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Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds
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JTICE-1059; No. of Pages 8 Journal of the Taiwan Institute of Chemical Engineers xxx (2014) xxx–xxx
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Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds J. Prakash Maran a,*, B. Priya b a b
Department of Food Technology, Kongu Engineering College, Perundurai, Erode 638052, TamilNadu, India Department of Food Process Engineering, SRM University, SRM Nagar, Kattankulathur, Chennai 603203, TamilNadu, India
A R T I C L E I N F O
A B S T R A C T
Article history: Received 20 May 2014 Received in revised form 1 October 2014 Accepted 5 October 2014 Available online xxx
The objective of this present study was to develop a suitable supercritical fluid extraction (SFE) method for extraction of oil from muskmelon seed (Cucumis melo). A Box–Behnken response surface design was applied to investigate and optimize the process variables (pressure, temperature, CO2 flow rate and time) on the yield of muskmelon seed oil. A second-order polynomial equation was developed to express the oil yield as a function of independent variables. The maximum oil yield (48.11%) was procured when SFE was carried out at 44 MPa of pressure, 49 8C of temperature, 0.64 g/min of CO2 flow rate and 81 min of extraction time. The total yield and fatty acids composition of muskmelon seed oil extracted by SFE was similar to that of oil extracted by Soxhlet extraction. Physicochemical properties of the oil at optimal SFE condition showed that the extracted oil could be adopted as food oil supplement. The experimental results indicated that SFE technique reduced the solvent consumption and extraction time with no adverse effect on the extraction yield and fatty acid composition of the oil. ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Supercritical fluid extraction Muskmelon seed oil Fatty acid Physicochemical property Optimization
1. Introduction Muskmelon (Cucumis melo) belongs to the Cucurbitaceae family and is one of the popular fruits in the tropical countries. It is originated from Iran and mostly grown in the warmer regions of the world [1]. Normally, after consuming the muskmelon fruit, seeds are thrown away and these seeds are normally restricted and treated as waste products. Seeds of musk melon are usually dried and used to add flavor to Indian dishes and desserts. Melon seeds boost immunity, reduce cardiovascular risks, help in normalizing blood-fat levels and contain essential nutrients for wound healing [2]. It also fights against osteoporosis and promotes healthy teeth and bone growth. These seeds are rich in protein and omega-3 fatty acids [3]. Several reports have been published on the melon seeds composition and its fatty acid profile [2–4] showing higher linoleic acid contents. A demand for vegetable oil is ever increasing, and the world relies mostly on the popular vegetable oil for the preparation of many products, muskmelon seed seems to be an economically viable alternative resource for oil production. Extraction is the most common method used to exploit and recover oil from seeds. Oil is mainly extracted from seeds by press
* Corresponding author. Tel.: +91 4294 226606; fax: +91 4294 220087. E-mail address: [email protected] (J.P. Maran).
and solvent extraction method. Press method is often associated with lower yield and high energy consumption, while solvent extraction often involves longer extraction time. The solvent extraction is accompanied with application of large quantities of organic solvents is undesirable to both consumers and the environment. Thus, to this end, distillation under vacuum was employed and possible degradation of thermally labile compounds in oil and incomplete hexane elimination are the drawbacks of this process. Therefore, it is vital to look for an effective solvent which excludes the aforementioned drawbacks to extract oil from seeds. The use of supercritical fluids as an alternative solvent for seed oil extraction has been attracting widespread interest owing to their particular properties (e.g., liquid-like solvent power, negligible surface tension, and gas-like transport properties), and changes in environmental regulations which foster the utilization of green solvents [5]. In this field, carbon dioxide has been especially adopted as it is essentially non-toxic, non-flammable, low-cost at the industrial level, can be recycled, has easily accessible supercritical conditions, and is totally dissipated from extracts at atmospheric pressure avoiding the necessity of further expensive and harmful refining treatments. Furthermore, CO2 has adequate solvent properties for extraction of triglycerides. In recent years, several researchers have been successfully applied supercritical fluid extraction (SFE) method to extract oil from seeds [5–17]. Furthermore, it is worth noting that, the SFE has been
http://dx.doi.org/10.1016/j.jtice.2014.10.007 1876-1070/ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: Maran JP, Priya B. Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds. J Taiwan Inst Chem Eng (2014), http://dx.doi.org/10.1016/j.jtice.2014.10.007
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proven to reach extraction yield equivalent to those achieved by conventional Soxhlet extraction with n-hexane [18]. An extensive literature analysis reveals that, SFE of oils from various seeds have been extensively studied. However, no studies have been reported on the SFE of total oil from muskmelon seeds. Hence, an attempt was made to develop suitable SFE method for the extraction of total oil from muskmelon seeds. Four factors three levels Box–Behnken response surface design was used in this work to investigate and optimize the process variables (pressure, temperature, CO2 flow rate and time) on the maximum extraction yield of oil. The optimum condition was validated and experimental results were compared with the results predicted by proposed mathematical equation. A comparison study with the results obtained from SFE and Soxhlet extraction was done. Fatty acids composition was analyzed in muskmelon extracts obtained using through both extraction methods to confirm the suitability of SFE as a preparative technique for fatty acid determination. The physical (viscosity, refractive index and color) and chemical (acid, iodine, saponification and peroxide value) properties of oil obtained at optimal SFE condition was also evaluated in this study to facilitate the potential use. 2. Materials and methods 2.1. Materials The musk melon seed used in this study was provided by local musk melon fruit processing industry near Chennai, TamilNadu, India. The seeds were dried at 55 8C for 9 h prior to processing and the chemical composition was determined to be: moisture content (4.3%), crude ash (1.97%), crude protein (23.15%) and crude fiber (12.08%), respectively. The moisture content, crude ash and crude fiber content was determined by using AOAC method. The crude protein content was determined by Kjeldahl method. The dried seeds were ground in a food grinder in order to reduce the size of the samples and to obtain maximum diameter of 500 mm as measured by a sieve. The ground seed was sealed in plastic container and stored in refrigerator prior to extraction. Carbon dioxide gas (99.99%) used for extraction was supplied by Chang Chun Gas (China). Chemicals used for seed oil analysis were hexane, ethanol, chloroform, phenolphthalein indicator, iodine monochloride, glacial acetic acid, acetone, ethyl acetate, acetic acid, phosphoric acid, potassium phosphate, sulfuric acid, carbon tetrachloride, diethyl ether and heptadecanoic acid were purchased from Sigma-Aldrich chemicals, Mumbai. All the chemicals used in this study were analytical grade.
