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Extraction of resveratrol from the pomace of Palomino fino grapes by supercritical
carbon dioxide
L. Casas, C. Mantell*, M. Rodríguez, E.J. Martínez de la Ossa, A. Roldán, I. De Ory, I. Caro, A. Blandino
Department of Chemical Engineering, Food Technology and Environmental Technologies, Faculty of Science, University of Cadiz, Box 40, 11510 Puerto Real, Cadiz, Spain
article info
Article history:
Received 29 May 2009Received in revised form 22 July 2009Accepted 4 August 2009Available online 9 August 2009
Keywords:
ResveratrolSupercritical carbon dioxide extraction
Palomino grape
HPLCabstract
Resveratrol is a phenolic compound that is present in grapes and has significant benefits for human
health. The development of methods to obtain concentrates of this compound is currently a major chal-
lenge in the food industry. In the work described here, resveratrol from grape seeds, stems, skin and pom-ace of the Palomino fino grape variety was extracted by supercritical carbon dioxide extraction. The effect
of pressure (100, 400 bar), temperature (35, 55 /C176C) and the addition of modifier (5% v/v of ethanol) was
evaluated to identify optimal resveratrol extraction from this by-product. Extraction yields and concen-trations of resveratrol in the extracts were determined. The best results were obtained on working at highpressure and low temperature using 5% v/v ethanol as a co-solvent.
/C2112009 Elsevier Ltd. All rights reserved.
1. Introduction
Phenolic compounds represent an important group of micronu-
trients present in the plant world, and which form a part of the
human food and animal feed. In particular, trans-resveratrol
(3,5,40-trihydroxystilbene) has gained significant worldwide atten-
tion due to its ability to inhibit or retard a wide variety of diseases
in animals (Baur et al., 2006 ), including cardiovascular disease and
cancer ( Bradamante et al., 2004 ), and to increase stress resistance
and lifespan ( Baur et al., 2006; Valenzano et al., 2006 ).
Resveratrol is commonly found in grape skins and seeds. Its
content in wine depends on the grape variety, the mechanical
pre-treatment (crushed and pressed) and the vinification process.
Generally, the concentration is higher in red than in white wines,
since the must is fermented with the skins (Romero-Pérez et al.,
1996 ). Furthermore, significant differences can be found in the res-
veratrol content from one vintage to another (Threlfall et al., 1999 ),
from different vineyard locations, and as a result of different
weather patterns. Among the white wines, Greek and Portuguese
wines are reported to contain the lowest levels of 0.03–0.14 mg/L
(Dourtoglou et al., 1999 ) and 0.01–0.51 mg/L ( De Revel et al.,
1996 ) resveratrol, respectively. Resveratrol contents between 0.8
and 8 mg/L in Spanish white wines from ‘‘D.O. Rías Baixas” and
the Galician wines are particularly notable (Rodríguez-Delgado
et al., 2002; Feijóo et al., 2008 ).In recent years, newer techniques such as extraction by super-
critical fluids (SFE), extraction by pressurized liquids (PLE), andextraction assisted by microwave irradiation (MAE) have replaced
conventional techniques like Soxhlet extraction for solid samples.
These alternative techniques simplify the process, considerably re-
duce the consumption of solvents, and also increase the rate of the
extraction process. Although SFE is limited to compounds of low or
medium polarity, literature reports on extraction of polyphenols by
SFE in the presence of organic solvent modifiers are available
(Mantell et al., 2003 ).
There are numerous reports on the recovery of polyphenolic
compounds from different varieties of grapes by SFE. Palma and
Taylor (1999) applied this technology to separate eight polypheno-
lic compounds on spiked inert matrices using ethyl acetate or
methanol as a modifier. Tena et al. (1998) used CO
2modified with
5% (v/v) methanol and the extraction parameters were 50 /C176C and
350 bar. Pascual-Martí et al. (2000) investigated the supercritical
fluid extraction process of resveratrol from grape skins of Vitis
vinifera , and found extraction at 40 /C176C, 150 bar, with 7.5% (v/v) eth-
anol as modifier to be optimum. Berna et al. (2001) showed the
influence of process conditions on the solubility of resveratrol in
supercritical carbon dioxide and ethanol. These authors suggested
the use of 7.5% ethanol as co-solvent and elevated pressure to carry
out the extraction.
Cho et al. (2006) used an ultrasonication-assisted method in
order to search an effective extraction of resveratrol from grape.
