Chemical Composition of the Essential Oil of Nigella sativa Seeds Extracted by Microwave Steam Distillation

Abstract

The essential oil of Algerian Nigella sativa seeds, isolated by microwave steam distillation (MSD) with cryogenic grinding of plant material (CG) were analysed by GC and GC-MS. Two procedures have been investigated, the MSD1 (seeds inside of oven apparatus) and MSD2 (seeds outside of oven apparatus). According to the data values reported in this study the effect of cryogrinding and the technique used on the chemical composition of the essential oils is very important. Monoterpene hydrocarbons (51.2-60.2%) were the main group of CG essential oils compared to CLG (classical grinding) essential oils (33.1-47.8 %). Whereas, the ketones formed the main proportion in CLG essential oils (46.1-59.9 %) followed by CG essential oils (32.7-40.8 %). Forty-nine compounds were identified and significant differences in quantities of the major constituents were observed, mainly were thymoquinone (CLG: 42.3-56.1 % and CG: 28.1-36.0 % ), p-cymene (CLG: 23.1-31.5 %, CG: 33.0- 38.0 %), dehydro-sabina ketone (CLG: 3.1- 3.3 %, GC: 4.4-4.5 %), carvacrol (CLG: 1.3-1.4 %, CG: 0.4-1.1 % ) and longifolene (CLG: 1.5-2.1 %, CG:1.3-1.7 % respectively). On the other hand, the N. sativa essential oil was investigated for its antioxidant activities using four different tests then compared with BHT. Results showed that it exhibit a good activity in each antioxidant system with a special attention for β-carotene bleaching test (IC50: 19 to 28 µg/ml) and reducing power (EC50: 8 to 15 µg/ml).