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Food Chemistry 101 (2007) 673–681

FoodChemistry

Nigella sativa L.: Chemical composition andphysicochemical characteristics of lipid fraction

Salma Cheikh-Rouhou a, Souhail Besbes a,*, Basma Hentati b, Christophe Blecker c,Claude Deroanne c, Hamadi Attia a

a Departement de biologie, Ecole Nationale d’Ingenieurs de Sfax, Unite Analyses Alimentaires, Route de Soukra, B. P. W., 3038 Sfax, Tunisiab Institut de Biotechnologie de Sfax, Unite de Biotechnologie et pathologie, Route de Soukra, 3038 Sfax, Tunisia

c Faculte Universitaire des Sciences Agronomiques de Gembloux, Unite de Technologie des Industries Agro-alimentaires, passage des Deportes 2,

5030 Gembloux, Belgium

Received 16 October 2005; received in revised form 16 December 2005; accepted 20 February 2006

Abstract

Physicochemical properties of two Nigella seed varieties, having a Tunisian and Iranian origin, were determined. Physical and chem-ical analyses of crude oils extracted from the seeds by a cold solvent method were also performed. The following results (on a dry-weightbasis) were obtained for Tunisian and Iranian varieties, respectively: protein 26.7% and 22.6%, oil 28.48% and 40.35%, ash 4.86% and4.41%, and total carbohydrate 40.0% and 32.7%. The major unsaturated fatty acids were linoleic acid (50.3–49.2%), followed by oleicacid (25.0–23.7%), while the main saturated fatty acid was palmitic acid (17.2–18.4%). Myristic, myristoleic, palmitoleic, margaric, marg-aroleic, stearic, linolenic, arachidic, eicosenoic, behenic and lignoceric acids were also detected. Thermal profiles of both Nigella seedvarieties, determined by their DSC melting curves, revealed different thermograms. Sensorial profiles of Tunisian and Iranian seed oilswere defined through the CieLab (L*, a*, b*) colour, oxidative stability by Rancimat test and viscosity. Physicochemical properties of theoils for Tunisian and Iranian varieties, respectively, include: saponification number 211 and 217, peroxide value 5.65 and 4.35, iodineindex 120 and 101, and an acidity of 22.7% and 18.6%. Results suggested that Nigella seed oil could deserve further considerationand investigation as a potential new multi-purpose product for industrial, cosmetic and pharmaceutical uses.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Nigella seeds; Oil; Fatty acids; Thermal properties; Sensorial properties

1. Introduction

Nigella (Nigella sativa L.) is an annual herbaceous plantbelonging to the Ranunculaceae family (Al-Gaby, 1998;Atta, 2003) growing in countries bordering the Mediterra-nean Sea (Gad, El-Dakhakhny, & Hassan, 1963). It tastesslightly bitter and peppery with a crunchy texture. Seedsare angular, of generally small size (1–5 mg), dark grey orblack colour. They represent the useful product. They areknown in Arabia as ‘Al-Habba Al-Sawdaa’ or ‘Al-Kam-moon Al-Aswad’ (Al-Gaby, 1998), ‘Habbet el Baraka’

0308-8146/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.foodchem.2006.02.022

* Corresponding author. Tel.: +216 74 274 088; fax: +216 74 275 595.E-mail address: besbes.s@voila.fr (S. Besbes).

and ‘Shunez’ (Burits & Bucar, 2000). In Tunisia, they arecalled ‘Sinouj’. Nigella sativa seeds are used for edibleand medicinal purposes in many countries, includingEgypt, Syria, Iran and to a slight extent in Tunisia. Theyare used as a condiment in bread and other dishes (Abou-tabl, El-Azzouny, & Hammerschmidt, 1986; Merfort et al.,1997). They are also used in the preparation of a traditionalsweet dish, composed of black cumin paste, which is sweet-ened with honey or syrup, and in flavouring of foods, espe-cially bakery products and cheese. Nigella seed oil orextract has protective and curative actions.

