In this study, the effect of extraction processes on the physicochemical characteristics and antioxidant potential of baobab ( Adansonia digitata L.) seed oil was evaluated. The oils were extracted, on the one hand, by cold pressing, and on the other hand, with three types of organic solvents (acetone, chloroform, n-hexane). The recorded results indicated that the extraction yield of baobab oil was significantly impacted by both the extraction method and the polarity of the solvent used. In addition, chloroform provides the best extraction yield (40.12 ± 0.607). However, extraction by cold pressure preserves at best the physicochemical and bioactive properties of the extracted oils. Indeed, the pressing oil contains a content of phenolic compounds (0.047 ± 0.0024 mgEAG/g of oil) and a very high radical scavenging activity (DPPH) (31.71% ± 0.61%). For the various oils extracted, the minimum and maximum values were 0.50 and 3.17 mEq ?kg -1; 56.26 and 99.113 mgI 2 ?100 g -1; 1.457 and 1.465; 205.37 and 233.587 mgKOH/g respectively for the peroxide, iodine, refractive and saponification values. The color parameters (L*, a* and b*) of the oils also differ depending on the nature of the organic solvent used. Principal component analysis (PCA) and correlation analysis were performed on the physicochemical properties and the antioxidant potential of the extracted oils. Therefore, the results suggest the mixed use of acetone and hexane to obtain oil comparable to that extracted by cold pressing.
The baobab (Adansonia digitata L.) is an emblematic tree of African savanna [
The fruits were collected in the locality of Bignona (12˚45'0'' North and 16˚30'0'' West), Senegal. A voucher specimen are stored and referenced under a specified identification number. The pulped seeds were washed and then dried at 65˚C for 24 hours in an oven. After drying, the seeds were crushed with a pestle and a mortar and then crushed with a hammer mill (Moulinex, AR 11). The ground product thus obtained was also sieved using a 600 μm mesh sieve to obtain a finer particle size used for the extraction procedures. All analyses such as extraction and chemical parameters were made in duplicate during this work.
The extraction of the oil was carried out using a mechanical press (DD85G, IBG MonfortsOekotec GmbH, Mönchenglabach, Germany). The 10 mm die was used throughout the extraction and the rotational speed of 25 rpm was maintained. The outlet head temperature was also maintained at 105˚C throughout the operation. Beforehand, the exit head was brought to this temperature for about 25 minutes before the start of the extraction operation. At the end of the extraction, the obtained crude baobab oil is a mixture of oil with gummy impurities. This crude oil was immediately packaged in bottles for two days for decantation. The oil was transferred to new bottles and centrifuged (centrifuge Hettich, Zentrifugen, Germany) at 4500 rpm for 10 minutes. The obtained oil was stored at 4˚C for later analyzes.
In this part, the baobab oil was extracted with Soxhlet on particles with particle sizes of less than 600 μm using acetone, chloroform or n-hexane. These solvents were purchased from Prolabo (VWR Chemicals, USA). During extraction of the oil, the temperature of 70˚C ± 2˚C, the extraction time of six (6) hours and the ratio of 1:8 (g/mL) were used based on the optimum parameters obtained on different seeds [
The physicochemical characteristics of extraction oils such as density, acidity, peroxide value, acid value, refractive index, iodine value, saponification value and color index of the extracted oils were determined. The saponification value was determined according to the French standard NF T60-206; The acid value according to standard NF T60-204. The acidity which corresponds to the percentage expression of oleic acid was calculated from the acid value. The iodine value is determined according to the French standard NF T60-203; The peroxide value according to the French standard NF T60-220; The extraction yield according to the standard soxhlet extraction method (NF V03-905). The density was measured by the NF T60-214 method at 25˚C. The polyphenols were assayed according to the method of Georgé et al. [
The antioxidant activity was evaluated with 2.2-diphenyl-1-pyridyrazyl (DPPH) according to the method described by Adaramola et al. [
A principal component analysis (PCA) and a hierarchical classification were carried out on the physicochemical data of the oils in order to find the best correlations between the random variables. The results obtained have been studied by correlation analyzes (Pearson correlation coefficients) between the physicochemical properties and the antioxidant potential of the extracted oils. To compare the averages, this analyzes of variance with the Fisher LSD test at the significance level of 5% were also performed. Thus, all analyzes were carried out with software R (version 3.2.4, 2016).
