Antioxidant properties of trans-epsilon-viniferin as compared to stilbene derivatives in aqueous and nonaqueous media.

Article abstract of DOI:10.1021/jf010676t

trans-Epsilon-viniferin, the dimer of resveratrol, extracted from Vitis vinifera, has been evaluated for its antioxidant capacity. Its properties have been compared to those of resveratrol and synthetic stilbenic derivatives (4-hydroxystilbene, 4,4'-dihydroxystilbene, 3,5-dihydroxystilbene, and trimethylresveratrol), in regard to their liposolubility using two media with different polarity. The bleaching of beta-carotene by lipoperoxyl (LOO.) radicals in an oil/water (O/W) emulsion and the scavenging of superoxide anions (O(-)(2) in dimethyl sulfoxide (DMSO) using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap were followed using UV-visible and electron paramagnetic resonance, respectively. Epsilon-viniferin exhibits the best antioxidant capacity in the DMSO/O(-)(2) polar system (IC(50) = 0.14 mM) while 4,4'-dihydroxystilbene presents the highest antioxidant capacity in the O/W/LOO. system (inhibition of beta-carotene bleaching, 82%). Partition coefficients and kinetics of partition between 1-octanol and water were measured to discuss the antioxidant efficiency of the compounds in relation with their chemical structure.

Full text of DOI:10.1021/jf010676t

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J. Agric. Food Chem. 2002, 50, 1213−1217 1213
Antioxidant Properties of trans-E-Viniferin As Compared to
Stilbene Derivatives in Aqueous and Nonaqueous Media
CHRISTELLE PRIVAT,† JOA˜ O PAULO TELO,‡ VANIA BERNARDES-GENISSON,†
ABEL VIEIRA,§ JEAN-PIERRE SOUCHARD,† AND FRANC¸ OISE NEPVEU*,†
Laboratoire Pharmacophores Redox, Phytochimie et Radiobiologie, EA-3030,
Universite´ Paul Sabatier, 35 Chemin des Maraˆıchers, 31062 Toulouse Cedex 4, France,
Instituto Superior Tecnico, Avenidad Rovisco Pais, P-1096 Lisboa Codex, Portugal, and
Departamento de Quimica, Faculdade de Cieˆncias e Tecnologia, Universidade Nova de Lisboa,
2825-114 Monte da Caparica, Portugal
trans-ꢀ-Viniferin, the dimer of resveratrol, extracted from Vitis vinifera, has been evaluated for its
antioxidant capacity. Its properties have been compared to those of resveratrol and synthetic stilbenic
derivatives (4-hydroxystilbene, 4,4′-dihydroxystilbene, 3,5-dihydroxystilbene, and trimethylresveratrol),
in regard to their liposolubility using two media with different polarity. The bleaching of â-carotene by
lipoperoxyl (LOO•) radicals in an oil/water (O/W) emulsion and the scavenging of superoxide anions
(O2-) in dimethyl sulfoxide (DMSO) using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap were followed
using UV-visible and electron paramagnetic resonance, respectively. ꢀ-Viniferin exhibits the best
-
antioxidant capacity in the DMSO/O2 polar system (IC50 ) 0.14 mM) while 4,4′-dihydroxystilbene
presents the highest antioxidant capacity in the O/W/LOO• system (inhibition of â-carotene bleaching,
82%). Partition coefficients and kinetics of partition between 1-octanol and water were measured to
discuss the antioxidant efficiency of the compounds in relation with their chemical structure.
KEYWORDS: Viniferin; resveratrol; antioxidant activity; hydrophilic/lipophilic partition
INTRODUCTION
that the antioxidant activity of different estrogens depended not
only on the hydrophilic or lipophilic nature of the scavenged
radical but also on the chemical structure of the compound.
ROS are implicated in oxidative damage of biological
molecules and involved in the development of many pathologi-
cal disturbances such as atherosclerosis, cancer, and inflamma-
tion. Moreover, epidemiological studies have shown that natural
antioxidants present in food or beverages might be beneficial
for health (1-6). ROS are also responsible for the deterioration
of foods by lipid oxidation during processing and storage (7).
In living systems, various endogenous (i.e., enzymes such as
catalase and superoxide dismutase) and exogenous molecules
(ascorbic acid and tocopherol) play a role in neutralizing these
radicals. The presence of antioxidants in food, for example, is
effective in preventing the development of various off-flavors
and undesirable compounds that result from lipid oxidation.
