Black cumin essential oil as a valuable source of bioactive compounds: Evaluation of the conventional vs. modern extraction technique

Abstract

Within this investigation, the effect of conventional and sophisticated extraction method was evaluated on the chemical composition of black cumin seeds (Nigella sativa L.) essential oils and their bioactive characteristics. Soxhlet extraction at 60 °C by hexane (SEH) and petroleum ether (SEP) was adopted as traditionally used technique, while the supercritical extraction with CO2 (SFE), under the pressure of 10 MPa and temperature of 40 °C, was performed as a modern method, expected to overcome the drawbacks of the conventional solvent extraction. The results showed that SFE enabled up to ten times higher extraction yields, compared to essential oils derived after Soxhlet extraction, however, the bioactive compounds content, such as polyphenols, flavonoids and carotenoids, were extracted in higher quantities in the oil from Soxhlet extraction performance. Thereby, the strongest antioxidant agent was found to be the essential oil obtained from SEP, followed by the oil from SFE and oil obtained from SEH, respectively. The GC-MS analysis revealed that the content of thymoquinone was the highest in the essential oil from SEP (69.58%), and the obtained values are among the highest reported within the available literature data. Also, this oil sample contained about eleven times higher thymoquinone quantities than the essential oil obtained by SFE, which was mostly constituted of a methyl linoleate, a fatty acid methyl ester of linoleic acid. In addition, the essential oil from SEP exerted a value added antimicrobial properties, where it was found to be particularly effective in suppression of the Gram-positive bacteria growth.