Classifying Sesame Oil Seed Varieties And Origins Using Mass Spectrometry

The quality and authenticity of vegetable oils are of importance not only for their nutritional value but also for their miscellaneous biomedical and industrial applications. Hence, the knowledge of their main constituents, triacylglycerols (TAGs), is mandatory for classification and adulteration detection. However, the analysis of TAG composition of vegetable oils is a challenging task because of the number and physicochemical diversity of the constitutive TAGs.

Having in common a glycerol skeleton these compounds differ in fatty acids nature, including lengths, the number, the position, and the cis-trans configuration of potential double-bonds, as well as positions of fatty acids on the glycerol moiety (region-isomers, enantiomers).

Current methods of TAG analysis are tedious and time-consuming because of their lack of selectivity and/or sensitivity. Nowadays, the recent developments in liquid chromatography, notably the advent of ultra-high pressure liquid chromatography (UHPLC) allow for speeding the separation without excessive loss of efficiency. Based on these recent advances we report the development and validation of a simple and rapid UHPLC-APCI-MS/MS method allowing for unambiguous identification and accurate quantification of the whole TAGs detectable in a vegetable oil.

The proposed method is applied to the analysis of four North African sesame seed oils from different biotopes of Tunisia. Among vegetable oils, sesame oil is the lesser-known although it is one of the healthiest alternatives to most edible oils. Due to its high commercial value, sesame oil became an attractive target for adulteration.

With the proposed method we show that sesame oil contains at least 30 TAG species. Previous methods detected only 19 TAGs in different sesame oil samples originating from Asia or sub-Saharan Africa.

Since all TAG standards are not available, we only assess the absolute concentrations of major ones while we quantify the minor ones according to their relative intensities. Principal Component Analysis (PCA) is applied to the four studied sesame oil samples to check the ability to distinguish these samples based on their TAG composition.

To sum it up, we show that in order to accurately characterize vegetable oils according to their TAG profiles, it is necessary to consider both their major and minors TAGs.  This objective is fully achieved with the proposed method.

We are currently applying this method to a large set of sesame seed oils of different origins in order to set up a precise classification. Such a classification will guarantee the quality and the authenticity of sesame seed oils. Also, we are planning to use this method to revisit some standards currently used to classify other edible oils such as olive oils.

These findings are described in the article entitled UHPLC-APCI-MS Profiling of Triacylglycerols in Vegetable Oils—Application to the Analysis of Four North African Sesame Seed Varieties, recently published in the journal Food Analytical Methods. This work was led by Sylvie Héron and Fathi Moussa from Université Paris-Sud, Université Paris-Saclay.