Antioxidant activity of soybean oil containing 4-vinylsyringol obtained from decarboxylated sinapic acid

Article abstract of DOI:10.1007/s11746-014-2492-4

4-Vinylsyringol was produced by decarboxylation from sinapic acid. To evaluate the antioxidant activity of 4-vinylsyringol, 500 ppm of 4-vinylsyringol, sinapic acid, or α-tocopherol was added to soybean oil and the oxidation processes were monitored by the peroxide value (PV), the thiobarbituric acid reactive substances value (TBARS) assay, and ¹H-NMR spectroscopy. The results obtained by PV and TBARS indicated that soybean oil containing 4-vinylsyringol (SBO-VS) showed the highest oxidative stability. ¹H-NMR analysis also showed concurring results. After 19 days of oxidation, the degradation rates of linoleic acid (4.2 %) and linolenic acid (4.4 %) in SBO-VS were significantly lower than those in other oils. Secondary oxidation products (i.e. aldehydes) were undetectable in SBO-VS by ¹H NMR, whereas concentrations of such compounds in soybean oils containing α-tocopherol or sinapic acid were 38.0 ± 0.4 and 2.75 ± 0.2 mM oil, respectively. In addition, synergistic antioxidant effect between any two antioxidants was not observed.

Full text of DOI:10.1007/s11746-014-2492-4

J Am Oil Chem Soc
DOI 10.1007/s11746-014-2492-4
ORIGINAL PAPER
Antioxidant Activity of Soybean Oil Containing 4-Vinylsyringol
Obtained from Decarboxylated Sinapic Acid
•
Xiang-Yu Wang Dan Yang Hua Zhang Cai-Hua Jia Jung-Ah Shin
•
•
•
•
•
Soon Taek Hong Yong-Hwa Lee Young-Seok Jang Ki-Teak Lee
•
•
Received: 27 November 2013 / Revised: 8 May 2014 / Accepted: 15 May 2014
Ó AOCS 2014
Abstract 4-Vinylsyringol was produced by decarboxyl-
ation from sinapic acid. To evaluate the antioxidant activity
of 4-vinylsyringol, 500 ppm of 4-vinylsyringol, sinapic
acid, or a-tocopherol was added to soybean oil and the
oxidation processes were monitored by the peroxide value
(PV), the thiobarbituric acid reactive substances value
Introduction
Oils and fats are important ingredients of the human diet.
They not only influence the organoleptic and textural
properties of foods, but they also play important roles in
human health. However, lipids that contain unsaturated
fatty acids are prone to oxidation. The secondary oxidation
products, especially 4-hydroxy-(E)-2-alkenal, have been
proven to be related to atherosclerosis, cancer, and car-
diovascular disease [1, 2]. Hence, antioxidants have been
employed for inhibiting lipid oxidation in the food
industry.
1
(TBARS) assay, and H-NMR spectroscopy. The results
obtained by PV and TBARS indicated that soybean oil
containing 4-vinylsyringol (SBO-VS) showed the highest
oxidative stability. 1H-NMR analysis also showed con-
curring results. After 19 days of oxidation, the degradation
rates of linoleic acid (4.2 %) and linolenic acid (4.4 %) in
SBO-VS were significantly lower than those in other oils.
Secondary oxidation products (i.e. aldehydes) were unde-
Polar phenolics, which are abundant in plant tissues, are
an important class of antioxidants and much attention has
been paid to the antioxidant activities of these compounds
in crude oils. For example, Baldioli et al. [3] suggested that
total polar phenolic levels were well correlated with the
oxidative stability of crude olive oil, whereas tocopherols
correlated poorly. Crude rapeseed oil, which contains a
high concentration of polar phenols, has been reported to
be more stable than refined oils [4, 5]. Besides, other
researchers have reported that polar phenols, such as hy-
droxycinnamates and flavonoids, have higher antioxidant
activities than tocopherols [6, 7].
1
tectable in SBO-VS by H NMR, whereas concentrations
of such compounds in soybean oils containing a-tocopherol
or sinapic acid were 38.0 0.4 and 2.75 0.2 mM oil,
respectively. In addition, synergistic antioxidant effect
between any two antioxidants was not observed.
Keywords 1H NMR Á 4-Vinylsyringol Á
Decarboxylation Á Sinapic acid Á Oxidative stability
X.-Y. Wang Á D. Yang Á C.-H. Jia Á J.-A. Shin Á
S. T. Hong Á K.-T. Lee (&)
However, the limited solubility of polar phenolics in
lipids inhibits their application as antioxidants in foods.
Recently, researchers have examined the use of nonpolar-
derivatives of hydroxycinnamic acids as potential antioxi-
dants. For example, vinylguaiacol (extracted from coffee)
has been reported to have a greater antioxidant effect than
a-tocopherol [8], and vinylsyringol (produced from sinapic
acid by a pressing and roasting procedure) improved the
oxidative stabilities of protein and lipids in cooked pork [9,
10]. Furthermore, according to Terpinc et al. [11], decar-
boxylation products of hydroxycinnamic acids were more
Department of Food Science and Technology, Chungnam
National University, Daejeon 305-764, Republic of Korea
e-mail: ktlee@cnu.ac.kr
H. Zhang
Department of Food Science and Engineering, Yanbian
University, Yanji, China
Y.-H. Lee Á Y.-S. Jang
Bioenergy Crop Research Center, National Institute of Crop
Science, Rural Development Administration, Muan 533-834,
Republic of Korea
123

