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Rubber seed oil extraction: Effects of solvent polarity, extraction time and solid-solvent ratio on its yield and quality
Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
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Rubber seed oil extraction: Effects of solvent polarity, extraction time and solid-solvent ratio on its yield and quality Chiazor Faustina Jisieike a, Eriola Betiku a, b, * a b
Biochemical Engineering Laboratory, Department of Chemical Engineering, Obafemi Awolowo University, Ile-Ife, Osun State, 220005, Nigeria Department of Biological Sciences, Florida Agricultural and Mechanical Engineering University, Tallahassee, FL, 32307, USA
A R T I C L E I N F O
A B S T R A C T
Keywords: Rubber seed Solvent extraction Modeling Optimization Fatty acid
Two solvents (isopropanol and n-hexane) with different polarity were employed in oil extraction from rubber seed with the aim of determining their effects on its yield and properties. The solvent extraction process deployed through Soxhlet technique was modeled and vital parameters affecting the characteristics of the rubber seed oil (RSO) were identified and optimized by D-Optimal design. Physical and chemical characteristics of the RSO were examined. The fatty acid content and functional groups in the RSO were investigated using gas chromatography and Fourier transform infrared (FT-IR) techniques, respectively. Optimum RSO yield of 63.14 wt% was observed in 2.7 h using solid:solvent ratio of 0.05 g/mL and n-hexane (a non-polar solvent). Maximum RSO yield obtained with isopropanol (a polar solvent) was 56.7 wt% in 3 h using solid:solvent ratio of 0.05 g/mL. Statistics of the model developed demonstrate that solid:solvent ratio had the highest impact on the RSO yield followed by solvent type. Unlike fatty acid content of the RSO, both the quality and yield were affected by isopropanol and nhexane. In both cases of the solvents, the RSO samples obtained were highly unsaturated (79%) with linoleic and oleic being the main fatty acids. The fatty acid contents were confirmed qualitatively with FT-IR spectra showing regions of double bond stretching and bending vibrations of esters of the triglycerides and trans-unsaturation. The quality of the RSO showed that it is a viable feedstock for oleochemical industries such as biodiesel but needs acid treatment preceding to its transesterification.
1. Introduction Rubber tree with biological name of Hevea brasiliensis originated from the Amazon rainforest in South America (Atabani et al., 2013; Ahmad et al., 2014; Reshad et al., 2015). It is mainly cultivated as an industrial crop for the production of natural rubber obtained from latex extract of the tree. Rubber tree produces lustrous mottled brown seeds walled in a pod of three-ellipsoidal case which on drying disperses the seeds by an explosive mechanism (Ramadhas et al., 2005). As much as 35 – 60 wt% non-edible oil can be obtained from rubber seed kernel (Ramadhas et al., 2005; Iyayi et al., 2008; Ebewele et al., 2010; Atabani et al., 2013; Gimbun et al., 2013; Onoji et al., 2016). The oil is high in unsaturated fatty acids (77–82%) comprising mainly of linoleic, oleic and linolenic acids and less of saturated acids (17–20 wt %) (Ramadhas et al., 2005; Iyayi et al., 2008; Ebewele et al., 2010; Onoji et al., 2016). Oil from rubber seed has potential applications in various industries such as paints and coatings (Ikhuoria et al., 2004; Aigbodion and Bakare,
2005; Iyayi et al., 2008; Eka et al., 2010), biodiesel production (Ikwuagwu et al., 2000; Ramadhas et al., 2005; Gui et al., 2008; Ahmad et al., 2014; Reshad et al., 2015; Dhawane et al., 2016; Onoji et al., 2017), semi-drying oil (Iyayi et al., 2008; Ebewele et al., 2010; Eka et al., 2010), lubricants (Iyayi et al., 2008; Kittigowittana et al., 2013), surface coating formulation and productions (Ebewele et al., 2010), replace ment for linseed oil in vanish and paint (Iyayi et al., 2008; Ebewele et al., 2010), printing ink (Igeleke and Omorusi, 2007; Iyayi et al., 2008). Currently, rubber seed oil (RSO) is underutilized in comparison to the rate of seed production and its industrial application (Ramadhas et al., 2005; Dhawane et al., 2016; Onoji et al., 2017). Solvent extraction method and mechanical pressing are the most frequently used techniques for industrial oil extraction (Atabani et al., 2013; Ajala and Betiku, 2015; Reshad et al., 2015). Although oil yield from mechanical pressing is low, it is well suited to rural places due to low initial and running costs (Willems et al., 2008). Ebewele et al. (2010) extracted RSO mechanically using a hydraulic press and obtained
* Corresponding author.Biochemical Engineering Laboratory, Department of Chemical Engineering, Obafemi Awolowo University, Ile-Ife, Osun State, 220005, Nigeria. E-mail addresses: [email protected], [email protected] (E. Betiku). https://doi.org/10.1016/j.bcab.2020.101522 Received 28 October 2019; Received in revised form 30 January 2020; Accepted 31 January 2020 Available online 1 February 2020 1878-8181/© 2020 Elsevier Ltd. All rights reserved.
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Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
28.46% at 8 MPa and 70 � C. Moshed et al. (2011) combined solvent extraction with mechanical pressing and obtain 49% RSO yield at solid: hexane ratio of 1:0.8. Solvent extraction procedure has many benefits viz. high yield, moderately low running cost and low turbidity (Ajala and Betiku, 2015). Oil extraction investigations using solvent extraction procedures from seeds of sorrel (Betiku and Adepoju, 2013), sesame (Betiku et al., 2012), rubber (Onoji et al., 2016) and yellow oleander (Ajala and Betiku, 2015) have been reported. It is required to select a suitable solvent for oil extraction so as to achieve quality oil. Several solvents have been used for oil extraction which include both polar and non-polar. Besides solvent type, other notable process parameters that have been shown to influence both oil yield and quality under solvent extraction include solid:solvent ratio, extraction time and particle size (Morshed et al., 2011; Reshad et al., 2015; Ibrahim et al., 2019; Okeleye and Betiku, 2019; Oladipo and Betiku, 2019). Optimization of extraction process is pertinent as it helps to give information on the design of processes. Statistical tool known as response surface methodology (RSM) with mathematical techniques suitable for modeling processes with the goal to optimize the response, has been applied to oil extraction studies. Unlike Box Behnken design (BBD) or central composite design (CCD), the D-optimality principle allows a more effective formation of a second order mathematical model (Myers et al., 2009). Another benefit of the D-optimal design method is that it provides the opportunity to evaluate non-numerical parameters such as type of solvent. While D-optimal design method has been demonstrated as an effective technique for oil extraction from Thevetia peruviana (yellow oleander), Hildegardia barteri (kariya), Hura crepitans (sandbox), Bauhunia monandra (Napoleon’s plume) and Moringa oleifera (Ajala and Betiku, 2015; Akintunde et al., 2015; Ibrahim et al., 2019; Okeleye and Betiku, 2019; Oladipo and Betiku, 2019) seeds, this has not yet been investigated on RSO extraction. For instance, Onoji et al. (2019) evaluated performance of artificial neural network-genetic algorithm and BBD-RSM in maximizing RSO yield. It was shown that ~ 43 wt% RSO could obtained by both methods under varying conditions. Mabayo et al. (2018) used CCD with RSM to optimize the process input variables for RSO extraction via solvent extraction assisted with ultrasonication method and maximum of 30.3 � 0.3% RSO yield was observed using rubber seed of 15 g, n-hexane:solid of 5:1, amplitude of 50 mm, time of 15 min and temperature of 60 � 5 � C. Reshad et al. (2015) used CCD with RSM to optimize RSO extraction and obtained maximum yield of 49.22% under the condition of hexane, solid:solvent ratio of 0.08 and 8 h of extraction time. There is the need for an investigation that evaluates extraction ca pacity of solvents on RSO based on polarity since this has been shown to affect the yield and characteristics of other oils (Attah and Ibemesi, 1990; Lohani et al., 2015; Ibrahim et al., 2019; Okeleye and Betiku, 2019; Oladipo and Betiku, 2019). Most of the past works on RSO extraction used non-polar n-hexane as solvent of extraction. However, we found one study in which the performance of hexane, methanol, ethyl acetate and ethyl acetate-water on RSO yield were evaluated (Reshad et al., 2015). The interactive effects of the solid:solvent ratio and time with the various solvents were not carried out. Also, quality characterization of RSO based on the solvents was not reported. These investigations were only done for hexane. In order to evaluate the effect of solvent type on the characteristics of RSO, this work was directed at optimization of the extraction process by considering the extraction capacities of isopropanol (polar solvent) and n-hexane (non-polar solvent) using D-optimal design method. Other process parameters evaluated for maximum RSO yield were solid:sol vent ratio and time of extraction. In both instances, the quality of RSO obtained in terms of its physicochemical properties, fatty acid profile and the functional groups were determined.
