Supercritical fluid extraction of coriander seeds: Process optimization, chemical profile and antioxidant activity of lipid extracts

Industrial Crops and Products 94 (2016) 353–362

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Supercritical fluid extraction of coriander seeds: Process optimization, chemical profile and antioxidant activity of lipid extracts ´ Branimir Pavlic, ´ Aleksandra Cvetanovic, ´ Saˇsa Ðurovic´ ∗ Zoran Zekovic, University of Novi Sad, Faculty of Technology, Bulevar Cara Lazara 1, 21000 Novi Sad, Serbia

a r t i c l e

i n f o

Article history: Received 25 May 2016 Received in revised form 31 August 2016 Accepted 2 September 2016 Keywords: Supercritical fluid extraction Coriander seed extracts Process optimization Chemical profile Antioxidant activity

a b s t r a c t Coriander seeds have been used in traditional medicine for the treatment of various ailments. Taking into account that operational conditions may influence the chemical composition optimization of supercritical extraction was performed. Influence of three different extraction parameters (pressure, temperature and CO2 flow) was explored while optimization of the process was performed by using Box-Behnken experimental design (BBD) in combination with response surface methodology (RSM). Experimental results were fitted to a second-order polynomial model with multiple regression, while analysis of variance (ANOVA) was employed in order to assess model fitness and determine optimal conditions for extraction yield (199.50 bar, 40.15 ◦ C, 0.396 kg/h of CO2 ). Investigation of chemical composition showed that linalool was the most abundant compound in all samples, followed by camphor, methyl chavicol, (+)limonene, eucalyptol, eugenol, geraniol, ␥-terpinene and ␣-terpineol. Results showed that 100 bar was the best pressure for isolation of monoterpenes, while temperature and CO2 flow rate values differ with the structure of desired monoterpene class. Furthermore, antioxidant activity of obtained extracts was determined using two different assays. Obtained results showed that observed extracts exhibit higher activity against lipid peroxidation, than against DPPH radical with the lowest inhibitory concentrations of 0.101 mg/mL and 2.364 mg/mL, respectively. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Coriander (Coriandrum sativum L., Apiaceae) is annual Mediterranean herb (Eikani et al., 2007; Grosso et al., 2008; Pavlic´ et al., 2015; Wangensteen et al., 2004) known for its bittersweet taste and its usage in cooking (Dima et al., 2016), and application in industries such as food (Aluko et al., 2001; Mhemdi et al., 2011; Pavlic´ et al., 2015), pharmaceutical (Jabeen et al., 2009; Mhemdi et al., 2011) and cosmetic (Eyres et al., 2005; Mhemdi et al., 2011). Seeds of this plant, which have been marked as the most important part of the plant, are held responsible for such exploitation (Wangensteen et al., 2004). Conducted studies showed diversity of biological activities of coriander seed extracts, such as antioxidant (Chen et al., 2009; Madsen and Bertelsen, 1995; Ramadan et al., 2003; Wangensteen et al., 2004), antimicrobial (Delaquis et al., 2002; Grosso et al., 2008; Lo Cantore et al., 2004; Wangensteen

∗ Corresponding author at: Department of Biotechnology and Pharmaceutical Engineering, Faculty of Technology, University of Novi Sad, Bulevar Cara Lazara 1, 21000 Novi Sad, Serbia. ´ E-mail address: [email protected] (S. Ðurovic). http://dx.doi.org/10.1016/j.indcrop.2016.09.008 0926-6690/© 2016 Elsevier B.V. All rights reserved.

et al., 2004), antidiabetic (Chen et al., 2009; Gallagher et al., 2003), anti-carcinogenic and anti-mutagenic (Chen et al., 2009; Chithra and Leelamma, 2000) and for treatment of rheumatism and pain in the joints (Pavlic´ et al., 2015; Wangensteen et al., 2004). Such diversity of activities is the main reason why coriander still attracts considerable attention of scientific community. One of the most important constituent of the seed itself is essential oil, which contains linalool as the main compound (>50%) (Eikani et al., 2007; Grosso et al., 2008; Pavlic´ et al., 2015; Wangensteen et al., 2004) followed by limonene, camphor and geraniol (Bajpai et al., 2005; Pavlic´ et al., 2015; Zekovic´ et al., 2011). Supercritical fluid extraction (SFE) represents the so-called green extraction method. The most common solvent in this extraction technique is carbon dioxide, which showed some advantages over the other methods and solvents such as lack of solvent residue and low operational conditions (Akgun et al., 1999; Sahena et al., 2009), as well as inexpensiveness, nontoxicity, non-flammability, chemical inactivity and possesses moderate critical parameters (pc = 73.8 bar and Tc = 31.1 ◦ C) (Filip et al., 2014; Temelli, 2009). Usage of this method helps to overcome some problems which occurred during the exploitation of classical extraction techniques.

