Natural oils are a class of materials that are becoming more important to the cosmetic chemist. Since these materials are made by living systems, they are sustainable. Natural oils are esters of glycerin and part of a class of compounds called triglycerides. Their structure is shown in Figure 1.
The formation of these materials by living systems is carried out through metabolic pathways with specific controls over the R groups. Most commonly, natural oils are derived from fatty acids with 18 carbon atoms and unsaturation in the molecule. The 18 carbon acids are shown in Table 1.
Man-made glyceryl esters are not made by living systems using enzymes. Consequently, when glycerin is esterified with a mixture of fatty acids, there is no control over the location the R groups. The products are complex mixtures. Additionally, the efficiency of the non-enzymatic reaction is not as great as in living systems. This means that depending upon how the reaction is conducted, there are differing amounts of monoester, diester, triester glycerin and fatty acid. The possible products present are shown in Figure 2.
While man-made glyceryl esters produced using traditional esterification chemistry and natural oils derived from living systems are part of the same family of compounds (glyceryl esters), the pathway used to create the two types of materials are substantially different; thus the resulting compositions are substantially different.