2. Experimental 2.1. Materials Matured seeds from rubber (H. brasiliensis) tree used for the extrac tion studies were collected from a farm in Ejophre Community, Delta State, Nigeria between August and September 2017. The chemicals and reagents (n-hexane, isopropanol, ethanol, potassium hydroxide, diethyl ether, cyclohexane, Wij’s solution, potassium iodide, starch, potassium chloride, and hydrogen chloride) used in this work are of analytical grade. 2.2. Methods 2.2.1. Kernel preparation The rubber seeds were sundried for 3 days, shelled manually and the kernels were collected. The kernels were dried in an oven at 60 � C for 8 h to constant weight. The dried kernels were milled into fine powder. 2.2.2. RSO extraction design and data analysis The design adopted for this work has two factors that are numeric; extraction time (h) and solid:solvent ratio (g/mL), and a non-numeric factor (solvent type) labeled as A, B and C, respectively. Fourteen (14) set of experimental conditions were generated with the D-optimal design for the extraction studies (Table 1). Design-Expert version 10.0 was used for the entire work. Equation (1) describes the fitted quadratic poly nomial response model, including all interaction terms. where, R is the RSO yield (response variable); θ0 denotes the intercept; θ1 , θ2 and θ3 are the coefficients of the linear terms; θ11 , θ22 , and θ33 are the coefficients of the quadratic terms; A (solid:solvent ratio), B (extraction time) and C (solvent type) denote the independent variables. 2.2.3. Procedure for RSO extraction QuickfitTM Borosilicate glass Soxhlet apparatus with 500-mL capac ity was used for this work following the method earlier described in our previous studies (Okeleye and Betiku, 2019; Oladipo and Betiku, 2019). The round bottom flask of the extractor was charged with solvent (n-hexane or isopropanol) while powdered rubber seed kernel was placed in the extraction chamber. The flask was heated in a water-bath (SM801D SURGIFRIEND Medical, England, U.K.) set at the boiling points of solvents (Table 2) for the period stipulated in the design matrix. The RSO yield was estimated gravimetrically (Eq. (2)). The predicted condition for optimum RSO yield by the model developed was verified in the laboratory by repeating the experiment in three replicates and the average value presented. Table 1 Experimental design for RSO extraction studies. (1)
R ¼ θ0 þ θ1 A þ θ2 B þ θ3 C þ θ12 AB þ θ13 AC þ θ23 BC þ θ11 A2 þ θ22 B2 þ θ33 C2
2
Run no
Solid:solvent ratio (g/mL) (A)
Extraction time (h) (B)
Solvent type (C)
RSO yield (wt.%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
0.105 0.15 0.15 0.105 0.095 0.05 0.05 0.05 0.05 0.1 0.05 0.15 0.15 0.15
1 1 3 1 3 1 1.9 3 1 2 3 2.1 1 2.1
Isopropanol n-Hexane n-Hexane Isopropanol Isopropanol n-Hexane Isopropanol n-Hexane n-Hexane n-Hexane Isopropanol Isopropanol n-Hexane Isopropanol
40.1 39.2 50.36 38.95 48.19 56.6 55.5 62.6 56.2 57.05 56.16 33.2 39.2 33.27
C.F. Jisieike and E. Betiku
Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
Table 2 Extraction solvents characteristics.
Table 3 Significance levels of model terms and ANOVA results.
Parameter
Isopropanol
n-Hexane
Structure Refractive Index at 25 � C Boiling point (oC) Density (g/mL) at 25 � C Dielectric constant Cost of solvent ($/L)
CH3HCOHCH3 1.3772 78 0.785 18.6 13.44
C6H14 1.3778 68 0.648 1.89 5.6
RSO yield ðwt:%Þ ¼
mass in gram of seed oil extracted � 100 mass in gram of powdered kernels
(2)
2.2.4. Characterization of extracted RSO The quality of the RSO extracted using isopropanol and n-hexane such as refractive index, density, moisture content, kinematic viscosity (physical properties); iodine value; peroxide value, acid value, saponi fication value (chemical properties); higher heating value, and cetane number (fuel properties) were determined by established methods (AOAC, 1995). The fatty acid and spectral profiles of the RSO extracted were analyzed using a gas chromatography (GC) and Fourier Transform Infrared (FT-IR) as previously described in our past work (Okeleye and Betiku, 2019).
Factor
Sum of Squares
df
Mean Square
F-value
p-value
A
779.32
1
779.32
3295.78
B
123.99
1
123.99
524.37
C
274.62
1
274.62
1161.39
AB AC
7.77 35.65
1 1
7.77 35.65
32.87 150.77
BC A2 B2 ANOVA Model Residual Lack of Fit Pure Error Correction for total sum R2 % Coefficient of variance Adjusted R2 Predicted R2
1.97 10.62 13.30
1 1 1
1.97 10.62 13.30
8.32 44.90 56.24
< 0.0001 < 0.0001 < 0.0001 0.0023 < 0.0001 0.0344 0.0011 0.0007
1296.63 1.18 0.44 0.74 1297.81
8 5 1 4 13
162.08 0.24 0.44 0.19
685.43
<0.0001
2.36
0.1994
0.9991 1.02 0.9976 0.9271
df – degrees of freedom.
3. Results and discussion 3.1. RSO extraction process modeling and optimization The regression model which relates the RSO yield (response) to the process input parameters (independent variables) investigated in this work in terms of the actual RSO yields is described as follows; For Isopropanol: R ¼ 49:11
103:10A þ 10:91B þ 23:28AB
880:25A2
2:47B2
(3)
For n-hexane: R ¼ 48:88
18:21 þ 11:91B þ 23:28AB
880:25A2
2:47B2
(4)
where, R denotes the RSO yield (wt. %), A denotes the solid:solvent ratio (g/mL) and B denotes the extraction time (h). The statistical significance of each term of the model together with their interactions were evaluated by ANOVA which reflect the strength of significance of each process input variable (Table 3). The results showed the high significance of all the terms of the model except the interaction between B and C (extraction time and solvent type). Based on the large F-value and corresponding low p-values, all the linear terms have very strong effects on the oil yield with solid:solvent ratio (A) being the most significant term. Similar observations have been reported for oil extraction from beniseed (Betiku et al., 2012) and rubber (Reshad et al., 2015; Onoji et al., 2019) seeds. The model is statistical significant with p- and F-values of <0.0001 and 685.43, respectively. The lack of fit of the model was 0.1994 which is not significant, this also support the good fit of the model. The coefficient of determination (R2), adjusted R2 and predicted R2 were used to determine the fitness of the model. The R2, adjusted R2 and predicted R2 for the mathematical model were 0.9991, 0.9976 and 0.9271, respectively. The value of R2 suggests that 99.91% of the experimental data is consistent with the predicted data by the model. This is also supported by Fig. 1 which depicts a high corre spondence between the experimental and predicted RSO yields. Both the values of the adjusted and predicted R2 support significance of the model. Joglekar and May (1987) proposed that for a model to be acceptable, R2 value must be � 0.80.
