1 Introduction

Black cumin (Nigella sativa, NS) is a member of the family Ranunculaceae and is widely grown and consumed in many countries around the world, such as Turkey, Iran, Yemen, India, Pakistan, and Bangladesh [1, 2]. It is an annual-blooming herbaceous seed spice crop locally known as kalozira (Bangladesh), black caraway (USA), habba-tusawda (Arabic), and kalonji (India) [3]. Numerous chemical and biological activities are found in NS seeds, and the seed oil plays an important role in promoting human nutrition and health. NS seeds are largely used in several cosmetics, pharmaceuticals, foods, and processed products due to their spicy, bitter flavor, bioactive, antioxidant, and antimicrobial properties [4]. Besides this, in Bangladesh and other Asian nations, NS plays a vital role in traditional medicine. Furthermore, black cumin seed is a major ingredient in conventional medicines, e.g., Unani, Homeopathy, Ayurveda, and Siddha, and provides therapeutic benefits, to treat various ailments [2]. The seed is also utilized as a natural therapy for asthma, bronchitis, cough, influenza, headaches, fever, digestive disorders, dysentery, stomachaches, appetite stimulants, antibacterials, skin disorders, diuretics, insect repellents, and to improve liver and kidney functions [5]. Moreover, the people in the Indian subcontinent used the seeds to prepare different types of traditional food items, e.g., pickles, sweet dishes, cheese, bakery products, spice flavored foods, etc. The seed of black cumin is an important source of oil (32–38%), carbohydrates (17–19%), proteins (14–18%), ash (4.5–7.5%), fibers (8–16.4%), as well as vitamins [6]. Besides, its seeds also contain a high level of linoleic (C18:2, 56–60%), oleic (C18:1, 18–24%), palmitic (C16:0, 12–14%), and stearic (C18:0, 2–4%) acids [7]. Linoleic and oleic acids are the most abundant unsaturated fatty acids that play significant roles in health and nutrition. Moreover, NS seeds are rich sources of different minerals, viz., iron, potassium, phosphorus, calcium, sodium, manganese, iron, and zinc [8]. The seeds are also good sources of different types of metabolites (phenolics, alkaloids, flavonoids), and other bioactive chemicals, which are considered remedies against various types of diseases, including inflammation, analgesia, cancer, anti-convulsant, anti-microbial, anti-histaminic, bronchodilator, diabetic, gastroprotective, diuretic, and anti-hypertensive activity [4, 9, 10].

Like India, Bangladesh's cuisine habits are centered around spices, and being a potentially high-value spices crop, cumin seed has considerable economic importance [7, 11] in the subcontinental cuisines. In recent years, during the COVID-19 pandemic, the use of cumin seeds has increased noticeably in Bangladesh to boost immunity. However, only a few scientific reports about the nutritional compositions, bioactive chemicals, and antioxidant compositions and their activities of different genotypes of black cumin have been published so far. Hence, the purpose of this investigation was to estimate and compare the major constituents of the seeds of different black cumin varieties and promising genotypes available in Bangladesh.

2 Materials and methods

2.1 Samples collection

The experiment was implemented at the Research Wing, Bangladesh Agricultural Research Institute (BARI), Gazipur, Bangladesh. Thirty-four black cumin genotypes were collected from the Spices Research Centre, BARI, Bangladesh. The genotypes were previously screened against yield and yield-contributing characters, as well as some qualitative parameters [12]. Among them, genotypes BSK-2074 and BSK-2081, the BARI-released variety, the BARI Kalozira-1, and the local Kalozira variety were considered in the present study. Fresh, mature seeds were cleaned, washed, and dried at room temperature and blotted on blotting paper. The seeds of black cumin were taken and ground to powder by using a grinder. Finally, sieves with a 60 micron opening were used to pass the powder, and were stored in sealed containers for further researches.

2.2 Determination of the proximate composition of black cumin seeds

The proximate composition of the powdered black cumin seed sample was analyzed, according to the Association of Official Analytical Chemists (AOAC) method [13]. Ash content was estimated by heating plant sample in a muffle furnace for about 5–6 h at 500 °C (AOAC, 923.03) whereas moisture content were determined by heating plant sample in an air oven at 100–110 °C (AOAC, 950.46). The crude lipid was extracted from moisture free sample with petroleum ether (60–80 °C) in a Soxhlet apparatus for about 6–8 h (AOAC, 920.39c). Estimation of crude fibre content in the plant materials were carried out by treating the fat and moisture free materials with 1.25% dilute acid and 1.25% alkali followed by washing with water and ignition of the residue (AOAC, 921.13). The crude protein was measured using micro Kjeldahl method as described in procedures AOAC (928.08), using 6.25 as the conversion factor. The total carbohydrate content was estimated as described in the method of Hedge and Hofreiter [14].

