Physiochemical Analysis, Nutritional Characterization and Antioxidant Activities of Black Cumin (Nigella sativa) Seeds and Extracted Oil Available in Bangladesh

Abstract

Black cumin seed oil has a long history of uses for food flavors, perfumes, medicinal value, cosmetics industry, sausages, cheese, cakes, candies and for preparation curries, bread, preservation of butter and flavored food. The core objective of this research was to characterize two indigenous variety of black cumin (Nigella sativa L.), locally known as “ Kali jira” and “Kalonji” and its proximate and mineral analysis, extraction of essential oil and characterization, followed by determination of iodine value, saponification, acid value, pH, kinematics viscosity and specific gravity, investigation of the effects of extraction time and particle size, identification of the essential oil by GC-MS & FT-IR and antioxidant activity. The extraction was carried out using Soxhlet method, and determination of proximate compositions, physicochemical and functional properties was done. Soxhlet extraction using n-hexane was chosen to investigate the effect of time and particle size on yield and quality of the extracted oil. A general full factorial design was applied to both seed varieties, and 54 experimental runs were performed followed by optimization of the two varieties of essential oil. The value of moisture content, crude protein content, crude fat, crude fiber, total ash and carbohydrate of Kali jira seed were 5.29g/100g, 19.83g/100g, 41.3g/100g, 18.96g/100g, 5.10 g/100g and 9.52 g/100g whereas Kalonji registered 5.43g/100g, 19.95g/100g, 40.3 g/100g, 14.28g/100g, 4.35g/100g and 14.69g/100g, respectively. The mineral analysis indicated that potassium was the dominant one (829.11mg/100g, 746.27mg/100mg) followed by phosphorous, calcium, sodium, iron and zinc in Kali jira and Kalonji varieties. The results obtained from the experiment were analyzed using Design Expert software. The minimum oil yield was found to be 46.77% in Kalonji variety whereas Kali jira contained 49.57%, after the extraction time of 2 hours with a particle size of 1.4-2.5mm. A maximum oil yield of 91.08 and 94.767% was found for Kalonji seed and Kali jira seed, respectively at the extraction time of 6 hours and at a particle size of 0.25-0.5mm. Finally, GC-MS and FT-IR analysis has been carried out on the two seed oil varieties contains of linoleic, oleic and palmitic acids were the dominant fractions respectively and both seed varieties of the dominant functional component contain p-cymene but longifolene available only in Kalonji oil by 0.51%. Due to the above properties and characteristics Kali jira varieties have been found to possess higher yield variety. In “Kali jira”, carotenoids and tocopherols were 450.66±16.21 mg/kg-oil, whereas thymoquinone xiv contents were observed to be 201.31±13.17 mg/kg of seeds. In comparison, analysis of essential oil revealed that it contains functional ingredients like thymoquinone, dihydrothymoquinone, p-cymene, carvacrol, α-thujene, thymol, α-pinene, β-pinene and t-anethole as major constituents. Furthermore, In vitro antioxidant capacity indicated that fixed and essential oils inhibited lipid peroxidation by 25.62 and 92.56% and 2, 2-diphenyl-1- picrylhydrazyl (DPPH) radical scavenging activity by 32.32 and 80.25%, respectively. The present findings showed that black cumin fixed, and essential oils are rich source of phytochemicals and can be utilized against lifestyle disorders like hyperglycemia and hypercholesterolemia.