Fig. 1. Graph of the experimental and predicted RSO yields.
3.2. Interactions of parameters on RSO yield The interactive pattern of solid:solvent ratio and time on RSO yield is presented in Fig. 2. In both cases of isopropanol and n-hexane, an inverse relationship between the solid:solvent ratio and time on the RSO yield is observed. As solid:solvent ratio decreases and time increases, RSO yield increases. This is apparently due to more penetration of the ground rubber seed kernel by the solvent. This finding agrees with the obser vations made in the literature (Reshad et al., 2015; Onoji et al., 2019). The plots show that at solid:solvent ratio of 0.05 g/mL and extraction time of 3 h, maximum RSO yield of 56.7 and 62.9 wt% can be obtained using isopropanol and n-hexane, respectively. Generally, oil yield should be higher at high extraction time and low solid:solvent ratio. Low solid: solvent ratio produces large surface area which boosts oil yield by 3
C.F. Jisieike and E. Betiku
Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
Fig. 2. Plots of interactive effects of solid:solvent ratio and extraction time for RSO extraction. (a) Isopropanol; (b) n-hexane.
accelerating the solvent diffusivity in the powdered kernel. This is in agreement with observations for oil extraction from rubber seed (Reshad et al., 2015; Onoji et al., 2019), beniseed (Betiku et al., 2012), yellow oleander seed (Ajala and Betiku, 2015), Napoleon’s plume (Akintunde et al., 2015), kariya seed (Okeleye and Betiku, 2019) and moringa seed (Oladipo and Betiku, 2019).
The extraction level of an oil from its seeds depends on its nature, the solvent used, the process variables and the technique applied (Attah and Ibemesi, 1990). The characteristics of the solvents (Table 2) used for the RSO extraction seem to impact the yield and quality of the RSO. The oil yield obtained with n-hexane, which is a non-polar solvent, was found to be 62.9 wt% using solid:solvent ratio of 0.05 g/mL and 3 h of extraction, while oil yield of 56.7 wt% was obtained at the same experimental condition using isopropanol, a polar solvent. Based on the results, the use of n-hexane resulted into higher oil recovery indicating that it is a better solvent for RSO extraction. This observations correlates with the report by Reshad et al. (2015) for rubber seeds, Sayyar et al. (2009) for jatropha seeds and Oladipo and Betiku (2019) for moringa seeds. This observation may be because n-hexane has a lower vaporization tem perature and higher stability and hence the higher yield. The higher yield observed using n-hexane (non-polar) over isopropanol (polar) may be due to the existence of fatty acids with non-polar long chain hydro carbon in rubber seeds (Reshad et al., 2015). Dielectric constant can be used to examine whether polarity is responsible for the observed differences in this work. High dielectric constant of a solvent correlates to its high polarity and low solubility of oil (Johnson and Lusas, 1983). Isopropanol has a high dielectric constant (18.6), while that of n-hexane is 1.89 (Johnson and Lusas, 1983). Since
3.3. Optimization of RSO extraction The optimal condition suggested for the process is n-hexane, time of 2.7 h and solid:solvent ratio of 0.05 g/mL with predicted RSO yield of 63.29 wt%. This condition was used to carry out RSO extraction in the laboratory in three replicates to validate the model, the average yield obtained was 63.14 � 0.02 wt%, which corroborates the efficacy of the model. It is important to note that previous optimization studies on RSO extraction using BBD and CCD gave maximum yield of 30.3 – 49.22% with n-hexane as the solvent of extraction (Reshad et al., 2015; Mabayo et al., 2018; Onoji et al., 2019). This observation demonstrates that the outcome of this present work is superior to the previous studies even when the solvent extraction process was aided with ultrasonication (Mabayo et al., 2018). This suggest that D-optimal design used in this work is efficient. 4
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Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
alcohols such as isopropanol are more polar than n-hexane, more non-triglyceride compounds are extracted. Typically, such oils contain more non-saponifiables and phosphatides, and when the alcohol phase is separated, very little is extracted thereafter, hence the low oil yield. 3.4. Characterization of RSO The characteristics of the RSO extracted samples were evaluated (Table 4). The oil extracted using isopropanol at room temperature appears to be brown in colour whereas that of n-hexane is golden yellow (Fig. 3). It has been observed that alcohols extract more non-triglyceride constituents than n-hexane due to their higher polarity, so such oils contain more phosphatide and unsaponifiable compounds (Johnson and Lusas, 1983; Hu et al., 1996). Also, alcohols tend to remove colouring matter than other types of solvents (Attah and Ibemesi, 1990). Except for the moisture content, refractive index and calorific value, the choice of solvent of extraction affected the quality of the RSO obtained in this work. This observation has been reported for moringa oil extracted with ethanol, ethyl acetate and n-hexane (Oladipo and Betiku, 2019). The acid values observed for the extracted RSO samples are higher than 2 mg KOH/g oil suggesting that an acid treatment will be needed prior to its conversion by transesterification process to biodiesel. The higher the – C bonds are present in the fat/oil (Wibowo, iodine number, the more C– 2013). The high iodine values of the RSO samples is suggestive that the oil is mostly composed of unsaturated fatty acids which could cause oxidation if not stored appropriately. Peroxide value measures the extent of rancidity occurrence during storage. High peroxide value is indicative of high level of oxidative rancidity of oil (Chakrabarty, 2003). Peroxide values of fresh oils are <10 meqO2/kg oil (Onyeike and Acheru, 2002; Chakrabarty, 2003). The peroxide values obtained from this study fall within the range for fresh oils. Cetane number determines the ease of ignition of fuel in an engine. The cetane numbers obtained satisfied the limit suggested by ASTM D6751 and EN 14214 for biodiesel. The quality of the RSO samples obtained in this work appears better compared with those reported in literature. Higher oil content, higher calorific value, higher cetane number, lower acid value, lower kinematic viscosity and lower peroxide value were observed in present work. The chromatograms of the RSO samples which depict the peaks of the fatty acids present are presented in Fig. 4. The fatty acids contents of the RSO samples observed in this work compared with literature are displayed in Table 5, which show that the oil is highly unsaturated. This in agreement with results from liter ature though Onoji et al. (2016) seems to differ (Table 5). The choice of
Fig. 3. Appearance of RSO extracted with (a) n-hexane and (b) isopropanol.