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Some of those problems are: thermal degradation of compounds of interest, occurrence of hydrolysis and residue of organic solvents in obtained extracts (Grosso et al., 2008). Desired selectivity of the SFE process may be achieved using the proper combination of pressure and temperature, which finally affect the yield and chemical profile of obtained extracts (Filip et al., 2014). Due to significance of the proper choice of the operational conditions, and their influence on the extraction process itself, response surface methodology (RSM) has been employed to optimize the extraction process. It used statistics and other mathematical techniques, thus providing the optimization of the extraction process. Optimization of the process by RSM includes the optimization of the desired responses, which are affected by variables (Zekovic´ et al., 2014), in this case pressure, temperature and CO2 flow rate. Up-to-date conducted studies examined the influence of parameters on yield of SFE process and antioxidant activity of obtained extracts (Anitescu et al., 1997; Chen et al., 2009; Dima et al., 2016; Grosso et al., 2008; Mhemdi et al., 2011; Pavlic´ et al., 2015; Reis Machado et al., 1993; Yepez et al., 2002; Zekovic´ et al., 2015). Extraction yield and chemical composition of the extracts were compared with extracts obtained using other extraction techniques (Anitescu et al., 1997; Mhemdi et al., 2011; Pavlic´ et al., 2015; Reis Machado et al., 1993; Zekovic´ et al., 2015). Examined operational conditions in available literature varied in following ranges: pressure 50–300 bar, temperature 21–50 ◦ C and CO2 flow rate 0.194–21.8 kg/h. The next logical step would be optimization of the SFE process and determination of the relationship between chemical composition and operational parameters. In order to accomplish those goals, the influence of three different factors (temperature, pressure and CO2 flow rate) on yield of SFE process, antioxidant activity and chemical composition of obtained extracts were investigated, while the extraction yield was optimized using RSM. Operational parameter ranges were determined according the available literature data. Chemical profile of extracted oil was particularly evaluated in order to establish the above mentioned relationship.

2. Materials and methods 2.1. Plant material Coriander seeds (CS) were acquired from the Institute of Field and Vegetable Crops, Novi Sad, Republic of Serbia (year 2011). Plant material was air-dried and stored at the room temperature. Dried seeds were milled in the blender and mean particle size (0.6216 mm) was determined by sieve set (CISA Cedaceria Industrial, Barcelona, Spain).

2.3. Supercritical fluid extraction SFE was performed on laboratory-scale high pressure extraction plant (HPEP, NOVA-Swiss, Effretikon, Switzerland) described elsewhere (Filip et al., 2014). The main parts and properties of this plant are: gas cylinder with carbon dioxide, diaphragm type compressor (with pressure range up to 1000 bar), extractor vessel (with internal volume 200 mL, maximum operating pressure of 700 bar) with heating jacket, separator with internal volume 200 mL and maximum operating pressure of 250 bar, pressure control valve, temperature regulation system and regulation valves. Extraction processes were performed at three different pressures (100, 150 and 200 bar), temperatures (40, 55 and 70 ◦ C) and CO2 flow rates (0.2, 0.3 and 0.4 kg/h), while extraction time (4 h) was constant for all experiments. After finishing the extraction processes, total extraction yields (Y) were measured. Separator conditions were 15 bar and 23 ◦ C. Obtained extracts were transferred into the glass bottles, sealed and stored at 4 ◦ C in order to prevent any possible degradation of extract components until analysis.

2.4. Chemical analysis GC–MS and GC-FID analysis were performed on Agilent GC6890N system according to previously described procedure (Filip et al., 2016). In the case of GC–MS analysis, gas chromatograph was coupled with Agilent MS5759 mass spectrometer. The HP-5MS column (30 m length, 0.25 mm inner diameter with 0.25 ␮m film thickness) was used. Helium flow rate was 2 mL/min, while temperature was as follows: injector 250 ◦ C, detector 300 ◦ C, initial 60 ◦ C with linear increase of 4 ◦ C/min to 150 ◦ C. Samples were dissolved in methylene chloride, while injected volume of those solutions was 5 ␮L with split ratio of 30:1. Compounds were identified by comparing obtained spectral data to those one from NIST 05 and Wiley 7n mass spectral libraries and with spectral data of analytical standards. GC-FID analysis was employed for quantitative analysis of compounds in analyzed samples. Standard solutions were prepared dissolving standard compounds in methylene chloride in concentration range of 1–500 ␮g/mL. Standard solutions were used to create calibration curve, which described the dependence of peak area on concentration of standard compounds (R2 > 0.99). Obtained results were expressed as mg of compound per g of coriander seeds extract (mg/g).

2.5. Lipid peroxidation 2.2. Chemicals Commercial carbon dioxide (Messer, Novi Sad, Serbia) with >99.98% (w/w) purity was used for laboratory scale supercritical fluid extraction. Tween 80 was purchased from J. T. Backer, iron(II) ˇ (Serbia), l-(+)-ascorbic acid sulfate heptahydrate from Zorka Sabac and trichloroacetic acid (TCA) were purchased from Centrohem (Stara Pazova, Serbia), perchloric acid was purchased from Merck (Darmstadt, Germany) and 2-thiobarbituric acid (TBA) from SigmaAldrich (Steinheim, Germany). The standard compounds for GC analysis: ␣-pinene, ␤-pinene, camphor, methyl chavicol (estragole) and eucalyptol (1,8-cineole) were purchased from Dr Ehrenstorfer (Germany), while ␥-terpinene, (+)-limonene, linalool, geraniol, carvacrol, eugenol and ␣-terpineol were purchased from Carl Roth (Germany). All other used chemicals were of analytical reagent grade.

Lipid peroxidation that was induced by extent of Fe2+ /ascorbate system has been determined by TBA assay according to procedure described in previous research (Beara et al., 2012). Substrate in this method are polyunsaturated fatty acids (PUFA) obtained from linseed by Soxhlet extraction. Those PUFAs were added to phosphate buffer pH 7.4 in presence of Tween 80 and sonicated for 1.5 h to obtain emulsion. This emulsion was mixed with FeSO4 , ascorbic acid and extract solutions (concentration ranging of extract solutions were from 20 to 200 mg/mL, diluted with 80% aqueous isopropyl alcohol). In control, instead of samples, 80% aqueous isopropyl alcohol was added. Phosphate buffer and extract dilution were added in blank. After incubation at 37 ◦ C for 1 h, EDTA solution was added to all samples followed by TBA reagent (aqueous mixture of TBA, HClO4 and TCA) and the heating at 100 ◦ C for 15 min. Cooled mixtures were centrifuged for 15 min and absorbance of the colored product malondialdehyde (MDA) was measured at 532 nm.

