Effect of different extraction solvents on the content of Thymoquinone content of Nigella sativa L. seeds using UV-Visible spectroscopy and evaluation of the free radical scavenging activity

To develop and validate HPLC and UV-visible spectroscopy methods for the determination of Thymoquinone (TMQ) content in different solvent extracts of N. sativa L. seed. The evaluation of the free radical scavenging effect of different solvent extracts of TMQ was investigated. Extraction of solvent was done by adding 20 mL of the solvent (hexane, methanol, ethanol, ethyl acetate, and water) to 1 g of blackseed and in a conical flask, respectively. The mixtures were then incubated in a water bath at 40°C for 2 and 4 h, respectively. The mixtures were then centrifuged at 4000 rpm for 10 min at 4°C. The extracts were then quantitatively analyzed using HPLC and UV-visible spectrophotometry. The free radical scavenging activity of TMQ extracts was studied using 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The results obtained from HPLC indicate that TMQ extracted using hexane at 4 h (0.075 mg/mL, P <0.05) was significantly higher compared to other extraction solvents used. The results obtained from UV-vis spectroscopy analysis indicate that the methanol extract at 4 h (0.00957 mg/mL, P <0.05) was significantly higher compared to other extraction solvents used. Methanol extracts at 2 h showed the highest free radical scavenging activity (95.8%) compared to other extraction solvents. The results obtained show that hexane extracted the most TMQ at 4 h. Methanol extract demonstrated the highest free radical scavenging activity.