solvent appears not to affect the composition significantly. Fig. 5 (a and b) shows spectra obtained for RSO extracted using n-hexane and iso propanol, respectively. While the functional groups and their bands are described in Table 6. The spectra obtained using n-hexane and isopropanol look similar. The observation corroborates results of the fatty acid profiles of the samples which show that there was no significant difference between them. Similar peaks observed in this work have been reported in literature for fried mustard and corn oil (Zahir et al., 2014), RSO (Reshad et al., 2015; Onoji et al., 2016), moringa oil (Oladipo and Betiku, 2019) and kariya (Okeleye and Betiku, 2019). 4. Conclusion RSO was extracted with polar and non-polar solvents via solvent extraction techniques. In order to understand the dynamics of the extraction process, the effects of vital process input parameters (solid: solvent ratio, time and solvent type) and their interactions on the oil yield were examined using D-optimal design. The choice of n-hexane, a non-polar solvent, as the solvent of extraction resulted into higher oil recovery than isopropanol. Chemical properties such as kinematic vis cosity, acid value, saponification value and the peroxide value of the RSO were impacted by the polarity of the solvent used. RSO yield of 63.29 wt% was observed under the optimal condition established for the process. The fatty acid profiles of the RSO samples showed that it is highly unsaturated. The quality of the RSO demonstrated that it is a viable feedstock for oleochemicals production such as biodiesel but
Table 4 Characteristics of RSO compared with literature. Parameters
This study
Solvent Oil content (wt.%) Colour
n-hexane 63.14 Golden yellow 3.47 � 0.06 0.23 � 0.00006 34.48 � 0.5
Isopropanol 56.7 Liquid/dark brown 4.1 � 0.1 0.27 � 0.00006
pH Moisture content (%) Kinematic viscosity (mm2/s) at 40 � C Refractive index Density (kg/m3) at 25 � C Acid value (mg KOH/g oil) Saponification value (mg KOH/ g oil) Iodine value (gI2/100 g oil) Peroxide value (meqO2/kg oil) Calorific value (MJ/kg) Cetane number
Bello and Otu (2015)
Onoji et al. (2016)
Omorogbe et al. (2013)
Ebewele et al. (2010)
Asuquo et al. (2012)
– Black
43 � 0.1 Dark brown
– Golden yellow
Dark brown
– Dark brown
7.4 –
6 � 0.141 –
– –
6 8.6
25.24 � 0.1
74.31
40.18 � 0.028
38.1
11.22
1.46 � 0.0005 869.43 � 0.4 13.02 � 0.1 170.24 � 1.4
1.45 � 0.0002
1.47
1.47 � 0.00028
–
1.46
857.63 � 1.2 11.64 � 0.03 155.86 � 0.21
910 47.12 183.7
886 � 0.002 18.20 � 0.141 195.30 � 0.282
920.9 42.41 191.37
943
72.03 � 1.9 6.8 � 0.06 41.4 62.15
73.29 � 2.10 4.1 � 0.1 41.95 64.83
106 25.30 37 46.3
137.02 � 0.028 10.46 � 0.098 39.37 43.42
140.06 – 39.73 49.73
142.45 16
5
226.02
920 1.68 193.61 134.51 14.4 – –
Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
C.F. Jisieike and E. Betiku
Fig. 4. Chromatograms of RSO samples extracted with (a) n-hexane and (b) isopropanol. Table 5 Fatty acid profile of RSO. Fatty acid
Structure
%Composition This study
Saturated fatty acid Myristic C14:0 Palmitic C16:0 Stearic C18:0 Arachidic C20:0 Total Unsaturated fatty acid Palmitoleic C16:1 Oleic C18:1 Linoleic C18:2 Linolenic C18:3 Erucic C22:1 Total
Onoji et al. (2016)
Ramadhas et al. (2005)
Roschat et al. (2017)
Aigbodion and Bakare (2005)
Okieimen et al. (2002)
n-hexane
Isopropanol
n-hexane
NR
Hexane
Pilot mill
NR
0.09 9.32 11.42 0.51 21.34
0.10 10.16 10.88 0.43 21.57
– 13.85 16.82 – 30.67
– 10.2 8.7 – 18.90
– 9.1 5.6 – 14.7
– 17.51 4.82 – 22.33
2.2 7.6 10.7 – 20.5
0.14 24.95 33.41 20.17 – 78.67
0.17 25.19 33.55 19.52 – 78.43
– 64.11 – – 5.22 69.33
– 24.6 39.6 16.3 – 80.5
– 24.0 46.2 14.2 – 84.4
– 25.33 37.50 14.21 – 77.04
– 20.0 36.0 23.5 – 79.5
6
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Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
Fig. 5. FT-IR spectra of RSO extracted with (a) n-hexane and (b) isopropanol.
Acknowledgements
Table 6 IR absorption frequencies and functional group for RSO. Wavenumber (cm1 )
Functional group
Vibration
Intensity
3466.20–3435.34
O–H
Stretch, H-bonded
3010.98
¼ C–H
2926.11–2854.74 1745.64
C–H –C– –O
Stretching of nonconjugated unsaturation (Methylene group) Stretching of methyl group Stretching of esters
Strong, broad Medium
1651.12 1464.02 1377.22 1238.34
C¼C –C-H
914.29–964.44
¼ C–H
C–O
Stretch Bending vibration of CH2, CH3 and C– –C aliphatic group Stretching vibration of carboxylic acids, esters Bending
Technical assistance by TA Adebayo is acknowledged. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.bcab.2020.101522. References
Strong Strong and sharp Variable Variable
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Variable Strong
needs acid treatment prior to its transesterification. CRediT authorship contribution statement Chiazor Faustina Jisieike: Methodology, Investigation, Validation, Writing - original draft. Eriola Betiku: Conceptualization, Software, Data curation, Visualization, Supervision, Writing - review & editing. 7
C.F. Jisieike and E. Betiku
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Attah, J., Ibemesi, J., 1990. Solvent extraction of the oils of rubber, melon, pumpkin and oilbean seeds. J. Am. Oil Chem. Soc. 67, 25–27. Bello, E.I., Otu, F., 2015. Physicochemical properties of rubber (Hevea brasiliensis) seed oil, its biodiesel and blends with diesel. Br. J. Appl. Sci. Technol. 6, 261–275. Betiku, E., Adepoju, T., 2013. Sorrel (Hibiscus sabdariffa) seed oil extraction optimization and quality characterization. Am. Chem. Sci. J. 3, 449–458. Betiku, E., Adepoju, T.F., Omole, A.K., Aluko, S.E., 2012. Statistical approach to the optimization of oil extraction from beniseed (Sesamum indicum) Oilseeds. J. Food Sci. Eng. 2, 351–357. Chakrabarty, M., 2003. Chemistry and Technology of Oils & Fats. Allied Publishers. Dhawane, S.H., Kumar, T., Halder, G., 2016. Biodiesel synthesis from Hevea brasiliensis oil employing carbon supported heterogeneous catalyst: optimization by Taguchi method. Renew. Energy 89, 506–514. Ebewele, R., Iyayi, A., Hymore, F., 2010. Considerations of the extraction process and potential technical applications of Nigerian rubber seed oil. Int. J. Phys. Sci. 5, 826–831. Eka, H., Tajul Aris, Y., Wan Nadiah, W., 2010. Potential use of Malaysian rubber (Hevea brasiliensis) seed as food, feed and biofuel. Int. Food Res.J. 17, 527–534. Gimbun, J., Ali, S., Kanwal, C.C.S.C., Shah, L.A., Muhamad, N.H., Cheng, C.K., Nurdin, S., 2013. Biodiesel production from rubber seed oil using activated cement clinker as catalyst. Procedia Engineering 53, 13–19. Gui, M.M., Lee, K., Bhatia, S., 2008. Feasibility of edible oil vs. non-edible oil vs. waste edible oil as biodiesel feedstock. Energy 33, 1646–1653. Hu, W., Wells, J.H., Shin, T.