INTRODUCTION:
The genus Curcuma, which belongs to the zingiberaceae
family, is one of the most abundant in the world, with over 100 species; it is very
well known in Asia and Africa for the coloring agents it provides in the culinary
arts1. Essential oils extracted from Curcuma species have been
extensively studied and in a recent review Dosoky and Setzer2 identified
over 170 works relating to the composition and properties of their essential oils,
with Curcuma longa topping the list with 34 % citations, followed by C.
zedoaria (12 %), C. aromatica (12 %), C. aeruginosa (6 %), C.
angustifolia (3 %) and the last third of citations remaining concerns 25 species.
Rhizomes have been studied much more than leaves and in C. longa, for example,
70 % of studies relating to rhizomes, 28 % to leaves and 3 % to flowers were identified.
These studies have demonstrated a very wide variety of chemical profiles, leading
to extremely varied pharmacological properties: anti-inflammatory, anti-cancer,
antiproliferative, hypocholesterolemic, anti-diabetic, antihepatotoxic, anti-diarrheal,
diuretic, anti-rheumatic, hypotensive properties, antioxidant, antimicrobial, antiviral,
insecticidal, larvicidal, antivenom, antithrombotic, antityrosinase properties1,2.
Chemical composition and biological properties studies were available in the literature3
and four at least concern C. mangga rhizomes4-7. The kinetic modeling
of oil extraction, which has been very less studied for the zingiberaceae, almost
exclusively concerns Zingiber Cassumunar8.
In Congo-Brazzaville the Curcuma mangga is used as a food plant to flavor and enhance the taste of stewed fish with its spicy ginger flavor. It could be valued as a medicinal plant as in other parts of the world, although it receives much less attention than C. longa, C. zedoaria and C. aromatica. We have previously evaluated the variability of the chemical composition of the essential oils of the leaves and rhizomes of Curcuma mangga from the “plateau des Cataractes” over three years9 and their antioxidant properties10.
The present work, on the kinetic modeling of the extraction by hydrodistillation of essential oils from the leaves aims at understanding the intimate mechanisms involved during this extraction, which is the basis of any work to scale-up any process.
MATERIAL AND METHOD:
Extraction of essential oil:
The leaves were dried in the shade for 7 days. Plant material (300 g of leaves (m1, dried matter-dm-)) placed in the 1 L flask with 500 mL of water were distillated for 6 hours. The essential oil were extracted with diethyl ether, and dried with the anhydrous sodium sulfate (m2). The yield Y (%) of essential oil extraction is given by:
Y (%) = 100 (m2/m1) dm
Determination
of physico-chemical characteristics:
The
acid value (AV), the ester value (EV) the refractive index (n), the relative density
d20 and the rotary power were determined according to AFNOR standards11.
Gas
chromatography (GC-FID):
The
quantitative analysis of essential oils was carried out by an Agilent model 6890
chromatograph equipped with a DB5 column (20 m × 0.18 mm × 0.18 μm). The oven
temperature was programmed at 50°C for 3.2 min, then heated to 300°C at a speed
of 10°C/min. The temperature of the injector and the flame ionization detector (FID)
were maintained at 280°C. The essential oils were diluted in acetone at 3.5% (v/v)
and injected in mode fractionated (1/60), helium was used as carrier gas (1 ml/min),
the injection volume was 1 μl. At the same time, a solution of n -alkanes (C8-C30)
was analyzed under the same conditions to calculate the retention indices (RI) with
the equation of Van den Dool and Kratz12. The relative concentrations
of the compounds were calculated from the area of the peak obtained by gas chromatography
without using correction factors.
Gas
chromatography/mass spectrometry (GC-MS) tandem:
The
qualitative analysis was carried out using a gas chromatograph model Agilent 7890
coupled to a mass spectrometer model Agilent 5975, equipped with a DB5 column (20
m × 0.18 mm × 0.18 μm). The oven temperature was set up at 50°C and remains
constant for 3.2 min, then raised to 300°C at a speed of 8°C per minute, the temperature
of the injector was 280°C. The ionization was obtained by electronic impact at 70
eV and the electron multiplier was at 2200 eV. The temperature of the ion source
was 230°C. Mass spectral data was acquired in scanning mode in the range m/z 33-450.
