A metabolomics study for the quality control of Black seed oil (Nigella sativa) based on Gas Chromatography-Mass Spectrometry

Black cumin seed oil (BCSO) is the cold-pressed oil obtained from the seeds of Nigella sativa, Ranunculaceae. Nigella sativa is widely cultivated throughout southern Europe and the middle east for culinary and medicinal purposes. Recently, attention has been focused on BCSO as an edible oil with high nutritive value and role in human health attributed to high content in unsaturated fatty acids including linoleic and oleic acids among other components [1]. BSCO is available as a dietary supplement and marketed worldwide, which prompted to study the quality differences in the oil metabolome globally and conclude an association with geographic distribution. A total of 28 samples of marketed BSCO were collected from Egypt, Libya, Saudi Arabia, Ethiopia, Syria and Europe. The oils were analyzed using GC-MS carried out on a RTX-5MS column using temperature programming from 45 to 300 ° at 5 °/min rate and fatty acid composition was determined following the reported protocol [1]. A total of 125 of oil components were identified using Kovat's index and comparison of mass spectra to NIST Mass Spectral Library. The normalised GC peak areas were measured, expressed as percentages and 14 common components were used in the Principal Component Analysis (PCA) data set.

The loading plot revealed the major peaks: linoleic acid (LA 0%-33.5%), oleic acid-methyl ester (OAM 7.3%-49.6%) and oleic acid (OA 0%-12.9%) as main chemical markers contributing to the segregation. The PCA score plot showed that most Egyptian samples were segregated above the line demarcating PC2 showing high concentrations in all three components while European, Ethiopian and Syrian samples were clearly segregated below the PC2 line with much lower values.

Fig. 1: PC A score plot showing segregation of 28 samples of black cumin seeds oil

Fig. 2: Loading plot showing major chemical markers

References:

[1] Lutterodt H, Luther M, Slavin M, Yin J-J, Parry J, Gao J-M, Yu L. Fatty acid profile, thymoquinone content, oxidative stability, and antioxidant properties of cold-pressed black cumin seed oils. LWT – Food Sci Technol 2010; 43: 1409 – 1413