Selective separation of mono glyceryl ferulate using water from an ionic liquid solution of enzymatic transesterification

Article abstract of DOI:10.1007/s11746-014-2491-5

Mono glyceryl ferulate (MFG), an all-natural derivative of ferulic acid, can be used as antioxidant and a UV filter in food and cosmetic formulations. However, the applications of MFG in these fields are limited due to its low availability in nature. In this work, a novel method for selective separation of MFG from a room temperature ionic liquid (RTIL) solution of enzymatic transesterification of ethyl ferulate with glycerol was investigated. The effects of different extractants and extraction conditions on the selective separation of MFG were also studied. High extraction yields of MFG (98.23 ± 1.09 %) and the relative content of MFG in the extracts (97.76 ± 1.25 %) were achieved using neutral deionized water as extractant under the following conditions: 0.5:1 volume ratio of water to RTIL solution, extraction time of 6 min, centrifugation time of 6 min, and extraction done eight times. The extraction thermodynamics showed that the extraction of MFG was an exothermic process. The purified MFG exhibited good UV adsorbing properties at 280-360 nm with a λ _max at 322 nm.

Full text of DOI:10.1007/s11746-014-2491-5

J Am Oil Chem Soc
DOI 10.1007/s11746-014-2491-5
ORIGINAL PAPER
Selective Separation of Mono Glyceryl Ferulate Using Water
from an Ionic Liquid Solution of Enzymatic Transesterification
•
•
•
Shangde Sun Xiaowei Chen Yanlan Bi
Guolong Yang
Received: 25 January 2014 / Revised: 13 May 2014 / Accepted: 13 May 2014
Ó AOCS 2014
Abstract Mono glyceryl ferulate (MFG), an all-natural
derivative of ferulic acid, can be used as antioxidant and a
UV filter in food and cosmetic formulations. However, the
applications of MFG in these fields are limited due to its
low availability in nature. In this work, a novel method for
selective separation of MFG from a room temperature ionic
liquid (RTIL) solution of enzymatic transesterification of
ethyl ferulate with glycerol was investigated. The effects of
different extractants and extraction conditions on the
selective separation of MFG were also studied. High
extraction yields of MFG (98.23 1.09 %) and the rela-
tive content of MFG in the extracts (97.76 1.25 %) were
achieved using neutral deionized water as extractant under
the following conditions: 0.5:1 volume ratio of water to
RTIL solution, extraction time of 6 min, centrifugation
time of 6 min, and extraction done eight times. The
extraction thermodynamics showed that the extraction of
MFG was an exothermic process. The purified MFG
exhibited good UV adsorbing properties at 280–360 nm
with a kmax at 322 nm.
Introduction
Mono glyceryl ferulate (MFG) is a water-soluble natural
derivative of ferulic acid (4-hydroxy-3-methoxy cinnamic
acid, FA) found ubiquitously throughout the plant king-
dom, which has a capacity for antioxidation, UV absorp-
tion and antitumor activity in food, pharmaceutical, and
cosmetic applications [1–4]. But, it is difficult to separate
MFG from raw materials in nature since the content of
MFG in nature is very low (\0.1 %) [5], which made MFG
synthesis very interesting [6–8].
In our previous reports, MFG was successfully prepared
by the transesterification of ethyl ferulate (EF) and glycerol
or monostearin in a solvent-free system, which required
a tenfold excess glycerol to EF as reactant and solvent
[9–11]. To separate and purify MFG from these trans-
esterification products, a C18 chromatography column and
excess aqueous methanol solution were used [12]. In order
to avoid the effect of excess glycerol used, we developed a
novel ionic liquid reaction system to obtain MFG and
glyceryl diferulate (DFG) using 1:1 molar ratio of EF and
glycerol [13]. However, the transesterification product was
a mixture of MFG (56.61 %) and DFG (39.76 %). For
obtaining high purity water-soluble MFG, selective sepa-
ration of MFG from the transesterification mixtures is
needed.
Keywords Room temperature ionic liquid ꢀ Mono
glyceryl ferulate ꢀ Selective separation ꢀ Extraction
thermodynamics ꢀ Enzymatic transesterification
Room-temperature ionic liquids (RTILs), as green and
designed solvents, are salts that are composed entirely of
ions with melting points below room temperature [14, 15].