The physical parameters studied on the various oils of baobab include the extraction yield, the density, the refractive index, the extinction coefficients and the color indices. The results obtained are listed in
Parameters | Pressure | Acetone | Chloroform | n-Hexane |
---|---|---|---|---|
Oilyield (%) | 6.280 ± 0.432a | 23.05 ± 0.614b | 40.12 ± 0.607d | 30.29 ± 0.521c |
Density | 0.911 ± 0.04b | 0.882 ± 0.016a | 0.945 ± 0.013c | 0.902 ± 0.020ab |
Refractive index | 1.464 ± 2.8.10−4 b | 1.459 ± 3.10−4 a | 1.457 ± 3.10−4a | 1.465 ± 3.10−4b |
Iodine value (mgI2・100g−1) | 99.113 ± 0.528d | 83.296 ± 0.558b | 56.266 ± 1.092a | 90.775 ± 0.842c |
Saponification value (mgKOH・g−1) | 233.587 ± 0.478d | 205.371 ± 0.808a | 205.494 ± 0.809c | 209.198 ± 0.791b |
Acid value (mgKOH・g−1) | 18.827 ± 0.309d | 13.701 ± 0.235c | 5.568 ± 0.107a | 12.442 ± 0.089b |
Free fatty acid (%) | 9.463 ± 0.155d | 6.915 ± 0.09c | 2,80 ± 0.054a | 6.254 ± 0.045b |
Peroxyde value (mEq・kg−1) | 2.091 ± 0.579a | 0.498 ± 0.01b | 2.365 ± 0.079a | 3.176 ± 0.244a |
k232 nm | 1.492 ± 0.177ab | 0.862 ± 0.162c | 1.284 ± 0.029a | 1.737 ± 0.292b |
k270 nm | 1.192 ± 0.204ab | 0.883 ± 0.281b | 1.571 ± 0.048a | 1.479 ± 0.471a |
L* | 85.42 ± 0.391a | 85.15 ± 0.13a | 89.30 ± 0.02b | 96.16 ± 0.01c |
a* | −7.74 ± 0.367b | −4.27 ± 0.10d | −6.96 ± 0.05c | −12.22 ± 0.01a |
b* | 92.77 ± 0.121a | 95.68 ± 0.04c | 92.78 ± 0.07a | 87.08 ± 0.02b |
Y1 | 89.64 ± 0.177c | 90.79 ± 0.03d | 88.29 ± 0.02b | 84.10 ± 0.01a |
c* | 93.09 ± 0.101a | 95.77 ± 0.04c | 93.05 ± 0.06a | 87.93 ± 0.01b |
h | 94.77 ± 0.229c | 92.55 ± 0.03a | 94.29 ± 0.03b | 97.99 ± 0.01d |
On the same line, averages with the same letter are not significantly different from the 5% threshold.
The extraction yield was higher with chloroform than with hexane or acetone. Indeed, these yields were 6.28%; 23.05%; 30.29% and 40.12% respectively with pressing, acetone, n-hexane and chloroform. Therefore, the lower polar solvents (n-hexane and chloroform) exhibited the highest oil extraction efficiencies. This difference noted between the hot extraction yields can be explained reasonably by the physicochemical properties of the solvents used [
With regard to density, a significant difference was noted on the extracted oils. Density is an important physical feature in the classification of oils. It depends on the fatty acid composition, the minor compounds and the temperature [
The refractive index for assessing the purity of the oils is between 1.457 and 1.465. The analysis of the variance indicates that there is a significant difference at the 5% threshold for the measured refractive indexes. The refractive index is also affected by the polarity of the extraction solvents. In fact, the oils extracted with the two most polar solvents (chloroform and acetone) had the lowest refractive index. As a result, these two oils would have more long chain fatty acids than other oils. According to Shahidi [
The specific absorption at 232 nm for oils extracted by pressing and solvents (n-hexane, acetone and chloroform) are below the limit values set by the International Oleic Council (IOC) [
The color parameters (L*, a*, b*, Y1, c* and h) of the extracted oils are given in
This value indicates that the oil extracted with acetone is more yellow than those obtained with chloroform, n-hexane and pressing. The b* parameter of the oil obtained by pressing is also similar to that obtained with chloroform. The yellowness index Y1 of the oil extracted with acetone (90.79 ± 0.03) confirms the accentuated coloration of the yolk. On the other hand, Y1 yellowing index values of the oil extracted by pressing and acetone are very close. As a result, the latter two would contain a larger amount of carotenoids [
Parameters | Pressure | Acetone | Chloroform | n-Hexane |
---|---|---|---|---|
Polyphenols (mgEAG/g) | 0.047 ± 0.0024b | 0.026 ± 0.003a | 0.025 ± 0.002a | 0.028 ± 0.004a |
DPPH (%) | 31.71 ± 0.610d | 26.38 ± 0.600c | 9.23 ± 0.670a | 15 27 ± 0.150b |
On the same line, averages with the same letter are not significantly different from the 5%.