pressure. Extracts obtained by SFE at the different experimental conditions (Table 1) were tested for oil content and the yield was calculated by the following equation: Oil yieldð%Þ ¼
Weight of extracted oil 100 Weight of seed
(1)
2.3. Experimental design and statistical analysis Four factors three levels Box–Behnken response surface design (BBD) was used in this study to investigate and optimize the effect of extraction process variables such as pressure (30–50 MPa, X1), temperature (40–60 8C, X2), CO2 flow rate (0.3–0.9 g/min, X3) and time (60–100 min, X4) on the maximum yield of oil from muskmelon seed. The extraction variables and their ranges were chosen from preliminary experimental results done in our laboratory. The independent variables were coded at three levels (1, 0, 1) for statistical calculation. The experimental design consists of 29 experiments (N = 2K(K 1) + C0, where N is total number of experiments, K is the number of independent variables and C0 is centre points) [19], which was carried out not only in triplicates but also in a randomized order to minimize the effect of unexpected variability in the observed response due to extraneous factors. Average experimental values were computed and shown in Table 1. A multiple regression model (second order polynomial equation) was used to fit the experimental data and the generalized form of that equation is shown as follows: Y ¼ b0 þ
k X
k X
j¼1
j¼1
b jX j þ
b j j X 2j þ
k X X i
bi j X i X j
(2)
< j¼2
where Y is the response; Xi and Xj are variables (i and j range from 1 to k); b0 is the model intercept coefficient; bj, bjj and bij are interaction coefficients of linear, quadratic and the second-order terms, respectively; k is the number of independent parameters (k = 4 in this study) [20]. The model includes linear, quadratic and interaction terms to determine the effect of process variables on the response. In addition the fitted polynomial equation could be used to generate response surface and contour plots in order to visualize the relationship between response and experimental levels of process variables and deduce the optimal condition. Statistical analysis of the experimental data was performed using the Stat ease Design Expert 8.0.7.1 statistical software (Stat-Ease Inc., Minneapolis, USA). 2.4. Soxhlet extraction
2.2. Supercritical fluid extraction of oil A laboratory scale assembled SFE system was used in this study with an extraction cell volume of 500 ml. Twenty five grams of ground musk melon seeds was mixed with glass wool in the ratio of 25:1 (w/w) packed as a cartridge and was placed inside the thermal controlled extraction cell. Liquefied CO2 was introduced into the cartridge through a piston pump with a cooling jacket. Both the pressure and temperature of the cartridge were automatically reached and maintained by a control unit according to settings. After the desired pressure and temperature were reached, the cell was placed in the thermal-controlled extraction cell (oven) and connected to the manifold and restrictors. The system was held for 30 min under the desired conditions, and then carbon dioxide was allowed to flow continuously through the extractor. The flow rate of CO2 was regulated by both the pressurereleasing valve and thermal-controlled restrictor and monitored by a flow meter. Extracts were finally separated from CO2 phase and collected in collector at ambient temperature and atmospheric
In order to compute the efficiency of SFE, Soxhlet extraction was carried out using n-hexane as the solvent. About 10 g of ground muskmelon seeds were placed in a cellulose thimble and transferred to a Soxhlet extractor. The round bottom extraction flask was filled with 150 ml of n-hexane which was heated at 78 8C. Extraction process was continuously run for 8 h. After completion of an extraction, oil was recovered by evaporating solvent using rotary evaporator (Bu¨chi, UK) and residual solvent was removed by flushing 99.9% nitrogen. The oil yield was determined in the same way as in supercritical fluid extraction method as mentioned earlier and the reported values were means of three determinations. 2.5. Fatty acid composition of musk melon seed oil Methylated oil samples were prepared according to the method described by Mitra et al. [21] prior to gas chromatography-flame ionization detector (GC-FID) analysis. The fatty acid composition of
Please cite this article in press as: Maran JP, Priya B. Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds. J Taiwan Inst Chem Eng (2014), http://dx.doi.org/10.1016/j.jtice.2014.10.007
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Table 1 Box–Behnken design matrix with observed and predicted results. Std (order)
Pressure (MPa)
Temperature (C)
CO2 flow rate (g/min)
Time (min)
Oil yield (%) Observed
Predicted
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
30 50 30 50 40 40 40 40 30 50 30 50 40 40 40 40 30 50 30 50 40 40 40 40 40 40 40 40 40
40 40 60 60 50 50 50 50 50 50 50 50 40 60 40 60 50 50 50 50 40 60 40 60 50 50 50 50 50
0.6 0.6 0.6 0.6 0.3 0.9 0.3 0.9 0.6 0.6 0.6 0.6 0.3 0.3 0.9 0.9 0.3 0.3 0.9 0.9 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6
80 80 80 80 60 60 100 100 60 60 100 100 80 80 80 80 80 80 80 80 60 60 100 100 80 80 80 80 80
18.04 35.07 18.04 26.05 31.06 34.07 25.05 37.07 27.05 36.07 21.04 41.08 32.06 11.02 25.05 36.07 14.03 36.07 31.37 38.09 35.10 26.05 27.05 26.05 46.09 46.34 48.10 47.09 45.09
18.16 36.48 17.82 27.12 31.30 35.53 24.78 38.03 28.14 36.44 20.62 39.94 32.10 11.22 24.80 35.99 14.21 35.69 30.61 36.76 33.43 24.56 27.40 26.57 46.49 46.49 46.49 46.49 46.49
the concentrated extracted oil at optimal condition was analyzed using an Agilent 6890N GC–FID (Agilent Technologies, USA), equipped with a HP-Innowax capillary column (30 m 0.25 mm i.d., 0.32 m film thickness, Agilent Technologies, CA, USA). The column was held at 150 8C for 5 min and raised to 220 8C at a rate of 4 8C/min. The injector and detector temperatures were held at 250 and 260 8C, respectively. Nitrogen was used as the carried gas at a flow rate of 1.0 ml/min and the split ratio of 100:1. The fatty acids peaks were identified by comparison of retention times with retention times of standards. Results were expressed as mass of fatty acid or fatty acid group (g) in 100 g of fatty acids. 2.6. Physicochemical analysis of muskmelon seed oil AOAC methods [22] were used to determine the acid, iodine, peroxide and saponification value of the extracted muskmelon seed oil. Color of the oil was measured by using Hunter lab color coordinates (L, a and b) with a colorimeter (Color QUEST XE 3399). Hand held refractometer was used to find out the refractive index of oil. The viscosity of the oil was determined using Brookfield viscometer at room temperature. All analysis was carried out with the oil extracted at optimal condition. 3. Results and discussion 3.1. Experimental data analysis Experimental data was obtained according to the BBD in order to study and investigate the individual and interactive effect of the process variables (pressure (30–50 MPa, X1), temperature (40– 60 8C, X2), CO2 flow rate (0.3–0.9 g/min, X3) and time (60–100 min, X4)) on the maximum yield of oil from muskmelon seed and the results are exhibited in Table 2. The experimental data was analyzed and fitted to various models such as linear, interactive
Residual error
Internally studentized residual
Cook’s distance
0.12 1.41 0.21 1.07 0.24 1.46 0.27 0.96 1.09 0.37 0.42 1.14 0.03 0.19 0.25 0.09 0.18 0.38 0.76 1.33 1.67 1.49 0.35 0.52 0.40 0.40 1.60 0.60 1.40
0.15 1.73 0.26 1.31 0.29 1.79 0.32 1.17 1.33 0.45 0.52 1.40 0.04 0.24 0.30 0.11 0.22 0.47 0.93 1.62 2.04 1.82 0.42 0.64 0.35 0.35 1.42 0.53 1.24
0.002 0.279 0.006 0.161 0.008 0.299 0.010 0.128 0.165 0.019 0.025 0.182 0.000 0.005 0.009 0.001 0.005 0.021 0.080 0.246 0.389 0.311 0.017 0.039 0.002 0.002 0.033 0.005 0.026
(2FI), quadratic and cubic, respectively. From the results (Table 2), it was observed that, linear and interactive (2FI) models showed lower R2, adjusted R2, predicted R2 and also high p-values, when compared with quadratic model. Cubic model was found to be aliased. Therefore the quadratic model incorporating linear, interactive and quadratic terms was chosen to describe and study the effect of process variables on the yield of oil from muskmelon seed [23]. 3.2. Model fitting and statistical analysis A second-order polynomial equation was fitted to the experimental data to develop a mathematical model, which will assist in predicting the extraction efficiency. The developed regression model obtained in terms of coded factors is given below: Oil yieldð%Þ ¼ 46:49 þ 6:91X 1 2:42X 2 þ 4:37X 3 1:00X 4 2:25X 1 X 2 3:83X 1 X 3 þ 2:75X 1 X 4 þ 8:02X 2 X 3 þ2:01X 2 X 4 þ 2:25X 3 X 4 9:15X12 12:44X22
(3)
8:02X32 6:06X42 Pareto analysis of variance (ANOVA) was used to analyze the experimental data and the results are listed in Table 3. The higher model F-value (123.73) and the associated lower p-values (p < 0.0001) demonstrated the significance of developed models and also indicate the best fit of the developed model. The high R2 (0.992), adj-R2 (0.984) and pre-R2 (0.962) values clearly demonstrates the model precision in exhibiting the relationship between the response and independent variables [24]. Low values of coefficient of variance (3.99) displayed the high degree of precision and good reliability of the conducted experiments [25]. In this study, the adequate precision (signal to noise ratio) was found to be >38 for response, which indicates the best fit of developed models [26].
