Variation in Nigella sativa quality and its standardization via instrumental analysis: A study based on geographical origin

Black seeds (Nigella sativa) owe an important place due to its more demand as a food as well as medicine. A lack of information does exist regarding the quality and safety for market-available food-grade samples of black seed (BS). The aim of this study is to investigate the quality and standardize the BS samples according to world health organization (WHO) guidelines of instrumental analysis and pharmacological activities. Instrumental analysis was performed with the help of ASE (accelerated solvent extraction), IR (infrared spectroscopy), UHPLC (ultra-high-performance liquid chromatography) and NMR (nuclear magnetic resonance spectroscopy) whereas ash values and chemical tests were applied for physicochemical analysis. DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) and cytotoxicity assay were performed as well. A high extract yield (g) with recovery of 4.4 ± 7.7 (22%) for Pakistani, 3.3 ± 4.7 (16.5%) for Indian and 3.02 ± 10.2 (15.1%) for Saudi Arabian sample. Chemical tests showed the presence of phenolic compounds and flavonoids. Saudi Arabian samples showed less amount for ash values (total-, water soluble- and acid insoluble ash). The samples were standardized further with the help of NMR and IR. A significant amount of micro- and macronutrients was observed in Saudi Arabian sample. With regard to the major active substance Thymoquinone (THQ; ng/mL), the order of concentration was observed as; Saudi Arabian sample (33141.1) > Pakistani (7677.2) > Indian sample (3998.6). A more potency for Saudi Arabian sample was observed during antioxidant and cytotoxicity assays. The method was successful to effectively discriminate the samples from different geographical origin, in terms of quality.