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PhytoChemia Acta

Popularization

The other side of oils: vegetable oils and fatty acids profiles

19 June 2018

Alexis St-Gelais, M. Sc., chimiste – Popularization

Quality control of essential oils is an important issue in the worlds of flavour & fragrances and aromatherapy. But most of the time, these oils are not used pure. It is in fact recommended to dilute them prior to use, and a logical and popular solution to that are carrier oils – which are vegetable oils, for the most. Aromatherapy-oriented businesses most of the time sell, alongside their essential oils, a selection of carrier oils.

If you have been using essential oils for a while and educated yourself on the subject, you probably know that a gas chromatographic (GC) profile from a reputable lab is a good step toward ensuring purity and identity of your essential oils.

Well, the same can be true about vegetable oils. But how can quality be checked in this case? A good part of the secret lies in fatty acids. Each vegetable oil will feature defined ratios of various fatty acids, which can be used as a criterion to attest botanical source and root out some adulterations.

There is a trick, however. Most fatty acids are not present under this form in vegetable oils. In majority (and with some exceptions), they are part of large molecules known as glycerides, which are esters of fatty acids and glycerol. One glycerol unit can be bound to up to three fatty acids, and this heavy molecule is rarely suitable for straightforward analysis. Before analysis, the bond between glycerol and its fatty acids is thus cleaved, and the fatty acids are typically converted to their methyl esters (Figure 1). These are the ones analyzed to give ratios between the fatty acids of the oil. Such an analysis is called FAMEs analysis (for Fatty Acids Methyl Esters analysis).

Figure 1. Chemical transformation of glycerides to fatty acid methyl esters (FAMEs).

Just like essential oils, vegetable oils can be adulterated. Monitoring the FAMEs profile allows to confirm botanical identification by comparing to scientifique references.

To illustrate what such an analysis looks like, we have checked this product sold in pet shops around here (please note that we have done this analysis on our own initiative, with no implication of the producer):

This bottle contains “100% pure hemp oil”. Hemp oil is obtained from the seeds of Cannabis sativa and should feature some specific fatty acids. Here are the main ones we found in this oil:

Comparing the percentages obtained and literature, one can conclude that the oil is indeed hemp seed oil. The key fatty acids here are the two linolenic acid isomers, which are proportionnally rarer than other fatty acids. The same goes for stearidonic acid, a rare fatty acid that is a characteristic of hemp seed oil [2].

The sample of the full analysis report can be found here: Report Hemp Supplement

References

[1] https://plantfadb.org/

[2] Callaway, J.C., T. Tennilä, D.W. Pate. (1996). Occurrence of “omega-3” stearidonic acid (cis-6,9,12,15-octadecatetraenoic acid) in hemp (Cannabis sativa L.) seed. Journal of the International Hemp Association, 3(2), 61-63.

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