The carrier gas flow rate (helium) was fixed at 0.9 milliliter per minute, the identification
of the compounds was made by comparison of their spectra and their retention indices
(RI) with those of libraries such as Adams13and NIST14, and
that made in our laboratory.
Kinetics of extraction:
Phenomenological approach:
Naturally, essential oils are present in very low content in the plant. Their production in profitable conditions over the time (sustainable production) requires basic good knowledge of the extraction mechanisms. During the extraction, the elementary mechanisms take place at molecular level, lower than the size of the particle obtained by grinding the plant matrix which is the macroscopic level of study. The phenomenological approach consists of a series of simplifying hypotheses, to be verified a posteriori, in order to relate the macroscopic manifestations to the phenomena taking place at the molecular level. It is based on Patricelli et al. works15 formalized by So and Macdonald16 and widely validated by Milojevic et al..17, Meziane et al.18 on a very large experimental data of essential oils.
These
hypotheses can be summarized up in seven points: (i) Plant particles are considered
to have properties such as shape, size and contain the initial essential oil (Milojevic
et al17; (ii) The concentration gradients in the fluid phase develop
at scales greater than the size of the particles; (iii) The solvent flow rate is
uniformly distributed in each section of the extractor; (iv) Part of the essential
oil is located on the outer surfaces of the plant particles, f, and the rest is
evenly distributed inside the plant particles (1-f); (v) The essential oil is considered
to be a single component; (vi) The effective diffusion coefficient through plant
particles is constant, and (vii) There is no resistance to essential oil mass transfer
from the outer surfaces of plant particles17.
Tableau
1: Formal kinetic data22
|
|
Zero order (n=0)
|
First order (n=1)
|
Second order (n=2)
|
|
Rate expression
|
Rate = k [A]0
|
Rate = k [A]1
|
Rate = k [A]2
|
|
Integrated rate equation
|
[A]= -k t + [A]0
|
ln[A] = - kt + ln[A]0
|
1/[A] = kt + 1/[A]0
|
|
Half-life expression
|
t1/2 = [A]0/2k
|
t1/2 =0.693/k
|
t1/2 = 1/k[A]0
|
|
Units for k (M1-n t-1)
|
M1 t-1
|
M0 t-1
|
M-1 t-1
|
Milojevic
model:
These
hypotheses lead to the general mathematical expression which describes a simultaneous
two-step extraction (washing and diffusion) proposed by Sovova et al19
which is a sum-expression of two exponential variations of these two steps:
qt/q∞ = Mt/M∞ =
1 – f. exp(-k1t) - (1-f) exp(-k2t) Eq1
If
one considers an instantaneous washing followed by slower diffusion when k1
tends to infinity:
qt/q∞=1- (1-f) exp (-k2t)
Eq2
In
the absence of any washing (f = 0) we obtain a pseudo first order model20:
qt/q∞ = 1- exp (-k2t)
Eq3
(q∞ – qt)/q∞ = exp(-k2t)
Eq4
ln[((q∞ – qt)/q∞] =
k2t Eq5
if qt/q∞ = y
ln[1/1-y] = k2t Eq6
This
first-order kinetic mechanism, known as a washing free mechanism, has, for example,
been valitaded by Hervas et al.21. Much, more recently, Meziane
et al.18 have just established that 80 % of the results from the
literature validate the pseudo first order kinetics independently of the assumptions
made on the models. When the extraction follows these kinetics, its representative
curve is a straight line passing through the origin, with slope k, the kinetic constant.
This allows rapid graphic validation of the models considered. The ordinate at time
origin different to 0, indicates a very fast washing step, this ordinate value is
related to washing step.
Table
1 summarizes the formal kinetic data with simple kinetic orders: 0, 1 and
2.