The composition and properties of this species havebeen fairly well investigated, particularly in Tunisia.Nigella seed oil is considered as one among newer sources

674 S. Cheikh-Rouhou et al. / Food Chemistry 101 (2007) 673–681

of edible oils, thanks to its important role in human nutri-tion and health. This seed oil has been reported to possessantitumor activity (Worthen, Ghosheh, & Crooks, 1998),antioxidant activity (Burits & Bucar, 2000), anti-inflamma-tory activity (Houghton, Zarka, de la Heras, & Hoult,1995), antibacterial activity (Morsi, 2000) and a stimula-tory effect on the immune system (Salem & Hossain,2000). Few works have considered physicochemical charac-teristics of black cumin seed oil. Proximate analysis ofwhole mature Nigella seeds showed that the moisture con-tent ranged from 5.52% to 7.43%, crude protein from 20%to 27%, ash from 3.77% to 4.92%, carbohydrates from23.5% to 33.2% and ether-extractable lipid from 34.49%to 38.72% (Abdel-Aal & Attia, 1993; Salem, 2001; Takruri& Dameh, 1998). This last fraction contains high amountsof linoleic, oleic and palmitic acids (Abdel-Aal & Attia,1993; Babayan, Koottungal, & Halaby, 1978; Gad et al.,1963). Actually, a great deal of attention has been focusedon black cumin seed oils, and thus their consumption hasincreased, especially in Middle East countries. As men-tioned in the literature, the oil has been usually producedby a hot solvent extraction method at 40–60 �C (Al-Gaby,1998; Burits & Bucar, 2000; D’Antuono, Moretti, &Lovato, 2002; Ramadan & Morsel, 2003; Takruri &Dameh, 1998) and even at 70 �C (Ramadan & Morsel,2004), using the Soxhlet extractor. This hot method ofextraction could affect the oil properties and may inducepartial alteration of the majority of minor constituents thathave many functional, antioxidative and pro-oxidativeeffects (Espin, Rivas, & Wichers, 2000; Koski et al., 2002;Tasioula-Margari & Okogeri, 2001).

To our knowledge, the study of thermal and sensorialaspects of black cumin seed oil has not yet been done,though they would provide much information about theoil. The availability of such data would facilitate the esti-mation of the oil shelf-life and the determination of itsquality.

This investigation was undertaken to obtain informa-tion about the chemical composition of Nigella seedscultivated in Tunisia and Iran and to determine fattyacid profiles, thermal profiles and sensorial profiles oftheir lipid fraction obtained by cold solventextraction.

2. Materials and methods

2.1. Seed material

Two varieties of mature black cumin (Nigella sativa L.)seeds were purchased from a herbal market in MenzelTemim, a little town situated in the North East of Tunisia.One sample was reported to be imported from Iran, andthe other was a Tunisian variety. The samples were directlystored at 15 �C for maximum 3 days. Then, they weresoaked in water, washed and air-dried. For the determina-tion of black cumin fractions, seed samples were separatelymilled in a heavy-duty grinder for 2 min, to pass 1–2 mm

screens and then were preserved in hermetic bags at�20 �C until analysis.

2.2. Oil extraction and preservation

Black cumin seeds (50 g) were placed in a dark flask(capacity = 1 l) and homogenized with 250 ml of hexane.After mixing for 4 h in a shaker (Selecta, Spain) at a rateof 180 U/min, the mixture was centrifuged for 15 min at1000g at ambiant temperature (20 �C). The supernatentwas then filtered through a filtering paper (WhattmanNo. 2). The extraction procedure was repeated twice andthe collected solvent was removed using a rotary evapora-tor at 40 �C. The seed oils obtained finally were drainedunder a stream of nitrogen and then stored in a freezer(�20 �C) for subsequent physico-chemical analyses.

2.3. Analytical methods

2.3.1. General

All analytical determinations were performed at least intriplicate. Values were expressed as the mean ± standarddeviation ð�x� SDÞ.

2.3.2. Chemical analysis of powdered seeds

2.3.2.1. Dry matter. The dry matter was determined accord-ing to the Association of Official Analytical Chemists(AOAC, 1990).

2.3.2.2. Fat content. Oil was extracted from 15 g of seedpowder in a Soxhlet extractor for 8 h using hexane as a sol-vent. The result was expressed as the percentage of lipids inthe dry matter of seed powder.

2.3.2.3. Protein content. Total protein was determined bythe Kjeldahl method. Protein was calculated using a nitro-gen conversion factor of 6.25 (Al-Gaby, 1998). Data wereexpressed as percent of dry weight.

2.3.2.4. Ash and mineral contents. To remove carbon, about0.5 g of powdered seed samples were ignited and inciner-ated in the muffle furnace at 550 �C for about 12 h. Theashes were dissolved in HNO3 (Larrauri, Ruperez, Bor-roto, & Saura-Calixto, 1996) and the mineral constituents(Ca, Na, K, Mg, Fe, Zn, Cu and Mn) were determinedusing an atomic absorption spectrophotometer (Hitachi Z6100, Japan). For the phosphorus content, the phospho-molybdovanadate method was used (AOAC, 1990). Thetotal ash was expressed as percent of dry matter.