Please cite this article in press as: Maran JP, Priya B. Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds. J Taiwan Inst Chem Eng (2014), http://dx.doi.org/10.1016/j.jtice.2014.10.007
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Table 2 Adequacy of model tested for response (oil yield). Sum of squares
Source
Sequential model sum of squares 29,197.37 Mean Linear 883.93 2FI 402.95 Quadratic 1488.48 Cubic 11.72 Residual 10.71 31995.17 Total Lack of fit tests Linear 1908.64 2FI 1505.69 Quadratic 17.21 Cubic 5.49 Pure error 5.22 Model summary statistics Linear 8.93 2FI 9.16 Quadratic 1.27 Cubic 1.34
DF
Mean square
1 4 6 4 8 6 29
29197.37 220.98 67.16 372.12 1.47 1.78 1103.28
20 14 10 2 4
95.43 107.55 1.72 2.74 1.31
0.316 0.460 0.992 0.996
F value
Prob > F
Remarks Suggested aliased
0.202 0.160 0.984 0.982
2.77 0.80 232.25 0.82
0.0503 0.5824 <0.0001 0.6129
73.12 82.40 1.32 2.10
0.0004 0.0003 0.4247 0.2377
0.122 0.087 0.962 0.715
2457.82 2555.53 107.29 798.25
Suggested aliased
Suggested aliased
Table 3 ANOVA and significance of regression coefficients. Source
Coefficient estimate
Sum of squares
Degree of freedom
Model X1 X2 X3 X4 X12 X13 X14 X23 X24 X34 X12 X22 X32 X42 Residual Std. Dev. Mean C.V.% Press
46.49 6.91 2.42 4.37 1.00 2.25 3.83 2.75 8.02 2.01 2.25 9.15 12.44 8.02 6.06
2775.36 572.29 70.52 229.02 12.10 20.33 58.75 30.35 257.03 16.16 20.33 543.22 1004.50 417.58 237.98 22.43
14 1 1 1 1 1 1 1 1 1 1 1 1 1 1 14
1.27 31.73 3.99 107.29
3.3. Diagnostics of model adequacy Generally, it is important to confirm that the fitted model gives a sufficient approximation to the actual values. Unless the model shows a satisfactory fit, proceeding with an investigation and optimization of the fitted response surface likely gives poor or misleading results [27]. In addition to determination coefficient, adequacy of the model was also evaluated by the residuals (difference between the observed and the predicted response value) and the influence plots for the experimental data obtained from this study. Residuals are thought as elements of variation, unexplained by the fitted model and it is expected to occur according to a normal distribution. Normal probability plots are a suitable graphical method for judging residuals normality. The observed residuals are plotted against the expected values, as they lie reasonably close on a straight line and show no deviation of the variance (Fig. 1a). It can be conformed that, the data are normally distributed [28]. By constructing residuals plot, a check was made to analyze the experimental data to find out its satisfactory fit and the plot shows that, all the data points lie within the limits (Fig. 1b). Diagnostic plots such as predicted versus actual (Fig. 1c) help us to
Standard error 0.57 0.37 0.37 0.37 0.37 0.63 0.63 0.63 0.63 0.63 0.63 0.50 0.50 0.50 0.50 R2 Adj-R2 Pred-R2 Adequate precision
Mean square
F value
p-Value
198.24 572.29 70.52 229.02 12.10 20.33 58.75 30.35 257.03 16.16 20.33 543.22 1004.50 417.58 237.98 1.60 0.992 0.984 0.962 38.751
123.73 357.18 44.01 142.94 7.55 12.69 36.67 18.94 160.42 10.09 12.69 339.04 626.94 260.63 148.53
<0.0001 <0.0001 <0.0001 <0.0001 0.0157 0.0031 <0.0001 0.0007 <0.0001 0.0067 0.0031 <0.0001 <0.0001 <0.0001 <0.0001
evaluate the model suitability and to analyze the relationship between predicted and experimental values [29]. The data points on this plot lie reasonably close to the straight line which indicates that an adequate agreement between real data and the data obtained from the models. Cook’s distance is used to diagnose and identify the possible influential outliers in the experimental data. Since the Cook’s distance values are in the determined range (Fig. 1d), there is no strong evidence of influential outliers in the observed data. Hence, trends observed in Fig. 1 revealed that, no obvious patterns were found and residuals appeared to be randomly scattered. 3.4. Response surface analysis In this study, the oil recovery was varied markedly from 11.02% to 48.096% with different levels of factors for SFE of muskmelon seed oil. To understand and study the individual and interaction effect of independent variables on the response, three dimensional (3D) response surface plots were constructed from the developed model. The model has more than two factors. So, the 3D plots have drawn by maintaining two factors at its constant level (in turn at its
Please cite this article in press as: Maran JP, Priya B. Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds. J Taiwan Inst Chem Eng (2014), http://dx.doi.org/10.1016/j.jtice.2014.10.007
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3.4.2. Effect of temperature As temperature increases, enhancement of extraction efficiency may be related to the increased vapor pressures and accelerated thermal desorption of the oil from the seed matrix. There are two distinguished trends observed in regard to the overall yield (Fig. 2a, d and e). In the range of 40–50 8C, the yield increases with a mild slope until it reaches its maximum value (48.12%), and a further increase up to 60 8C cause the decrease in yield. These two different regions of yields can be attributed to retrograde solubility in which the counter effect of solute vapor pressure and supercritical fluid density are affecting the extraction yield. In other words, in the first region of increasing temperature, the solute vapor pressure enhancement overlaps the supercritical fluid density decrease up to 50 8C where the maximum yield is obtained. At 50 8C, the retrograde solubility is reached in which the effect of solute vapor pressure becomes equivalent to the effect of CO2 density and subsequently beyond that the effect of density decrease prevails vapor pressure enhancement. Similar solubility behavior has been reported for other vegetable and seed oils [34]. 3.4.3. Effect of SC-CO2 fluid flow rate The oil recovery increased from low to medium level (code = 1 to 0) supercritical fluid flow rate (0.3–0.6 g/min). This was because during this stage, the extraction of the surface attached oil occurred and increasing the flow rate reduces the film thickness around the solid particles and this leads to lower external mass transfer resistance around the seed [35] and consequently enhanced oil extraction recovery. However, further increased in supercritical fluid flow rate could started to decrease the oil recovery (Fig. 2b, d and f). This was because this extraction was controlled mainly by diffusion of oil from the cell matrix and increasing the flow rate could not manipulate the rate of diffusion.
Fig. 1. Diagnostic plots of model adequacy.
3.4.4. Effect of extraction time The extraction of oil was increased dramatically with increasing extraction time and reached a maximum value at 80 min of fractionation then decreased gradually as the extraction time increased (Fig. 2c, e and f). Higher amount of oil recovery at initial extraction time (80 min) was caused by the higher extractable compounds contained in the surface of the seeds and supercritical CO2 had to diffuse deeply into the inner cell of the seeds to dissolve the extractable substance and increased the oil yield. However, further increase in the extraction times up to 100 min resulted in only a little change in the oil yield of oil. 3.5. Optimum operating conditions for maximizing the oil yield
central level), whereas the other two factors were varied in their range in order to understand their main and interactive effects on the dependent variables and the results were shown in Fig. 2. 3.4.1. Effect of pressure Pressure is one of the important factors in extraction of oil using SFE technique. From the results, it was observed that, the oil recovery was increased from 30 MPa to 43 MPa and then decreased (Fig. 2a–c). Increase in pressure up to 43 MPa could increase the fluid density, decreasing the distance between the molecules by the rupturing effect of pressure and thereby strengthening interactions between the fluid and matrix [30]. Therefore high pressure caused the compression of the seeds and extractable compounds in the seeds were easily dissolved in supercritical CO2. This experimental observation was attributed to the increased solute/solvent attractive interactions resulting from the highly compressed CO2 at high operating pressures [31]. These results are in agreement with the SC–CO2 extraction of rosehip seed oil [32] and borage seed oil [33]. Beyond 43 MPa, increasing the pressure decreased the essential oil recovery.
Regression model (Eq. (3)) was used to determine the optimum extraction condition for SC-CO2 extraction of oil from muskmelon seed. In order to obtain the optimum values, first and second order derivatives of the regression equation (Eq. (3)) were derived with respect to X1, X2, X3 and X4, respectively. The first order derivative of Eq. (3) gives the following equations:
@Y ¼ 6:91 18:3X 1 2:25X 2 3:83X 3 þ 2:75X 4 @X 1
(4)
@Y ¼ 2:42 2:25X 1 24:88X 2 þ 8:02X 3 þ 2:01X 4 @X 2
(5)
@Y ¼ 4:37 3:83X 1 þ 8:02X 2 16:04X 3 þ 2:25X 4 @X 3
(6)
@Y ¼ 1:00 þ 2:75X 1 þ 2:01X 2 þ 2:25X 3 12:12X 4 @X 4
(7)
Please cite this article in press as: Maran JP, Priya B. Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds. J Taiwan Inst Chem Eng (2014), http://dx.doi.org/10.1016/j.jtice.2014.10.007
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Fig. 2. Response surface plots showing the interactive effect of process variables on oil yield.