Apart from the fact that a broad spectrum of ROS-scavenging
capacities is required, a good antioxidant must be able to diffuse
in close proximity to its target at relatively high concentrations
according to its partition between aqueous and lipid compart-
ments (8). In vivo, polar antioxidants cannot cross biological
membranes or move freely by diffusion between different
compartments, a fact that could restrict their movement and their
antioxidant efficiency. Ruiz-Larrea and co-workers (9) showed
Methods for analyzing antioxidant properties of isolated
molecules, extracts, or matrixes are of great interest in food
and pharmaceutical industries as well as in biological studies.
They are needed for comparing antioxidant properties of plant
extracts and for evaluating antioxidant pools in foods depending
on processing and synergistic effects between the antioxidants
or the antioxidant status of living systems.
Polyphenol derivatives, which are naturally occurring anti-
oxidants, have been demonstrated to be efficient scavengers of
oxygen-centered radicals (1, 5, 10-11). Among them, hydroxy-
stilbenes, including resveratrol (2; 3,5,4′-trihydroxystilbene),
have been reported for their antioxidant properties (12-13).
However, its antioxidant properties have not been studied in
media with different polarities, and ꢀ-viniferin (1), its dimer,
extracted from the Vitis Vinifera grapevine, has not yet been
studied. Moreover, in contrast with 2, 1 was not detected in
wine (14-16). In this study, the antioxidant efficiency of 1 was
compared to those of 2 and stilbene derivatives (Figure 1) in
regard to the liposolubility using two media of different
polarities. The bleaching of â-carotene by LOO• in an O/W
emulsion was followed in the UV-visible range. Quantitative
† Universite´ Paul Sabatier.
‡ Instituto Superior Tecnico.
§ Universidade Nova de Lisboa.
-
EPR analysis using DMPO as a spin trap and O2 as a radical
was carried out in DMSO.
10.1021/jf010676t CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/25/2002

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1214 J. Agric. Food Chem., Vol. 50, No. 5, 2002
Privat et al.
4-Hydroxystilbene (3). A total of 4.0 g of phenylacetic acid, 3.7 g
of p-hydroxybenzaldehyde, and 0.5 mL of piperidine were heated
together at 120 °C for 18 h. The gummy product was digested with
aqueous 5% sodium hydroxide and neutralized with aqueous hydro-
chloric acid to pH 6-7, and the precipitated solid was filtered.
Chromatography on silica gel (toluene) afforded 4.2 g (71%) of 3 (mp
89-190 °C).
4,4′-Dihydroxystilbene (4) and 3,5-dihydroxystilbene (5). Compounds
4 and 5 were prepared according to known procedures from the
literature (17-18).
Purification of 1. A crude extract of vine roots containing about
20% viniferin and 1% compound 2 was first chromatographed on a
preparative column packed with silica gel. A solvent gradient, starting
with 100% dichloromethane and ending with 100% methanol, was used
for elution. The viniferin-enriched fraction was then purified on silica
1
gel preparative TLC (eluent: dichloromethane/methanol, 85:15). H
NMR (200 MHz, in deuterated acetone): 7.21 (2H, d, J ) 9.0 Hz,
H-2A and H-6A), 7.18 (2H, d, J ) 9.0 Hz, H-2E and H-6E), 7.00 (1H,
d, J ) 15.1 Hz, H-â), 6.83 (2H, d, J ) 8.0 Hz, H-3A and H-5A), 6.71
(4H, m, H-3E, 5E, 2D, R), 6.32 (1H, d, J ) 1.7 Hz, H-4D), 6.24 (3H,
s, H-2A and H-2B, 4B, 6B), 5.42 (1H, d, J ) 5.0 Hz, H-1C), 4.49
(1H, d, J ) 5.0 Hz, H-2C).
Figure 1. Chemical structures of 1−6.
MATERIALS AND METHODS
Comparison of the 1H NMR spectroscopic data of purified viniferin
with the data reported in the literature for oligomers of 2 led to the
identification of trans-1 (19-20). The purity of trans-1 (98%) was
evaluated by reverse phase HPLC, with a UV-visible detector working
at two wavelengths, 306 and 325 nm. This analysis was performed at
37 °C using a water/acetonitrile/ortho-phosphoric acid solvent gradient
(from 20/0/80 to 0/100/0) with a flow rate of 1 mL/min.
Determination of Antioxidant Effectiveness toward LOO• Radi-
cals. The evaluation of the antioxidant activity of stilbene derivatives
was based on the coupled oxidation of â-carotene and linoleic acid.
