Microwave-assisted extraction of Nigella sativa L. essential oil and evaluation of its antioxidant activity.

It has been previously reported that the essential oil of Nigella sativa L. seeds and its major active component, thymoquinone (TQ), possess a broad variety of biological activities and therapeutic properties. In this work, microwave-assisted extraction (MAE) of the essential oil from Nigella sativa L. seeds and its antioxidant activity were studied. Response surface methodology based on central composite design was used to evaluate the effects of extraction time, irradiation power and moisture content on extraction yield and TQ content. Optimal parameters obtained by CCD and RSM were extraction time 30 min, irradiation power 450 W, and moisture content 50%. The extraction yield and TQ content of the essential oil were 0.33 and 20% under the optimum conditions, respectively. In contrast, extraction yield and TQ amount of oil obtained by hydrodistillation (HD) were 0.23 and 3.71%, respectively. The main constituents of the essential oil extracted by MAE and HD were p-cymene, TQ, α-thujene and longifolene, comprising more than 60% of total peak area. The antioxidant capacity of essential oils extracted by different methods were evaluated using 2,2-diphenyl-1-picrylhydrazyl and Ferric reducing antioxidant power assays, and compared with traditional antioxidants. The results showed that MAE method was a viable alternative to HD for the essential oil extraction from N. sativa seeds due to the excellent extraction efficiency, higher thymoquinone content, and stronger antioxidant activity.