2.3 Energy value

Using the following formula, the energy content of sample was measured by multiplying the values obtained for protein, fat, and carbohydrate [15].

$${\text{Total energy values }}\left( {{\text{kcal}}/{1}00{\text{ g}}} \right) = \, (\% {\text{Crude protein}} \times {4}) \, + \, (\% {\text{ Crude fat}} \times {9}) \, + \, (\% {\text{Carbohydrate}} \times {4})$$

2.4 Mineral content

A mineralization process was applied to the samples according to the method proposed by Petersen [16] with modification. Seed samples (1 g) were treated with conc. nitric acid (HNO3) and perchloric acid (HClO4) (5:1, v/v), and then kept at normal room temperature overnight. The solution was digested at 160 °C to 240 °C. After that, the samples were cooled, diluted to an appropriate concentration, and filtered. These filtrates were considered as the stock solutions for further analysis. A flame photometer (JENWAY, Model: PFP7, Germany) was used to measure sodium (Na), calcium (Ca), and potassium (K), while an atomic absorption spectrophotometer (Thermo, Model: ICS-3000, USA) was used to measure iron (Fe), magnesium (Mg), manganese (Mn), copper (Cu), and zinc (Zn). UV-Spectrophotometry (Model-AA-7000S, Shimadzu, Tokyo, Japan) was used to measure phosphorus (P) as described by Jones and Case [17]. Individual minerals were quantified by comparing the corresponding standard mineral procured from Sigma Aldrich Chemical Co., USA.

2.5 Determination of fatty acid composition

The fatty acid extraction procedure was previously described by the authors Hossain et al. [18]. The black cumin seed powder (1 g) was treated with five milliliters (5 ml) of ethylated reagent (sodium hydroxide, ethanol, and petroleum ether mixed), then vortexed in plastic tubes and kept for 10–12 h at normal room temperature. Five milliliters of salt solution (sodium hydrogen sulphate and sodium chloride mixed) were added while mixing well. Afterward, the upper oily layer was transferred to a capped and labeled glass vial for gas chromatography (GC) analysis. The fatty acid composition was identified as fatty acid methyl esters (FAMEs) for each of the examined samples by GC. The carrier gas was helium at a flow rate of 1 ml/min, hydrogen (60 kPa), and make-up gas nitrogen (50 kPa). FAMEs were separated using a capillary column (30 m × 0.25 μM) with a flame ionization detector (FID) and an autosampler. The injected volume of the sample was 2 μl at a temperature of 270 °C. The total run time of each sample was about 40 min. The percentage of fatty acids was calculated as the ratio of the partial area to the total peak area of FAMEs.

2.6 Analysis of bioactive compounds and antioxidant activity

2.6.1 Sample preparation

The seeds of black cumin were taken and ground to powder by using a grinder, and 60 micron sieve was used to pass the powder. Finely powdered samples were defatted with n-hexane (1 g/40 ml) for 2 h in Soxhlet’s apparatus. Hexane was removed and the defatted samples were used for further analysis.

2.6.2 Sample extraction

The defatted samples (5 g) were treated with 50 ml 80% methanol (1:10, w/v and 80/20 methanol–water, v/v) in a shaker (GFL 3015, Germany) at room temperature for 12 h. Then extracts were centrifuged (11,500 rpm) for 15 min and supernatant was collected. The stock solutions were kept for further analysis according to the below procedure.

2.7 Determination of total phenolic content (TPC)

The TPC was determined spectrophotometrically using the Folin–Ciocalteau method described by John et al. [19] with modifications. In this analysis, gallic acid (mg/ml stock solution) was used as a standard. Briefly, 50 μl of the extract or standard solution was taken for mixing with 950 μl distil water, 1 ml of the Folin-Ciocalteu reagent (diluted 1:10 with deionized water), and neutralized with 1 ml of NaCO3 (7.5%, v/v). After gently shaking, the mixture was incubated for 30 min at room temperature, and the absorbance was recorded at 765 nm using a spectrophotometer (Shimadzu UV-3600i, Japan). The TPC values were expressed as mg of gallic acid equivalents (GAE) per gram of sample. All tests were performed in triplicates.