Second order derivatives of Eqs. (4–7) yield the following equations: 2
@ Y ¼ 18:3 @X12
(8)
@2 Y ¼ 16:04 @X32
(10)
@2 Y ¼ 12:12 @X42
(11)
2
@ Y ¼ 24:88 @X22
(9)
Since all the second order derivatives showed negative values, it signifies the applicability of maximization. Thus Eqs. (4–7) were
Please cite this article in press as: Maran JP, Priya B. Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds. J Taiwan Inst Chem Eng (2014), http://dx.doi.org/10.1016/j.jtice.2014.10.007
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equated with zero and solved for X1, X2, X3 and X4 to get the maximum values: 6:91 18:3X 1 2:25X 2 3:83X 3 þ 2:75X 4 ¼ 0
(12)
2:42 2:25X 1 24:88X 2 þ 8:02X 3 þ 2:01X 4 ¼ 0
(13)
4:37 3:83X 1 þ 8:02X 2 16:04X 3 þ 2:25X 4 ¼ 0
(14)
1:00 þ 2:75X 1 þ 2:01X 2 þ 2:25X 3 12:12X 4 ¼ 0
(15)
Algebraic solution to the above four equations gave in coded form of optimal condition was: X1 = 0.401 MPa, X2 = 0.085 8C, X3 = 0.121 g/min, X4 = 0.034 min. The corresponding experimental parametric values were: 44.01 MPa (pressure), 49.15 8C (temperature), 0.64 g/min (flow rate) and 80.69 min (extraction time), respectively. Under the optimal conditions, the predicted yield was 48.13%. The optimal point as obtained above can be a point of maximum or minimum or a saddle point response. In order to determine the nature of the optimal point, the regression equation was transformed to the canonical form and the Eigen values were computed using MATLAB 7.1 software. The Eigen values obtained were negative (X1 = 14.8194, X2 = 10.9609, X3 = 5.7261 and X4 = 4.1636) and it indicates that, the determined optimal condition was a maximum point. 3.6. Validation of optimized condition However, considering the operability in actual production, the optimal conditions can be modified as follows: 44 MPa of pressure, 49 8C of temperature, 0.64 g/min of flow rate and 81 min of extraction time, respectively. To compare the predicted results with experimental value, the experiments (triplicates) were carried out at the modified optimal extraction conditions. Under the modified conditions, the experimental yield of oil was 48.11 0.04% and was well matched with predicted values. As a result, Box–Behnken design was considered to be an accurate and decisive tool for predicting the maximum extraction yield of oil from muskmelon seed using SFE technique. 3.7. Comparison between SFE and Soxhlet extraction To investigate competence of SFE as a method for extraction of oil from muskmelon seed, yield of oil obtained under optimal SFE conditions was compared with total oil content extracted by Soxhlet method. SFE gave slightly higher extraction yield (48.11 0.04%) than Soxhlet (46.83 0.29%). Comparison of the two methods demonstrated that the SFE method provides a slightly higher yield with major reduction in solvent and energy consumption.
Fig. 3. GC-chromatograms for muskmelon seed oil extracted by Soxhlet (a) and SFE method (b).
easily synthesized in the human system and must be supplied externally through the diet, and muskmelon seed oil can be a good nutritional supplement as a source of linoleic acid. The oil has also been suggested to be used as a cooking or salad oil, or used in the preparation of margarine. It was concluded that, SFE appears to be a good alternative for other methods of extraction conventionally used in sample preparation for fatty acid determination. 3.9. Physicochemical properties of SFE extracts of oil The physical properties (viscosity, refractive index and color) and chemical properties (acid value, iodine value, peroxide value and saponification value) of the SFE muskmelon seed oil were determined in order to characterize the oil. The physical state of oil at room temperature is liquid. The seed oil has a low viscosity at room temperature with 14.07 0.13 cP, while it gives the refractive index reading of 1.38 0.01. Hunterlab coordinates (a = 1.46 0.29, b = 18.32 0.91 and L = 39.27 1.58) indicated that, the oil hold green to yellowish color. Peroxide value (3.46 0.42 milli-equivalent of peroxide/kg of oil) of the oil was very low, which showed the higher oxidative stability of the seed oil. The iodine value was high (124 3.82 g of I2/100 g of oil) and designated a high degree of unsaturation. The combination of high iodine value and low peroxide value demonstrate that the muskmelon seed oil possesses the desirable qualities of edible oil. Saponification number, 204 3.46 (mg of KOH/g of oil), observed for the oil was within range 175–250 normally found in other seed oils such as raspberry seed, safflower, sunflower and corn [36]. The acid
3.8. Fatty acid composition The fatty acid determination and composition of SFE and Soxhlet extracts of muskmelon seed oil was tested using GC-FID and the result was shown in Fig. 3. From Fig. 3, it was concluded that, no obvious difference were observed in the fatty oil composition of the oils extracted by the two methods. The results indicated that, five leading fatty acids were present in the recovered oil from muskmelon seed in both method and the results were shown in Table 4. The results showed that, the muskmelon seed oil is rich source of linoleic acid (C18:2), which accounting for 47% of the total oil. The ratio between unsaturated and saturated fatty acids (USFA/SFA ratio) results showed that, no significant differences in the oil profiles extracted by SFE and Soxhlet methods. The essential fatty acids like linoleic acid are not
Table 4 Comparison between fatty acid compositions (%w/w) of oil extracted by SFE and Soxhlet method. Fatty acid
Palmitic acid (C16:0) Palmitoleic acid (C16:1) Stearic acid (C18:0) Oleic acid (C18:1) Linoleic acid (C18:2) Saturated fatty acid (SFA) Monounsaturated fatty acid (MUFA) Polyunsaturated fatty acid (PUFA) USFA/SFA
Muskmelon seed oil SFE method
Soxhlet method
12.24 2.09 9.17 29.43 47.07 21.41 31.52 47.07 3.67
13.38 1.73 9.61 30.62 44.66 22.99 32.35 44.66 3.35
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value of the oil was 5.08 0.34 (mg of NaOH/g of oil). Therefore, both physical and chemical characteristics of the oil demonstrated that, the muskmelon seed oil is a good candidate for edible oil or supplement. 4. Conclusions Muskmelon (C. melo) seed oil was extracted by SFE and evaluated the quality (fatty acid composition and physicochemical properties) of the extracted oil. Four factors three levels BBD was successfully employed to study and optimize the extraction of oil from muskmelon seed. From the results, it was observed that, extraction yield was affected by supercritical CO2 extraction conditions such as pressure and temperature. The high regression coefficient of second order polynomial model was developed from the experimental data and it was fitted well with observed values. The oil yield was effectively modeled as a function of independent variables (pressure, temperature, CO2 flow rate and time) and the maximum oil yield (48.11%) was obtained at 44 MPa of pressure, 49 8C of temperature, 0.64 g/min of flow rate and 81 min of extraction time. The total yield of the extract using SFE and hexane Soxhlet extraction was 48.11% and 46.83%, respectively. The fatty acid composition of the oil extracted by SFE was similar that of oil extracted by hexane. Physicochemical properties of oil showed that, the oil possesses the desirable qualities of edible oil and has been used as nutrient rich food oil. References [1] Rashid U, Rehman HA, Hussain I, Ibrahim M, Haider MS. Muskmelon (Cucumis melo) seed oil: a potential non-food oil source for biodiesel production. Energy 2011;36:5632–9. [2] Yanty NAM, Lai OM, Osman A, Long K, Ghazali HM. Physicochemical properties of Cucumis melo var. Inodorus (Honeydew Melon) seed and seed oil. J Food Lipids 2008;15:42–55. [3] Mian-hao H, Yansong A. Characteristics of some nutritional composition of melon (Cucumis melo hybrid ‘ChunLi’) seeds. Int J Food Sci Technol 2007;42:1397–401. [4] Hemavathy J. Lipid composition of melon (Cucumis melo) kernel. J Food Compos Anal 1992;5:90–5. [5] Passos CP, Silva RM, Da Silva FA, Coimbra MA, Silva CM. Supercritical fluid extraction of grape seed (Vitis vinifera L.) oil: effect of the operating conditions upon oil composition and antioxidant capacity. Chem Eng J 2010;160:634–40. [6] Papamichail I, Louli V, Magoulas K. Supercritical fluid extraction of celery seed oil. J Supercrit Fluids 2000;18:213–26. [7] Tonthubthimthong P, Chuaprasert S, Douglas P, Luewisutthichat W. Supercritical CO2 extraction of nimbin from neem seeds—an experimental study. J Food Eng 2001;47:289–93. [8] Hu QH, Xu J, Chen SB, Yang FM. Antioxidant activity of extracts of black sesame seed (Sesamum indicum L.) by supercritical carbon dioxide extraction. J Agric Food Chem 2004;52:943–7. [9] Louli V, Folas G, Voutsas E, Magoulas K. Extraction of parsley seed oil by supercritical CO2. J Supercrit Fluids 2004;30:163–74. [10] Westerman D, Santos RCD, Bosley JA, Rogers JS, Al-Duri B. Extraction of Amaranth seed oil by supercritical carbon dioxide. J Supercrit Fluids 2006;37:38–52. [11] Zaidul ISM, Norulaini NAN, Omar AKM, Smith RL. Supercritical carbon dioxide (SC–CO2) extraction of palm kernel oil from palm kernel. J Food Eng 2007;79:1007–14. [12] Salgin U. Extraction of jojoba seed oil using supercritical CO2 + ethanol mixture in green and high-tech separation process. J Supercrit Fluids 2007;39: 330–7.