This methods exhibited more efficiency than the conventional
solvent extraction with ethanol/water (80:20%, v/v) maintained
at 60 /C176C for 30 min. In the new methods, the recovery of resveratrol
0260-8774/$ – see front matter /C2112009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jfoodeng.2009.08.002*Corresponding author. Tel.: +34 956 016458; fax: +34 956 016411.
E-mail address: casimiro.mawntell@uca.es (C. Mantell).Journal of Food Engineering 96 (2010) 304–308
Contents lists available at ScienceDirect
Journal of Food Engineering
journal homepage: www.elsevi er.com/locate/jfoodeng

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increase by 24–30%, compared with the conventional solvent
extraction.
Grape pomace is an industrial waste from the wine process, and
consists of grape seeds, skin and stems. Components such as resve-
ratrol remain in the pomace at concentrations that are dependent
on the wine manufacture process. de Campos et al. (2008) used
supercritical fluid extraction to extract grape pomace from theproduction of Cabernet sauvignon vintage. These authors use as
solvent SC-CO
2and analyze the effect of the addition of ethanol
as co-solvent at 150 bar and 40 /C176C. The percents of co-solvent in
the solvent were 10%, 15% and 20% w/w. The highest yields ofthe extracts were obtained by Soxhlet extraction using ethanol
(13.2% w/w), butanol (12.2% w/w), and also by SFE with 15% etha-
nol (9.2% w/w). Three varieties of grape marc, native to Slovenia
(Refošk, Merlot and Cabernet ), were studied by Tünde et al. (2009) .
These authors found a mixture of organic solvent and water at
60/C176C to be the most efficient in single-step extractions, and the
pre-treatment with SC-CO
2(with or without ethanol as co-solvent)
to improve the extraction of polyphenols from the grape marc. This
method provides an alternative to the pre-treatment of the plant
materials and replaces toxic organic solvents.
Palomino grape represents 95% of grape production in the Jerez
region (Cádiz, Spain) and this is dedicated to the production of gen-
erous wines ‘‘D.O. Jerez-Xerez-Sherry ”. The pressing of this grape
produces approximately 15–20% of pomace, and this is usuallyused as a fertilizer. Resveratrol has not been detected in the Jerez
wines ( Domínguez et al., 2001 ) or has been detected at very low
concentrations (0.03 mg/L) (Martínez-Ortega et al., 2000 ). How-
ever, Roldán et al. (2003) detected its presence in the Palomino fino
grape. Its content in the grape skins varies from 2.59 and 4.51 mg/kg depending on the vintage, and is increased on infection of the
grapes by the fungus, Botrytis cinerea .
The present work looks into the viability of using SC-CO
2for the
recovery of resveratrol from the pomace of the Palomino fino grape
press process. Experiments were designed using different parts ofthe grape pomace, stems, skin and seeds as raw materials. The
effect of temperature, pressure and modifier concentration of the
SC-CO
2on the total extraction yield, and on the recovery of
resveratrol in the extract was evaluated.
2. Materials and methods
2.1. Sampling and chemicals
White grape pomace from the Jerez -Xerez -Sherry area ( Palomino
fino variety) was used as the raw material. Samples of freshly
pressed white grape were collected from a local wine cellar and
placed in an oven for 48 h at 60 /C176C to obtain a dry solid. The result-
ing solid was manually separated into four fractions: whole grapepomace, seeds, stems and skin.
Each fraction was pulverizing with hammer mill to obtain a par-
ticle size distribution adequate. Subsequently, each sample was
vacuum-packed using household vacuum equipment (Professional
Family, Orved, Italy). The mean particle size of each fraction was as
follows: 0.165 ± 0.102 mm for stem, 0.261 ± 0.164 mm for skins
and 0.319 ± 0.239 mm for seeds. The pomace sample showed the
following distribution of weight fractions: 47.9% of skin, 43.7% of
seeds, 8.4% of stem and mean particle size of 0.408 ± 0.375 mm.
The packed samples were stored at room temperature under dark-
ness until used.