RTILs, owing to their excellent properties, such as low
vapor pressure, low combustibility, excellent thermal sta-
bility, wide liquid regions, and favorable solvating proper-
ties for a range of polar and non-polar compounds, have
been widely used as reaction media and extraction additives
for bioactive compounds from plants [16–23]. However, to
Electronic supplementary material The online version of this
article (doi:10.1007/s11746-014-2491-5) contains supplementary
material, which is available to authorized users.
S. Sun (&) ꢀ X. Chen ꢀ Y. Bi ꢀ G. Yang
Lipid Technology and Engineering, School of Food Science and
Engineering, Henan University of Technology, Lianhua Road,
Zhengzhou 450001, Henan, People’s Republic of China
e-mail: sunshangde@hotmail.com
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J Am Oil Chem Soc
Fig. 1 Synthesis of MFG by the enzymatic transesterification of EF with glycerol using Novozym 435 (an immobilized Candida Antarctica B
lipase) as a catalyst in [BMIM]PF6
Table 1 The composition of enzymatic transesterification mixture
the best of our knowledge, no information about MFG
separation from a RTILs solution has been found.
MFG
FA
DFG
EF
In this work, MFG was prepared by the transesterifica-
tion of EF with glycerol (molar ratio, 1:1) catalyzed by
Novozym 435 in [BMIM]PF6 (Fig. 1). A novel green and
effective method for selective separation of MFG from a
RTIL solution was developed. The effects of different
extractants (water, acetic acid, ethanol, 20 % aqueous
ethanol (v/v), 40 % aqueous ethanol (v/v), isopropanol, and
chloroform) and extraction conditions (extraction temper-
ature, pH value, extraction time, centrifugation time, vol-
ume ratio of water and RTIL solution) on the selective
separation of MFG from the transesterification mixture
were investigated. Multistep extraction and extraction
thermodynamics were studied. The UV absorption char-
acteristic of purified MFG was also evaluated.
Relative content (%)
Concentration (mol/L)
56.61
0.56
39.76
2.98
0.2264
0.0022
0.1590
0.0119
MFG Mono glyceryl ferulate, FA Ferulic acid, DFG Glyceryl difer-
ulate, EF Ethyl ferulate
Enzymatic Transesterification of EF with Glycerol
for MFG Synthesis in RTIL
Mono glyceryl ferulate was prepared in 100 mL round
bottom flasks with a vacuum evaporator. EF (15 mmol)
was mixed with glycerol (15 mmol), which was catalyzed
by Novozym 435 (2.58 g) at 85 °C in 33.5 mL
[BMIM]PF6. The reaction mixture was stirred with a
magnetic stirrer (300 rpm, radius 17.5 mm) for 10 h under
10 mm Hg vacuum pressure. Then, the RTIL solutions of
the transesterification mixture were obtained by filtration to
remove the immobilized Novozym 435. The composition
of the enzymatic transesterification mixture was analyzed
by HPLC and is shown in Table 1.
Materials and Methods
Materials
Ethyl ferulate (purity [ 99 %) was purchased from Suzhou
Chang Tong Chemical Co., Ltd. (Suzhou, China). Glycerol
(purity [ 99 %) was purchased from Tianjin Ke Mi Ou
Chemical Co., Ltd. (Tianjin, China). Novozym 435 (Can-
dida antarctica lipase immobilized on polyacrylic resin,
with an activity of 7,000 U/g solid enzyme, where one unit
(U) of activity is defined as the amount of enzyme, which
can catalyze the transformation of 1 lmol substrate per
minute under standard conditions) was provided by
Novozymes A/S (Bagsvaerd, Denmark). 1-butyl-3-meth-
ylimidazolium hexafluorophosphate [(BMIM)PF6, C99 %]
was obtained from Henan Lihua Pharmaceutical Co., Ltd.
(Anyang, China). Methanol and glacial acetic acid were of
HPLC grade. All other solvents were of analytical grade.