The technique was developed by Marco (21) and modified by Miller
(22) and Taga et al. (23). It consists of measuring the bleaching of
â-carotene resulting from its oxidation by degradation products of
linoleic acid such as LOO• radicals.
General Procedures. UV-visible absorbances were recorded on
an Uvikon 931 spectrophotometer (Kontron instruments). EPR spectra
were obtained on a Bruker ER 200 D spectrometer (Bruker Spectrospin,
Wissembourg, France). Standard EPR recording conditions were central
field, 3500 G; scan range field, 200 G; microwave frequency, 9.71
Hz; microwave power, 4 mW; modulation frequency, 100 kHz;
modulation amplitude, 1.0 G; time constant, 0.5 s; gain, variable but
constant for each experiment; and scan speed, 24 G per min. 1H NMR
spectra were obtained on a Bruker AC200 instrument (Bruker Spec-
trospin, Wissembourg, France) at 200 MHz. Acetone-d6 was used as a
solvent.
Thin-layer chromatography (TLC) was performed on Aldrich silica
gel TLC plates (200 µm thickness, 2-25 µm particle size; Sigma-
Aldrich Chemical Co., Saint-Quentin Fallavier, France). The high-
performance liquid chromatography (HPLC) equipment was from
Waters (Saint Quentin en Yvelines, France) with a 717 Plus automatic
sample injector, a 600 pump, and a 2487 Dual λ Absorbance UV-
visible detector. A Zorbax SB-C18 5 µm (150 mm × 4.6 mm) column
was used (Bios Analytique, Labege, France).
Compound 2, DMPO, DMSO, R-tocopherol, â-carotene, 1-octanol,
potassium superoxide, linoleic acid, and activated charcoal were
obtained from Sigma-Aldrich Chemical Co. (Saint-Quentin Fallavier,
France). Tween 40 and 18-crown-6 were purchased from Fluka (Sigma-
Aldrich Chemical Co., Saint-Quentin Fallavier, France), and solvents
were purchased from SDS (Peypin, France).
Synthesis of Stilbene Derivatives. TrimethylresVeratrol (6). With
5 mL of triethyl phosphite, 3.7 g of 3,5-dimethoxybenzyl bromide (17)
was heated at 130 °C until the evolution of ethyl bromide ceased. After
the excess of phosphite was removed by distillation in a vacuum, pure
diethyl(3,5-dimethoxybenzyl)phosphonate was distilled at 180 °C (0.05
mm Hg).
In a boiling flask, 100 µL of a 2 g L-1 â-carotene chloroform solution
was mixed with 20 mg of linoleic acid and 200 mg of Tween 40.
Chloroform was removed under a nitrogen flow, and 50 mL of
oxygenated distilled water was slowly added to the flask with stirring
to form an O/W emulsion. A 5 mL aliquot of this emulsion was then
pipetted into each of a series of tubes containing 20 µL of acetone
antioxidant solution. A control tube containing 20 µL of acetone alone
instead of antioxidant solution was also prepared. A zero reading was
taken at 470 nm on the reaction mixture in each tube immediately after
adding emulsion to the antioxidant solution or acetone. The tubes were
then stoppered and placed in a water bath at 50 °C. Subsequent readings
were taken at regular intervals (3 h maximum) until the absorbance of
the control read below 0.08, corresponding to the total bleaching of
carotene. The antioxidant effectiveness of each compound tested was
evaluated by the percentage of inhibition of carotene bleaching with
regard to the control. All determinations were made in triplicate.
Quantification of the Antioxidative Activity Using EPR. Quantita-
-
tive EPR analysis is based on the spin-trapping of O2 generated by
KO2 in DMSO with the addition of 18-crown-6 ether to complex K+.
In these conditions, a typical DMPO-OOH adduct is observed. DMPO,
the spin trap, was purified on active charcoal as reported in the literature
(24), aliquoted, stored frozen, and kept protected from light. As reported,
18-crown-6/potassium superoxide (1:1) was dissolved in DMSO (25).
A 1 mL DMSO solution was prepared in a glass tube by adding the
reagents in the following order: DMPO (50 mM), test compound (×
mM), and 18-crown-6/potassium superoxide (1:1, 5 µM). The reaction
mixture was transferred to a flat quartz cell that was inserted into the
cavity of an EPR instrument. The EPR spectra were recorded for 3
min at room temperature (about 20 °C) after the last addition. A control
mixture, without test compound, gave the EPR reference signal.