Peleg
model:
Moreover,
and starting from the similarity of the moisture desorption curves by flour 23
and metabolite desorption (extraction) from solid plant matrices, Bucic-Kojic et
al. 24 applied Peleg's model to the polyphenol extraction from grape
seeds. It is a non-exponential empirical model (Eq5), characterized by two parameters
K1 and K2:
C(t)
= C0 ± t/(K1 + K2t) Eq6
which
leads to the following linear form:
t/Ct
= K1 + K2t Eq7
Adaptated
to essential oil extraction, C(t) means the essential oil (EO) mass extracted (or
extract concentration) at time t; C0 = 0 : the EO mass extracted at t
= 0; C∞ = EO mass extracted at t∞; K1 and
K2 constants obtained (i) by the method of minimization of RMSE in numerical
computation or (ii) graphically by the equation Eq 7. According Jovic et al.25
and Bucic-Kojic et al.24, K1 and K2 mean
respectively Peleg kinetic constant in (t. C-1) unit and Peleg extraction
capacity constant in (C) unit. K1 is related to B0, kinetic
constant at initial times (t = t0) by: B0 = 1/K1
(C. t-1 units) and K2 to Ce, concentration of the
metabolite extracted at the end of extraction equilibrium (t∞)
by: Ce = 1/K2 (C units). This model was adapted to essential
oils by Farhana et al.26 with the same meaning for the constants
K1 (Peleg kinetic constant) and K2 (Peleg extraction capacity
constant). Starting from the equation Eq7, we graphically determined K2,
the slope of the straight line, and K1 ordinate at the origin of the
line t/Ct = f(t). In the two-step phenomenological approach, K1
characterizes the rapid washing from destroyed cells and K2, the balance
of essential oil at the solid/liquid interface governed by the diffusion of the
essential oil inner the plant material. The hydrodistillation kinetic constant was
given by k = K2/K1 (t-1). The phenomenological
approach using the formalism of formal kinetics makes it possible to achieve the
macroscopic kinetic and thermodynamic quantities necessary for the scaling up of
extraction processes27.
RESULTS AND DISCUSSION:
There
was no information on Curcuma mangga Val. and Zijp from Africa before the
present study, which was carried out for 3 years on the “plateau des Cataractes”
in Congo-Brazzaville and in four localities: Loukoko, Mindouli, Loulombo and Brazzaville.
The results relating to the chemical variability of essential oils and the biological
properties have just been published9-10. The physicochemical characteristics
and chemical compositions of the essential oils of the leaves are given here for
illustration and serve to support the kinetic modeling of the extraction.
Characterization
of essential oils:
The
physicochemical characteristics of the essential oils of the leaves of Curcuma
mangga from Loukoko and Mindouli studied are reported in Table 2. These are
pale yellow oils extracted respectively with a yield of 0.56 and 0.65 %, relative
densities d20 : 0.88 and 0.91, refractive indices n : 1.47and 1.48, rotary
power : - 0.04 and -0.05; acid values AV: 0.53 and 0.59 and ester
values EV : 16.25 and 16.29.
Table
3 gives the chemical composition of the leaf essential oils of Curcuma mangga
from the “plateau des Cataractes” in Congo-Brazzaville. Extraction leads an essential
oil consisting mainly of two sesquiterpene hydrocarbons: ar-curcumene (21.00-26.78
%), ᾳ-zingiberene (5.49-9.90 %), one monoterpene hydrocarbon in the two isomeric
forms: α and β pinenes (0.25 -7.76 %), monoterpenes oxygenated : 1,8cineole
(2.17-16.86 %) and monoterpene hydrocarbons, with lesser content: β- bisabolene
(4.40-6.06 %), Camphor (5.86-6.61 %)9.
Kinetic
modeling of the extraction of leaf essential oil of Curcuma mangga Val. and Zijp
Essential
oil extraction:
Table
4 gives the variation in the extraction yield of leaf essential oil of Curcuma
mangga as a function of the extraction time t. The low value of standard deviation suggests a similarity
of the extraction mechanism over the 3 years of the study.
Yt = f(t) has the general shape of the metabolite extraction curves (vegetable oil, essential oil, polyphenols, carotenoids, etc.) from solid plant matrices (stem, leaf, flower, roots, rhizome, bark, etc.) In Figure 1, one distinguishes its two characteristic steps, schematized by the straight lines a and b28. The break in slope supports the hypothesis of the two steps extraction: (i) rapid washing for the extraction of the metabolite in the broken cells (line a) and (ii) slow diffusion of the metabolite in the cells which have remained intact before extraction at the solid-liquid interface (line b). This is the 2 steps extraction as suggested by Milojevic et al.17 in the phenomenological approach. When the washing step of the broken cells is very rapid compared to that of the intra-particle diffusion of the intact cells, the process proceeds as pseudo first order kinetic. Otherwise, it proceeds like kinetic of order 2. The experimental results validate one of the two hypotheses.