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Results were expressed as radical scavenging capacity (%ILP), which were calculated using the following Eqs. ((1)–(3)):



ILP (%) = 1 −

 A  Acon

Table 1 Natural and coded levels of independent variables used in applied RSM design. Variable

× 100

Coded levels

(1)

A = Aws − Abp

−1

(3)

where A represents absorbance of probe, Acon is absorbance of control probe, Abp is absorbance of blank, Aws is absorbance of working solutions, and Acs is absorbance of control solution. Antioxidant activity was expressed as the inhibition concentration at ILP value 50% (ILP50 ), which represents the concentration of test solution required to obtain 50% of radical scavenging capacity expressed as mg per mL (mg/mL). All experiments were performed in three replicates and the results were expressed as mean value. 2.6. DPPH assay The free radical scavenging activity of coriander seeds extract was determined according the previously described method (Espín et al., 2000) with slight modification. The reaction mixture was prepared in the following manner: certain volume of obtained CS extract was dissolved in the ethyl acetate and added in the 90 ␮M solution of 2,2-diphenyl-1-pycril-hydrazyl (DPPH) radical in 95% methanol. Absorbance of such mixture was measured at 515 nm after the incubation period of 60 min at the room temperature. Blank solution was prepared by adding ethyl acetate instead sample. Radical scavenging capacity (%RSC) was calculated by following equation:





Asample × 100

(4)

Ablank

where: Asample is the absorbance of sample solution and Ablank is the absorbance of blank probe. Antioxidant activity was expressed as the inhibition concentration at RSC value 50% (IC50 ), which represents the concentration of test solution required to obtain 50% of radical scavenging capacity expressed as mg per mL (mg/mL). All experiments were performed in three replicates and the results were expressed as mean value. 2.7. Experimental design The Box-Behnken experimental design (BBD) of RSM was used to evaluate the effect of extraction parameters and to optimize the conditions for target response. Design was applied with three

0

1

150 55 0.3

200 70 0.4

Natural levels

(2)

Acon = Acs − Abp

%RSC = 100 −

355

Pressure (bar) Temperature (◦ C) CO2 flow rate (kg/h)

100 40 0.2

numerical factors on three levels. Experiment consisted of fifteen randomized runs with three replicates in central point. The independent variables employed in this design were pressure (X1 , 100–200 bar), temperature (X2 , 40–70 ◦ C) and CO2 flow rate (X3 , 0.2–0.4 kg/h). Each of the coded variables was force to range from −1 to 1 normalizing the parameters, thus affecting the response more evenly and making the units of the parameters irrelevant in the same time (Bas¸ and Boyacı, 2007). Variables were coded using the following equation: X=

Xi − X0 X

(5)

where X represents the coded value, Xi is the corresponding actual value, X0 represents actual value in the center of the domain and X is the increment of Xi corresponding to a variation of 1 unit of X. The natural and coded values of independent variables used in this experimental design are presented in Table 1. The response variables were fitted into the given second-order polynomial model, which is presented as competent for describing the relationship between the responses and the independent variable (Bezerra et al., 2008): Y = ˇ0 +

3  i=1

ˇi Xi +

3 

ˇii Xi2 +

i=1

3 

ˇij Xi Xj

(6)

i
where Y represents the response, ␤0 is constant, ␤j , ␤jj , ␤ij are the linear, quadratic and interactive coefficients of the model, respectively, Xi and Xj are the levels of the independent variables. Optimal conditions for SFE extraction process were determined considering total extraction yield as target response. BBD experimental design and multiple linear regression analysis were conducted using Design-Expert v.7 Trial (Stat-Ease, Minneapolis, Minnesota, USA). Obtained results were statistically tested employing analysis of variance (ANOVA) with the significance level of 0.05. Competence of model was evaluated according to the obtained coefficient of multiple determination (R2 ), coefficient of variance (CV) and pvalues for each model, as well as lack of fit testing.

Table 2 Experimental conditions applied in Box-Behnken design with natural and coded levels of independent variables and experimentally obtained measured response, Y. Sample No.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Independent variables

Measured response

X1 Pressure (bar)

X2 Temperature (◦ C)

X3 CO2 flow rate (kg/h)

Y (g/100 g CS)

0 (150) 1 (200) −1 (100) 0 (150) 1 (200) 0 (150) 1 (200) 0 (150) 0 (150) 0 (150) −1 (100) 1 (200) −1 (100) 0 (150) −1 (100)

1 (70) −1 (40) 0 (55) 1 (70) 1 (70) −1 (40) 0 (55) 0 (55) −1 (40) 0 (55) 0 (55) 0 (55) −1 (40) 0 (55) 1 (70)

−1 (0.2) 0 (0.3) 1 (0.4) 1 (0.4) 0 (0.3) −1 (0.2) −1 (0.2) 0 (0.3) 1 (0.4) 0 (0.3) −1 (0.2) 1 (0.4) 0 (0.3) 0 (0.3) 0 (0.3)

2.05 5.95 1.20 3.50 5.36 4.31 4.90 3.77 5.64 4.02 0.95 7.00 2.69 4.00 0.59

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Table 3 Estimated regression coefficients of the fitted second-order polynomial model for investigated response. Coefficient

Response Y

␤0

3.93

Linear 2.22* −0.89* 0.64*

␤1 ␤2 ␤3

Interaction ␤12 ␤13 ␤23

0.38 0.46 0.032

Quadratic ␤11 ␤22 ␤33 *

−0.32 0.038 −0.097

Statistically significant at p < 0.05.