2.8 Determination of total flavonoid content (TFC)

The TFC was measured using the aluminum chloride colorimetric assay described by John et al. [19] with slight modifications. Briefly, 0.5 ml extract or standard solution was mixed with 1.5 ml deionized water, and 0.25 ml of 5% sodium nitrate was added. The mixtures were then allowed for 10 min before the addition of 0.25 ml of 10% aluminum chloride solution (w/v). After 5 min of break, 1 ml of NaOH (4%, w/v) was added, and the volume was adjusted to 5 ml with deionized water. After shaking absorbance of the samples were recorded at 510 nm. The TFC values were expressed as mg of quercetin equivalents (QE) per g of sample. All tests were performed in triplicates.

2.9 Determination of antioxidant activity

2.9.1 DPPH (2, 2-diphenyl-1-picrylhydrazyl) radical scavenging capacity

2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay was performed according to a method Brand-Williams et al. [20] with few modifications. In this assay, ascorbic acid (mg/ml stock solution) was used as a standard. The extract or standard (0.1 ml) solution was mixed with 0.4 ml methanol and 2 ml of 0.1 mM DPPH (w/v in ethanol). After 30 min in the dark condition, the absorbance was measured at 517 nm, using a spectrophotometer. The percentage of DPPH radical scavenging activity was calculated using the following equation:

$${\text{Inhibition }}\% \, = \,\left[ {\left( {{\text{Abs}}.{\text{ of control }} - {\text{Abs}}.{\text{ of the sample}}} \right)/{\text{Abs}}.{\text{ of control}}} \right] \times {1}00.$$

2.9.2 Determination of ferric-reducing antioxidant power (FRAP)

The FRAP assay was determined according to a method suggested by Benzie and Strain [21]. Briefly, the FRAP reagent was prepared by mixing 300 mM acetate buffer, pH 3.6, 10 mM TPTZ (2,4,6-tripyridyl-s-triazine) in 40 ml of 40 mM HCl, and 20 mM FeCl3 at 10:1:1 (v/v/v). 0.2 ml extract or standard solution was mixed with 1.8 ml deionized water and 0.5 ml freshly prepared FRAP reagent, incubated at 37 °C, and the absorbance was recorded at 596 nm after 12 min, using a spectrophotometer. The FRAP values were presented as mg of gallic acid equivalent (GAE) per g of sample. All tests were performed in triplicates.

2.10 Statistical analysis

The data obtained for each analysis were expressed in triplicate. Mean values and standard deviations (SD) were used to express the results. The data was analyzed by one-way analysis of variance (ANOVA) using the Tukey Multiple Comparisons Test. The significance was defined at the 95% confidence level. Statistical analysis and data processing were performed using the software SPSS 17.0 (IBM inc., New York).

3 Results and discussions

3.1 Proximate composition and energy values of black cumin

The proximate nutrient contents of black cumin seeds are shown in Table 1. The crude fat, crude protein, total carbohydrate, moisture, ash, crude fiber, and energy values of BARI Kalozira-1, BSK-2074, BSK-2081, and local Kalozira variety seed ranged from 27.81 to 35.17%, 17.51 to 23.51%, 25.32 to 35.23%, 4.89 to 6.54%, 3.11 to 3.77%, 5.40 to 8.12%, and 368.08 to 644.88 kcal/100 g, respectively. The present study, genotype BSK-2074 had significantly higher content of proximate composition than the local Kalozira variety. Among them, it was observed that fat content representing the major constituent in Bangladeshi cumin seeds ranged from 27.81 to 35.17% which is almost like the fat values of black cumin of Sudan, Iran, and Turkey seeds, reported by [22]. However, the indexes found that the Chinese seeds are higher, 39.02%, as reported by Albakry et al. [10]. Subsequently, total carbohydrates ranged from 25.32 to 35.23% which is similar to the carbohydrate’s values (25.86%, 29.18%, and 27.05%) measured by [1, 23, 24]. Additionally, the seed of black cumin is a good source of protein the amount of 17.51 to 23.51%, while the protein content in black seeds of Yemen, Malaysia, Iranian and Turkey was determined to be in the range of 20.90 to 26.7% [11, 21]. Moreover, slight differences in moisture, ash, and crude fiber contents have been observed in the present study to the observations similar report published by [10, 24]. However, the trace proximate nutrients (crude fiber, ash, and moisture) content was found to be almost the same as the other valuable data sources and reports of [22, 24, 25] as ranged from 3.8 to 7.4%, 3.9 to 4.8%, 6.39 to 7.9%, respectively. The findings indicated that cumin seeds are a good source of various types of nutrients that are essential for human nutrition.