The carbon dioxide (99.995%) used was provided by Carburos
Metalicos (Barcelona, Spain). Standard of trans-resveratrol (99%)
was provided by Sigma–Aldrich and the other reagents (ethanol,methanol, hydrochloric acid and acetic acid, all with a purity of
HPLC gradient grade) by Panreac.2.2. Extraction at high pressure
The extractions were carried out in an Isco extractor (Nebraska,
USA, model SFX220). The equipment consisted of one extractor
with a maximum capacity of 10 mL and 2
lm filters at the inlet
and outlet to avoid haulage of the sample. The extractor was alsofitted with a thermostatic system that allowed the extraction to
be carried out at a constant temperature. The solvent was intro-
duced by syringe pumps (Isco, Nebraska, USA, model 260D and
100DX), which allowed a constant pressure. The samples left the
vessel through a micrometric valve, which was thermostated to
avoid obstructions at the exit due to the solidification of CO
2. The
automatic control of the equipment make possible to work withthe pumps at different programs. In this case, a consolvent pro-
gram is used that make possible to add a constant percent offlow-rate of one pump regarding to the other pump. The flow-rate
was automatically measured by the program based in the move-
ment of the piston inside of the syringe pump. This flow-rate
was measured in volumetric units at operation pressure and
20/C176C of temperature.
The extraction cartridge was loaded with approximately 4.6 g of
sample which had previously been homogenized to maintain a
constant apparent density in all experiments, and then introduced
into the extractor to reach the operating temperature. The pumps
were loaded with carbon dioxide and ethanol until the operating
pressure was reached. The automatic decompression valves of
the extractor were then closed. The valves connecting the pumps
were opened so as to open the extractor. The extractor was then
pressurized with CO
2and ethanol. When a balanced state was at-
tained, the micrometric valve was opened until a constant flowof 0.8 g/min was achieved. In order to achieve complete extraction
of the substances in question, a relatively long extraction time was
used (3 h). The extracts were collected in glass tubes containing
methanol and analyzed by high-performance liquid chromatogra-
phy (HPLC).
Extreme conditions of pressure were tested, i.e. 100 and
400 bar. Experiments were carried out at relatively low tempera-
tures between 35 and 55 /C176C because, according to many authors
(Chafer et al., 2005; Pascual-Martí et al., 2001; Romero-Pérez
et al., 2001 ), the yields of extraction of resveratrol decreases at
higher temperatures and prolonged extraction times. Experimentswere also carried out with 5% volume of ethanol as co-solvent,
since this is the most commonly used in the SC-CO
2extraction of
natural products. The results shown are averages of these twoindependent experiments with a reproducibility of approximately
7.8% CV (coefficient of variation).
2.3. Conventional extraction
The methodology described by Roldán et al. (2003) was used for
the conventional extraction. Samples of 25 g were macerated with
50 mL of a mixture of methanol/HCl (0.1%) for 30 min in an ultra-
sonic bath. After the extraction, the sample was centrifuged and fil-
tered [0.45
lm Teflon syringe filters (Millex-LCR, Milipore,
Bedford, MA)] prior to analysis by direct injection on HPLC.
2.4. Determination by HPLC
The HPLC equipment consisted of an Agilent Technologies 1100
Series chromatograph, with UV–visible detector, auto sampler and
PC software for the control and processing of the chromatographic
data. The method used was based in the published by Pascual-
Martí et al. (2000) . This method is adequate for quantification of
cis- and trans – isomers of resveratrol and their glucosides. The col-
umn (250 mm /C24.6 mm) was a C 18Hypersil ODS (5 lm particle
size) (Supelco). The solvent used was water:methanol:acetic acidL. Casas et al. / Journal of Food Engineering 96 (2010) 304–308 305

Author's personal copy
(75:20:5). The flow-rate was set to 1.5 mL/min and 20 lL of filtered
extract was injected for each sample. Detection was carried out at a
wavelength of 306 nm.
Trans-resveratrol was identified by comparison of its retention
times with that of the commercial standard (Sigma) and was quan-
tified by means of a calibration curve. The calibration curve was as
follow:
A¼55 :176Cț31 :192 ð1Ț
where Ais the area expressed in mAu and Cis the concentration ex-
pressed in mg/L. The correlation coefficient ( R) was 0.9999.
The experiments on each extraction were carried out in tripli-
cate in order to evaluate the variability of the measurements. Theresults are shown as the average of all the independent analyses
with a reproducibility of approximately 2.5% CV (coefficient of var-
iation). A typical chromatogram of the samples is included in Fig. 1 .
3. Results and discussion
In SFE, the solvating power of the fluids can be manipulated by
changing pressure and/or temperature so as to achieve a remark-ably high selectivity. This tuneable solvating power of SFE is partic-
ularly useful for the extraction of complex samples such as plant
materials.
SC-CO
2is not very suitable for the extraction of polar analytes.