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Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds J. Prakash Maran a,*, B. Priya b a b
Department of Food Technology, Kongu Engineering College, Perundurai, Erode 638052, TamilNadu, India Department of Food Process Engineering, SRM University, SRM Nagar, Kattankulathur, Chennai 603203, TamilNadu, India
A R T I C L E I N F O
A B S T R A C T
Article history: Received 20 May 2014 Received in revised form 1 October 2014 Accepted 5 October 2014 Available online xxx
The objective of this present study was to develop a suitable supercritical fluid extraction (SFE) method for extraction of oil from muskmelon seed (Cucumis melo). A Box–Behnken response surface design was applied to investigate and optimize the process variables (pressure, temperature, CO2 flow rate and time) on the yield of muskmelon seed oil. A second-order polynomial equation was developed to express the oil yield as a function of independent variables. The maximum oil yield (48.11%) was procured when SFE was carried out at 44 MPa of pressure, 49 8C of temperature, 0.64 g/min of CO2 flow rate and 81 min of extraction time. The total yield and fatty acids composition of muskmelon seed oil extracted by SFE was similar to that of oil extracted by Soxhlet extraction. Physicochemical properties of the oil at optimal SFE condition showed that the extracted oil could be adopted as food oil supplement. The experimental results indicated that SFE technique reduced the solvent consumption and extraction time with no adverse effect on the extraction yield and fatty acid composition of the oil. ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Supercritical fluid extraction Muskmelon seed oil Fatty acid Physicochemical property Optimization
1. Introduction Muskmelon (Cucumis melo) belongs to the Cucurbitaceae family and is one of the popular fruits in the tropical countries. It is originated from Iran and mostly grown in the warmer regions of the world [1]. Normally, after consuming the muskmelon fruit, seeds are thrown away and these seeds are normally restricted and treated as waste products. Seeds of musk melon are usually dried and used to add flavor to Indian dishes and desserts. Melon seeds boost immunity, reduce cardiovascular risks, help in normalizing blood-fat levels and contain essential nutrients for wound healing [2]. It also fights against osteoporosis and promotes healthy teeth and bone growth. These seeds are rich in protein and omega-3 fatty acids [3]. Several reports have been published on the melon seeds composition and its fatty acid profile [2–4] showing higher linoleic acid contents. A demand for vegetable oil is ever increasing, and the world relies mostly on the popular vegetable oil for the preparation of many products, muskmelon seed seems to be an economically viable alternative resource for oil production. Extraction is the most common method used to exploit and recover oil from seeds. Oil is mainly extracted from seeds by press
* Corresponding author. Tel.: +91 4294 226606; fax: +91 4294 220087. E-mail address: [email protected] (J.P. Maran).
and solvent extraction method. Press method is often associated with lower yield and high energy consumption, while solvent extraction often involves longer extraction time. The solvent extraction is accompanied with application of large quantities of organic solvents is undesirable to both consumers and the environment. Thus, to this end, distillation under vacuum was employed and possible degradation of thermally labile compounds in oil and incomplete hexane elimination are the drawbacks of this process. Therefore, it is vital to look for an effective solvent which excludes the aforementioned drawbacks to extract oil from seeds. The use of supercritical fluids as an alternative solvent for seed oil extraction has been attracting widespread interest owing to their particular properties (e.g., liquid-like solvent power, negligible surface tension, and gas-like transport properties), and changes in environmental regulations which foster the utilization of green solvents [5]. In this field, carbon dioxide has been especially adopted as it is essentially non-toxic, non-flammable, low-cost at the industrial level, can be recycled, has easily accessible supercritical conditions, and is totally dissipated from extracts at atmospheric pressure avoiding the necessity of further expensive and harmful refining treatments. Furthermore, CO2 has adequate solvent properties for extraction of triglycerides. In recent years, several researchers have been successfully applied supercritical fluid extraction (SFE) method to extract oil from seeds [5–17]. Furthermore, it is worth noting that, the SFE has been
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Please cite this article in press as: Maran JP, Priya B. Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds. J Taiwan Inst Chem Eng (2014), http://dx.doi.org/10.1016/j.jtice.2014.10.007
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proven to reach extraction yield equivalent to those achieved by conventional Soxhlet extraction with n-hexane [18]. An extensive literature analysis reveals that, SFE of oils from various seeds have been extensively studied. However, no studies have been reported on the SFE of total oil from muskmelon seeds. Hence, an attempt was made to develop suitable SFE method for the extraction of total oil from muskmelon seeds. Four factors three levels Box–Behnken response surface design was used in this work to investigate and optimize the process variables (pressure, temperature, CO2 flow rate and time) on the maximum extraction yield of oil. The optimum condition was validated and experimental results were compared with the results predicted by proposed mathematical equation. A comparison study with the results obtained from SFE and Soxhlet extraction was done. Fatty acids composition was analyzed in muskmelon extracts obtained using through both extraction methods to confirm the suitability of SFE as a preparative technique for fatty acid determination. The physical (viscosity, refractive index and color) and chemical (acid, iodine, saponification and peroxide value) properties of oil obtained at optimal SFE condition was also evaluated in this study to facilitate the potential use. 2. Materials and methods 2.1. Materials The musk melon seed used in this study was provided by local musk melon fruit processing industry near Chennai, TamilNadu, India. The seeds were dried at 55 8C for 9 h prior to processing and the chemical composition was determined to be: moisture content (4.3%), crude ash (1.97%), crude protein (23.15%) and crude fiber (12.08%), respectively. The moisture content, crude ash and crude fiber content was determined by using AOAC method. The crude protein content was determined by Kjeldahl method. The dried seeds were ground in a food grinder in order to reduce the size of the samples and to obtain maximum diameter of 500 mm as measured by a sieve. The ground seed was sealed in plastic container and stored in refrigerator prior to extraction. Carbon dioxide gas (99.99%) used for extraction was supplied by Chang Chun Gas (China). Chemicals used for seed oil analysis were hexane, ethanol, chloroform, phenolphthalein indicator, iodine monochloride, glacial acetic acid, acetone, ethyl acetate, acetic acid, phosphoric acid, potassium phosphate, sulfuric acid, carbon tetrachloride, diethyl ether and heptadecanoic acid were purchased from Sigma-Aldrich chemicals, Mumbai. All the chemicals used in this study were analytical grade.