The iodine value is used to determine the degree of unsaturation of a vegetable oil and to assess stability during storage [
The peroxide value permit to understand the degree of oxidation of the unsaturated fatty acids. Indeed, the oxidation of the oils leads to the formation of hydroperoxides, primary products of oxidation. Thus, the peroxide value corresponding to the hydroproxide content represents a very useful and very sensitive criterion for assessing the first stages of the oxidative deterioration of a fatty substance and an oil during production and storage [
The saponification values measured are 233.587; 205.494; 205.371 and 209.198 mgKOH・g−1 respectively for oils extracted with pressing, chloroform, acetone and n-hexane. This significant difference noted between the extracted oils can be attributed to the extraction time and/or the physicochemical properties of the solvents. The baobab seed-oil obtained by pressure reveals the highest saponification value. Therefore, this baling oil would contain more short-chain fatty acids for stability during storage. The baobab oils extracted with organic solvents showed the lowest saponification values. These indicate a predominance of long chain fatty acids in these oils [
In order to estimate the quality of the oils extracted, the polyphenol content and the radical scavenging activitywere measured. The results obtained are listed in
The results obtained reveal that oils have variableradical scavenging activities. In other words, our results reveal that the pressing oil has the highest polyphenol content and radical scavenging activity. This antioxidant activity of the pressing oil could be explained by its high content of phenolic compounds. Indeed, some studies have reported a positive correlation between antioxidant activity and phenol content [
The correlation analysis between the physicochemical characteristics of the extracted oils and the antioxidant potential shows a very strong negative correlation of the extraction yield with the radical scavenging activity, the polyphenol content, the acid value, the iodine value and saponification value (
Principal component analysis (PCA) was carried out to evaluate the effect of pressing and/or solvents (acetone, chloroform and n-hexane) on the physicochemical characteristics and antioxidant potential of the extracted oils (
Variables | O. yield | Density | DPPH | Polyph. | R.I. | A.V. | I.V. | P.V. | S.V. | k232 nm | k270 nm | L* | a* | b* | Y1 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Density | 0.170 | ||||||||||||||
DPPH | −0.970 | −0.322 | |||||||||||||
Polyph. | −0.832 | 0.404 | 0.729 | ||||||||||||
R.I. | −0.632 | 0.085 | 0.463 | 0.606 | |||||||||||
A.V. | −0.984 | −0.185 | 0.932 | 0.802 | 0.752 | ||||||||||
I.V. | −0.872 | −0.196 | 0.778 | 0.681 | 0.907 | 0.946 | |||||||||
P.V. | 0.319 | 0.730 | −0.525 | 0.091 | 0.423 | −0.209 | 0.008 | ||||||||
S.V. | −0.807 | 0.444 | 0.696 | 0.999 | 0.608 | 0.779 | 0.664 | 0.133 | |||||||
k232 nm | −0.002 | 0.654 | −0.224 | 0.342 | 0.692 | 0.124 | 0.334 | 0.944 | 0.377 | ||||||
k270 nm | 0.658 | 0.783 | −0.801 | −0.182 | −0.041 | −0.602 | −0.449 | 0.888 | −0.137 | 0.692 | |||||
L* | 0.575 | 0.267 | −0.717 | −0.413 | 0.270 | −0.426 | −0.119 | 0.824 | −0.381 | 0.711 | 0.753 | ||||
a* | −0.139 | −0.433 | 0.346 | −0.082 | −0.668 | −0.017 | −0.298 | −0.917 | −0.113 | −0.948 | −0.664 | −0.870 | |||
b* | −0.230 | −0.378 | 0.426 | 0.034 | −0.605 | 0.070 | −0.227 | −0.905 | 0.003 | −0.909 | −0.679 | −0.919 | 0.993 | ||
Y1 | −0.407 | −0.303 | 0.577 | 0.239 | −0.451 | 0.247 | −0.064 | −0.869 | 0.208 | −0.816 | −0.714 | −0.980 | 0.948 | 0.978 | |
h | 0.148 | 0.405 | −0.353 | 0.057 | 0.665 | 0.010 | 0.297 | 0.907 | 0.087 | 0.936 | 0.653 | 0.880 | −0.999 | −0.996 | −0.955 |
O. yield: oil yield; R.I.: refractive index; S.V.: saponification value; P.V.: peroxide value; A.V.: acid value; I.V.: iodine value; Polyph.: polyphenols.