This problem is often tackled by use of modifiers. Depending on the
type of sample matrix and the affinity of the analyte for the matrix,
the modifier may influence the extraction in three different ways:
(1) increase the solubility of the analyte in the supercritical fluid as
a result of analyte–modifier interactions in the fluid phase; (2)
facilitate analyte desorption – the molecules of polar modifiers
are able to interact with the matrix and compete efficiently with
the analyte for the active sites in the matrix; (3) distort the ma-
trix–analyte diffusion process and favour penetration of the super-
critical fluid into the matrix when the modifier swells the matrix.
The results for extraction yields are presented in Tables 1–3 .
The maximum extraction yields of pomace and its individual com-
ponents were obtained on addition of 5% volume of ethanol as co-
solvent to the SC-CO 2. This is attributed to the modification of the
properties of the carbon dioxide – a change that enables this fluidto extract the lipophilic and the hydrophilic compounds.
The fluid pressure is an essential parameter in SC-CO
2extrac-
tion, since fluid density is directly related to pressure. It can be ob-
served from Table 1 that at constant temperature, an increase in
the pressure increased the extraction yield. The density of carbondioxide is higher as higher pressure, and consequently, the sol-
vency of SC-CO
2also increases. Berna et al. (2001) also suggestthe extraction at elevated pressure to be advantageous. These re-sults are consistent with those reported in the bibliography by
other authors (Pascual-Martí et al., 2000 and Palma and Taylor,
1999 ).
Temperature also has a significant effect on the recovery of
components in SC-CO
2. According to the rules of kinetics, if the
other variables are constant, an increase in temperature is related
to a more intensive thermal motion of solutes in the active sites of
the matrix. This situation is beneficial for the solutes to overcome
the adsorbing energy forces on the matrix and to be desorbed more
efficiently from the active sites by SC-CO 2at higher temperature.
From a thermodynamic point of view, the saturated vapour pres-sure increases with a corresponding increase in the temperature,
thus enabling the solutes to dissolve in SC-CO
2more easily. More-
over, the density of SC-CO 2decreases with an increase in temper-
ature, thus decreasing the solvency of SC-CO 2. These three effects
compete with one another during the extraction process. The effect
of temperature on the extraction yield also is shown in Table 1 .A t
100 bar, an increase in the temperature from 35 to 55 /C176C did not
have a significant effect on the extraction yield. In some cases, a
decrease in yield was observed. This was seen in SC-CO 2, both with
and without the addition of co-solvent. This behaviour is attributedto compensation between factors with an increase in temperature.
Nevertheless, at a higher pressure of 400 bar, an increase in the
temperature was beneficial in the extraction. This effect is more
marked when co-solvent is not added to the system, with increases
in the extraction yields of 153%, 60%, 150% and 250% for seed, stem,
skin and grape pomace, respectively, compared to the yields ob-
tained at 100 bar.
The resveratrol concentration in the extracts obtained (mg res-
veratrol/g extract) are shown in Table 2 . It is evident that the use of
ethanol as co-solvent with SC-CO
2is more selective than the pro-
cess using SC-CO 2alone. This is due to the influence of the co-sol-
vent on the solubility of the solute, and therefore on the extractionyield of the process. On the other hand, pressure and temperature
appeared to have a less marked influence on resveratrol content.
Nevertheless, the use of high pressure (400 bar) and low tempera-
ture (35 /C176C) was desirable for the extraction. Best results were ob-
tained with grape skins as compared to the other raw materials.
Table 3 clearly shows the recovery of resveratrol from the raw
material to be optimum at 400 bar, 35 /C176C and 5% Ethanol. SC-CO
2
without the addition of co-solvent at low pressure (100 bar) was
not selective for resveratrol. In fact, resveratrol was not detected
under all the conditions analyzed at this pressure (35, 55 /C176C). An in-
crease in the pressure to 400 bar improved the extraction of resve-ratrol. However, it is necessary to add a co-solvent in order to
increase the extraction yields significantly.
Fig. 1. Chromatograms of the sample, the retention time were 19.487 and 21.652 min for trans -resveratrol and cis-resveratrol, respectively.306 L. Casas et al. / Journal of Food Engineering 96 (2010) 304–308

Author's personal copy
The recovery of resveratrol using SC-CO 2was higher than con-
ventional extraction with a solvent mixture at atmospheric pres-
sure [Methanol:HCl (0.1%)]. SC-CO 2extraction enabled resveratrol
to be obtained from seeds, which was not possible by conventionalmethods. This behaviour can be attributed to the higher diffusion
properties of SC fluids regarding conventional solvents. This fact al-
lows to the SC solvent to reach some active sites of the solid matrixinside the seed that the conventional solvent cannot reach. These
diffusional problems do not happen in the rest of the parts of the
pomace where the solute is accessible to the conventional solvent.