Selective Separation and Purification Process of MFG
The separation and purification process of MFG were per-
formed as shown in Fig. 2. RTIL solutions (2 mL), con-
taining the transesterification mixture and different
extractants (such as water, acetic acid, 20 % aqueous ethanol
(v/v), 40 % aqueous ethanol (v/v), 60 % aqueous ethanol (v/
v), 80 % aqueous ethanol (v/v), ethanol, isopropanol, chlo-
roform, acetone, and methanol), were transferred to 20 mL
centrifuge test-tubes, shaken to obtain a homogeneous sys-
tem, and then centrifuged at 1,795 or 12,000g (relative cen-
trifugal force) and 25 °C for 0–12 min to make the mixtures
layered. After the supernatant was removed, the [BMIM]PF6
solution at the bottom of the centrifuge tube was extracted
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J Am Oil Chem Soc
Fig. 2 Selective separation and purification process of MFG from RTIL solution
again according to the above extraction method. The super-
mS
CS ꢀ VS
ꢀ VRTIL
E ¼
D ¼
Sij ¼
R ¼
¼
ꢁ 100 %;
ð1Þ
ð2Þ
ð3Þ
ð4Þ
natants were combined and extractants were removed at
70 °C by a vacuum-rotary evaporator with 85 rpm (radius
16 mm) to obtain the raw MFG product. Then, the raw MFG
product was redissolved in water, and crystallized using a
program thermostat with agitation at 20 rpm. The program of
crystallization was as follows: samples were melted at 40 °C
and kept at this temperature for 0.5 h; then the solutions were
cooled to 10 °C at 1 °C/min; after 2 h, the solutions were
cooled again to 5 °C at 0.05 °C/min and then maintained at
5 °C for 30 h. Then, the crystal obtained in the crystallization
was isolated by filtration and dried in a freeze dryer (-49 °C,
0.1 MPa) to achieve the white MFG powder.
m
C
RTIL0
s0
CS
CS ꢀ VRTIL
¼
;
CRTIL CRTIL ꢀ VRTIL ꢂ CS ꢀ VS
Di
0
;
Dj
MFG
ꢁ 100 %;
MFG þ DFG þ FA þ EF
where CRTIL , CRTIL, and CS are the initial and equilibrium
0
concentrations of MFG in the RTIL phase and the equi-
librium concentrations (mol/l) of MFG in the solvent
phase, respectively. ms and ms (mg) are the initial mass of
0
MFG in the RTIL phase and the equilibrium mass of MFG
in the solvent phase, respectively. VRTIL and VS (mL) are
the volumes of the RTIL phase and the solvent phase at
25 °C, respectively.
Quantitative Analysis
The relative contents of MFG in the separation were ana-
lyzed by HPLC with a reversed-phase Symmetry C18
(5 lm, 250 9 4.6 mm) column fitted with a dual absor-
bance detector at 325 nm. The mobile phases were solvent
A (water, 0.5 % v/v glacial acetic acid) and solvent B
(methanol) at 1 mL/min. The elution sequence consisted
consecutively of a linear gradient from 20 % (v/v) B to
85 % (v/v) B in 24 min, then to 20 % B for 6 min, fol-
lowed by an isocratic flow of 20 % B for 5 min at 35 °C.
ET(30), a measure of solvent polarity referring to the molar
electronic transition energies (ET) of the dissolved substance,
was measured according to a published procedure [24].
In the separation process, the extraction efficiency of MFG
was evaluated by the extraction yield (E), the distribution
coefficient (D), the selectivity coefficient of the solute i to
the solute j (Si/j), and the relative content (R) of MFG, which
can be calculated as Eqs. (1), (2), (3), and (4), respectively.
Statistical Analyses
All experiments were performed at least in triplicate.
Results were expressed as average SEM. A two-way
analysis of variance (ANOVA) was used. Statistical sig-
nificance was considered as p \ 0.05.