2.3.2.5. Carbohydrate content. Carbohydrate was estimatedby difference of mean values, i.e. [total solids �(protein + lipids + minerals)].

2.3.3. Analysis of oil extract

2.3.3.1. Fatty acid composition. Fatty acid composition wasanalysed by gas-liquid chromatography after derivatisation

S. Cheikh-Rouhou et al. / Food Chemistry 101 (2007) 673–681 675

to fatty methyl esters (FAMEs) with 2 M KOH in metha-nol at room temperature according to the IUPAC standardmethod (IUPAC, 1992). Analyses of FAMEs were carriedout with a Hewlett-Packard 5890 Series II gas chromato-graph (H.P. Co., Amsterdam, The Netherlands) equippedwith a hydrogen flame ionisation detector and a capillarycolumn: HP Inovax cross-linked PEG (30 m ·0.32 mm · 0.25 lm film). The column temperature wasprogrammed from 180 to 240 �C at 5 �C/min and the injec-tor and detector temperatures were set at 250 �C. Identifi-cation and quantification of FAMEs was accomplishedby comparing the retention times of peaks with those ofpure standards purchased from Sigma and analyzed underthe same conditions. The results were expressed as a per-centage of individual fatty acids in the lipid fraction.

2.3.3.2. Differential scanning calorimetry (DSC). Thermalcharacteristics of black cumin seed oils were performedusing a modulated differential scanning calorimeter (DSC2920 Modulated DSC-TA Instruments, Newcastle, DE,USA). Oil samples (2 ± 0.10 mg) were weighed directlyinto a DSC-pan (SFI-Aluminium, TA InstrumentT11024). The samples were quickly cooled to �50 �C witha speed of 15 �C/min, maintained at this temperature for15 min and heated to 90 �C with a heating speed of15 �C/min. The same operation (cooling and heating) wasrepeated and the DSC thermographs were recorded duringthe second melting. An empty DSC-pan was used as refer-ence. The instrument was calibrated for temperature andheat flow using eicosane (Tp = 36.80 �C, H = 247.70 J/g)and dodecane (Tp = �9.65 �C, H = 216.73 J/g). Resultsare the averages of triplicate samples.

2.3.3.3. Oxidative stability. Oxidative stability was evalu-ated by the Rancimat method (Gutierrez, 1989). Stabilitywas expressed as the oxidation induction time (h), withthe use of the Rancimat 679 apparatus (Metrohm AG,Herison, Switzerland). A flow of air (15 l/h) was bubbledthrough the oil (2.5 g) heated at 100 �C and the volatiledegradation products were trapped in distilled water,increasing the water conductivity. The induction time wasdefined as the time necessary to reach the inflection pointof the conductivity curve (Halbault, Barbe, Aroztegui, &De La Torre, 1997).

2.3.3.4. UV – spectrophotometric analyses. Absorbances ofoil solutions in hexane were measured with UV-240 spec-trophotometer (Schimmadzu-Corporation, Kyoto, Japan).

2.3.3.5. Colour. The CieLab coordinates (L*, a*, b*) weremeasured with a spectrophotometer MS/Y-2500 (Hunter-lab, In., Reston, VA, USA), calibrated with a white tile.Under the tristimulus colour coordinate system, the L*

value is a measure of lightness and varies from �100(black) to +100 (white), the a* value varies from �100(green) to +100 (red), and the b* value varies from �100(blue) to +100 (yellow). As the values of a* and b* rise,

the colour becomes more saturated or chromatic, but thesevalues approach zero for neutral colours (white, grey orblack). Absorbance of oil solutions in hexane were mea-sured with a spectrophotometer UV-240 (Shimmadzu Cor-poration, Kyoto, Japan) with light of wavelengths between205 and 800 nm.

2.3.3.6. Index determination. AOCS official methods(American Oil Chemists’ Society, AOCS, 1997) were usedto evaluate the peroxide, iodine, saponification and acidityvalues (method number Cd 8–53, Cd 3d-63, Cd 3–25 andCd 3d-63, respectively). Determination of refractive index(at 40 �C) was determined with a refractometer (type Abbeoptic system).