Table 1 Results of the proximal analysis in black cumin genotypes
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3.2 Fatty acid composition of black cumin seed

The fatty acid composition of the N. sativa seeds is shown in Table 2. The fatty acids, linoleic acid (53.32 to 59.39%), oleic acid (20.63 to 25.72%), palmitic acid (11.79 to 13.11%), stearic acid (2.25 to 3.32%), arachidic (0.22 to 0.47%), linolenic (0.15 to 0.25%), myristic (0.32 to 0.51%), behenic (0.55 to 0.87%), palmitoleic (0.12 to 0.23%), lignoceric (0.13 to 0.34%), and eicosadienoic (0.67 to 0.99%) acids found in BARI Kalozira-1, BSK-2074, BSK-2081, and local Kalozira seeds (Table 2; Figs. 1, 2, 3, and 4). Among them, it was observed that genotype BSK-2074 had significantly higher content of oleic acid, linoleic acid, palmitic acid, and stearic acid than the local Kalozira variety. The levels of oleic acid, palmitic acid, and stearic acid were the major fatty acids in all tested samples. The composition of linoleic acid in fatty acids measured in the current study is almost similar to previously reported values [25,26,27]. Linoleic acid (53.32 to 59.39%) was found to be the major fatty acid in the Bangladeshi genotypes [4, 10, 27]. It has been reported that linoleic acid-enriched dietary fats help prevent cardiovascular disorders, heart diseases, atherosclerosis, and high blood pressure. In the current study, we found that unsaturated fatty acids (UFA, linoleic, and oleic) were the principal fatty acids, and they can be a major source of essential fatty acids for human diets. Besides, comparatively low amounts of saturated fatty acids (SFA), viz., arachidic, myristic, linolenic, behenic, lignoceric, and palmitic acids, were also found in black cumin seeds (Table 2; Figs. 1–4). The genotype BSK-2074 had significantly higher content of 85.03% UFA and a lower 15.02% SFA than the local Kalozira variety (75.12% UFA and 17.83% SFA) variety. The content of UFA in the seed oil of black cumin is higher than in other vegetable oils, indicating a beneficial effect on human health [26, 27]. Moreover, the percentage of linoleic acid in the seed oil of black cumin was higher than in vegetable oils, olive oil (11.72%), and flaxseed oil (13.02%) [28]. According to Bayati [27], black seed oil has a significant concentration of oleic and palmitic acids, suggesting that its use in cosmetics may be possible, given its suitable texture and spreading capacity. Several studies have reported that fatty acid compositions vary in different black cumin seeds depending on their country of origin. For example, the Egyptian black cumin seeds contain high percentages of oleic (18.9 to 22.1%) and linoleic (47.5 to 58.0%) compared to the black cumin that originated from Tunisia (25.0 and 50.3%) and Iran (23.7 and 49.2%) [6, 29]. In our study, we found that Bangladeshi-origin black cumin seeds contained higher or similar (oleic, 23–25% and linoleic, 55–59%) fatty acids as compared to Egyptian, Tunisian, and Iranian origins.

Table 2 The fatty acid content in black cumin genotypes
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Fig. 1
figure 1

Chromatogram of the fatty acid composition of BARI Kalozira-1 variety

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Fig. 2
figure 2

Chromatogram of the fatty acid composition of BSK-2074 genotype

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Fig. 3
figure 3

Chromatogram of the fatty acid composition of BSK-2081genotype

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Fig. 4
figure 4

Chromatogram of the fatty acid composition of local Kalozira variety

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As shown in Table 3 and Figs. 1–4, the ratio of the UFA to the SFA was more than 4.58, which agreed with the observed fatty acids indices in black cumin by [10]. The lipid profile of the samples shows a high content of UFA (80–85%), while a low content (15–18%) of SFA indicates good agreement with reports of [6, 10, 11, 29]. The ratio of UFA to SFA was much higher (4.39–5.3) than that of the fatty acid ratio found in black cumin seeds of Iranian (2.9), Egyptian (2.4–3.0), and Tunisian (3.4) origins [6], but similar ratio (4.29) of Iraqi black cumin seeds [29]. The variations in fatty acid compositions might be due to different varieties of black cumin, seed quality (maturity, post-harvesting practice, storage conditions), oil extraction method, etc.