3. Results and discussion 3.1. Model fitting RSM was employed to investigate influence of extraction parameters, in this case pressure (100–200 bar), temperature (40–70 ◦ C) and CO2 flow rate (0.2–0.4 kg/h), on total extraction yield (Y) as investigated response, and to optimize extraction process. Results of experimentally obtained results for measured responses in BBD design are presented in Table 2. ANOVA had been used for determination of regression coefficients of the linear, quadratic and interaction terms of desired response. Results of ANOVA analysis are presented in Table 3. Influence of each term could be statistically significant (p < 0.05) or insignificant (p > 0.05). Calculated statistical parameters are presented in Table 4, while coefficients of multiple regression (R2 ), together with ANOVA results, were used as the first indicator of the model adequacy. Value of R2 was particularly high for Y (0.9847). Obtained R2 value indicated that second-order polynomial model represented a good approximation of experimental results. Detailed information on statistical significance of investigated model were provided by ANOVA. Experimental results of investigated response showed good fitting with mathematical model, since regression for model was significant (p < 0.05), while lack of fit was insignificant (p > 0.05) (Table 4). Therefore, regression equations could be successfully used as predictors of these responses in investigated experimental domain. 3.2. Total extraction yield (Y) Presented data (Table 2) showed that Y varied in range of 0.59–7.00 g/100 g CS. The highest yield was obtained under following conditions: 200 bar, 55 ◦ C and 0.4 kg/h of CO2 . However, the lowest Y was observed under 100 bar, 70 ◦ C and 0.3 kg/h of CO2 . According to Zekovic´ et al. (2015), Y values were 0.94, 1.42 and 1.44 g/100 g of CS at the following operational conditions 100 bar, 40 ◦ C and CO2 flow rate of 0.194 kg/h, using the plant material with three different mean particle size (1.368, 0.775 and 0.631 mm). Results showed that Y increasing with decreasing in mean particle size. Dima et al. (2016) were conducted two sets of experiments using following conditions: 99 bar, 31 ◦ C and 21.8 kg/h of CO2 for the first experimental set and 100 bar, 40 ◦ C and 20.6 kg/h of CO2 for the second experimental set. Also, CS with three different particle size were used in those experiments (0.50, 0.63 and 0.71 mm). Obtained Y under described conditions were 0.51, 0.57 and 0.36 g/100 g CS for the first experimental set and 0.21, 0.23 and 0.18 g/100 g CS

for the second experimental set. It could be noticed that in this case, in both experiments, Y increased with the particle size in the beginning, but then decreased. Under the operation conditions of 115.5–279.2 bar and 47.85–57.85 ◦ C, achieved Y was in the range of 0.880–1.997 g/100 g CS (Yepez et al., 2002). Those results fit into the obtained range for Y in this research, however represented a lower values comparing to maximal achieved Y value. On the other hand, Y values of 1.52 and 8.88 g/100 g CS were achieved under the operational conditions of 100 bar, 40 ◦ C and 0.194 kg CO2 /h and 300 bar, 40 ◦ C and 0.194 kg CO2 /h, respectively (Pavlic´ et al., 2015). Applied experimental conditions in that study showed that pressure exhibited the positive influence on Y, obtaining maximal Y of 8.88 g/100 g CS (Pavlic´ et al., 2015), which was significantly higher yield than 7.00 g/100 g CS obtained in this study. Combined effects of SFE parameters on Y were presented in Fig. 1, while their significance determined by RSM analysis and regression coefficients calculated using Eq. (6) are presented in Table 3. According to ANOVA, linear terms of pressure, temperature and CO2 flow rate exhibited significant influence on Y (p < 0.05). Linear terms of pressure and CO2 flow rate were positive, while linear term of temperature was negative. On the other hand, quadratic terms of pressure and CO2 flow rate exhibited negative influence, while quadratic term of temperature was positive. This suggested that Y would increase with pressure and CO2 flow rate, although the influence of pressure would be stronger than influence of temperature. Actually, linear term of pressure exhibited the strongest influence according the regression coefficients presented in Table 3. Positive effect of pressure on extraction yield was rather expected since the elevation of this parameter results in an increase in CO2 density, which further results in higher solubility of the compounds (Paixao Coelho and Figueiredo Palavra, 2015; Pourmortazavi and Hajimirsadeghi, 2007). Positive effect of CO2 flow rate was the result of the reduced thickness of the film layer around the solid particles thus decreasing the mass transfer resistance surrounding the particles (Döker et al., 2004). On the other hand, negative linear term of temperature suggested that Y would decrease with increasing in temperature. Influence of this factor is rather complex comparing to the influence of pressure. This is due to combination of two variables, density and vapor pressure. Vapor pressure increases with temperature causing the increasing in solubility, while density decreases with temperature which results in decreased solubility (Jesus and Meireles, 2014; Paixao Coelho and Figueiredo Palavra, 2015). In this particular case, decreasing in density with temperature increasing would be the dominant and, therefore, there was decrease in Y with temperature elevation. Predicted second-order polynomial model for Y was given by following equation: Y = 3.93 + 2.22X1 − 0.89X2 + 0.64X3 + 0.38X1 X2 +0.46X1 X3 + 0.032X2 X3 − 0.32X12 + 0.038X22 − 0.097X32

(7)

3.3. Optimization of supercritical fluid extraction In order to accomplish maximal Y, desired response was optimized. Optimization process itself was based on the obtained results from previously obtained extractions and conducted statistical analysis. As the final result of performed optimization, predicted maximal values of investigated responses and estimated optimal conditions of SFE process was obtained (Table 5). From the data presented in Table 5 it could be noticed that estimated values for pressure and CO2 flow rate was near maximal value. On the other hand, estimated temperature was almost equal to minimal investigated temperature. Under these estimated conditions, predicted value of Y was 7.30 g/100 g CS.

