Subcritical CO2 extraction of a volatile oil-rich fraction from the seeds of Nigella sativa for potential pharmaceutical and nutraceutical applications

Abstract

Seeds of black cumin (Nigella sativa L.) were subjected to subcritical CO2 extraction (SbFE) at 70 bar and 30 °C for 2 h in a trial to isolate a volatile oil-rich fraction. That treatment led to obtaining an oleoresin which constituted 1.74 wt.% of the total seeds’ weight and was found to be rich in its volatile oil content (66.6 wt.%). Traditional methods of extracting the oleoresin using n-hexane at room temperature or at 60 °C led to much higher yields (23.6 and 32.9 wt.%), respectively. The volatile oils’ content of these oleoresins was 4.75 and 3.59 wt.%. GC-MS analysis showed that the volatile oil obtained after SbFE is characterized by the highest thymoquinone (TQ) content (60.5%) compared to that obtained after hexane extraction at room temperature (37.6%) or at 60 °C (41.6%). On the other hand, TQ content of the volatile oils isolated directly from the seeds by hydrodistillation and steam distillation was much lower (10.2 and 23.7%), respectively. Based on the above mentioned, SbFE of N. sativa seeds was found to be a useful green tool for obtaining a volatile oil-rich oleoresin with high TQ percentage which can be applied in pharmaceutical and nutraceutical products.