-S., Godber, J.S., 1996. Comparison of isopropanol and hexane for extraction of vitamin E and oryzanols from stabilized rice bran. JAOCS (J. Am. Oil Chem. Soc.) 73, 1653–1656. Ibrahim, A.P., Omilakin, R.O., Betiku, E., 2019. Optimization of microwave-assisted solvent extraction of non-edible sandbox (Hura crepitans) seed oil: a potential biodiesel feedstock. Renew. Energy 141, 349–358. Igeleke, C.L., Omorusi, V., 2007. Review of post-harvest deterioration of rubber seeds. J. Agric. Soc. Res. 7, 11–19. Ikhuoria, E.U., Aigbodion, A.I., Okieimen, F.E., 2004. Enhancing the quality of alkyd resins using methyl esters of rubber seed oil. Trop. J. Pharmaceut. Res. 3, 311–317. Ikwuagwu, O., Ononogbu, I., Njoku, O., 2000. Production of biodiesel using rubber [Hevea brasiliensis (Kunth. Muell.)] seed oil. Ind. Crop. Prod. 12, 57–62. Iyayi, A., Akpaka, P., Ukpeoyibo, U., 2008. Rubber seed processing for value-added latex production in Nigeria. Afr. J. Agric. Res. 3, 505–509. Joglekar, A., May, A., 1987. Product excellence through design of experiments. Cereal Foods World 32, 857–868. Johnson, L., Lusas, E., 1983. Comparison of alternative solvents for oils extraction. JAOCS (J. Am. Oil Chem. Soc.) 60, 229–242. Kittigowittana, K., Wongsakul, S., Krisdaphong, P., Jimtaisong, A., Saewan, N., 2013. Fatty acid composition and biological activities of seed oil from rubber (Hevea brasiliensis) cultivar RRIM 600. Int. J. Appl.Res. Nat.Prod. 6, 1–7. Lohani, U.C., Fallahi, P., Muthukumarappan, K., 2015. Comparison of ethyl acetate with hexane for oil extraction from various oilseeds. J. Am. Oil Chem. Soc. 92, 743–754. Mabayo, V.I.F., Aranas, J.R.C., Cagas, V.J.B., Cagas, D.P.A., Ido, A.L., Arazo, R.O., 2018. Optimization of oil yield from Hevea brasiliensis seeds through ultrasonic-assisted
8
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Biocatalysis and Agricultural Biotechnology journal homepage: http://www.elsevier.com/locate/bab
Rubber seed oil extraction: Effects of solvent polarity, extraction time and solid-solvent ratio on its yield and quality Chiazor Faustina Jisieike a, Eriola Betiku a, b, * a b
Biochemical Engineering Laboratory, Department of Chemical Engineering, Obafemi Awolowo University, Ile-Ife, Osun State, 220005, Nigeria Department of Biological Sciences, Florida Agricultural and Mechanical Engineering University, Tallahassee, FL, 32307, USA
A R T I C L E I N F O
A B S T R A C T
Keywords: Rubber seed Solvent extraction Modeling Optimization Fatty acid
Two solvents (isopropanol and n-hexane) with different polarity were employed in oil extraction from rubber seed with the aim of determining their effects on its yield and properties. The solvent extraction process deployed through Soxhlet technique was modeled and vital parameters affecting the characteristics of the rubber seed oil (RSO) were identified and optimized by D-Optimal design. Physical and chemical characteristics of the RSO were examined. The fatty acid content and functional groups in the RSO were investigated using gas chromatography and Fourier transform infrared (FT-IR) techniques, respectively. Optimum RSO yield of 63.14 wt% was observed in 2.7 h using solid:solvent ratio of 0.05 g/mL and n-hexane (a non-polar solvent). Maximum RSO yield obtained with isopropanol (a polar solvent) was 56.7 wt% in 3 h using solid:solvent ratio of 0.05 g/mL. Statistics of the model developed demonstrate that solid:solvent ratio had the highest impact on the RSO yield followed by solvent type. Unlike fatty acid content of the RSO, both the quality and yield were affected by isopropanol and nhexane. In both cases of the solvents, the RSO samples obtained were highly unsaturated (79%) with linoleic and oleic being the main fatty acids. The fatty acid contents were confirmed qualitatively with FT-IR spectra showing regions of double bond stretching and bending vibrations of esters of the triglycerides and trans-unsaturation. The quality of the RSO showed that it is a viable feedstock for oleochemical industries such as biodiesel but needs acid treatment preceding to its transesterification.
1. Introduction Rubber tree with biological name of Hevea brasiliensis originated from the Amazon rainforest in South America (Atabani et al., 2013; Ahmad et al., 2014; Reshad et al., 2015). It is mainly cultivated as an industrial crop for the production of natural rubber obtained from latex extract of the tree. Rubber tree produces lustrous mottled brown seeds walled in a pod of three-ellipsoidal case which on drying disperses the seeds by an explosive mechanism (Ramadhas et al., 2005). As much as 35 – 60 wt% non-edible oil can be obtained from rubber seed kernel (Ramadhas et al., 2005; Iyayi et al., 2008; Ebewele et al., 2010; Atabani et al., 2013; Gimbun et al., 2013; Onoji et al., 2016). The oil is high in unsaturated fatty acids (77–82%) comprising mainly of linoleic, oleic and linolenic acids and less of saturated acids (17–20 wt %) (Ramadhas et al., 2005; Iyayi et al., 2008; Ebewele et al., 2010; Onoji et al., 2016). Oil from rubber seed has potential applications in various industries such as paints and coatings (Ikhuoria et al., 2004; Aigbodion and Bakare,
2005; Iyayi et al., 2008; Eka et al., 2010), biodiesel production (Ikwuagwu et al., 2000; Ramadhas et al., 2005; Gui et al., 2008; Ahmad et al., 2014; Reshad et al., 2015; Dhawane et al., 2016; Onoji et al., 2017), semi-drying oil (Iyayi et al., 2008; Ebewele et al., 2010; Eka et al., 2010), lubricants (Iyayi et al., 2008; Kittigowittana et al., 2013), surface coating formulation and productions (Ebewele et al., 2010), replace ment for linseed oil in vanish and paint (Iyayi et al., 2008; Ebewele et al., 2010), printing ink (Igeleke and Omorusi, 2007; Iyayi et al., 2008). Currently, rubber seed oil (RSO) is underutilized in comparison to the rate of seed production and its industrial application (Ramadhas et al., 2005; Dhawane et al., 2016; Onoji et al., 2017). Solvent extraction method and mechanical pressing are the most frequently used techniques for industrial oil extraction (Atabani et al., 2013; Ajala and Betiku, 2015; Reshad et al., 2015). Although oil yield from mechanical pressing is low, it is well suited to rural places due to low initial and running costs (Willems et al., 2008). Ebewele et al. (2010) extracted RSO mechanically using a hydraulic press and obtained
* Corresponding author.Biochemical Engineering Laboratory, Department of Chemical Engineering, Obafemi Awolowo University, Ile-Ife, Osun State, 220005, Nigeria. E-mail addresses: [email protected], [email protected] (E. Betiku). https://doi.org/10.1016/j.bcab.2020.101522 Received 28 October 2019; Received in revised form 30 January 2020; Accepted 31 January 2020 Available online 1 February 2020 1878-8181/© 2020 Elsevier Ltd. All rights reserved.