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Fig. 1. Response surface plots showing combined effects of SFE parameters on total extraction yield.

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Table 4 Analysis of variance (ANOVA) of the fitted second-order polynomial models. Source

Sum of squares

DF

Mean square

F-value

p-value

Total extraction yield (Y) Model Residual Lack of fit Pure error Total R2 = 0.9847

51.00 0.79 0.76 0.038 51.80

9 5 3 2 14

5.67 0.16 0.25 0.019

35.70

0.0005

13.38

0.0703

Table 5 Predicted maximal values of investigated response and estimated optimal conditions for the process. Optimal conditions

Investigated response Y (g/100 g CS)

Predicted value Pressure (bar) Temperature (◦ C) CO2 flow rate (kg/h)

7.30 199.50 40.15 0.396

3.4. Chemical analysis of extracts Chemical profile of extract samples obtained by GC–MS and GC-FID analysis is presented in Table 6, operational conditions of extraction processes in Table 2, while GC chromatogram of samples 3, 13 and 15 are presented in Fig. 2. From the data in Table 6, it could be seen that the main compound in the essential oil of coriander was linalool, which confirmed results obtained in previous studies (Grosso et al., 2008; Mhemdi et al., 2011; Pavlic´ et al., 2015; Zekovic´ et al., 2015), followed by camphor. Those two compounds were detected and quantified in all fifteen samples and could be considered as main compounds of CS extracts. Comparing obtained results (Table 6) with the previously obtained, domination of linalool was confirmed (Anitescu et al., 1997; Grosso et al., 2008; Mhemdi et al., 2011; Pavlic´ et al., 2015; Zekovic´ et al., 2015). Pavlic´ et al. (2015) obtained linalool in amounts of 90 and 64.7 mg/g E using following experimental conditions 100 bar, 40 ◦ C, 0.194 kg/h of CO2 and 300 bar, 40 ◦ C, 0.194 kg/h of CO2 , respectively. These results showed that linalool was more soluble in supercritical CO2 under the lower value of pressure. On the other hand, Zekovic´ et al. (2015) reported linalool contents of 532.0, 596.1 and 502.1 mg/g of extract at 100 bar, 40 ◦ C and 0.194 kg/h of CO2 using CS with following values of mean particle size 1.368, 0.775 and 0.631 mm, respectively. Study conducted by Pavlic´ et al. (2015) and Zekovic´ et al. (2015) demonstrated lower results regarding the linalool content in obtained CS extracts comparing with the maximal yield of this compound achieved in this study (717 mg/g). Beside the linalool, camphor (21.0 mg/g), eugenol (20.7 mg/g), methyl chavicol (18.2 mg/g) and geraniol (10.0 mg/g) were presented in higher amount. Previous conducted studies confirmed the presence of camphor and geraniol in higher content, while methyl chavicol and eugenol were detected at trace levels (Pavlic´ et al., 2015; Zekovic´ et al., 2015). Obtained chemical profile of CS extracts suggested that chemical compositions of extracts varied depending on the applied conditions. Thus, obtained data showed that (+)-limonene and -terpinene were only two quantified monoterpenes. ␣- and ␤pinene were detected at trace levels, while p-cymene was detected in all samples except in sample 5. The highest amount of (+)limonene (4.1 mg/g) was achieved in sample 15 (100 bar, 70 ◦ C and 0.3 kg CO2 /h), while the highest amount of -terpinene was achieved in sample 3 (100 bar, 55 ◦ C and 0.4 kg CO2 /h). Result similar to the highest one for (+)-limonene (4.0 mg/g) was achieved in sample 6 (150 bar, 40 ◦ C and 0.2 kg CO2 /h). Linalool and geraniol were only two acyclic oxygenated monoterpenes detected and

quantified in CS extracts. The highest yield of linalool (717.0 mg/g) was achieved in sample 3 (100 bar, 55 ◦ C and 0.4 kg/h of CO2 ). On the other hand, the highest yield of geraniol (10.7 mg/g) was detected in the sample 15 obtained under the 100 bar, 70 ◦ C and 0.3 kg/h of CO2 . Camphor, eucalyptol and ␣-terpineol were quantified in all CS extracts, while terpinen-4-ol was detected only in samples 1, 3 and 4. The highest amount of camphor (21.0 mg/g) was detected in the sample 3 (100 bar, 55 ◦ C and 0.4 kg/h of CO2 ), ␣-terpineol (6.1 mg/g) was detected in the sample 11 (100 bar, 55 ◦ C and 0.2 kg/h of CO2 ), while maximal yield of eucalyptol (3.2 mg/g) was achieved in sample 10 (150 bar, 55 ◦ C and CO2 flow rate of 0.3 kg/h). As far as aromatic oxygenated monoterpenes are concerned, eugenol was quantified in samples 11, 14 and 15, while methyl chavicol was quantified in most of the samples. On the other hand, carvacrol was detected in all fifteen samples in rather trace amounts. The highest yield of eugenol (20.7 mg/g) was detected in sample 15 (100 bar, 70 ◦ C and 0.3 kg/h of CO2 ), while the highest yield of methyl chavicol (18.2 mg/g) was achieved in sample 11 at 100 bar, 55 ◦ C and CO2 flow rate of 0.2 kg/h. Explanation of such diversity of chemical composition of obtained CS extracts may be the structural diversity of compounds which affects their solubility in supercritical CO2 . Thus, limonene and -terpinene possess the same chemical formula (C10 H16 ), as well as geraniol and linalool, ␣-terpineol and eucalyptol (C10 H18 0), but they differ in their structure among themselves. Chemical formulas and structure of quantified compounds in CS extracts are presented in Table 7. Presented structures of (+)-limonene and -terpinene indicated that they differ in position of double bond in the structure. This difference is the most probable cause of their different solubility under the following conditions. Solubility of limonene under this conditions is in an agreement with literature data which indicated that this compound is highly or completely miscible with supercritical CO2 under the 100 bar and 50 ◦ C (Di Giacomo et al., 1989; Matos et al., 1989; Reverchon, 1997). On the other hand, geraniol and linalool are differing in position of hydroxyl functional group in their structure. While geraniol is primary alcohol, linalool is tertiary alcohol. Different position of hydroxyl functional group in those two oxygenated monoterpenes influence their solubility in supercritical CO2 . Obtained results (Table 6) showed that geraniol was better extracted at higher temperature, while linalool was better extracted at lower temperature. Such behavior of these two compounds could be explained by the occurrence of self-association of aliphatic alcohols (Tufeu et al., 1993). Relationship between the structure, association and solubility of alcohols in supercritical CO2 was established showing that with increase of branching association decrease, while solubility increase (Friedrich and Schneider, 1989). Consequently, the higher temperature would be required for extraction of geraniol as a primary alcohol. Structures in Table 7 showed that ␣-terpineol is tertiary alcohol with one double bond in the ring. Due to branching, suitable position of hydroxyl group and presence of double bond, this alcohol would exhibit low level of association and consequently extracted under the low pressure and temperature (Dandge et al., 1985; Friedrich and Schneider, 1989; Tufeu et al., 1993). Camphor pos-