Figure
1: Variation of the extraction yield Y (%) as a function of extraction time t for
Curcuma mangga from «Plateau des Cataractes».
The
results of Table 5 and straight line in figure 2 validate the first order kinetics
(Figure 2).
Figure
2: Validation of the pseudo first order model with experimental data of Curcuma
mangga leaf essential oils from « plateau des Cataractes »
Without washing step, the extraction of the essential oil of Curcuma mannga from the “plateau des Cataractes” run under a pseudo first order diffusion mechanism given by the equation ln(1/(1-y)) =0.6714 t - 0.1152 with a kinetic constant k = 0.6714 h-1, a good coefficient of determination R2 = 0,9798 and a half-process time t1/2 = 0.693/k = 1.03 h. The intercept of the straight line and time axis (ordinate at the origin) different of 0 validates the existence of a rapid washing step prior to the diffusion controlled one (Figure 2). One needs Y∞, yield at t = ∞ for validation of the pseudo first order kinetics; it corresponds to the value of the asymptotic ending of Yt = f (t), and is equal to 1.66 %. The straight line 1/Yt = f(1/t) leads to Y∞, by extrapolation to t = ∞ (1/t = 0). Figure 3 gives, by its ordinate at the origin, Y∞ = 2.19 %.
Figure 3: Graphical determination of Y∞ by 1/Yt = 0.8513(1/t) + 0.4557 (R² = 0.9985).
Moreover, the straight line 1/Yt = f (1/t) is also used for the validation of the Monod model which postulates a variation Yt = f(t) similar to that of the enzymatic kinetics based on the Michaelis –Menten equation22, 29:
Yt = Ymax [1 / (Km + t)] Eq1
1/Yt = (Km/Ymax) (1/t) + (1/Ymax) Eq2
with Y: yield of extracted oil at time t (g/100g); Ymax, yield at time t∞,; Ymax/Km: slope of straight line, Km: Monod equation parameter.
The equation 1/Yt = 0.8513(1/t) + 0.4557, (R² = 0.9985, Figure 3) leads to Ymax = 1/0.4557 = 2.19 % and kinetic constant Km = 0.8513x 2.19 % = 1.87 % h-1. Mejri29 validate the Monod model with experimental data of essential oil extraction from Ruta chalepensis: Km=80.28 min (ml/100g)-1; Ymax= 7.69 mL/100g, R2= 0.99. The essential oil extraction of Ruta chalepensis according to the Monod model is done twice as slowly but leads to more than 4 times more essential oil than in Curcuma mangga.
Data on Table 6 validate Peleg's model with a very good coefficient of determination (Figure 4, R2 = 0,9983).
The
extraction of leaf essential oil from Curcuma mangga from the “Plateau des
Cataractes” can be considered as a two-step extraction (washing/diffusion) based
on Peleg's modified model. The straight line t/Yt = f(t) leads to the
Peleg kinetic constant K1 = 0.852 h.%-1, the Peleg extraction
capacity constant: K2 = 0.4537 %-1 and kinetic constant of
hydrodistilation k= K2/K1 = 0.5325 h-1
Figure
4: Validation of the Peleg model with experimental data of Curcuma mangga from « plateau des Cataractes »
These
values should be compared with the those obtained elsewhere relating: Cymbopogon
nardus30, K1 = 0.76 min. %-1; K2=35.08
%-1, k= 0,0200 – 0.0215 min-1; Ocimum basilicum31 :
the second order rate constant K1 varies from 3.4468-7.4456 min.
%-1 and the extraction capacity constant K2 from 0.9361 to
0.9701 %-1, k =0.1303-0.271 min-1, Cymbopogon winterianius26 :
K1 = 19.09 min. (g/g)-1 and K2 = 0.0301 (g/g)-1.