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Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
28.46% at 8 MPa and 70 � C. Moshed et al. (2011) combined solvent extraction with mechanical pressing and obtain 49% RSO yield at solid: hexane ratio of 1:0.8. Solvent extraction procedure has many benefits viz. high yield, moderately low running cost and low turbidity (Ajala and Betiku, 2015). Oil extraction investigations using solvent extraction procedures from seeds of sorrel (Betiku and Adepoju, 2013), sesame (Betiku et al., 2012), rubber (Onoji et al., 2016) and yellow oleander (Ajala and Betiku, 2015) have been reported. It is required to select a suitable solvent for oil extraction so as to achieve quality oil. Several solvents have been used for oil extraction which include both polar and non-polar. Besides solvent type, other notable process parameters that have been shown to influence both oil yield and quality under solvent extraction include solid:solvent ratio, extraction time and particle size (Morshed et al., 2011; Reshad et al., 2015; Ibrahim et al., 2019; Okeleye and Betiku, 2019; Oladipo and Betiku, 2019). Optimization of extraction process is pertinent as it helps to give information on the design of processes. Statistical tool known as response surface methodology (RSM) with mathematical techniques suitable for modeling processes with the goal to optimize the response, has been applied to oil extraction studies. Unlike Box Behnken design (BBD) or central composite design (CCD), the D-optimality principle allows a more effective formation of a second order mathematical model (Myers et al., 2009). Another benefit of the D-optimal design method is that it provides the opportunity to evaluate non-numerical parameters such as type of solvent. While D-optimal design method has been demonstrated as an effective technique for oil extraction from Thevetia peruviana (yellow oleander), Hildegardia barteri (kariya), Hura crepitans (sandbox), Bauhunia monandra (Napoleon’s plume) and Moringa oleifera (Ajala and Betiku, 2015; Akintunde et al., 2015; Ibrahim et al., 2019; Okeleye and Betiku, 2019; Oladipo and Betiku, 2019) seeds, this has not yet been investigated on RSO extraction. For instance, Onoji et al. (2019) evaluated performance of artificial neural network-genetic algorithm and BBD-RSM in maximizing RSO yield. It was shown that ~ 43 wt% RSO could obtained by both methods under varying conditions. Mabayo et al. (2018) used CCD with RSM to optimize the process input variables for RSO extraction via solvent extraction assisted with ultrasonication method and maximum of 30.3 � 0.3% RSO yield was observed using rubber seed of 15 g, n-hexane:solid of 5:1, amplitude of 50 mm, time of 15 min and temperature of 60 � 5 � C. Reshad et al. (2015) used CCD with RSM to optimize RSO extraction and obtained maximum yield of 49.22% under the condition of hexane, solid:solvent ratio of 0.08 and 8 h of extraction time. There is the need for an investigation that evaluates extraction ca pacity of solvents on RSO based on polarity since this has been shown to affect the yield and characteristics of other oils (Attah and Ibemesi, 1990; Lohani et al., 2015; Ibrahim et al., 2019; Okeleye and Betiku, 2019; Oladipo and Betiku, 2019). Most of the past works on RSO extraction used non-polar n-hexane as solvent of extraction. However, we found one study in which the performance of hexane, methanol, ethyl acetate and ethyl acetate-water on RSO yield were evaluated (Reshad et al., 2015). The interactive effects of the solid:solvent ratio and time with the various solvents were not carried out. Also, quality characterization of RSO based on the solvents was not reported. These investigations were only done for hexane. In order to evaluate the effect of solvent type on the characteristics of RSO, this work was directed at optimization of the extraction process by considering the extraction capacities of isopropanol (polar solvent) and n-hexane (non-polar solvent) using D-optimal design method. Other process parameters evaluated for maximum RSO yield were solid:sol vent ratio and time of extraction. In both instances, the quality of RSO obtained in terms of its physicochemical properties, fatty acid profile and the functional groups were determined.
2. Experimental 2.1. Materials Matured seeds from rubber (H. brasiliensis) tree used for the extrac tion studies were collected from a farm in Ejophre Community, Delta State, Nigeria between August and September 2017. The chemicals and reagents (n-hexane, isopropanol, ethanol, potassium hydroxide, diethyl ether, cyclohexane, Wij’s solution, potassium iodide, starch, potassium chloride, and hydrogen chloride) used in this work are of analytical grade. 2.2. Methods 2.2.1. Kernel preparation The rubber seeds were sundried for 3 days, shelled manually and the kernels were collected. The kernels were dried in an oven at 60 � C for 8 h to constant weight. The dried kernels were milled into fine powder. 2.2.2. RSO extraction design and data analysis The design adopted for this work has two factors that are numeric; extraction time (h) and solid:solvent ratio (g/mL), and a non-numeric factor (solvent type) labeled as A, B and C, respectively. Fourteen (14) set of experimental conditions were generated with the D-optimal design for the extraction studies (Table 1). Design-Expert version 10.0 was used for the entire work. Equation (1) describes the fitted quadratic poly nomial response model, including all interaction terms. where, R is the RSO yield (response variable); θ0 denotes the intercept; θ1 , θ2 and θ3 are the coefficients of the linear terms; θ11 , θ22 , and θ33 are the coefficients of the quadratic terms; A (solid:solvent ratio), B (extraction time) and C (solvent type) denote the independent variables. 2.2.3. Procedure for RSO extraction QuickfitTM Borosilicate glass Soxhlet apparatus with 500-mL capac ity was used for this work following the method earlier described in our previous studies (Okeleye and Betiku, 2019; Oladipo and Betiku, 2019). The round bottom flask of the extractor was charged with solvent (n-hexane or isopropanol) while powdered rubber seed kernel was placed in the extraction chamber. The flask was heated in a water-bath (SM801D SURGIFRIEND Medical, England, U.K.) set at the boiling points of solvents (Table 2) for the period stipulated in the design matrix. The RSO yield was estimated gravimetrically (Eq. (2)). The predicted condition for optimum RSO yield by the model developed was verified in the laboratory by repeating the experiment in three replicates and the average value presented. Table 1 Experimental design for RSO extraction studies. (1)
R ¼ θ0 þ θ1 A þ θ2 B þ θ3 C þ θ12 AB þ θ13 AC þ θ23 BC þ θ11 A2 þ θ22 B2 þ θ33 C2
2
Run no
Solid:solvent ratio (g/mL) (A)
Extraction time (h) (B)
Solvent type (C)
RSO yield (wt.%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
0.105 0.15 0.15 0.105 0.095 0.05 0.05 0.05 0.05 0.1 0.05 0.15 0.15 0.15
1 1 3 1 3 1 1.9 3 1 2 3 2.1 1 2.1
Isopropanol n-Hexane n-Hexane Isopropanol Isopropanol n-Hexane Isopropanol n-Hexane n-Hexane n-Hexane Isopropanol Isopropanol n-Hexane Isopropanol
40.1 39.2 50.36 38.95 48.19 56.6 55.5 62.6 56.2 57.05 56.16 33.2 39.2 33.27
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Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
Table 2 Extraction solvents characteristics.
Table 3 Significance levels of model terms and ANOVA results.
Parameter
Isopropanol
n-Hexane
Structure Refractive Index at 25 � C Boiling point (oC) Density (g/mL) at 25 � C Dielectric constant Cost of solvent ($/L)
CH3HCOHCH3 1.3772 78 0.785 18.6 13.44
C6H14 1.3778 68 0.648 1.89 5.6
RSO yield ðwt:%Þ ¼
mass in gram of seed oil extracted � 100 mass in gram of powdered kernels
(2)
2.2.4. Characterization of extracted RSO The quality of the RSO extracted using isopropanol and n-hexane such as refractive index, density, moisture content, kinematic viscosity (physical properties); iodine value; peroxide value, acid value, saponi fication value (chemical properties); higher heating value, and cetane number (fuel properties) were determined by established methods (AOAC, 1995). The fatty acid and spectral profiles of the RSO extracted were analyzed using a gas chromatography (GC) and Fourier Transform Infrared (FT-IR) as previously described in our past work (Okeleye and Betiku, 2019).