pressure. Extracts obtained by SFE at the different experimental conditions (Table 1) were tested for oil content and the yield was calculated by the following equation: Oil yieldð%Þ ¼
Weight of extracted oil 100 Weight of seed
(1)
2.3. Experimental design and statistical analysis Four factors three levels Box–Behnken response surface design (BBD) was used in this study to investigate and optimize the effect of extraction process variables such as pressure (30–50 MPa, X1), temperature (40–60 8C, X2), CO2 flow rate (0.3–0.9 g/min, X3) and time (60–100 min, X4) on the maximum yield of oil from muskmelon seed. The extraction variables and their ranges were chosen from preliminary experimental results done in our laboratory. The independent variables were coded at three levels (1, 0, 1) for statistical calculation. The experimental design consists of 29 experiments (N = 2K(K 1) + C0, where N is total number of experiments, K is the number of independent variables and C0 is centre points) [19], which was carried out not only in triplicates but also in a randomized order to minimize the effect of unexpected variability in the observed response due to extraneous factors. Average experimental values were computed and shown in Table 1. A multiple regression model (second order polynomial equation) was used to fit the experimental data and the generalized form of that equation is shown as follows: Y ¼ b0 þ
k X
k X
j¼1
j¼1
b jX j þ
b j j X 2j þ
k X X i
bi j X i X j
(2)
< j¼2
where Y is the response; Xi and Xj are variables (i and j range from 1 to k); b0 is the model intercept coefficient; bj, bjj and bij are interaction coefficients of linear, quadratic and the second-order terms, respectively; k is the number of independent parameters (k = 4 in this study) [20]. The model includes linear, quadratic and interaction terms to determine the effect of process variables on the response. In addition the fitted polynomial equation could be used to generate response surface and contour plots in order to visualize the relationship between response and experimental levels of process variables and deduce the optimal condition. Statistical analysis of the experimental data was performed using the Stat ease Design Expert 8.0.7.1 statistical software (Stat-Ease Inc., Minneapolis, USA). 2.4. Soxhlet extraction
2.2. Supercritical fluid extraction of oil A laboratory scale assembled SFE system was used in this study with an extraction cell volume of 500 ml. Twenty five grams of ground musk melon seeds was mixed with glass wool in the ratio of 25:1 (w/w) packed as a cartridge and was placed inside the thermal controlled extraction cell. Liquefied CO2 was introduced into the cartridge through a piston pump with a cooling jacket. Both the pressure and temperature of the cartridge were automatically reached and maintained by a control unit according to settings. After the desired pressure and temperature were reached, the cell was placed in the thermal-controlled extraction cell (oven) and connected to the manifold and restrictors. The system was held for 30 min under the desired conditions, and then carbon dioxide was allowed to flow continuously through the extractor. The flow rate of CO2 was regulated by both the pressurereleasing valve and thermal-controlled restrictor and monitored by a flow meter. Extracts were finally separated from CO2 phase and collected in collector at ambient temperature and atmospheric
In order to compute the efficiency of SFE, Soxhlet extraction was carried out using n-hexane as the solvent. About 10 g of ground muskmelon seeds were placed in a cellulose thimble and transferred to a Soxhlet extractor. The round bottom extraction flask was filled with 150 ml of n-hexane which was heated at 78 8C. Extraction process was continuously run for 8 h. After completion of an extraction, oil was recovered by evaporating solvent using rotary evaporator (Bu¨chi, UK) and residual solvent was removed by flushing 99.9% nitrogen. The oil yield was determined in the same way as in supercritical fluid extraction method as mentioned earlier and the reported values were means of three determinations. 2.5. Fatty acid composition of musk melon seed oil Methylated oil samples were prepared according to the method described by Mitra et al. [21] prior to gas chromatography-flame ionization detector (GC-FID) analysis. The fatty acid composition of
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3
Table 1 Box–Behnken design matrix with observed and predicted results. Std (order)
Pressure (MPa)
Temperature (C)
CO2 flow rate (g/min)
Time (min)
Oil yield (%) Observed
Predicted
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
30 50 30 50 40 40 40 40 30 50 30 50 40 40 40 40 30 50 30 50 40 40 40 40 40 40 40 40 40
40 40 60 60 50 50 50 50 50 50 50 50 40 60 40 60 50 50 50 50 40 60 40 60 50 50 50 50 50
0.6 0.6 0.6 0.6 0.3 0.9 0.3 0.9 0.6 0.6 0.6 0.6 0.3 0.3 0.9 0.9 0.3 0.3 0.9 0.9 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6
80 80 80 80 60 60 100 100 60 60 100 100 80 80 80 80 80 80 80 80 60 60 100 100 80 80 80 80 80
18.04 35.07 18.04 26.05 31.06 34.07 25.05 37.07 27.05 36.07 21.04 41.08 32.06 11.02 25.05 36.07 14.03 36.07 31.37 38.09 35.10 26.05 27.05 26.05 46.09 46.34 48.10 47.09 45.09
18.16 36.48 17.82 27.12 31.30 35.53 24.78 38.03 28.14 36.44 20.62 39.94 32.10 11.22 24.80 35.99 14.21 35.69 30.61 36.76 33.43 24.56 27.40 26.57 46.49 46.49 46.49 46.49 46.49
the concentrated extracted oil at optimal condition was analyzed using an Agilent 6890N GC–FID (Agilent Technologies, USA), equipped with a HP-Innowax capillary column (30 m 0.25 mm i.d., 0.32 m film thickness, Agilent Technologies, CA, USA). The column was held at 150 8C for 5 min and raised to 220 8C at a rate of 4 8C/min. The injector and detector temperatures were held at 250 and 260 8C, respectively. Nitrogen was used as the carried gas at a flow rate of 1.0 ml/min and the split ratio of 100:1. The fatty acids peaks were identified by comparison of retention times with retention times of standards. Results were expressed as mass of fatty acid or fatty acid group (g) in 100 g of fatty acids. 2.6. Physicochemical analysis of muskmelon seed oil AOAC methods [22] were used to determine the acid, iodine, peroxide and saponification value of the extracted muskmelon seed oil. Color of the oil was measured by using Hunter lab color coordinates (L, a and b) with a colorimeter (Color QUEST XE 3399). Hand held refractometer was used to find out the refractive index of oil. The viscosity of the oil was determined using Brookfield viscometer at room temperature. All analysis was carried out with the oil extracted at optimal condition. 3. Results and discussion 3.1. Experimental data analysis Experimental data was obtained according to the BBD in order to study and investigate the individual and interactive effect of the process variables (pressure (30–50 MPa, X1), temperature (40– 60 8C, X2), CO2 flow rate (0.3–0.9 g/min, X3) and time (60–100 min, X4)) on the maximum yield of oil from muskmelon seed and the results are exhibited in Table 2. The experimental data was analyzed and fitted to various models such as linear, interactive
Residual error
Internally studentized residual
Cook’s distance
0.12 1.41 0.21 1.07 0.24 1.46 0.27 0.96 1.09 0.37 0.42 1.14 0.03 0.19 0.25 0.09 0.18 0.38 0.76 1.33 1.67 1.49 0.35 0.52 0.40 0.40 1.60 0.60 1.40
0.15 1.73 0.26 1.31 0.29 1.79 0.32 1.17 1.33 0.45 0.52 1.40 0.04 0.24 0.30 0.11 0.22 0.47 0.93 1.62 2.04 1.82 0.42 0.64 0.35 0.35 1.42 0.53 1.24
0.002 0.279 0.006 0.161 0.008 0.299 0.010 0.128 0.165 0.019 0.025 0.182 0.000 0.005 0.009 0.001 0.005 0.021 0.080 0.246 0.389 0.311 0.017 0.039 0.002 0.002 0.033 0.005 0.026
(2FI), quadratic and cubic, respectively. From the results (Table 2), it was observed that, linear and interactive (2FI) models showed lower R2, adjusted R2, predicted R2 and also high p-values, when compared with quadratic model. Cubic model was found to be aliased. Therefore the quadratic model incorporating linear, interactive and quadratic terms was chosen to describe and study the effect of process variables on the yield of oil from muskmelon seed [23]. 3.2. Model fitting and statistical analysis A second-order polynomial equation was fitted to the experimental data to develop a mathematical model, which will assist in predicting the extraction efficiency. The developed regression model obtained in terms of coded factors is given below: Oil yieldð%Þ ¼ 46:49 þ 6:91X 1 2:42X 2 þ 4:37X 3 1:00X 4 2:25X 1 X 2 3:83X 1 X 3 þ 2:75X 1 X 4 þ 8:02X 2 X 3 þ2:01X 2 X 4 þ 2:25X 3 X 4 9:15X12 12:44X22
(3)
8:02X32 6:06X42 Pareto analysis of variance (ANOVA) was used to analyze the experimental data and the results are listed in Table 3. The higher model F-value (123.73) and the associated lower p-values (p < 0.0001) demonstrated the significance of developed models and also indicate the best fit of the developed model. The high R2 (0.992), adj-R2 (0.984) and pre-R2 (0.962) values clearly demonstrates the model precision in exhibiting the relationship between the response and independent variables [24]. Low values of coefficient of variance (3.99) displayed the high degree of precision and good reliability of the conducted experiments [25]. In this study, the adequate precision (signal to noise ratio) was found to be >38 for response, which indicates the best fit of developed models [26].