J Am Oil Chem Soc
efficient at inhibiting oxidation in emulsion systems than
their parent compounds.
to the oxidation study. The tocopherol contents of stripped
soybean oil were determined as described previously [13].
However, little research has been performed on the
oxidation of bulk oils with hydroxycinnamic acids and
their decarboxylated products as antioxidants. Sinapic acid
(3,5-dimethoxy-4-hydroxycinnamic acid) and its decar-
boxylated product 4-vinylsyringol are good examples of
such antioxidant compounds. In the present study, the
peroxide value (PV) and thiobarbituric acid reactive sub-
stances (TBARS) assay were performed to measure the
concentrations of hydroperoxides and malondialdehydes in
soybean oils containing different antioxidants (a-tocoph-
erol, sinapic acid, or 4-vinylsyringol). The effect of syn-
ergistically inhibiting oxidation between any two
Synthesis of 4-Vinylsyringol
4-Vinylsyringol (4-VS) was synthesized by a modified
method described in previous study [11]. Sinapic acid
(100 mg) was dissolved in 2 mL of N,N-dimethylform-
amide (DMF) containing 20 mg of sodium acetate as a
catalyst for the decarboxylation reaction. The reaction was
carried out at 130 °C in an oil bath for 15 min. After
cooling to room temperature, 4-VS was extracted with n-
hexane (2 mL each time) several times. The solvent was
removed by flushing with nitrogen, and 4-VS obtained was
stored at -70 °C for further experiments.
1
antioxidants was also determined. Furthermore, H NMR
was used to compare the antioxidant activities of
a-tocopherol, sinapic acid, and 4-vinylsyringol in stripped
soybean oil by monitoring the degradation of polyunsatu-
rated fatty acids (PUFA), the evolution of conjugated
forms, and the formation of aldehydes during oxidation.
Oxidation Process
Different antioxidants, namely a-tocopherol, sinapic acid,
or 4-VS, were added to 10 g of SSO at a concentration of
500 ppm. In order to determine synergistic antioxidant
effect between two antioxidants, soybean oil containing
250 ppm of a-tocopherol and 250 ppm of sinapic acid
(SBO-toco ? SA), 250 ppm of a-tocopherol and 250 ppm
of 4-VS (SBO-toco ? VS), or 250 ppm of sinapic acid and
250 ppm of 4-VS (SBO-SA ? VS) were submitted to
oxidation. The oil (6 g) was placed into a Petri dish
(35 9 10 mm) and exposed to air for 19 days in an oven at
60 °C in the dark. Oxidized samples were flushed with
nitrogen and frozen at -70 °C until required for analysis.
Experimental Procedures
Materials
Soybean oil was purchased from a local market (Daejeon,
South Korea). Silicic acid, deuterated chloroform (99.9
atom % D, containing 0.1 % v/v TMS) and dimethyl
sulfoxide-d6 (99.9 at.% D, contains 0.03 % (v/v) TMS)
were obtained from Sigma-Aldrich (St. Louis, MO, USA).
Activated charcoal for column chromatography was
obtained from Daejung Chemical Reagent (Daejung
Chemicals & Metals Co., Ltd). N,N-Dimethylformamide
(DMF) was purchased from TCI (Tokyo Chemical Industry
Co., Ltd).
Peroxide Value (PV) and Thiobarbituric Acid Reactive
Substances Value (TBARS Value)
Peroxide values of oxidized oils were measured using the
IDF method described in the previous study [14]. TBARS
values were determined as described previously [15].
Preparation of Stripped Soybean Oil
1H-NMR Experiment
Stripped soybean oil (SSO) was obtained by passing soy-
bean oil through a vacuum liquid chromatographic column
(3.5 cm diameter, 20 cm length) [12]. Samples were pre-
pared by diluting 120 g of soybean oil with 120 mL of n-
hexane. The lower layer of the column was packed with
15 g of silicic acid to remove minor diacylglycerol (DAG),
monoacylglycerol (MAG), and free fatty acid (FFA) in
soybean oil, and an upper layer of 30 g of active charcoal
was used to remove tocopherols. After eluting the oil with
300 mL of n-hexane, the solvent was removed using a
vacuum rotary unit (RE 111, Bu¨chi, Flawil, Switzerland) at
40 °C. Traces of n-hexane were removed by flushing with
nitrogen. Stripped soybean oil was stored at -70 °C prior
1H-NMR experiments were carried out using a Bruker
Avance III 600 spectrometer operated at 600.23 MHz.
Typically, 200 mg of oil was mixed with 400 lL of CDCl3
containing 0.1 % tetramethylsilane as an internal standard,
and this mixture was placed in a 5-mm diameter NMR