2.3.3.7. Specific extinction. K232 and K270 extinction coeffi-cients were calculated from absorbances at 232 and270 nm, respectively, with UV spectrophotometer (SECO-MAN, Type: ANTHELIE 70 MI 0291, No. 344, France),using a 1% solution of oil in cyclohexane and a path lengthof 1 cm.

2.3.3.8. Chlorophyll and polyphenolic compounds. Chloro-phyll (mg/kg) was quantified by spectrophotometry(SECOMAN, Type: ANTHELIE 70 MI 0291, No. 344,France), following the methodology described by Mınguez,Rejano, Gandul, Higinio, and Garrido (1991). The pheno-lic compounds of Nigella seed oils were determinedcolorimetrically at 725 nm, using the Folin–Ciocalteaureagent as previously done by Gutfinger (1981) on virginolive oil.

2.3.3.9. Viscosity determination. Viscosity of the oil sampleswas measured with a Stress Tech Rheologica Rheometer(Rheologica Instruments AB, Lund, Sweden). Measure-ments were performed at 25 �C with a steel cone-plate(C40/4) at a constant shear rate of 100 s�1.

3. Results and discussion

3.1. Chemical characteristics of black cumin seeds

The average compositions of the two different Nigellaseed samples are shown in Table 1. Proximate analysis ofTunisian Nigella seeds showed that moisture content(8.65%), crude protein (26.7%), ash content (4.86%) andtotal carbohydrates (40.0%) were slightly higher than theamounts of the Iranian variety, while the lipid fraction ofthe TNS variety was relatively lower than the INS one(28.48% against 40.35%). Such variation in nutrient con-centrations among species and varieties may be related tothe variations of cultivated regions, storage conditionsand maturity stage. It may also be due to geographicaland climatic differences where Nigella seeds had beengrown (Atta, 2003). Data on nutrient contents mentionthat Nigella seeds are considered as a beneficient sourceof oil and many minerals.

Table 1Chemical characteristics (dry basis) of the Tunisian Nigella seeds (TNS)and the Iranian variety (INS)

Component TNS INS

Dry matter (%) 91.35 ± 0.26 95.92 ± 0.70Oila 28.48 ± 0.05 40.35 ± 0.16Crude proteina 26.7 ± 0.35 22.6 ± 0.24Asha 4.86 ± 0.06 4.41 ± 0.01Potassiumb 783 ± 6.61 708 ± 7.98Magnesiumb 235 ± 4.87 260 ± 48.70Calciumb 572 ± 21.5 564 ± 33.4Phosphorusb 48.9 ± 0.04 51.9 ± 0.01Sodiumb 20.8 ± 2.21 18.5 ± 3.17Ironb 8.65 ± 0.65 9.42 ± 0.88Copperb 1.65 ± 0.03 1.48 ± 0.21Zincb 8.04 ± 0.21 7.03 ± 0.49Manganeseb 4.43 ± 0.11 3.37 ± 0.21Total carbohydratea 40.0 ± 0.46 32.7 ± 0.41

All values given are means of three determinations.a In % dry matter basis.b In mg/kg of dry matter.

Table 2Fatty acid compositions (g/100 g of total fatty acid) of TNS and INS oils

Fatty acid TNS INS

Myristic C14:0 0.35 ± 0.02 0.41 ± 0.05Myristoleic C14:1 Tr. Tr.Palmitic C16:0 17.2 ± 0.15 18.4 ± 0.25Palmitoleic C16:1 1.15 ± 0.05 0.78 ± 0.25Margaric C17:0 Tr. Tr.Margaroleic C17:1 Tr. Tr.Stearic C18:0 2.84 ± 0.08 3.69 ± 0.12Oleic C18:1 25.0 ± 0.24 23.7 ± 0.06Linoleic C18:2 50.31 ± 0.25 49.15 ± 0.06Linolenic C18:3 0.34 ± 0.06 0.32 ± 0.05Arachidic C20:0 0.14 ± 0.02 0.22 ± 0.01Eicosenoic C20:1 0.32 ± 0.04 0.34 ± 0.05Behenic C22:0 1.98 ± 0.08 2.60 ± 0.05Lignoceric C24:0 Tr. Tr.SAFA 22.7 ± 0.37 25.5 ± 0.69MUFA 26.6 ± 0.39 25.0 ± 0.58PUFA 50.7 ± 0.70 49.8 ± 0.20

All values given are means of three determinations.SAFA, saturated fatty acids; MUFA, monounsaturated fatty acids;PUFA, polyunsaturated fatty acidsl; Tr., trace amounts (less than 0.2%).