Please cite this article in press as: Maran JP, Priya B. Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds. J Taiwan Inst Chem Eng (2014), http://dx.doi.org/10.1016/j.jtice.2014.10.007
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Table 2 Adequacy of model tested for response (oil yield). Sum of squares
Source
Sequential model sum of squares 29,197.37 Mean Linear 883.93 2FI 402.95 Quadratic 1488.48 Cubic 11.72 Residual 10.71 31995.17 Total Lack of fit tests Linear 1908.64 2FI 1505.69 Quadratic 17.21 Cubic 5.49 Pure error 5.22 Model summary statistics Linear 8.93 2FI 9.16 Quadratic 1.27 Cubic 1.34
DF
Mean square
1 4 6 4 8 6 29
29197.37 220.98 67.16 372.12 1.47 1.78 1103.28
20 14 10 2 4
95.43 107.55 1.72 2.74 1.31
0.316 0.460 0.992 0.996
F value
Prob > F
Remarks Suggested aliased
0.202 0.160 0.984 0.982
2.77 0.80 232.25 0.82
0.0503 0.5824 <0.0001 0.6129
73.12 82.40 1.32 2.10
0.0004 0.0003 0.4247 0.2377
0.122 0.087 0.962 0.715
2457.82 2555.53 107.29 798.25
Suggested aliased
Suggested aliased
Table 3 ANOVA and significance of regression coefficients. Source
Coefficient estimate
Sum of squares
Degree of freedom
Model X1 X2 X3 X4 X12 X13 X14 X23 X24 X34 X12 X22 X32 X42 Residual Std. Dev. Mean C.V.% Press
46.49 6.91 2.42 4.37 1.00 2.25 3.83 2.75 8.02 2.01 2.25 9.15 12.44 8.02 6.06
2775.36 572.29 70.52 229.02 12.10 20.33 58.75 30.35 257.03 16.16 20.33 543.22 1004.50 417.58 237.98 22.43
14 1 1 1 1 1 1 1 1 1 1 1 1 1 1 14
1.27 31.73 3.99 107.29
3.3. Diagnostics of model adequacy Generally, it is important to confirm that the fitted model gives a sufficient approximation to the actual values. Unless the model shows a satisfactory fit, proceeding with an investigation and optimization of the fitted response surface likely gives poor or misleading results [27]. In addition to determination coefficient, adequacy of the model was also evaluated by the residuals (difference between the observed and the predicted response value) and the influence plots for the experimental data obtained from this study. Residuals are thought as elements of variation, unexplained by the fitted model and it is expected to occur according to a normal distribution. Normal probability plots are a suitable graphical method for judging residuals normality. The observed residuals are plotted against the expected values, as they lie reasonably close on a straight line and show no deviation of the variance (Fig. 1a). It can be conformed that, the data are normally distributed [28]. By constructing residuals plot, a check was made to analyze the experimental data to find out its satisfactory fit and the plot shows that, all the data points lie within the limits (Fig. 1b). Diagnostic plots such as predicted versus actual (Fig. 1c) help us to
Standard error 0.57 0.37 0.37 0.37 0.37 0.63 0.63 0.63 0.63 0.63 0.63 0.50 0.50 0.50 0.50 R2 Adj-R2 Pred-R2 Adequate precision
Mean square
F value
p-Value
198.24 572.29 70.52 229.02 12.10 20.33 58.75 30.35 257.03 16.16 20.33 543.22 1004.50 417.58 237.98 1.60 0.992 0.984 0.962 38.751
123.73 357.18 44.01 142.94 7.55 12.69 36.67 18.94 160.42 10.09 12.69 339.04 626.94 260.63 148.53
<0.0001 <0.0001 <0.0001 <0.0001 0.0157 0.0031 <0.0001 0.0007 <0.0001 0.0067 0.0031 <0.0001 <0.0001 <0.0001 <0.0001
evaluate the model suitability and to analyze the relationship between predicted and experimental values [29]. The data points on this plot lie reasonably close to the straight line which indicates that an adequate agreement between real data and the data obtained from the models. Cook’s distance is used to diagnose and identify the possible influential outliers in the experimental data. Since the Cook’s distance values are in the determined range (Fig. 1d), there is no strong evidence of influential outliers in the observed data. Hence, trends observed in Fig. 1 revealed that, no obvious patterns were found and residuals appeared to be randomly scattered. 3.4. Response surface analysis In this study, the oil recovery was varied markedly from 11.02% to 48.096% with different levels of factors for SFE of muskmelon seed oil. To understand and study the individual and interaction effect of independent variables on the response, three dimensional (3D) response surface plots were constructed from the developed model. The model has more than two factors. So, the 3D plots have drawn by maintaining two factors at its constant level (in turn at its
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3.4.2. Effect of temperature As temperature increases, enhancement of extraction efficiency may be related to the increased vapor pressures and accelerated thermal desorption of the oil from the seed matrix. There are two distinguished trends observed in regard to the overall yield (Fig. 2a, d and e). In the range of 40–50 8C, the yield increases with a mild slope until it reaches its maximum value (48.12%), and a further increase up to 60 8C cause the decrease in yield. These two different regions of yields can be attributed to retrograde solubility in which the counter effect of solute vapor pressure and supercritical fluid density are affecting the extraction yield. In other words, in the first region of increasing temperature, the solute vapor pressure enhancement overlaps the supercritical fluid density decrease up to 50 8C where the maximum yield is obtained. At 50 8C, the retrograde solubility is reached in which the effect of solute vapor pressure becomes equivalent to the effect of CO2 density and subsequently beyond that the effect of density decrease prevails vapor pressure enhancement. Similar solubility behavior has been reported for other vegetable and seed oils [34]. 3.4.3. Effect of SC-CO2 fluid flow rate The oil recovery increased from low to medium level (code = 1 to 0) supercritical fluid flow rate (0.3–0.6 g/min). This was because during this stage, the extraction of the surface attached oil occurred and increasing the flow rate reduces the film thickness around the solid particles and this leads to lower external mass transfer resistance around the seed [35] and consequently enhanced oil extraction recovery. However, further increased in supercritical fluid flow rate could started to decrease the oil recovery (Fig. 2b, d and f). This was because this extraction was controlled mainly by diffusion of oil from the cell matrix and increasing the flow rate could not manipulate the rate of diffusion.
Fig. 1. Diagnostic plots of model adequacy.
3.4.4. Effect of extraction time The extraction of oil was increased dramatically with increasing extraction time and reached a maximum value at 80 min of fractionation then decreased gradually as the extraction time increased (Fig. 2c, e and f). Higher amount of oil recovery at initial extraction time (80 min) was caused by the higher extractable compounds contained in the surface of the seeds and supercritical CO2 had to diffuse deeply into the inner cell of the seeds to dissolve the extractable substance and increased the oil yield. However, further increase in the extraction times up to 100 min resulted in only a little change in the oil yield of oil. 3.5. Optimum operating conditions for maximizing the oil yield
central level), whereas the other two factors were varied in their range in order to understand their main and interactive effects on the dependent variables and the results were shown in Fig. 2. 3.4.1. Effect of pressure Pressure is one of the important factors in extraction of oil using SFE technique. From the results, it was observed that, the oil recovery was increased from 30 MPa to 43 MPa and then decreased (Fig. 2a–c). Increase in pressure up to 43 MPa could increase the fluid density, decreasing the distance between the molecules by the rupturing effect of pressure and thereby strengthening interactions between the fluid and matrix [30]. Therefore high pressure caused the compression of the seeds and extractable compounds in the seeds were easily dissolved in supercritical CO2. This experimental observation was attributed to the increased solute/solvent attractive interactions resulting from the highly compressed CO2 at high operating pressures [31]. These results are in agreement with the SC–CO2 extraction of rosehip seed oil [32] and borage seed oil [33]. Beyond 43 MPa, increasing the pressure decreased the essential oil recovery.
Regression model (Eq. (3)) was used to determine the optimum extraction condition for SC-CO2 extraction of oil from muskmelon seed. In order to obtain the optimum values, first and second order derivatives of the regression equation (Eq. (3)) were derived with respect to X1, X2, X3 and X4, respectively. The first order derivative of Eq. (3) gives the following equations:
@Y ¼ 6:91 18:3X 1 2:25X 2 3:83X 3 þ 2:75X 4 @X 1
(4)
@Y ¼ 2:42 2:25X 1 24:88X 2 þ 8:02X 3 þ 2:01X 4 @X 2
(5)
@Y ¼ 4:37 3:83X 1 þ 8:02X 2 16:04X 3 þ 2:25X 4 @X 3
(6)
@Y ¼ 1:00 þ 2:75X 1 þ 2:01X 2 þ 2:25X 3 12:12X 4 @X 4
(7)
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Fig. 2. Response surface plots showing the interactive effect of process variables on oil yield.