Factor
Sum of Squares
df
Mean Square
F-value
p-value
A
779.32
1
779.32
3295.78
B
123.99
1
123.99
524.37
C
274.62
1
274.62
1161.39
AB AC
7.77 35.65
1 1
7.77 35.65
32.87 150.77
BC A2 B2 ANOVA Model Residual Lack of Fit Pure Error Correction for total sum R2 % Coefficient of variance Adjusted R2 Predicted R2
1.97 10.62 13.30
1 1 1
1.97 10.62 13.30
8.32 44.90 56.24
< 0.0001 < 0.0001 < 0.0001 0.0023 < 0.0001 0.0344 0.0011 0.0007
1296.63 1.18 0.44 0.74 1297.81
8 5 1 4 13
162.08 0.24 0.44 0.19
685.43
<0.0001
2.36
0.1994
0.9991 1.02 0.9976 0.9271
df – degrees of freedom.
3. Results and discussion 3.1. RSO extraction process modeling and optimization The regression model which relates the RSO yield (response) to the process input parameters (independent variables) investigated in this work in terms of the actual RSO yields is described as follows; For Isopropanol: R ¼ 49:11
103:10A þ 10:91B þ 23:28AB
880:25A2
2:47B2
(3)
For n-hexane: R ¼ 48:88
18:21 þ 11:91B þ 23:28AB
880:25A2
2:47B2
(4)
where, R denotes the RSO yield (wt. %), A denotes the solid:solvent ratio (g/mL) and B denotes the extraction time (h). The statistical significance of each term of the model together with their interactions were evaluated by ANOVA which reflect the strength of significance of each process input variable (Table 3). The results showed the high significance of all the terms of the model except the interaction between B and C (extraction time and solvent type). Based on the large F-value and corresponding low p-values, all the linear terms have very strong effects on the oil yield with solid:solvent ratio (A) being the most significant term. Similar observations have been reported for oil extraction from beniseed (Betiku et al., 2012) and rubber (Reshad et al., 2015; Onoji et al., 2019) seeds. The model is statistical significant with p- and F-values of <0.0001 and 685.43, respectively. The lack of fit of the model was 0.1994 which is not significant, this also support the good fit of the model. The coefficient of determination (R2), adjusted R2 and predicted R2 were used to determine the fitness of the model. The R2, adjusted R2 and predicted R2 for the mathematical model were 0.9991, 0.9976 and 0.9271, respectively. The value of R2 suggests that 99.91% of the experimental data is consistent with the predicted data by the model. This is also supported by Fig. 1 which depicts a high corre spondence between the experimental and predicted RSO yields. Both the values of the adjusted and predicted R2 support significance of the model. Joglekar and May (1987) proposed that for a model to be acceptable, R2 value must be � 0.80.
Fig. 1. Graph of the experimental and predicted RSO yields.
3.2. Interactions of parameters on RSO yield The interactive pattern of solid:solvent ratio and time on RSO yield is presented in Fig. 2. In both cases of isopropanol and n-hexane, an inverse relationship between the solid:solvent ratio and time on the RSO yield is observed. As solid:solvent ratio decreases and time increases, RSO yield increases. This is apparently due to more penetration of the ground rubber seed kernel by the solvent. This finding agrees with the obser vations made in the literature (Reshad et al., 2015; Onoji et al., 2019). The plots show that at solid:solvent ratio of 0.05 g/mL and extraction time of 3 h, maximum RSO yield of 56.7 and 62.9 wt% can be obtained using isopropanol and n-hexane, respectively. Generally, oil yield should be higher at high extraction time and low solid:solvent ratio. Low solid: solvent ratio produces large surface area which boosts oil yield by 3
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Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
Fig. 2. Plots of interactive effects of solid:solvent ratio and extraction time for RSO extraction. (a) Isopropanol; (b) n-hexane.
accelerating the solvent diffusivity in the powdered kernel. This is in agreement with observations for oil extraction from rubber seed (Reshad et al., 2015; Onoji et al., 2019), beniseed (Betiku et al., 2012), yellow oleander seed (Ajala and Betiku, 2015), Napoleon’s plume (Akintunde et al., 2015), kariya seed (Okeleye and Betiku, 2019) and moringa seed (Oladipo and Betiku, 2019).
The extraction level of an oil from its seeds depends on its nature, the solvent used, the process variables and the technique applied (Attah and Ibemesi, 1990). The characteristics of the solvents (Table 2) used for the RSO extraction seem to impact the yield and quality of the RSO. The oil yield obtained with n-hexane, which is a non-polar solvent, was found to be 62.9 wt% using solid:solvent ratio of 0.05 g/mL and 3 h of extraction, while oil yield of 56.7 wt% was obtained at the same experimental condition using isopropanol, a polar solvent. Based on the results, the use of n-hexane resulted into higher oil recovery indicating that it is a better solvent for RSO extraction. This observations correlates with the report by Reshad et al. (2015) for rubber seeds, Sayyar et al. (2009) for jatropha seeds and Oladipo and Betiku (2019) for moringa seeds. This observation may be because n-hexane has a lower vaporization tem perature and higher stability and hence the higher yield. The higher yield observed using n-hexane (non-polar) over isopropanol (polar) may be due to the existence of fatty acids with non-polar long chain hydro carbon in rubber seeds (Reshad et al., 2015). Dielectric constant can be used to examine whether polarity is responsible for the observed differences in this work. High dielectric constant of a solvent correlates to its high polarity and low solubility of oil (Johnson and Lusas, 1983). Isopropanol has a high dielectric constant (18.6), while that of n-hexane is 1.89 (Johnson and Lusas, 1983). Since
3.3. Optimization of RSO extraction The optimal condition suggested for the process is n-hexane, time of 2.7 h and solid:solvent ratio of 0.05 g/mL with predicted RSO yield of 63.29 wt%. This condition was used to carry out RSO extraction in the laboratory in three replicates to validate the model, the average yield obtained was 63.14 � 0.02 wt%, which corroborates the efficacy of the model. It is important to note that previous optimization studies on RSO extraction using BBD and CCD gave maximum yield of 30.3 – 49.22% with n-hexane as the solvent of extraction (Reshad et al., 2015; Mabayo et al., 2018; Onoji et al., 2019). This observation demonstrates that the outcome of this present work is superior to the previous studies even when the solvent extraction process was aided with ultrasonication (Mabayo et al., 2018). This suggest that D-optimal design used in this work is efficient. 4
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Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
alcohols such as isopropanol are more polar than n-hexane, more non-triglyceride compounds are extracted. Typically, such oils contain more non-saponifiables and phosphatides, and when the alcohol phase is separated, very little is extracted thereafter, hence the low oil yield. 3.4. Characterization of RSO The characteristics of the RSO extracted samples were evaluated (Table 4). The oil extracted using isopropanol at room temperature appears to be brown in colour whereas that of n-hexane is golden yellow (Fig. 3). It has been observed that alcohols extract more non-triglyceride constituents than n-hexane due to their higher polarity, so such oils contain more phosphatide and unsaponifiable compounds (Johnson and Lusas, 1983; Hu et al., 1996). Also, alcohols tend to remove colouring matter than other types of solvents (Attah and Ibemesi, 1990). Except for the moisture content, refractive index and calorific value, the choice of solvent of extraction affected the quality of the RSO obtained in this work. This observation has been reported for moringa oil extracted with ethanol, ethyl acetate and n-hexane (Oladipo and Betiku, 2019). The acid values observed for the extracted RSO samples are higher than 2 mg KOH/g oil suggesting that an acid treatment will be needed prior to its conversion by transesterification process to biodiesel. The higher the – C bonds are present in the fat/oil (Wibowo, iodine number, the more C– 2013). The high iodine values of the RSO samples is suggestive that the oil is mostly composed of unsaturated fatty acids which could cause oxidation if not stored appropriately. Peroxide value measures the extent of rancidity occurrence during storage. High peroxide value is indicative of high level of oxidative rancidity of oil (Chakrabarty, 2003). Peroxide values of fresh oils are <10 meqO2/kg oil (Onyeike and Acheru, 2002; Chakrabarty, 2003). The peroxide values obtained from this study fall within the range for fresh oils. Cetane number determines the ease of ignition of fuel in an engine. The cetane numbers obtained satisfied the limit suggested by ASTM D6751 and EN 14214 for biodiesel. The quality of the RSO samples obtained in this work appears better compared with those reported in literature. Higher oil content, higher calorific value, higher cetane number, lower acid value, lower kinematic viscosity and lower peroxide value were observed in present work. The chromatograms of the RSO samples which depict the peaks of the fatty acids present are presented in Fig. 4. The fatty acids contents of the RSO samples observed in this work compared with literature are displayed in Table 5, which show that the oil is highly unsaturated. This in agreement with results from liter ature though Onoji et al. (2016) seems to differ (Table 5). The choice of
Fig. 3. Appearance of RSO extracted with (a) n-hexane and (b) isopropanol.
