much as possible and formulate it with other ingredients to harness its potency in skincare. 
All Citations [1-13] can be provided on request.