The intensity of the EPR signal was calculated by adding the height
of the quadruplet peaks. For each concentration of the compound tested,
the percentage of inhibition of the EPR signal intensity was calculated
with respect to the reference signal. The antioxidative activity of the
test compounds was quantified by an IC50 value representing the
Under an argon atmosphere, 2.0 g of the phosphonate was added to
9 mL of dry dimethylformamide containing 0.4 g of sodium methoxide.
The mixture was then cooled to 0 °C, 1.0 g of p-anisaldehyde was
added, and the solution was allowed to stand at room temperature for
1 h. After the solution was heated at 100 °C for 1 h, the excess of
dimethylformamide was evaporated in a vacuum. The addition of 20
mL of water/methanol 1:1 precipitated the crude product (1.7 g, 93%).
Recrystallization from methanol afforded pure trans-6 (mp 54-56 °C).
ResVeratrol (2). In 180 mL of dry methylene chloride, 1 g of 6 was
dissolved and cooled to -30 °C under argon. BBr3 (2.4 mL) in dry
methylene chloride (15 mL) was added slowly, and the mixture was
allowed to reach room temperature overnight. Water was added to
destroy the excess BBr3, and the mixture was extracted twice with ethyl
acetate. The organic extracts were washed with 10% sodium bicarbonate
and water and dried, and the solvent evaporated. The crude product
was purified by column chromatography on silica gel (2% ethyl acetate
in ethyl ether) yielding 0.8 g (95%) of pure 2 (mp 267-268 °C).

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Antioxidant Properties of Viniferin in Media
J. Agric. Food Chem., Vol. 50, No. 5, 2002 1215
Table 1. Antioxidant Activity of 1 As Compared to Stilbene Derivatives
.
against LOO Evaluated by the Inhibition of â-Carotene Bleaching at
a
470 nm
absorbance decrease at
470 nm (SEM)b
inhibition of â-carotene
compd
bleaching (%) (SEM)b
control
0.257 (0.017)
0.156 (0.012)
0.089 (0.011)
0.104 (0.009)
0.049 (0.003)
0.216 (0.017)
0.257 (0.017)
1
2
3
4
5
6
39.1 (2.7)
66.9 (1.9)
58.5 (1.8)
81.5 (0.4)
15.9 (6)
0 (0)
a The concentration of compounds was 40 µM. b Each value is the mean of
triplicate measurements.
concentration necessary for 50% diminution of the EPR signal. This
IC50 was deduced graphically by plotting the percentage of inhibition
of the EPR signal intensity against the test compound concentration.
The antioxidative activity of each compound was investigated by
three independent experiments. For each experiment, at least four
concentrations giving an inhibition between 10 and 90% were assayed.
Each experiment was performed with fresh solutions (except for
DMPO).
Figure 2. Inhibition of the DMPO−OOH EPR signal intensity by different
concentrations of 1.
Partition Coefficient Determination. Partition coefficients were
determined according to Janzen et al. (26). In all cases, water-saturated
1-octanol and 1-octanol-saturated water were used. These solutions were
made by shaking together equal volumes of each solution and then
letting them separate. Stock solutions of the different compounds were
made up in 1-octanol, and a full spectrum scan was run in order to
determine the wavelength corresponding to maximum absorbance. (The
Beer-Lambert law was verified at each maximum absorbance wave-
length.) Three 10 mg samples of each compound were weighed into
stoppered tubes and dissolved first in 2 mL of 1-octanol. The absorbance
(A0) of each solution was measured. Each 1-octanol solution was mixed
with 2 mL of water. The tubes were shaken for 23 h at 20 °C and then
separated. The absorbance of the 1-octanol phase (A) was evaluated.
The partition coefficient (P) was determined from P ) A/(A0 - A).
Kinetics of Stilbene Derivative Partition between 1-Octanol and
Water. Water-saturated 1-octanol and 1-octanol-saturated water were
used. Each compound was dissolved at a concentration of 20 µM in
1-octanol, and the absorbance (A0) of each solution was measured at
the wavelength corresponding to the maximum absorbance of the test
compound. A total of 2 mL of 1-octanol solution and 2 mL of water
were added to each in stoppered tubes and mixed for 23 h at 20 °C.
The absorbance of the 1-octanol solution (A) was measured every 1 h.
The kinetics of stilbene derivative partition was represented by plotting
(A × 100)/A0 against the time.