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359

Table 6 Chemical profile of SFE extracts of coriander seeds. Compound

Content in sample (mg/g) 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Cyclic monoterpenes (+)-Limonene ␣-Pinene ␤-Pinene -Terpinene p-Cymene

1.0 <0.1 <0.1 <0.1 D

1.0 <0.1 <0.1 <0.1 D

2.0 <0.1 <0.1 3.0 D

1.0 <0.1 <0.1 <0.1 D

<0.1 <0.1 <0.1 <0.1 ND

4.0 <0.1 <0.1 1.0 D

1.0 <0.1 <0.1 <0.1 D

<0.1 <0.1 <0.1 <0.1 D

<0.1 <0.1 <0.1 <0.1 D

<0.1 <0.1 <0.1 2.2 D

1.0 <0.1 <0.1 <0.1 D

1.0 <0.1 <0.1 <0.1 D

<0.1 <0.1 <0.1 <0.1 D

<0.1 <0.1 <0.1 1.1 D

4.1 <0.1 <0.1 2.1 D

Acyclic oxygenated monoterpenes Geraniol Geranyl acetate Linalool Nerol

<0.1 ND 441.0 ND

<0.1 ND 291.0 D

3.0 D 717.0 D

<0.1 ND 412.0 ND

1.0 ND 322.0 ND

<0.1 ND 400.0 ND

<0.1 ND 302.0 ND

<0.1 ND 322.0 ND

<0.1 ND 215.0 ND

1.0 ND 264.0 ND

5.2 ND 642.0 ND

<0.1 ND 155.0 ND

<0.1 ND 257.1 ND

2.8 ND 269.0 ND

10.7 ND 608.2 ND

Cyclic oxygenated monoterpenes Camphor Eucalyptol Terpinen-4-ol ␣-Terpineol

9.0 <0.1 D 1.0

4.1 <0.1 ND <0.1

21.0 <0.1 D 2.0

1.0 <0.1 D 1.0

8.0 <0.1 ND 1.0

1.0 1.0 ND 1.0

6.1 <0.1 ND 1.2

1.2 1.0 ND <0.1

5.0 1.2 ND <0.1

9.1 3.2 ND <0.1

10.9 <0.1 ND 6.1

7.2 <0.1 ND 1.1

3.7 <0.1 ND <0.1

2.3 <0.1 ND <0.1

9.6 1.2 ND 4.2

Aromatic oxygenated monoterpenes Carvacrol Eugenol Methyl chavicol

<0.1 <0.1 1.0

<0.1 <0.1 1.0

<0.1 <0.1 2.0

<0.1 <0.1 <0.1

<0.1 <0.1 <0.1

<0.1 <0.1 <0.1

<0.1 <0.1 <0.1

<0.1 <0.1 <0.1

<0.1 <0.1 2.1

<0.1 <0.1 7.2

<0.1 2.0 18.2

<0.1 <0.1 <0.1

<0.1 <0.1 7.3

<0.1 2.9 2.9

<0.1 20.7 13.2

Furanoids cis-Linalool oxide trans-Linalool oxide Acyclic oxygenated monoterpenes Cyclic oxygenated monoterpenes Aromatic oxygenated monoterpenes Oxygenated monoterpenes Monoterpenes Total

ND D 441.0 10.0 1.0 452.0 1.0 453.0

D D 291.0 4.1 1.0 296.1 1.0 297.1

D D 720.0 23.0 2.0 745.0 5.0 750.0

D D 412.0 2.0 <0.1 414.0 1.0 415.0

D D 323.0 9.0 <0.1 332.0 <0.1 332.0

D D 400.0 3.0 <0.1 403.0 5.0 408.0

D D 302.0 7.3 <0.1 309.3 1.0 310.3

D D 322.0 2.2 <0.1 324.2 <0.1 324.2

D D 215.0 6.2 2.1 223.3 <0.1 223.3

D D 265.0 12.3 7.2 284.5 2.2 286.7

D D 647.2 17.0 20.2 684.4 1.0 685.4

D D 155.0 8.3 <0.1 163.3 1.0 164.3

D D 257.1 3.7 7.3 268.1 <0.1 268.1

D D 271.8 2.3 5.8 279.9 1.1 281.0

D D 618.9 15.0 33.9 667.8 6.2 674.0

Fig. 2. GC chromatograms of samples 3, 11 and 15.