Table 3 Total saturated and unsaturated fatty acid contents and their ratio in different black cumin seeds
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3.3 Mineral composition of black cumin seeds

Minerals are inorganic chemicals that are required in specific amounts for human cells to operate correctly. The composition of minerals in the four different genotypes of N. sativa is presented in Table 4. The average results indicated that 100 g of seeds contain calcium (545.46 to 878.16 mg), potassium (674.24 to 836.7 mg), magnesium (219.28 to 455.76 mg), phosphorus (334.62 to 395.57 mg), sodium (36.55 to 54.87 mg), iron (3.62 to 5.73 mg), zinc (4.10 to 7.12 mg), manganese (2.35 to 4.01 mg), and copper (2.01 to 3.63 mg) of BARI Kalozira-1, BSK-2074, BSK-2081, and local Kalozira varieties. Our study, the genotypes BSK-2074 and BARI Kalozira-1 had significantly higher mineral content than the genotypes BSK-2081 and local Kalozira. The results also showed that N. sativa seeds were rich in calcium and potassium in all tested samples. The highest content of calcium and potassium in black seeds was reported by Sultan [11] and Albakry et al. [10]. Besides, slight differences in micronutrients (iron, zinc, and copper) contents were found among the four samples of N. sativa [8, 21, 23]. Moreover, the nutritional role of these macro- and micro-nutrients cannot be considered, given the small amount of black cumin consumed [24]. Therefore, mineral content may vary depending on genotypes, regions, post-harvest practices, storage conditions, maturity stage, and climatic geographical conditions where the sample seeds were grown [6].

Table 4 Mineral content of different black cumin genotypes
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3.4 The phenolic content of black cumin

Plant secondary metabolites, such as phenolic compounds, play an important role in plant protection from disease attacks and are responsible for antioxidant activity. The total phenolic content (TPC) of black cumin seeds is given in Table 5. The TPC of BARI Kalozira-1, BSK-2074, BSK-2081, and local Kalozira seeds were found to be 347.05 ± 2.72, 478.07 ± 1.83, 351.60 ± 3.53, and 316.48 ± 2.33 mg GAE/100 g, respectively. The results indicated that genotype BSK-2074 (478.07 ± 1.83 mg GAE/100 g) had significantly higher TPC than local Kalozira Varity (316.48 ± 2.33 mg GAE/100 g) (Table 5). Phenolic compounds structures consist of ring (one or more) with a hydroxyl group (different in number and position) that influences antioxidant effects on free radicals. Phenolic antioxidants can give an H‐atom to the free radical substrate and produce a non-radical substrate (RH, ROH, or ROOH) species and antioxidant free radicals, for example, gallic acid, a phenolic acid containing three hydroxyls and one carboxylic acid group in which the hydroxyl group is capable the hydrogen-donor to react with ROS or reactive nitrogen species to block the overproduction of damaging free radicals, including peroxyl radicals, hydroxyl, and superoxide radicals [30], these results are agreed with the most current studies. So, plant phenolic compounds or polyphenols are responsible for antioxidant activity and to protect against cancer, cardiovascular disease, osteoporosis, diabetes, and neurological diseases. Moreover, the TPC of the black cumin in this study was greater than that reported by Sultan et al. (160 ± 1.12 mg GAE/100 g) [11] and lower than those reported by Zielinska et al. (480 mg GAE/100 g and 589 ± 0.02 mg GAE/100 g) [31]. These results are similar to those reported in [31, 32]. The TPC in black seeds depends on several extraction techniques and solvents, such as 80% methanol with soxhlet extraction, whose TPC content was found to be 410 mg GAE/100 g DW [33], and the non-irradiated methanolic extract with gamma-irradiation, whose TPC content was also found to be similar [33]. On the other hand, the ethanol 95% extraction method resulted in the highest contents of TPC, as reported by Al-Bishri and Danial [34].

Table 5 Extractable phenolic, flavonoid, and antioxidant capacities of black cumin seed
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3.5 Total flavonoid content (TFC) in black cumin seed

Flavonoids are another secondary metabolites that are very abundant in plants and have a multitude of functions in regulating plant development and pigmentation, as well as in defense and signaling between plants and microorganisms. Indeed, flavonoids have been shown to obtain higher antioxidant activity as compared to phenolic acids [35, 36]. For example, quercetin containing five hydroxyl groups has comparatively more prominent antioxidant potential than those lacking neutralizing free radicals [37]. Our results are very important because many polyphenols, phenolic compound, have been reported to be strong antioxidants and suppressors of oxidative stress‐related damage, inhibition of lipid peroxidation and anti‐inflammatory effects [38]. As shown in Table 5, the results indicated that the genotype BSK-2074 contained significantly higher TFC (284.34 ± 2.08 mg QE/100 g) than the local Kalozira (120.53 ± 3.57 mg QE/100 g). The TFC in black cumin in this study was higher than the flavonoid content reported by Tura et al. [20], while the observed total flavonoid content was also found to be smaller than the TFC content of 378 ± 4.20 mg QE/100 g reported by Thomas et al. [39]. In addition, black cumin is a high-value crop that is cultivated in different regions of Bangladesh and is a good source of bioactive compounds.