Results and Discussion
Effect of Different Extractants
Six extractants with different polarities were selected for
evaluating the separation of MFG (Fig. 3). The extraction
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J Am Oil Chem Soc
Table 2 Distribution ratios and selectivity coefficients of different
extractants
Solvent
ET(30)
D
SMFG/DFG
Water
63.1
51.7
51.9
0.4126 0.0029a
0.4054 0.0003
0.1270 0.0002
0.1700 0.0022
627.35 4.43
2.58 0.16
2.30 0.01
44.99 0.58
Acetic acid
Ethanol
20 % Aqueous
ethanol (v/v)
40 % Aqueous
ethanol (v/v)
0.2672 0.0027
6.38 0.06
Isopropanol
Chloroform
48.4
39.1
0.2133 0.0024
0.0986 0.0021
3.22 0.04
0.49 0.01
Extraction conditions: extraction time, 6 min; centrifugation time,
6 min; volume ratio of water to RTIL solution of transesterification
mixture, 6:1; room temperature (25 °C)
D distribution ratio of FG in extractants other than that of RTIL
solution
Fig. 3 Effects of different extractants (water; acetic acid; ethanol;
20 % aqueous ethanol (v/v); 40 % aqueous ethanol (v/v); isopropa-
nol; chloroform) on the extraction yield (column) and the relative
content (line) of MFG
SMFG/DFG selectivity coefficient, the molar ratio of MFG to DFG
a
Error bars reflect the standard deviation associated with three
replicates
yield of MFG using different extractants decreased in the
order of water [ acetic acid [ 40 % aqueous ethanol
(v/v) [ isopropanol [ 20 % aqueous ethanol (v/v) [ eth-
anol [ chloroform. However, for MFG content in the ex-
tractants, the order was water [ 40 % aqueous ethanol
(v/v) [ chloroform [ 20 % aqueous ethanol (v/v) [ iso-
propanol [ ethanol [ acetic acid. The distribution ratios
([0.4) of water were higher than those (\0.3) of other
extractants (Table 2), which may be attributed to the higher
polarity (ET(30)) of water (63.1) than that of other ex-
tractants (B51.9) and [BMIM]PF6 (52.5) [25]. The selec-
tivity capability for MFG using water ([600) as extractant
was much higher than those (\50) of other extractants,
which can be explained by the fact that the hydrophilicity
and polarity of MFG with two free hydroxyl groups were
greater than those of DFG and EF. When 60 % aqueous
ethanol (v/v), 80 % aqueous ethanol (v/v) (ET(30), 53.7),
acetone (ET(30), 42.2), and methanol (ET(30), 55.4) were
used as extractants [24], MFG can not be separated from
RTIL solution (data not shown). The effect of extractants
on the separation of MFG also suggested that the separa-
tion driving force was hydrophilic interaction. Considering
the selective separation efficiency for MFG and environ-
ment-friendly extractants, water was the best extractant for
the next experiments.
of MFG rapidly decreased to 55.55 0.07 %; which may be
attributed to the fact that, using high pH water as extractant,
the organics of DFG, FA, and EF are easily ionized, and
partition into water from the RTIL solution. Therefore,
considering the environment-friendly separation, the next
experiments were carried out using neutral deionized water.
Effect of Extraction Temperature and Extraction Time
When the extraction temperature increased from 10 to 30 °C,
the extraction yield and the relative content of MFG were
almost maintained at the same levels (65.05 1.20 % and
94.57 0.30 %). When the temperature was above 30 °C,
with the increasing of extraction temperature, the extraction
yield of MFG gradually decreased from 65.67 0.40 % at
30 °C to 56.63 0.64 % at 90 °C, which can be explained
by the fact that higher extraction temperatures can decrease
the viscosity of [BMIM]PF6 and increase the dissolving
capacity of [BMIM]PF6 for MFG. Among tested extraction
temperatures, the relative content of MFG was almost
maintained at 94.88 0.10 %. Therefore, the best extrac-
tion temperature was room temperature (25 °C).