Table 2. Antioxidant Activity (IC ) of 1 As Compared to Stilbene
Derivatives against Superoxide Radicals in DMSO
50
a
compd
IC50 (mM) (SEM)b
compd
IC50 (mM) (SEM)b
1
2
3
0.14 (0.02)
0.95 (0.03)
1.10 (0.06)
4
5
6
0.82 (0.05)
1.68 (0.08)
>100
a IC50 corresponds to the stilbene concentration necessary for a 50% decrease
of EPR signal intensity according to a control realized without additives. The
concentration of O - generated was 5 µM. b Each value is the mean of triplicate
2
independent experiments.
-
Antioxidant Properties of Compounds 1-6 toward O2
Radicals in DMSO Medium. When the concentration of
compounds 1-6 was increased, a decrease of the EPR signal
intensity was observed as shown in Figure 2 with compound
1. The antioxidant properties of various stilbenes evaluated by
their IC50 value are shown in Table 2. Compound 1 exhibited
the highest activity (IC50 ) 0.14 ( 0.02 mM). It was about
25-fold more active than R-tocopherol (IC50 ) 3.91 ( 0.28 mM)
in the same conditions. Although the activities of 2-4 were
comparable, 4 had a better antioxidant ability than 3. All of
these compounds were more active than 5. Compound 6 did
RESULTS
-
not scavenge O2 efficiently.
Antioxidant Properties of Compounds 1-6 toward LOO•
Radicals in an O/W Emulsion. The inhibitory activity against
peroxidation of â-carotene in an O/W emulsion was examined
for compounds 1-6. Their inhibitory potency is summarized
in Table 1.
It was found that compounds 1-5 were able to reduce the
absorbance decrease of the â-carotene emulsion at a concentra-
tion of 40 µM in comparison with the control sample without
additive. In contrast, 6 did not possess any antioxidant activity.
Among the active compounds, 4 proved to be the most
efficient. It showed an absorbance decrease of 0.049 (control
value, 0.257) corresponding to 81.5% inhibition of â-carotene
bleaching. Its antioxidant ability was comparable to that of
R-tocopherol tested in the same conditions (78.9 ( 2.7%). It is
interesting to note that 2, in these conditions, exhibited a better
antioxidant activity than 3, which in turn presented a greater
activity than 1. Compound 5 remained the weakest antioxidant
of these active compounds.
Partition Coefficient of Compounds 1-5. The bar graph
(Figure 3), which represents 1-octanol/water partition coef-
ficients, gives an instant visual indication of stilbene derivative
solubility. All of the test compounds exhibited a close partition
coefficient corresponding to a hydrophobic character. In this
series, 2 (Log P ) 1.53 ( 0.01) and 1 (Log P ) 1.58 ( 0.02)
presented the lowest hydrophobicity. Compounds 4 and 5 had
similar partition coefficients (Log P ) 1.72 ( 0.01), and 3 had
the highest (Log P ) 1.77 ( 0.02).
Kinetics of Partition between 1-Octanol and Water of
Compounds 1, 2, 4, and 5. Only kinetics of compounds with
similar P was compared as 1 and 2 or 4 and 5. The concentra-
tions of 1 and 2 in the 1-octanol phase decreased with time and
reached similar values after 23 h (Figure 4). However, the
concentration lowering of 2 in organic medium was faster than
that of 1. So, it appears that 2 diffused more rapidly from the
1-octanol phase into the water phase than 1. In the case of 4
and 5, the kinetics was similar between them (data not shown).

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1216 J. Agric. Food Chem., Vol. 50, No. 5, 2002
Privat et al.
efficiently. These observations were in agreement with the
results on R-tocopherol, which is the reference antioxidant in
lipophilic media: it exhibited a high activity in the O/W emulsion
(inhibition of â-carotene bleaching ) 78.9%) and a lower one
in DMSO (IC50 ) 3.91 mM). Talodini et al. (29), in a recent
study, compared the antioxidant activity of 2 to R-tocopherol:
they demonstrated that the capacity of these compounds to
inhibit lipid peroxidation changes with the model systems used.
In the case of 2 and 1, which have similar P values, it was
important to observe the kinetics of the partition of these
compounds between 1-octanol and water to explain the differ-
ence of antioxidant activity between the different tests. Indeed,
the kinetics of partition depends on the polarity and the
molecular weight of the compound in question; heavy com-
pounds diffuse slower than light ones. Taking into account this
result, it suggests that 1 is less efficient than 2 at concentrating
in the lipidic phase of O/W emulsions during short times (about
3 h), limiting its antioxidant activity against LOO• radicals.