88.62% of the total variance. Indeed, the first dimension (Dim 1) contributes to 50.81% and the second dimension (Dim 2) to 37.81%. The density variables, peroxide value, specific extinction coefficients (k232 and k270), luminescence L* and chromatic tone h are positively correlated with the first axis, while variables a* (color shade between green and red), b* (shade of color between blue and yellow) and yellowness index Y1 are negative. The parameters for evaluating the oxidation state of the extracted oils are well aligned with this first dimension (Dim 1), which could be considered as an axis of quality. Moreover, the polyphenol variables, radical scavenging activity, refractive index, acid value and iodine value are positively correlated to the second dimension (Dim 2). On the other hand, the yield variable is negatively correlated with this dimension (Dim 2). Furthermore, the parameters representing the antioxidant potential, the state of conservation and the identification of the oils obtained are well aligned with this second dimension. The dimensional axes (Dim 1 and Dim 2) delimit the types of solvents and extraction used. The position on the axis Dim 1 differentiates the oil with the peroxide value, density, specific extinction coefficients (k232 and k270 nm), luminescence L* and h (n-hexane) color tone, to the other oils characterized by the color parameters (a* and b*) and yellowness index Y1 (acetone and chloroform). However, the position on the axis Dim 2 opposes the oils with a polyphenol content, an free radical scavenging activity, a refractive index, a saponification value and a high iodine value (oil extracted by pressing), oils (extracted with chloroform and acetone) in low yield. Thus, based on the physicochemical properties of the oils, it is clear that the oil extracted by pressing best retains its quality. Nevertheless, the solvents (acetone, chloroform and n-hexane) make it possible to obtain oils with a lower radical scavenging activity and Y1 yellowing index. The oil extraction methods have been grouped into three classes. The first class is the oil extracted with acetone. The latter is characterized by a yellowness index and color parameters (a* and b*). Class 2 consists of oil extracted by cold pressing. Finally, class 3 consists of the less polar solvents (chloroform and n-hexane).
In this study, the impact of pressing and solvents on physicochemical characteristics, polyphenol content and radical scavenging activity of baobab oils extracted was determined. The results obtained reveal that the oil extracted by pressing retains at best its physicochemical properties and contains a very high content of phenolic compounds and radical scavenging activity. Also, this oil produced by pressing exhibits a more intense yellow coloration than that obtained from the solvents. However, chloroform provides the best extraction yield. The extraction with n-hexane makes it possible to obtain oils whose physicochemical characteristics are less attenuated. With organic solvents, the oil extracted with acetone, the most polar solvent, exhibits an acceptable radical scavenging activity. Taken together, these results provide fundamental element for decision making regarding the method of extraction to use for specific addressed use of baobab oil. These results suggest the mixed use of acetone and hexane for better conservation of the chemical and bioactive characteristics of baobab oil. Therefore, further studies will be needed to determine the optimal conditions for extracting oil comparable to cold pressed oil and for identifying bioactive compounds.
The authors declare no conflicts of interest regarding the publication of this paper.
Cissé, M., Sow, A., Poucheret, P., Margout, D., Ayessou, N.C., Faye, P.G., Sakho, M. and Diop, C.M.G. (2018) Impact of Extraction Method on Physicochemical Characteristics and Antioxidant Potential of Adansonia digitata Oil. Food and Nutrition Sciences, 9, 937-955. https://doi.org/10.4236/fns.2018.98069