solvent appears not to affect the composition significantly. Fig. 5 (a and b) shows spectra obtained for RSO extracted using n-hexane and iso propanol, respectively. While the functional groups and their bands are described in Table 6. The spectra obtained using n-hexane and isopropanol look similar. The observation corroborates results of the fatty acid profiles of the samples which show that there was no significant difference between them. Similar peaks observed in this work have been reported in literature for fried mustard and corn oil (Zahir et al., 2014), RSO (Reshad et al., 2015; Onoji et al., 2016), moringa oil (Oladipo and Betiku, 2019) and kariya (Okeleye and Betiku, 2019). 4. Conclusion RSO was extracted with polar and non-polar solvents via solvent extraction techniques. In order to understand the dynamics of the extraction process, the effects of vital process input parameters (solid: solvent ratio, time and solvent type) and their interactions on the oil yield were examined using D-optimal design. The choice of n-hexane, a non-polar solvent, as the solvent of extraction resulted into higher oil recovery than isopropanol. Chemical properties such as kinematic vis cosity, acid value, saponification value and the peroxide value of the RSO were impacted by the polarity of the solvent used. RSO yield of 63.29 wt% was observed under the optimal condition established for the process. The fatty acid profiles of the RSO samples showed that it is highly unsaturated. The quality of the RSO demonstrated that it is a viable feedstock for oleochemicals production such as biodiesel but
Table 4 Characteristics of RSO compared with literature. Parameters
This study
Solvent Oil content (wt.%) Colour
n-hexane 63.14 Golden yellow 3.47 � 0.06 0.23 � 0.00006 34.48 � 0.5
Isopropanol 56.7 Liquid/dark brown 4.1 � 0.1 0.27 � 0.00006
pH Moisture content (%) Kinematic viscosity (mm2/s) at 40 � C Refractive index Density (kg/m3) at 25 � C Acid value (mg KOH/g oil) Saponification value (mg KOH/ g oil) Iodine value (gI2/100 g oil) Peroxide value (meqO2/kg oil) Calorific value (MJ/kg) Cetane number
Bello and Otu (2015)
Onoji et al. (2016)
Omorogbe et al. (2013)
Ebewele et al. (2010)
Asuquo et al. (2012)
– Black
43 � 0.1 Dark brown
– Golden yellow
Dark brown
– Dark brown
7.4 –
6 � 0.141 –
– –
6 8.6
25.24 � 0.1
74.31
40.18 � 0.028
38.1
11.22
1.46 � 0.0005 869.43 � 0.4 13.02 � 0.1 170.24 � 1.4
1.45 � 0.0002
1.47
1.47 � 0.00028
–
1.46
857.63 � 1.2 11.64 � 0.03 155.86 � 0.21
910 47.12 183.7
886 � 0.002 18.20 � 0.141 195.30 � 0.282
920.9 42.41 191.37
943
72.03 � 1.9 6.8 � 0.06 41.4 62.15
73.29 � 2.10 4.1 � 0.1 41.95 64.83
106 25.30 37 46.3
137.02 � 0.028 10.46 � 0.098 39.37 43.42
140.06 – 39.73 49.73
142.45 16
5
226.02
920 1.68 193.61 134.51 14.4 – –
Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
C.F. Jisieike and E. Betiku
Fig. 4. Chromatograms of RSO samples extracted with (a) n-hexane and (b) isopropanol. Table 5 Fatty acid profile of RSO. Fatty acid
Structure
%Composition This study
Saturated fatty acid Myristic C14:0 Palmitic C16:0 Stearic C18:0 Arachidic C20:0 Total Unsaturated fatty acid Palmitoleic C16:1 Oleic C18:1 Linoleic C18:2 Linolenic C18:3 Erucic C22:1 Total
Onoji et al. (2016)
Ramadhas et al. (2005)
Roschat et al. (2017)
Aigbodion and Bakare (2005)
Okieimen et al. (2002)
n-hexane
Isopropanol
n-hexane
NR
Hexane
Pilot mill
NR
0.09 9.32 11.42 0.51 21.34
0.10 10.16 10.88 0.43 21.57
– 13.85 16.82 – 30.67
– 10.2 8.7 – 18.90
– 9.1 5.6 – 14.7
– 17.51 4.82 – 22.33
2.2 7.6 10.7 – 20.5
0.14 24.95 33.41 20.17 – 78.67
0.17 25.19 33.55 19.52 – 78.43
– 64.11 – – 5.22 69.33
– 24.6 39.6 16.3 – 80.5
– 24.0 46.2 14.2 – 84.4
– 25.33 37.50 14.21 – 77.04
– 20.0 36.0 23.5 – 79.5
6
C.F. Jisieike and E. Betiku
Biocatalysis and Agricultural Biotechnology 24 (2020) 101522
Fig. 5. FT-IR spectra of RSO extracted with (a) n-hexane and (b) isopropanol.
Acknowledgements
Table 6 IR absorption frequencies and functional group for RSO. Wavenumber (cm1 )
Functional group
Vibration
Intensity
3466.20–3435.34
O–H
Stretch, H-bonded
3010.98
¼ C–H
2926.11–2854.74 1745.64
C–H –C– –O
Stretching of nonconjugated unsaturation (Methylene group) Stretching of methyl group Stretching of esters
Strong, broad Medium
1651.12 1464.02 1377.22 1238.34
C¼C –C-H
914.29–964.44
¼ C–H
C–O
Stretch Bending vibration of CH2, CH3 and C– –C aliphatic group Stretching vibration of carboxylic acids, esters Bending
Technical assistance by TA Adebayo is acknowledged. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.bcab.2020.101522. References
Strong Strong and sharp Variable Variable
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