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Nigella seeds contained significant amounts of impor-tant mineral elements. Potassium is the most abundant ele-ment in the black cumin seeds, followed by phosphorusand calcium. The other elements, in descending order byquantity, were Mg, Na, Fe, Zn, Mn and Cu. These resultsagree with those found by Takruri and Dameh (1998) forfive varieties of black cumin seeds (Iranian, two Syrian,Turkish and Jordanian). Nigella seeds provide relativelyhigh amounts of minerals (Mn, Zn, Cu and Fe). However,the nutritional status of these minerals cannot be predictedfrom the quantity of black cumin consumed (Takruri &Dameh, 1998).

3.2. Profiles of black cumin seed oil

3.2.1. General

Since the lipid fraction was found to be the most abun-dant one in black cumin seeds, it is very interesting to studyits physicochemical characteristics in order to seek itsadded value. We were interested in determining fatty acidcomposition, thermal, sensorial and physical descriptorsof Nigella seeds.

3.2.2. Fatty acid composition

Fatty acid composition of Nigella seed oil is given inTable 2, which shows that linoleic, oleic and palmitoleicacids account for more than 73% of the total fatty acidsfor INS oil and 76% for TNS oil. They represent the mainunsaturated fatty acids. The ratio of linoleic acid to oleicacid was more than 2:1. This result agreed with thosereported in soybean oil (C18:2 = 52%, C18:1 = 25%) and incorn oil (C18:2 = 58.7%, C18:1 = 26.6%) (Ramadan & Mor-sel, 2002). The ratio of saturated to unsaturated fatty acids(S/U%) was 34.1% in INS oil and 29.4% in TNS oil. Theseratios were higher than that reported by Ramadan andMorsel (2003) for black cumin seed oil (25.7%). Atta(2003) showed that the oils of black cumin varieties con-

tained oleic and linoleic acids at relatively high levels(18.9–20.1 and 47.5–49.0, respectively) but these are lowerthan those corresponding to the Tunisian variety (25.0 and50.3, respectively) and to the Iranian variety (23.7 and 49.2,respectively) (Table 2). In this study, saturated acidsaccounted for 25.5% and 22.7% of total fatty acids, forINS and TNS oils, respectively. Among them, the main sat-urated normal chain fatty acids were palmitic, stearic,behenic, myristic and arachidic, with minute amounts ofmargaric and lignoceric acids. Margaric and margaroleicacids were not detected in previously published data(Abdel-Aal & Attia, 1993; Atta, 2003; Babayan et al.,1978; Gad et al., 1963; Ustun, Kent, Cekin, & Clvelekoglu,1990). A negligible amount of eicosenoic acid (�0.33%)was detected and was in accordance with that reportedby Ramadan and Morsel (2002) but was absent in the studydone by Babayan et al. (1978). The source of variabilitymay be genetic (plant cultivar, variety grown), seed quality(maturity, harvesting-caused damage and handling/storageconditions), oil processing variables, or accuracy of detec-tion, lipid extraction method and quantitative techniques(Ramadan & Morsel, 2002).

3.2.3. Thermal profile

DSC provides information on the excess specific heatover a wide range of temperatures (Gloria & Aguilera,1998). Any endothermic or exothermic event is registeredas a peak in the chart, and its area is proportional to theenthalpy gained or lost, respectively. Nigella seed oils, ofboth Iranian and Tunisian varieties, showed differentDSC melting profiles (see Fig. 1). The INS oil exhibited asimple thermogram with a single peak having the followingcharacteristics: melting peak (�29.34 �C), melting enthalpy(60.68 J/g) and onset temperature (�33.41 �C). Therefore,the TNS oil thermogram presented two distinct peaks: a

Fig. 1. Melting thermograms of TNS oil (- - -) and INS oil (—) studied.

Table 4Oxidation induction time, viscosity, phenolic content and chlorophyllpigments of TNS and INS oils

TNS INS

Induction time (h) 12.0 ± 0.05 50.33 ± 2.48Viscosity (mPa s) 11.23 ± 0.08 5.99 ± 0.03Polyphenols (as mg gallic acid/kg of oil) 245 ± 9.16 309 ± 12.31Chlorophyll (mg/kg) 6.04 ± 0.06 2.26 ± 0.06

All values given are means of three determinations.

Fig. 2. CieLab coordinates (L*, a*, b*) of nigella seed oils from the twostudied varieties (h: L, n: a, : b).