In order to evaluate the best separation conditions of
MFG, two kinds of mixing mode (ultrasound and vortex
mixing) were compared. Results showed that the separation
efficiency of MFG using vortex mixing was higher than
that of ultrasound (Table 3). The effect of extraction time
from 0.5 to 14 min on the separation of MFG was also
evaluated (Electronic Supplementary Materials 1). The
extraction yield of MFG rapidly increased up to the max-
imum (69.91 1.68 %) at 6 min. The relative content of
MFG in water also showed a similar change to that of the
Effect of pH of Water
When the pH of water increased from 2 to 10, the extraction
yield and the relative content of MFG remained nearly
constant, at 72.54 2.81 % and 93.62 2.95 %, respec-
tively. When the pH of water was 12, the extraction yield of
MFG increased to 91.22 2.01 %, but, the relative content
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J Am Oil Chem Soc
Table 3 Effect of mixed modes on extraction efficiency of MFG
Mixed mode
Extraction yield
of MFG (%)
Relative content
of MFG (%)
Ultrasounda
Vortex mixingb
53.57 0.34c
71.23 1.72
88.94 0.19
94.81 2.87
a
Ultrasonic power: 400 W for 15 min
b
c
Extraction time: 6 min, and the vortex speed: 2,800 r/min
Error bars reflect the standard deviation associated with three
replicates
extraction yield of MFG. However, a longer extraction
time (C14 min) at 25 °C may be increasing the oxidation
of FA and MFG at normal pressure [26]. Therefore, 6 min
was employed as the best extraction time in the following
experiments.
Fig. 4 Effect of volume ratios (0.5:1; 1:1; 2:1; 4:1; 6:1; 8:1; 10:1;
12:1) of water to the RTIL solution of transesterification mixture on
the extraction yield (column) and the relative content (line) of MFG.
Extraction conditions: extraction time: 6 min; centrifugation time,
6 min; and 25 °C
Effect of Centrifugation Time
The centrifugation speed showed no significant effect on
the extraction yield and the relative content of MFG among
the tested speeds (Electronic Supplementary Materials 2).
However, the extraction yield and the relative content of
MFG in water increased with the increased centrifugation
the selective separation of MFG was investigated (Fig. 5).
When the RTIL solution was extracted by water (water to
RTIL solution, 0.5:1, v/v) for three times, the relative
content of MFG in water increased to the maximum
(98.39 0.11 %). After four times, the relative content of
MFG in water smoothly decreased. However, the total
extraction yield of MFG rapidly increased to the maximum
(98.23 1.09 %) when the RTIL solution was extracted
for eight times. When the RTIL solution was extracted by
water (water to RTIL solution, 1:1, v/v) for seven times,
the total extraction yield of MFG showed the similar
change with that of 0.5:1 (water to RTIL solution, v/v). The
total extraction yield of MFG increased to the maximum
(*99 %). However, the relative content of MFG in water
using a 1:1 volume ratio of water to the RTIL solution
smoothly decreased from 97.63 0.46 % for one time to
93.79 0.68 % at seven times. Thus, extraction at eight
times using 0.5:1 volume ratio of water to the RTIL
solution was used to achieve a better extraction efficiency
of MFG.
time from
0 to 12 min, and reached equilibrium
(69.27 1.96 %) at 6 min. So, 6 min of centrifugation
time was used in subsequent experiments.
Effect of Volume Ratio of Water to the RTIL Solution
of Transesterification Mixture
To evaluate the effect of the volume ratio of water to the
RTIL solution on the extraction efficiency, experiments
were performed at the volume ratios of water to the RTIL
solution ranging from 0.5:1 to 12:1 (v/v) (Fig. 4). Results
showed that the increase of the volume ratios of water to
the RTIL solution from 0.5:1 to 4:1 resulted in a linear
increase of the extraction yield of MFG, and the relation-
ship between the concentration of MFG (CW) in water at
equilibrium and the initial concentration of MFG in RTIL
(CRTIL ) can be written as: CW ¼ ðVRTIL=VWÞCRTIL . When
0
0
the volume ratio of water to the RTIL solution was greater
than 4:1, the extraction yield of MFG smoothly increased
and then reached equilibrium. However, the relative con-
tent of MFG in water smoothly decreased with the
increasing of the volume ratios from 0.5:1 to 12:1, which
may be attributed to more DFG dissolved in water at higher
volume ratios of water to the RTIL solution.
Extraction Thermodynamics
From the viewpoint of thermodynamics, the extraction of
MFG can be regarded as a transfer process of MFG from
the RTIL-rich lower phase to the water-rich upper phase.