The extraction of essential oils from Cymbopogon nardus, Ocimum basilicum, Cymbopogon
winterianus and Curcuma mangga which can be described by the same model,
involves very variable extraction times. Two types of hypotheses on the extraction
mechanism are validated by the experimental data for Cucurma mangga leaves:
(i) A washing step negligible to the intra-particle diffusion, the extraction follows
pseudo first order kinetics with k = 0.6714 h-1; t1/2 =
1.03 h; Y∞exp = 1.66 % and Y∞th = 2.19%. (ii)
the extraction behaves as a two-step process, according to the modified Peleg model,
with a kinetic constant of order 2, K1 = 0, 852 h.%-1 and
an extraction capacity constant, K2 = 0,4537 %-1.
Do
the major constituents analyzed for each fraction collected as a function of the
extraction time (Table 6) obey the same kinetics or do they evolve independently
of the overall total essential oil kinetics on the one hand and independently of
each other’s during the extraction, on another hand?
Oil
major constituent extraction:
Figure 5 shows the behavior of the first seven major constituents of oil. .
Figure 5: Extraction curves for the main constituents of the leaf essential oil of Cucurma mangga from the « Plateau des Cataractes » in Congo-Brazzaville
The variation of their constituent contents during the extraction process was highlighted by the radar-plots of the essential oils collected in different fractions of the total oil: the content of ar-cucurmene, α-zingiberene, β-bisabolone and β-sesquiphellandrene increases and that of 1,8-cineole decreases (figure 6).
Figure
6 : Radar-plots of major constituents of different fractions of the leaf curcuma
manga leaf essential oils from
“plateau des Cataractes”
Figure 5 highlights at least three extraction patterns : (i) the behavior similar to that of total essential oil with regard to ar-cucurmene, the most abundant constituent in the oil; (ii) the almost linear increase in content of β bisabolone, β sequiphellandrene and α zingiberene, constituents in the middle of the scale of individual contents; (ii) the steady decrease in the content of cineole, camphor and pinenes, constituents at the bottom of the scale, after a maximum increase during the first hour of extraction.
Table
6: Extraction of the main constituents of Curcuma mangga leaf essential oil
from the « Plateau des Cataractes » in Congo-Brazzaville
|
Time t (h)
|
1
|
2
|
3
|
4
|
5
|
6
|
|
ᾳ-pinene
|
5.38
|
1.36
|
0.34
|
0.00
|
0.00
|
0.00
|
|
β-pinene
|
4.32
|
1.20
|
0.00
|
0.00
|
0.00
|
0.00
|
|
1,8-cinéole
|
21.34
|
7.29
|
2.36
|
1.05
|
0.22
|
0.45
|
|
Camphor
|
6.11
|
2.58
|
1.15
|
0.53
|
0.27
|
0.394
|
|
Ar-curcumene
|
8.74
|
18.99
|
23.13
|
23.6
|
20.72
|
18.61
|
|
ᾳ-zingiberene
|
4.22
|
9.54
|
15.62
|
24.08
|
27.81
|
31.31
|
|
β-bisabolone
|
1.87
|
4.26
|
6.32
|
8.41
|
9.22
|
9.37
|
|
β-sesquiphellandrene
|
5.04
|
10.92
|
16.1
|
20.83
|
23.13
|
24.82
|
|
Caryophyllene-oxide
|
1.31
|
0.62
|
0.28
|
0.00
|
0.00
|
0.00
|
|
Curzerenone
|
2.90
|
4.26
|
0.37
|
2.66
|
2.00
|
1.63
|
|
Germacrone
|
5.22
|
3.89
|
3.33
|
2.06
|
1.16
|
0.62
|
|
bisabolone<6S,7R->
|
1.84
|
2.34
|
1.68
|
0.85
|
0.71
|
0.25
|
Pattern 1:
Ar-cucurmene, the first constituent of oil, presents an extraction curve similar to that of the extraction of the total oil up to 4 hours of extraction, which is a sufficient time for the extraction in the labo-scale of almost all of the essential oils met in the literature. Beyond 4 hours, the essential oil evolves in an asymptotic ending, while the curve of ar-cucurmene begins a gradually decreasing (Figure 5). The experimental data validate the kinetic model of the pseudo first order, despite the reduced number of experimental points and do not validate the modified Peleg model (Table 7). The extraction of the major constituent is carried out as for the total oil according to the pseudo first order kinetic model up to 4 hours of extraction, out of the 6 hours required to extract 90 % of total essential oil (Figure 7 : ln[1/(1-y)] = 1.75t - 1.5233 with R² = 0.9681). The content of this constituent gradually decreases during the asymptotic cessation of the extraction of total oil.