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first low temperature melting peak (LTMP) with a meltingtemperature of �14.2 �C, a melting enthalpy of 59.52 J/gand an onset temperature of �19.96 �C, followed by a sec-ond high temperature melting peak (HTMP) having a melt-ing temperature of 24.77 �C, a melting enthalpy of 18.37 J/g and an onset temperature of 8.54 �C (Table 3). The pres-ence of two distinct peaks may be due to the appearance ofa second, more stable, polymorphic form or to the presenceof higher-melting triacylglycerols. The presence of thisHTMP could explain the presence of some crystals at roomtemperature (25 �C), leading to a higher viscosity (11.23against 5.99 mPa s for TNS and INS oils, respectively)(Table 4). In fact, contrary to the INS oil, TNS oil is notentirely in the liquid state at 25 �C (see Fig. 1).

3.2.4. Sensorial and physical profiles3.2.4.1. General. To determine sensorial and physicaldescriptors of black cumin seed oils, colour, oxidative sta-bility, viscosity and physicochemical parameters werestudied.

3.2.4.2. Colour. In this study, we compared L*, a* and b*

parameters of TNS and INS oils (see Fig. 2). The TNSvariety showed a higher a* value and lower L* and b* val-ues. This means that the TNS oil was lighter-coloured andmore yellow; otherwise, it contained more yellow pigmentsthan did the INS oil. Such a colour seems to attract con-sumers (Hsu & Chung, 1998). The CieLab (L*, a*, b*) val-ues of other vegetable oils, such as palm, soybean,sunflower, olive and corn, ranged from 63.4 to 69.5, 3.8to 4.4 and 9.2 to 10.4, respectively (Hsu & Yu, 2002). This

Table 3Thermal parameters, from DSC melting curves, of seed oil from the two stud

Parameter TNS

First peak Sec

Onset temperature (�C) �19.96 ± 0.2 8.Peak temperature (�C) �14.2 ± 0.07 24.Melting enthalpy (J/g) 59.52 ± 0.04 18.

All values given are means of three determinations.

shows that Nigella seed oil b* values were higher than thoseof other vegetable oils. Thus, Nigella seed oils were moreyellow-coloured than vegetable oils studied by Hsu andYu (2002). This may suggest the presence of more yellowpigments (carotenoids) in Nigella seed oils. The INS oilshowed other colour particularity: Hunter a* negative value(�1.08) was markedly lower than the Hunter a* of commonvegetable oils.

UV absorption, although outside the visible spectrum,was related to colour changes (Mazza & Qi, 1992; Melton,Jafar, Sykes, & Trigiano, 1994). TNS oil absorbed in theUV-C (100–290 nm), UV-B (290–320 nm) and UV-A(320–400 nm) ranges, while the INS oil showed absorbanceonly in the UV-C and UV-B ranges (see Fig. 3). Thus,Nigella seed oil can be used to give protection againstUV radiations with relatively high shielding power (SPF)and protection factor (PFA) scores. Nigella seed oil may

ied Nigella varieties

INS

ond peak First peak Second peak

54 ± 5.37 �33.41 ± 0.03 –77 ± 2.38 �29.34 ± 0.21 –37 ± 0.48 60.68 ± 0.72 –

0

1

2

3

200 245 290

0

0.5

1

290 335 380

0

0.5

1

400 600 800

(nm)

Abs

orba

nce

Abs

orba

nce

Abs

orba

nce

Fig. 3. Ultraviolet/visible spectra of TNS oil (- - -) and INS oil (—). Figurederived from scans (k = 200–290) of oil diluted 1:800; from scans(k = 290–400) of oil diluted 1:100 and from scans (k = 400–800) of oildiluted 1:10, all in hexane.

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provide protection against both UV-A (an origin of skinoxidative stress) and UV-B. The optical transmission ofNigella seed oil, especially in the UV range (290–400 nm)was comparable to those of date seed oil, raspberry seedoil and titanium dioxide preparations, which can be usedas sun protection factors for UV-B (SPF) and protectionfactors for UV-A (PFA) (Besbes, Blecker, Deroanne,Drira, & Attia, 2004a; Oomah, Ladet, Godfrey, Liang, &Girard, 2000).

The strong absorptivity of TNS oil at 450 nm, a wave-length which is approximately at the lower limit of detect-ability for the human eye, corresponded to high levels ofyellow pigments in this oil. TNS oil contained more yel-low-colouring than did INS oil, as indicated by the absor-bance (0.7 against 0.25) at 440–460 nm for 1% oil inhexane.