The Gibbs energy of such a transfer process can be cal-
culated as follows:
DG0T ¼ ꢂRT ln D;
ð5Þ
Multistep Extraction
where D is the distribution ratio of MFG in water and the
RTIL solution. T (K) is the temperature in Kelvin, and
R (8.314 J/(mol K)) is the ideal gas law constant.
To reduce the amount of water used and guarantee the
separation efficiency, the effect of multistep extraction on
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J Am Oil Chem Soc
Table 4 The thermodynamic properties for MFG transfer from the
RTIL phase to the water phase
DG0T
(kJ/mol)
DS0T
(J/(mol K))
DHT0
(kJ/mol)
T (K)
D
(910-2
)
283.15
303.15
323.15
343.15
363.15
33.87
31.74
29.38
24.47
21.77
2.55
2.89
3.29
4.02
4.60
-25.62
-4.81
increase of the extraction temperature. The entropy (DS0T,
-25.6188 J/(mol K)) also suggests that the separation of
MFG is controlled by hydrogen bonds, which can be
formed between the oxygen atom in water and the hydro-
gen atom in the hydroxy group of MFG. These results
suggested that hydrogen bonds are the main driving force
for the selective separation of MFG from RTIL solution.
The expense of recovering the product can also be
decreased, since the RTIL can be reused many times. In our
lab, [BMIM]PF6 had been reused four times without any
structural changes detected.
Purification and the Cosmetic Efficiency of MFG
The water phases enriched in MFG were combined, and
water was removed by evaporation. The isolated MFG was
dissolved in water, and crystallized (Fig. 2). After filtered,
the white MFG crystal was obtained by evaporation and
freeze-drying. The purified MFG product consisted of
97.76 0.25 % MFG, 1.58 0.38 % FA, and
0.66 0.18 % EF. The UV spectra of FA, EF, and MFG
are similar and the maximum UV absorption in the UVB
and UVA region were 322 nm (Fig. 6). In addition, the
maximum UV absorbance capacity decreased in the order
of MFG [ FA [ EF.
Fig. 5 Effect of multistep extraction on the extraction yield (column)
(a) and the relative content (line) (b) of MFG from RTIL using
different volume ratios of water to RTIL solution (square 0.5:1; filled
square 1:1). Extraction conditions: extraction time, 6 min; centrifu-
gation time, 6 min; deionized water, and 25 °C
The enthalpy and entropy change associated with the
separation of MFG can be calculated from the slope and
intercept of the linear equation between ln D and 1/T,
respectively [27].
Conclusions
In the work, a novel method for the selective separation of
MFG using neutral deionized water from a RTIL solution
of enzymatic transesterification of EF with glycerol was
successfully established to obtain high purity MFG. The
extraction conditions were optimized as follows: 0.5:1
volume ratio of water to RTIL solution, extraction time
6 min, and centrifugation time 6 min. After the RTIL
solution was extracted under the optimized conditions for
eight times, the maximum extraction yield and relative
content of MFG in the extracts were 98.23 1.09 % and
97.76 1.25 %, respectively. The extraction of MFG was
an exothermic process, and hydrogen bonds are the main
driving force for the selective separation of MFG. The
ꢂDHT0 DS0T
ln D¼
þ
:
ð6Þ
RT
R
The resultant DG0T, DHT0, and DS0s values for the transfer
of MFG from the RTIL-rich phase to the water-rich phase
can be obtained using a linear least-square analysis
(Table 4). Positive standard free energy changes (DG0T)
were achieved, which indicate that MFG extraction is an
inverse spontaneous process. The negative value of DHT0
(-4.8088 kJ/mol) indicates the exothermic process for
MFG extraction, which can also be confirmed by the fact
that extraction efficiency of MFG decreased with the
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J Am Oil Chem Soc
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Acknowledgments The authors gratefully acknowledge financial
support from the National Natural Science Foundation of China
(31101301), Funding Scheme for Young Teachers in Colleges and
Universities in Henan Province (2012GGJS-83), and the Plan for
Scientific Innovation Talent of Henan University of Technology
(11CXRC03).
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