3.6 Antioxidant activities of black cumin seed

The 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay was performed on black cumin samples and is given in Table 5. The DPPH radical activity of BARI Kalozira-1, BSK-2074, BSK-2081, and local Kalozira seeds were observed to be 67.89 ± 1.67%, 37.93 ± 0.53%, 90.33 ± 0.29%, and 98.09 ± 0.29%, respectively. Our results indicate that the genotype BKS-2074 has significantly highest inhibition activity compared to the activities of the local Kalozira and BSK-2081 genotype (Table 5). DPPH is a stable free radical commonly used in antioxidant assays to evaluate the antioxidant capacity of compounds. It's often used in the form of a purple-colored solution, which becomes colorless upon reduction by an antioxidant compound. The possible mechanisms for the antioxidant function (deactivation of free radicals) of different dietary phytochemicals include single electron transfer (SET) and hydrogen atom transfer (HAT) [40]. HAT-based mechanisms assess an antioxidant’s capacity to scavenge free radicals through hydrogen donation. Methods based on SET detect an antioxidant’s capacity to transfer one electron to reduce any compound, including metals, carbonyls, and radicals [41]. Our results indicate that genotype BK-2074 (37.93 ± 0.53%) has the highest DPPH radical activity compared to the activities of the local Kalozira (98.09 ± 0.29%) (Table 5). However, lower DPPH activities in black seeds were obtained by Toma et al. [42]

3.7 Ferric-reducing antioxidant power (FRAP) activity in black cumin seed.

The FRAP technique converts Fe3+ TPTZ complex to ferrous (Fe2+) form (intense blue colour) using electron-donating antioxidants at low pH, measuring FRAP values by absorbance change with the increase in absorbance of blue Fe3+ concentrations as mg of gallic acid equivalent per gram. The change in absorbance is directly related to the combined or total reducing power of the electron donating antioxidants present in reaction mixture. As shown in Table 5, the FRAP activity of BARI Kalozira-1, BSK-2074, BSK-2081, and local Kalozira seeds were observed as 149.57 ± 1.75 mg GAE/100 g, 129.65 ± 0.19 mg GAE/100 g, 186.08 ± 0.55 mg GAE/100 g, and 193.75 ± 0.19 mg GAE/100 g, respectively. Indeed, a single method’s specificity and sensitivity do not ensure a reliable assessment of all types of dietary antioxidants, or no single antioxidant can provide the same health benefits as compared to a combination of natural phytochemicals found in our foods [43]; thus, a combination of various assays is considered a more accurate measure of antioxidant activity. Our results observed that the genotype BSK-2074 (129.65 ± 0.19 mg GAE/100 g) had the significantly highest reducing effect than the local Kalozira variety (193.75 ± 0.19 mg GAE/100 g). Besides, higher ferric reducing capacity was obtained in black seed by Toma et al. [42] and lower activation was reported by Dalli et al. [44]

4 Conclusion

Black cumin seeds are rich in several chemical components, phytochemicals, and biological activities that play important roles in human health and nutrition. It is a good source of high-quality protein and essential fatty acids (polyunsaturated and linoleic). Nevertheless, the seeds are a potentially attractive source of linoleic (ω-6) fatty acids and minerals that play vital and positive roles in human health. The cumin seeds also contain phenolic compounds, flavonoids, and natural antioxidants. Additionally, the present results confirmed the antioxidant potential of the seed extract in terms of high DPPH radical scavenging ability and showed higher antioxidant activity. Phenolic compounds act as antioxidants by reacting with a variety of radical scavenging activities, which are responsible for deactivating free radicals based on their ability. However, it is possible that the antioxidant activity of the seed extracts is due to the high presence of phenolic and flavonoid compounds. Therefore, black cumin seeds are a nutritionally rich spice crop that can be used in the food, medicinal, and cosmetic industries. Here, BK-2074 was identified as a promising and nutritionally rich genotype; hence, the genotype can be utilized in breeding programs to develop as a variety.