sesses keto group in the structure, while eucalyptol is saturated cyclic ether. Aldehydes and ketones are soluble in supercritical CO2 , while the cyclic structure and absence of double bonds negatively affects the solubility of eucalyptol, although it possesses side groups and ether functional group (Dandge et al., 1985). As far as oxygenated monoterpenes are concerned, both compounds, eugenol and methyl chavicol, possess the propenyl and methoxy groups attached to phenyl ring, while eugenol possesses additional

hydroxyl group. Generally, the presence of hydrocarbon group and etherified hydroxyl group increase solubility (Dandge et al., 1985). In this case, presence of 2-propenyl and methoxy groups increase the solubility of methyl chavicol in supercritical CO2 , while presence of free hydroxyl group in eugenol modified its solubility requiring the higher temperature. In summary, the highest yields of acyclic oxygenated monoterpenes (720.0 mg/g) and cyclic oxygenated monoterpenes

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Table 7 Molecular formulas and structures of quantified compounds in CS extracts. Compound

Molecular formula

(+)-Limonene

C10 H16

-Terpinene

C10 H16

Linalool

C10 H18 O

Geraniol

C10 H18 O

Eucalyptol

C10 H18 0

␣-Terpineol

C10 H18 0

Camphor

C10 H16 0

Eugenol

C10 H12 02

Methyl chavicol

C10 H12 0

Structure

Table 8 Antioxidant activity of CS extracts. Sample

IC50 (mg/mL)

ILP50 (mg/mL)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

5.626 2.726 11.984 5.897 5.643 2.364 3.132 5.032 3.696 2.794 10.697 7.885 5.269 3.277 7.323

0.352 0.408 0.873 0.264 0.283 1.546 0.234 0.176 0.215 0.156 0.138 0.340 0.106 0.150 0.101

(23.0 mg/g), as well as yield of total oxygenated monoterpenes were achieved at 100 bar, 55 ◦ C and 0.4 kg/h of CO2 (sample 3, Fig. 2), while the highest yields of aromatic oxygenated monoterpenes (33.9 mg/g) and monoterpenes (6.2 mg/g) were achieved under 100 bar, 70 ◦ C and 0.3 kg/h of CO2 (sample 15, Fig. 2). Amount of 750.0 mg/g was the highest total yield of CS extract (100 bar, 55 ◦ C and CO2 flow rate of 0.4 kg/h) and was achieved in sample 3 (Fig. 2). It could be noticed that low pressure value was beneficial for all class of monoterpenes, while temperature and CO2 flow rate differed. 3.5. Antioxidant activity Antioxidant activity was determined by DPPH assay and lipid peroxidation test. Lower IC50 and EC50 values indicated higher antioxidant activity. Obtained results for the assays are presented in Table 8. Measured values of IC50 ranged from 2.364

to 11.984 mg/mL. The highest antioxidant activity was achieved at the following conditions: 150 bar, 40 ◦ C and 0.2 kg/h of CO2 , while the lowest antioxidant activity was detected in the sample obtained at 100 bar, 55 ◦ C and 0.4 kg/h of CO2 . Comparing obtained results with results of previously conducted studies on antioxidant activity of CS extracts obtained by SFE technique revealed the similar activity of SFE extracts. Obtained extracts (experimental conditions: pressure in range of 115.5–279.5 bar, temperature in range of 37.85–57.85 ◦ C and CO2 flow rate of 0.08 kg/h) in concentration of 2.5 mg/mL expressed antioxidant activity in the range of 32.0–57.4% of DPPH scavenging (Yepez et al., 2002). On the other hand, extracts obtained using ultrasound-assisted (UAE) extraction showed antioxidant activity in concentration range of 0.02479–0.04183 mg/mL (for 70% ethanolic extracts), while aqueous extracts obtained by the same extraction technique exhibited activity in concentration range of 0.07499–0.1007 mg/mL (Zekovic´ et al., 2015). Extracts obtained during the optimization of microwave-assisted extraction (MAE) expressed activity against DPPH radical in concentration range of 0.0302–0.0665 mg/mL (Zekovic´ et al., 2016), while the subcritical water extracts (SWE) exhibited activity in concentration range of 0.01706–0.06336 mg/mL (Zekovic´ et al., 2014). Comparing the activity obtained in this study with activity of CS extracts obtained by other extraction techniques, it could be concluded that SFE extracts exhibited the lowest activity toward DPPH radical. Reason for such difference in activity against DPPH radicals may lie in fact that UAE, MAE and SCW techniques provide extracts with high content of polyphenolic compounds unlike the SFE technique which mostly isolate volatile oil components and other nonpolar compounds such are fatty acids. Lipid peroxidation represents a series of chain reactions which may be initiated by hydroxyl radical, alkoxyl radicals, peroxyl radicals, and peroxynitrite (Dasgupta and Klein, 2014). As a result of such reactions peroxyl and alkoxyl radical are formed (Li, 2011). Both radical species, which represent strong oxidants, are capable to damage cell membrane, oxidize proteins and DNA molecules and are responsible for propagation reaction of lipid peroxidation process (Dasgupta and Klein, 2014; Li, 2011). Peroxyl radicals are also capable to react among each other producing singlet oxygen which is also highly reactive species capable of damaging biomolecules (Miyamoto et al., 2007). For those reasons, it is very important to establish the activity of obtained extracts against above described reactive species. Activity of CS extracts range from 0.101 mg/mL to 1.546 mg/mL (Table 8). The highest activity was achieved in extract obtained at 100 bar, 70 ◦ C and 0.3 kg/h of CO2 . On the other hand, the lowest activity was achieved at 150 bar, 40 ◦ C and CO2 flow rate of 0.2 kg/h. Comparing results of this test with the results obtained from DPPH assay, it could be noticed that extract samples exhibited higher activity against lipid peroxidation than against DPPH radical. Sample obtained at 150 bar, 40 ◦ C and CO2 flow rate of 0.2 kg/h exhibited the highest activity against DPPH radical, while in the case of lipid peroxidation showed the lowest activity. Samples with lowest activities against DPPH radical and lipid peroxidation were obtained at different operational conditions (100 bar, 55 ◦ C, 0.4 kg/h of CO2 and 150 bar, 40 ◦ C and CO2 flow rate of 0.2 kg/h, respectively). The highest activity against lipid peroxidation (sample 15) exhibited the sample with the highest content of monoterpenes (6.2 mg/g) and aromatic oxygenated monoterpenes (33.9 mg/g), while the lowest activity was achieved by the sample (sample 6) with the low content of aromatic oxygenated monoterpenes. Sample 11, which possess high content of aromatic oxygenated monoterpenes (20.7 mg/g), also exhibited high activity against lipid peroxidation. This might indicate that aromatic oxygenated monoterpenes are one of the responsible class of the compounds responsible for activity against lipid peroxidation.

