Evaluation of the in vitro antioxidant activity of different extracts of Nigella sativa L. seeds, and the quantification of their bioactive compounds

Abstract

Nigella sativa or Black cumin belongs to the Ranunculaceae family, largely distributed in the Mediterranean region and considered as medicinal spice worldwide for its good potential as a natural antioxidant because of the existence of terpenoids, flavonoids, tannins, alkaloids, and polyphenols [1].Oxidative stress is due to free radicals and is considered as one of the major risk factors of different diseases such as cardiovascular diseases mainly atherosclerosis, diabetes, hypertension, and cancer [2]. Black cumin was used as a remedy in traditional medicine so, it was logical to investigate its antioxidant activity and this for the different extracts obtained by Soxhlet apparatus, and this was assessed based on two methods: Radical scavenging activity test (DPPH) and Reducing power assay (FRAP).Among the objectives of our study is to Determine Total phenolic, flavonoids content, and condensed tannins of different Nigella sativa seed extracts. The determination of total phenolic content was assessed according to the Folin-Ciocalteu method. The flavonoids were determined spectrophotometrically by a method that depends on the formation of flavonoid-aluminum complex. While the tannins were determined by the vanillin method.The results obtained showed that the aqueous extract was characterized by the presence of highest amount of total polyphenols (51.17 ± 1.95) μg GAE/mg dry weight. The flavonoids were highly concentrated in the ethanolic extract (43.06 ± 1.25) µg QE/mg dry weight. While tannins were condensed in the dichloromethane extract (43.06 ± 1.25) µg CA/mg dry weight.The antiradical activity showed that the aqueous extract has registered the smallest value among all extracts tested with an Ic50 = 1489.34 ± 28.64 µg/ml, with no activity observed in chloroform and dichloromethane extracts. Concerning, the ferric reducing power test, the methanolic extract has the lowest value with an Ic50 = 1026.437 ± 3.61 µg/ml.