This confirms the results obtained with the CieLabMiniscan instrument. These yellow colours, which includecarotenoids, are beneficial, since they simulate the appear-ance of butter without the use of primary colorants, such ascarotenes and annattos, commonly used in the oil and fatindustry (Oomah et al., 2000).

3.2.4.3. Oxidative stability. Oxidative stability is an impor-tant parameter in evaluating the quality of oils and fats, asit gives a good estimation of their susceptibility to oxidative

degeneration, the main cause of their alteration (Aparicio,Roda, Albi, & Gutierrez, 1999).

The results of the Rancimat test are shown in Table 4.Stability, expressed as the oxidation induction time, wasabout 55 h for INS oil and about 12 h for TNS oil. This dif-ference could be attributed to a higher natural antioxidantscontent in INS oil, since no significant difference in thefatty acid profile, essentially in MUFA and PUFA con-tents, was observed. Aparicio et al. (1999) mentioned a sig-nificant correlation of phenols, oleic/linoleic ratio andtocopherols, with oil stability measured by Rancimat, invirgin olive oil. A high direct correlation was observedbetween total phenol content and oxidative stability byRancimat (Gutfinger, 1981; Salvador, Aranda, Gomez-Alonso, & Fregapane, 2001). The INS oil had a higher phe-nolic compounds content than had TNS oil (309 mg/kgagainst 245 mg/kg, respectively), which mainly determinea greater resistance to auto-oxidation (Baldioli, Servili,Perretti, & Montedoro, 1996; Perrin, 1992; Tsimidou,Papadopoulos, & Boskou, 1992). The amount of phenolsin crude seed oils is an important factor when evaluatingthe quality of the oil because these compounds have beencorrelated with sensory quality, the shelf life of oil and inparticular, its resistance to oxidation (Cinquanta, Esti, &La Notte, 1997).

The oxidative stability of INS oil was higher than that ofmost vegetable oils and comparable to some varieties ofolive oil and date seed oil, mainly because they have highphenolics contents (Aparicio et al., 1999; Besbes et al.,2004a, 2004b, 2004c, 2005). The oxidation induction timeof sunflower oil, under the same experimental conditions,is only about 7.7 h (Farag, El-Baroty, & Basumy, 2003).Salvador et al. (2001) reported that the induction time ofolive oil varied from �9 to 143 h. Besbes et al. (2004a,2004b, 2004c) found that date seed oil presented a high oxi-dation stability (33–45 h), measured by Rancimat underthe same conditions. This high stability was explained bythe relatively low content of PUFA and a high content ofnatural antioxidants, such as phenolic compounds. Thecontribution of phenolic and orthophenolic compoundsin the oxidation stability of olive oil was about 51%, fattyacids 24% and, in less percentages a-tocopherols, carote-noids and chlorophylls (Aparicio et al., 1999).

A study of phenolic, tocopherol and sterol profiles ofNigella sativa L. seed oil should be undertaken becausethey are of capital importance for achieving high oxidativestability; and they could also present some functional mol-ecules having a high added value, improving economic util-ity of Nigella sativa seeds as a source of edible lipids.

3.2.4.4. Viscosity. Table 3 shows that the viscosity of INSoil was lower than that of TNS oil (5.99 against 11.23mPa s). This result was in agreement with DSC resultswhich showed the presence of HTMP in TNS oil at roomtemperature. From fundamental physics of polymers, it isknown that the viscosity has a power dependence onmolecular weight (Gloria & Aguilera, 1998). It is worth

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noting that the viscosity of Nigella seed oil is much lowerthan that of most vegetable oils.

3.2.4.5. Polyphenols, induction time and chlorophylls.

Nigella seed oil has a higher phenol content (Table 4) thanmost edible oils, except for olive oil, which is considered tobe a rich source of phenolic compounds. Salvador et al.(2001) reported that total phenolic content of virgin oliveoil, measured by Folin–Ciocalteau method, ranged from19 to 380 mg/kg and from 124 to 516 mg/kg according toNissiotis and Tasioula-Margari (2002). This may explainthe fact that Nigella seed oil presents oxidation inductiontimes comparable to virgin olive oil.