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Compounds presented in tested SFE extracts were proved to be better scavenger of peroxyl and alkoxyl radicals than DPPH radical. 4. Conclusion Optimization of extraction process was successfully conducted using the RSM. Second-order polynomial model was able to adequately describe extraction process and antioxidant activity. Obtained results confirmed the influence of all three parameters on extraction process, while pressure exhibited the strongest influence. The highest extraction yield was predicted at the almost highest pressure and CO2 flow rate and at the almost lowest temperature. Examination of the influence of extraction parameters of SFE process on yield and chemical composition of CS essential oil revealed their significant influence on the process itself. Obtained results showed that combined effect of pressure and temperature on density of CO2 and vapor pressure directly influence and modulate the solubility of volatile compound in subcritical CO2 , thus affecting their yield and efficiency of the extraction process. Chemical profile of obtained samples demonstrated the significance of parameters. Linalool, the most abundant compound in samples, achieved its highest yield at the 100 bar, 55 ◦ C and 0.4 kg/h of CO2 . The highest total yield was achieved at the same conditions. Generally, lower pressure, temperature and CO2 flow rate were showed as better condition for acyclic and cyclic oxygenated monoterpenes, while higher temperature was beneficial for aromatic oxygenated monoterpenes and monoterpenes yield. Different requirements in operational conditions is connected with difference in structure of monoterpene classes. This relationship between structure and solubility was described in this study. Acknowledgement The financial support of the Ministry of Education, Science and Technological development of the Republic of Serbia is gratefully acknowledged (Project No. TR31013). References Akgun, M., Akgun, N.A., Dincer, S., 1999. Phase behaviour of essential oil components in supercritical carbon dioxide. J. Supercrit. Fluids 15, 117–125. Aluko, R.E., McIntosh, T., Reaney, M., 2001. Comparative study of the emulsifying and foaming properties of defatted coriander (Coriandrum sativum) seed flour and protein concentrate. Food Res. Int. 34, 733–738. Anitescu, G., Doneanu, C., Radulescu, V., 1997. Isolation of coriander oil: comparison between steam distillation and supercritical CO2 extraction. Flavour Fragr. J. 12, 173–176. Bas¸, D., Boyacı, I˙ .H., 2007. Modeling and optimization I: usability of response surface methodology. J. Food Eng. 78, 836–845. Bajpai, M., Mishra, A., Prakash, D., 2005. Antioxidant and free radical scavenging activities of some leafy vegetables. Int. J. Food Sci. Nutr. 56, 473–481. ˇ ´ ´ D.Z., Jankovic, ´ T., Anaˇckov, Beara, I.N., Lesjak, M.M., Cetojevi c-Simin, D.D., Orˇcic, ´ N.M., 2012. Phenolic profile, antioxidant, G.T., Mimica-Dukic, anti-inflammatory and cytotoxic activities of endemic Plantago reniformis G. Beck. Food Res. Int. 49, 501–507. Bezerra, M.A., Santelli, R.E., Oliveira, E.P., Villar, L.S., Escaleira, L.A., 2008. Response surface methodology (RSM) as a tool for optimization in analytical chemistry. Talanta 76, 965–977. Chen, Q., Yao, S., Huang, X., Luo, J., Wang, J., Kong, L., 2009. Supercritical fluid extraction of Coriandrum sativum and subsequent separation of isocoumarins by high-speed counter-current chromatography. Food Chem. 117, 504–508. Chithra, V., Leelamma, S., 2000. Coriandrum sativum—effect on lipid metabolism in 1,2-dimethyl hydrazine induced colon cancer. J. Ethnopharmacol. 71, 457–463. Döker, O., Salgın, U., S¸anal, I˙ ., Mehmeto˘glu, Ü., C¸alımlı, A., 2004. Modeling of extraction of ˇ-carotene from apricot bagasse using supercritical CO2 in packed bed extractor. J. Supercrit. Fluids 28, 11–19. Dandge, D.K., Heller, J.P., Wilson, K.V., 1985. Structure solubility correlations: organic compounds and dense carbon dioxide binary systems. Ind. Eng. Chem. Prod. Res. Dev. 24, 162–166. Dasgupta, A., Klein, K., 2014. Antioxidants in Food, Vitamins and Supplements. Prevention and Treatment of Disease, 1st ed. Elsevier Inc., London.

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