The extract obtained from the skins had higher levels of resveratrol
than that obtained from seeds and stems. The amount of resvera-
trol in grape pomace, therefore, depends on the proportion of skin,
seeds and stems in the whole by-product.
Although literature on the recuperation of resveratrol from
Palomino fino grape pomace has not been published previously,
that from other varieties of grape skins, seeds and pomace havebeen analyzed. For example, Pezet and Cuenat (1999) found res-
veratrol at 0.68 and 0.39 mg/100 g of fresh weight in the skinand grape pomace, respectively. The values in the Muscadine
variety were 1.17 and 5.32 mg/100 g of dry weight in the skinand pomace, respectively (Ector et al., 1996 ). In the case of red
varieties, Sun et al. (2006) reported resveratrol levels of 1455,
68 and 656 mg/100 g of dry weight in stems, seeds and skin,
respectively. Pascual-Martí et al. (2000) confirmed that the res-veratrol content in the skins of red grape varieties to be higherthan in white grape varieties and found 356 and 1706 mg/
100 g of fresh weight in the skins of Chardonnay and Tempranillo
varieties, respectively.
It is important to note that in our work, the extraction of resve-
ratrol was carried out on the by-product of Jerez-Xerez-Sherry wine
production process. Hence, the resveratrol content would dependon the pressure applied in this press process. During this step, a
large amount of the grape compounds, essentially from the skins,
is transported to the must and this increases on increasing the
pressure of the press process. In the production of Jerez-Xerez-Sher-
rywines, the press process was continued until the pomace was
exhausted. Consequently, high levels of compounds are transferred
to the must. Nevertheless, the amount of resveratrol obtained with
SC-CO
2is comparable to those obtained by other authors. The val-
ues obtained from the skins and the pomace are higher than the re-sults obtained by Ector et al. (1996) and Pascual-Martí et al. (2000)
for the Chardonnay variety, and by Tünde et al. (2009) using con-
ventional methods and SC-CO
2extraction.
4. Conclusion
Grape pomace of Palomino fino is a potential source of resvera-
trol. SC-CO 2extraction under optimized conditions ensures itsTable 1
Total extraction yields expressed as mg of extract/100 g of dry sample.
Extraction conditions Seed Stem Skin Grape pomace
CO2 100 bar 35/C176C 132 129 123 165
55/C176C9 0 8 0 7 0 9 0
400 bar 35/C176C 650 320 590 430
55/C176C 1648 513 1445 1514
CO2+ EtOH 100 bar 35/C176C 1223 489 1556 1288
55/C176C 1190 500 1600 760
400 bar 35/C176C 1390 800 2300 1500
55/C176C 2122 1026 2805 2176
Table 2Extraction yields of resveratrol expressed as mg of resveratrol/100 g of dry sample.
Extraction conditions Seed Stem Skin Grape pomace
CO2 100 bar 35/C176C– – – –
55/C176C– – – –
400 bar 35/C176C 0.2 0.6 0.5 0.4
55/C176C 0.3 0.6 0.4 0.3
CO2+ EtOH 100 bar 35/C176C 6.1 0.7 13.1 10.1
55/C176C 5.0 – 14.0 7.0
400 bar 35/C176C 8.3 0.9 49.1 16.1
55/C176C 11.1 0.7 45.5 19.2
Conventional extraction – 1.7 3.1 0.9
(–) Not detectable.
Table 3Concentration of resveratrol in the extract (mg resveratrol/g extractor).
Extraction conditions Seed Stem Skin Grape pomace
CO2 100 bar 35/C176C– – – –
55/C176C– – – –
400 bar 35/C176C 0.31 1.87 0.84 0.93
55/C176C 0.18 1.17 0.27 0.19
CO2+ EtOH 100 bar 35/C176C 4.99 1.43 8.42 7.84
55/C176C 4.20 – 8.75 9.21
400 bar 35/C176C 5.97 1.12 21.35 10.73
55/C176C 5.23 0.68 16.22 8.82
(–) Not detectable.L. Casas et al. / Journal of Food Engineering 96 (2010) 304–308 307

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extraction, thus allowing the final by-product to be reused for
other activities.
Acknowledgements
The authors thank the Junta de Andalucia for financial support
(Project PAI05-TEP-00231), which enabled this work to be carried
out.
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