Evaluation of the Volatile Oils from Different Local Cultivars of Nigella sativa L. Grown in Egypt with Emphasis on the Effect of Extraction Method on Thymoquinone

The seeds and the total oil (fixed plus volatile) of Nigella sativa L (Black cumin) have well known flavoring, neutraceutical and pharmaceutical characteristics. These properties are attributed mainly to the content of the volatile oil fraction. The aim of this study was to investigate the content and the chemical composition of N. saliva volatile oil from seeds grown organically in the major traditional growing locations of that herb in Middle Egypt and anew location in the Upper Egypt. In addition, the investigation also aimed to verify the effect of the extraction method on the volatile oil composition with respect to thymoquinone, which is the major constituent and the reportedly most potent biologically active component of the volatile oil. Results indicated that the volatile oil content in the seeds varied greatly among the different growing locations from 0.01 % w/w to 0.4 % w/w of the whole seed. These percentages are equivalent to 0.11 % w/w to 1.8 % w/w of the corresponding total oil (fixed plus volatile). GC-FID and GC-MS analysis revealed that the chemical composition of the volatile oils from the different growing locations varied only quantitatively. The major differences found by GC analysis were for the levels of thymoquinone (TQ) (30.2 % - 63.3 %) and gamma-terpinene (0.4% - 11.8 %). GC analysis also confirmed that extraction of the volatile oil directly from the seeds in one step by hydro-distillation led to a dramatic decrease in the amount of TQ to 2.5 %. This investigation highlights the importance of both the growing location and the extraction method on the chemical characteristics of N. saliva volatile oil especially TQ.