Total phenol levels of TNS and INS oils 10-fold higherthan that of black cumin seed oil studied by Ramadan andMorsel (2004). Nigella seed oil, could be considered as apotential source of natural phenolic compounds. Althoughtheir participation in conferring specific flavour to oil(Caponio, Alloggio, & Gomes, 1999), phenolic compoundsmay have a positive effect in the prevention of coronaryheart disease and cancer (Owen et al., 2000; Tuck & Hay-ball, 2002).

The content of chlorophyll pigments is an importantquality parameter because it correlates with colour, whichis a basic attribute for evaluating oil quality (Salvadoret al., 2001). These pigments are involved in autoxidationand photo-oxidation mechanisms (Gutierrez, Garrido,Gallardo, Gandul, & Minguez, 1992; Mınguez-Mosquera,Gandul, & Garrido, 1990). The amounts of chlorophyllin TNS oil as mentioned in Table 4 was 6.04 ppm against2.26 ppm for INS oil. These amounts are situated insidethe interval range of the chlorophyll pigments in Cornic-abra olive oils (2–27 ppm) (Salvador et al., 2001).

3.2.4.6. Physical characteristics of Nigella seed oils. Physicalcharacteristics of Nigella seed oils are presented in Table 5.Refractive index of Nigella seed oil was similar to that ofolive oils studied by Lalas and Tsakins (2002). The sapon-ification value of about 211–218 is comparable to Xylopia

aethiopica oil (Barminas, James, & Abubakar, 1999). Thelower acidity of INS oil than TNS oil shows that it is edibleand could have a long shelf life. The iodine index of 100–120 indicates that Nigella oil is a highly unsaturated oiland suggests that it contains high levels of oleic and linoleicacids, as previously shown in Table 2. The iodine values of

Table 5Physicochemical characterisation of TNS and INS oils

Parameter TNS INS

Refractive index (at 40 �C) 1.47 ± 0.01 1.46 ± 0.01FFA (%) 22.7 ± 0.35 18.6 ± 0.28Saponification index (mg of KOH/g of oil) 211 ± 5.32 218 ± 8.24Iodine index (g of I2/100 g of oil) 119 ± 3.45 101 ± 2.72Peroxide index (meq O2/kg of oil) 5.65 ± 1.87 4.35 ± 1.38k232 1.07 ± 0.01 0.74 ± 0.03k270 0.27 ± 0.31 0.18 ± 18.68

All values given are means of three determinations.

Nigella seed oils are situated inside the interval range of thevalues mentioned by Tan, Che Man, Selamat, and Yusoff(2002) in some edible oils (9.37–145 g of I2/100 g oil).Iodine values of INS and TNS oils are similar to thosereported by Atta (2003) (IV = 115–128), Babayan et al.(1978) (IV = 125) and Abdel-Aal and Attia (1993)(IV = 107–110) for black cumin seed oils. A lower iodinevalue confers, to INS oil, more stability. Peroxide valueof oil is a valuable measure of oil quality. Peroxide valuesof INS and TNS oils (4.3 and 5.65 meq O2/kg of oil,respectively) are 3-fold lower than those reported by Atta(2003) (PV = 10.7–13.5) but higher than those reportedby Ramadan and Morsel (2002) for black cumin seed oil(0.22–0.36).

TNS oil showed a higher absorptivity at 232 and270 nm, thus containing more oxidation primary (hydro-peroxides) and secondary products than INS oil. Com-pared to TNS and INS oils, absorptivities at 232 and270 nm of black cumin seed oil studied by Ramadan andMorsel (2004) were relatively higher (3.6 and 1.2,respectively).

4. Conclusion

This study has revealed that Nigella sativa seeds are arich source of many important nutrients that appear tohave a very positive effect on human health. They consti-tute a good alternative source of essential fatty acids com-pared with common vegetable oils and could contribute tothe overall dietary intake of the mineral elements studied.

This preliminary study shows that Nigella seed oils con-tain high relative percentages of linoleic acid. They are alsomore yellow-coloured than other vegetable oils and theycan protect against UV light, which justifies their use inthe cosmetic industry. Black cumin seed oils are very stableand could be conserved safely for a long time due to theirconsiderable polyphenolic content. The use of Nigella seedoil for industrial applications could necessitate its exposureto high thermal treatments that could lead to changes inquality characteristics of the oil. So, a study of thermo-oxi-dation effects on physicochemical parameters of Nigellaseed oil must be undertaken.

Acknowledgements

Authors thank Mr. Hammami Mohamed, responsiblefor U.S.C.R. spectrometry, for chromatographic analysis.

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