Figure
7: Fitting pseudo first order model to experimental data for ar-curcumene
Table
7: Data used for model test for ar- curcumene.
|
t(h)
|
0
|
1
|
2
|
3
|
4
|
5
|
6
|
|
Y(%)
|
0
|
8.74
|
18.99
|
23.13
|
23.60
|
20.72
|
18.61
|
|
y=Yt/Y∞
|
0
|
0.37
|
0.80
|
0.98
|
1.00
|
-
|
-
|
|
ln[1 /(1-y)]
|
-
|
0.41
|
1.61
|
3.91
|
-
|
|
|
Pattern
2:
Three
sesquiterpenes which follow ar-cucurmene: α-zingiberene, β-bisabolone
and β-sesquiphellandrene are extracted according to a kinetic of order 0, i.e.
at constant rate (table 1), with very good coefficients of determination varying
from 0.9267 to 0.9828 (Figure 8), with, α-zingiberene and β-sesquiphellandrene
which come out 3 to 4 times faster (k = 5.6777 %.h-1 and 4.0074 %.h-1)
than β-bisabolone (k = 1.5563 %.h-1).
Pattern 3:
Three other constituents:
1,8 cineole, α and β pinenes and
β bisabolone constitute
the third example. Their representative curves go through a maximum oil content
greater than 5% and which may exceed 20 % from the first hour of extraction. Taking
into account the uncertainty of the oil evolution at the initial instants of the
extraction, it is difficult to discuss meaning of the passage through a maximum
content for these three constituents, two of which are minor constituents and the
third behaves like minor in 5 out of 6 samples. It seems more judicious to focus
attention on the continuous decrease in the contents of these three constituents
after the first hour (about 17 % of the total duration of extraction) to characterize
the process.
Figure 8: Validation of 0-order kinetics by the experimental extraction data of α-zingiberene, β-bisabolone and β-sesquiphellandrene
However, one can well imagine a provision of all of these constituents by an extremely fast mechanism at the diffusion stage which controls a much slower extraction. It would be more judicious to move towards a numerical simulation to test empirical models according Semerdjieva et al. work32. But such work has a limited impact on the practical aspects of our research on the “plateau des Cataractes” in Congo-Brazzaville. However, the general appearance of the extraction curves in the figure refers to the Monod model based on the basic assumptions of enzymatic kinetics and as we saw previously is validated by the line 1/Yt = f (1/t). These curves recall the evolution of the enzyme- substrate complex from the quasi-stationary state in enzymatic kinetics for species present in low or even very low concentration. Unfortunately the experimental results do not validate this last model.
CONCLUSION:
The
experimental data of the extraction of essential oil from the leaves of Curcuma
manga from the “plateau des Cataractes” validate two models of the phenonenological
approach. These are in increasing order of relevance: (i) the pseudo first order
Milojevic model and (ii) the Peleg model. The extraction takes place in two steps:
(i) a step of rapid washing of the essential oil located at the surface of the broken
cells and (ii) a step controlled by the intra-particular diffusion of the essential
oil into the cells remaining intact. When the washing step is very fast compared
to the diffusion step, the mechanism involves in a simple pseudo first order kinetic.
Otherwise, the mechanism is related to the empirical model of Peleg characterized
by a kinetic constant allowing to access the kinetic constant of extraction of order
2 and a constant of extraction capacity allowing to reach the oil concentration
at equilibrium at the end of extraction (t∞). These two models
lead to concordant results which can be used for scaling-up of extraction processes.
The extraction of the first five constituents, representing (61 -66 %) of the total
oil is carried out according to 3 highly probable patterns: (i) pseudo first order
kinetics for the most abundant constituent representing nearly a third of the essential
oil (ar- curcumene); (ii) zero order kinetics for the abundant constituents of the
oil and (iii) complex kinetics with the passage through a maximum after one hour
of extraction for constituents in small quantities. This observation reflects the
extreme complexity of the phenomenon of extracting essential oils.
CONFLICT OF INTEREST:
The authors declare no conflict of interest.
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