Second order derivatives of Eqs. (4–7) yield the following equations: 2
@ Y ¼ 18:3 @X12
(8)
@2 Y ¼ 16:04 @X32
(10)
@2 Y ¼ 12:12 @X42
(11)
2
@ Y ¼ 24:88 @X22
(9)
Since all the second order derivatives showed negative values, it signifies the applicability of maximization. Thus Eqs. (4–7) were
Please cite this article in press as: Maran JP, Priya B. Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds. J Taiwan Inst Chem Eng (2014), http://dx.doi.org/10.1016/j.jtice.2014.10.007
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equated with zero and solved for X1, X2, X3 and X4 to get the maximum values: 6:91 18:3X 1 2:25X 2 3:83X 3 þ 2:75X 4 ¼ 0
(12)
2:42 2:25X 1 24:88X 2 þ 8:02X 3 þ 2:01X 4 ¼ 0
(13)
4:37 3:83X 1 þ 8:02X 2 16:04X 3 þ 2:25X 4 ¼ 0
(14)
1:00 þ 2:75X 1 þ 2:01X 2 þ 2:25X 3 12:12X 4 ¼ 0
(15)
Algebraic solution to the above four equations gave in coded form of optimal condition was: X1 = 0.401 MPa, X2 = 0.085 8C, X3 = 0.121 g/min, X4 = 0.034 min. The corresponding experimental parametric values were: 44.01 MPa (pressure), 49.15 8C (temperature), 0.64 g/min (flow rate) and 80.69 min (extraction time), respectively. Under the optimal conditions, the predicted yield was 48.13%. The optimal point as obtained above can be a point of maximum or minimum or a saddle point response. In order to determine the nature of the optimal point, the regression equation was transformed to the canonical form and the Eigen values were computed using MATLAB 7.1 software. The Eigen values obtained were negative (X1 = 14.8194, X2 = 10.9609, X3 = 5.7261 and X4 = 4.1636) and it indicates that, the determined optimal condition was a maximum point. 3.6. Validation of optimized condition However, considering the operability in actual production, the optimal conditions can be modified as follows: 44 MPa of pressure, 49 8C of temperature, 0.64 g/min of flow rate and 81 min of extraction time, respectively. To compare the predicted results with experimental value, the experiments (triplicates) were carried out at the modified optimal extraction conditions. Under the modified conditions, the experimental yield of oil was 48.11 0.04% and was well matched with predicted values. As a result, Box–Behnken design was considered to be an accurate and decisive tool for predicting the maximum extraction yield of oil from muskmelon seed using SFE technique. 3.7. Comparison between SFE and Soxhlet extraction To investigate competence of SFE as a method for extraction of oil from muskmelon seed, yield of oil obtained under optimal SFE conditions was compared with total oil content extracted by Soxhlet method. SFE gave slightly higher extraction yield (48.11 0.04%) than Soxhlet (46.83 0.29%). Comparison of the two methods demonstrated that the SFE method provides a slightly higher yield with major reduction in solvent and energy consumption.
Fig. 3. GC-chromatograms for muskmelon seed oil extracted by Soxhlet (a) and SFE method (b).
easily synthesized in the human system and must be supplied externally through the diet, and muskmelon seed oil can be a good nutritional supplement as a source of linoleic acid. The oil has also been suggested to be used as a cooking or salad oil, or used in the preparation of margarine. It was concluded that, SFE appears to be a good alternative for other methods of extraction conventionally used in sample preparation for fatty acid determination. 3.9. Physicochemical properties of SFE extracts of oil The physical properties (viscosity, refractive index and color) and chemical properties (acid value, iodine value, peroxide value and saponification value) of the SFE muskmelon seed oil were determined in order to characterize the oil. The physical state of oil at room temperature is liquid. The seed oil has a low viscosity at room temperature with 14.07 0.13 cP, while it gives the refractive index reading of 1.38 0.01. Hunterlab coordinates (a = 1.46 0.29, b = 18.32 0.91 and L = 39.27 1.58) indicated that, the oil hold green to yellowish color. Peroxide value (3.46 0.42 milli-equivalent of peroxide/kg of oil) of the oil was very low, which showed the higher oxidative stability of the seed oil. The iodine value was high (124 3.82 g of I2/100 g of oil) and designated a high degree of unsaturation. The combination of high iodine value and low peroxide value demonstrate that the muskmelon seed oil possesses the desirable qualities of edible oil. Saponification number, 204 3.46 (mg of KOH/g of oil), observed for the oil was within range 175–250 normally found in other seed oils such as raspberry seed, safflower, sunflower and corn [36]. The acid
3.8. Fatty acid composition The fatty acid determination and composition of SFE and Soxhlet extracts of muskmelon seed oil was tested using GC-FID and the result was shown in Fig. 3. From Fig. 3, it was concluded that, no obvious difference were observed in the fatty oil composition of the oils extracted by the two methods. The results indicated that, five leading fatty acids were present in the recovered oil from muskmelon seed in both method and the results were shown in Table 4. The results showed that, the muskmelon seed oil is rich source of linoleic acid (C18:2), which accounting for 47% of the total oil. The ratio between unsaturated and saturated fatty acids (USFA/SFA ratio) results showed that, no significant differences in the oil profiles extracted by SFE and Soxhlet methods. The essential fatty acids like linoleic acid are not
Table 4 Comparison between fatty acid compositions (%w/w) of oil extracted by SFE and Soxhlet method. Fatty acid
Palmitic acid (C16:0) Palmitoleic acid (C16:1) Stearic acid (C18:0) Oleic acid (C18:1) Linoleic acid (C18:2) Saturated fatty acid (SFA) Monounsaturated fatty acid (MUFA) Polyunsaturated fatty acid (PUFA) USFA/SFA
Muskmelon seed oil SFE method
Soxhlet method
12.24 2.09 9.17 29.43 47.07 21.41 31.52 47.07 3.67
13.38 1.73 9.61 30.62 44.66 22.99 32.35 44.66 3.35
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value of the oil was 5.08 0.34 (mg of NaOH/g of oil). Therefore, both physical and chemical characteristics of the oil demonstrated that, the muskmelon seed oil is a good candidate for edible oil or supplement. 4. Conclusions Muskmelon (C. melo) seed oil was extracted by SFE and evaluated the quality (fatty acid composition and physicochemical properties) of the extracted oil. Four factors three levels BBD was successfully employed to study and optimize the extraction of oil from muskmelon seed. From the results, it was observed that, extraction yield was affected by supercritical CO2 extraction conditions such as pressure and temperature. The high regression coefficient of second order polynomial model was developed from the experimental data and it was fitted well with observed values. The oil yield was effectively modeled as a function of independent variables (pressure, temperature, CO2 flow rate and time) and the maximum oil yield (48.11%) was obtained at 44 MPa of pressure, 49 8C of temperature, 0.64 g/min of flow rate and 81 min of extraction time. The total yield of the extract using SFE and hexane Soxhlet extraction was 48.11% and 46.83%, respectively. The fatty acid composition of the oil extracted by SFE was similar that of oil extracted by hexane. Physicochemical properties of oil showed that, the oil possesses the desirable qualities of edible oil and has been used as nutrient rich food oil. References [1] Rashid U, Rehman HA, Hussain I, Ibrahim M, Haider MS. Muskmelon (Cucumis melo) seed oil: a potential non-food oil source for biodiesel production. Energy 2011;36:5632–9. [2] Yanty NAM, Lai OM, Osman A, Long K, Ghazali HM. Physicochemical properties of Cucumis melo var. Inodorus (Honeydew Melon) seed and seed oil. J Food Lipids 2008;15:42–55. [3] Mian-hao H, Yansong A. Characteristics of some nutritional composition of melon (Cucumis melo hybrid ‘ChunLi’) seeds. Int J Food Sci Technol 2007;42:1397–401. [4] Hemavathy J. Lipid composition of melon (Cucumis melo) kernel. J Food Compos Anal 1992;5:90–5. [5] Passos CP, Silva RM, Da Silva FA, Coimbra MA, Silva CM. Supercritical fluid extraction of grape seed (Vitis vinifera L.) oil: effect of the operating conditions upon oil composition and antioxidant capacity. Chem Eng J 2010;160:634–40. [6] Papamichail I, Louli V, Magoulas K. Supercritical fluid extraction of celery seed oil. J Supercrit Fluids 2000;18:213–26. [7] Tonthubthimthong P, Chuaprasert S, Douglas P, Luewisutthichat W. Supercritical CO2 extraction of nimbin from neem seeds—an experimental study. J Food Eng 2001;47:289–93. [8] Hu QH, Xu J, Chen SB, Yang FM. Antioxidant activity of extracts of black sesame seed (Sesamum indicum L.) by supercritical carbon dioxide extraction. J Agric Food Chem 2004;52:943–7. [9] Louli V, Folas G, Voutsas E, Magoulas K. Extraction of parsley seed oil by supercritical CO2. J Supercrit Fluids 2004;30:163–74. [10] Westerman D, Santos RCD, Bosley JA, Rogers JS, Al-Duri B. Extraction of Amaranth seed oil by supercritical carbon dioxide. J Supercrit Fluids 2006;37:38–52. [11] Zaidul ISM, Norulaini NAN, Omar AKM, Smith RL. Supercritical carbon dioxide (SC–CO2) extraction of palm kernel oil from palm kernel. J Food Eng 2007;79:1007–14. [12] Salgin U. Extraction of jojoba seed oil using supercritical CO2 + ethanol mixture in green and high-tech separation process. J Supercrit Fluids 2007;39: 330–7.
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Please cite this article in press as: Maran JP, Priya B. Supercritical fluid extraction of oil from muskmelon (Cucumis melo) seeds. J Taiwan Inst Chem Eng (2014), http://dx.doi.org/10.1016/j.jtice.2014.10.007