Figure 3. Bar graph displaying relative solubilities (Log P) of 1 and stilbene
derivatives in 1-octanol/water mixtures on a logarithmic scale (left side is
water solubility; right side is 1-octanol solubility). Each value is the mean
± SEM of three or five independent experiments.
In conclusion, among the stilbene structures studied in this
series, 1, the dimer of 2, shows the best antioxidant capacity in
-
the polar DMSO/O2 system. Compound 1 combines the
required structural parameters: conjugated bonds and four OH
groups with two in the para position. However, its dimeric
character and steric properties seem to limit its rapidity to diffuse
in the lipidic phase. It would now be interesting to compare
the antioxidant properties of 2 and its dimer in in vitro and in
vivo biological tests. Nevertheless, this study underscores the
high antioxidant potential of 1, which may be of interest,
associated with polyphenolic compounds or not, for food
industry applications.
In this paper, we also confirmed the antioxidant efficiency
of 2 in both media. It is known that 2 has an antioxidant activity
on copper-induced low-density lipoprotein peroxidation (30).
Its very strong activity against lipid peroxidation depends on
the chelating properties with respect to copper (31, 32) and an
antiradical activity by scavenging lipid peroxyl radicals within
the cell membrane (29). Moreover, 2 is also able to scavenge
O2- (33) and DPPH (13, 34). However, a recent study showed
that 2 is not a simple antioxidant but may act as a pro-oxidant
of the DNA system through the reduction of iron or copper
(35-37). It may also stimulate the reduction of iron in adenosine
5′-diphosphatesbut not ethylenediaminetetraacetic acids
complexes (37), in contrast with stilbene derivatives such as
diethylstilbestrol and stilbene itself. It could be interesting to
prepare stilbenic structures as antioxidants of 2 but without any
pro-oxidative effect. Compound 4 exhibits very high antioxidant
capacity in both hydrophilic and lipophilic media. Moreover, it
has a molecular structure close to that of diethylstilbestrol
allowing it to be a potential estrogen without pro-oxidative
effects. It would then be interesting to evaluate its estrogenic
activities in different biological systems.
Figure 4. Kinetics of 1 (9) and 2 (2) partition between 1-octanol and
water. Each compound was initially dissolved in the 1-octanol phase at a
concentration of 20 µM. The kinetics represented the average (±SEM) of
three independent experiments.
DISCUSSION
In this paper, phenolic compounds exhibited an antioxidant
activity, whereas 6, which bears only methoxy groups, was not
active. These results showed that, as expected, the phenolic
function is involved in the mechanism of radical-scavenging.
It has been reported in precedent studies that the antioxidant
potential of polyphenols increases with the hydrogen-donating
ability of the OH groups (9-10, 13, 27). It can be observed in
our tests that the antioxidant potency of these compounds was
highest when the OH groups occurred in the para position.
Indeed, the phenoxyl radical generated in the para position can
be stabilized by electronic delocalization through the stilbene
framework lowering the oxygen-hydrogen bond energy (28).
Even though the presence of a para-OH group is very important
for a high activity, the number of OH groups on the aromatic
rings also has an influence on the radical-scavenging potential.
These results are in agreement with those of Wang et al. (13)
who studied scavenging free radical processes of stilbenes
against DPPH radicals.
ABBREVIATIONS USED
DMPO, 5,5-dimethyl-1-pyrroline-N-oxide; DMSO, dimethyl
sulfoxide; DPPH, 2,2-diphenyl-1-picryhydrazyl; EPR, electron
paramagnetic resonance; LOO•, lipoperoxyl radicals; O/W, oil/
water; P, partition coefficient; ROS, reactive oxygen species;
SEM, standard error of the mean.
However, it is worth noting that antioxidant efficiency of
stilbene derivatives differed with the test used. This can be partly
attributed to their capacity to be partitioned between lipophilic
and hydrophilic phases, performed by P. Indeed, LOO• radicals
were generated in the lipophilic area of an O/W emulsion and
-
O2 in a continuous and hydrophilic medium. Compound 1,
according to its P, is the least hydrophobic agent, which limits
its antioxidant activity in the O/W emulsion, while 4 and 3 are
in a greater concentration in the lipid phase and at the lipid/
water interface allowing them to scavenge LOO• radicals more
ACKNOWLEDGMENT
We thank J. C. Izard (ACTICHEM, Montauban, France) for
providing the crude extract of vine roots.