tube. The acquisition parameters used were: spectral width
12,335.5 Hz, number of scans 16, and acquisition time
2.656 s. The experiment was carried out at 28 °C. All
spectra were processed using ACD labs NMR Processor,
version 10.0. Chemical shifts (d) were referred to the TMS
at d = 0 ppm. Conjugated forms (–CH=CH–CH=CH–),
hydroperoxides (–OOH), and aldehydes (–CHO) can be
presented in mol/mol oil directly by normalizing the peak
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J Am Oil Chem Soc
area of b hydrogen atom ([CHOCOR) in the glycerol
backbone to 1. For recalculating the amounts of above
oxidation products in mmol/L of oil, the molecular weights
of oils were considered.
activity of 4-VS, the main antioxidants (tocopherols) in
soybean oil were removed by a vacuum liquid chromato-
graphic column (yield: 84.6 %, by weight). The total
tocopherol content of stripped soybean oil was 9.2 ppm. As
shown in Fig. 1a, among the soybean oils containing single
antioxidant, SBO-VS showed the lowest evolution rate of
peroxides. On day 3, the concentrations of peroxides in
SBO-VS (11.5 0.3 milliequivalents/kg oil) were signif-
icantly lower than that in the SBO-control (355.2
21.8 milliequivalents/kg oil), SBO-toco (55.9 1.1 milli-
equivalents/kg oil) and SBO-SA (23.0 0.2 milliequiva-
lents/kg oil) (p \ 0.05). Thereafter, from day 3 to day 10,
619.7, 289.7, and 103.8 milliequivalents/kg oil of perox-
ides were respectively increased in SBO-control, SBO-
toco, and SBO-SA while only 31.3 milliequivalents/kg oil
of peroxides were generated in SBO-VS over the same
period. After day 10, the concentrations of peroxides in
SBO-control showed a gradual decrease due to conversion
from primary to secondary oxidation products [19]. Fur-
thermore, from day 10 to day 19, SBO-VS showed less
peroxides formation than SBO-toco or SBO-SA, and the
final concentrations of peroxides in SBO-VS (326.9
26.0 milliequivalents/kg oil) on day 19 were significantly
lower than that in SBO-toco (884.9 22.6 milliequiva-
lents/kg oil) and SBO-SA (424.4 19.3 milliequivalents/
kg oil) (p \ 0.05). According to the above results, although
the long time (19 days) accelerated oxidation process
(exposed to air in an oven at 60 °C) led to a high con-
centration of peroxide in SBO-VS for consumption, 4-VS
still showed higher antioxidant activity in oil system than
sinapic acid and a-tocopherol.
Statistical Analysis
Oxidation reactions were conducted in duplicate and
results are presented as averages. Analysis of variance
(ANOVA) was performed using SPSS 16.0 (SPSS Inc.,
Chicago, IL). Statistical significance was accepted for
p \ 0.05 [16].
Results and Discussion
Identification of 4-Vinylsyringol
The 1H-NMR spectroscopic data of 4-vinylsyringol (4-VS)
is shown in Table 1. The structure of 4-VS was confirmed
by comparison with previous studies [11, 17, 18].
Peroxide Value (PV) and Thiobarbituric Acid Reactive
Substances Value (TBARS Value)
Peroxide values (PV) and TBARS assays were used to
monitor the oxidation processes of SBO-control (soybean
oil without antioxidant), SBO-toco (soybean oil containing
500 ppm a-tocopherol), SBO-SA (soybean oil containing
500 ppm sinapic acid), and SBO-VS (soybean oil con-
taining 500 ppm 4-VS) as described previously [14, 15]. It
is worth mentioning that 500 ppm of 4-VS or a-tocopherol
was easily dissolved in soybean oil while heating (in
boiling water for 5 min) and sonication (50 °C for 15 min)
were performed for dissolving 500 ppm of sinapic acid.
Furthermore, to accurately determine the antioxidant
TBARS values of SBO-control, SBO-toco, SBO-SA,
and SBO-VS are shown in Fig. 1b. The results indicated
that SBO-control and SBO-toco were more susceptible to
oxidation than SBO-SA and SBO-VS. On the other hand,
although TBARS value of SBO-SA and SBO-VS increased
1
Table 1 Assignments and the H-NMR spectroscopic data of 4-vinylsyringol (4-VS)
Position
Chemical shifta (ppm)
1
2
3
4
5
6
8.47 (1H, s, –OH)
6.75 (2H, s, Ar–H)
6.60 (1H, dd, J34 = 17.50, J35 = 10.73, –CH=)
5.69 (1H, d, J34 = 17.50, J45 = 0.94, =CH2)
5.10 (1H, d, J35 = 10.73, J45 = 0.94, =CH2)
3.79 (6H, S, –OCH3)
a
s singlet, d doublet, dd doublet of doublets
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J Am Oil Chem Soc
Fig. 1 Peroxide value (PV) and
TBARS value of soybean oils
containing different
antioxidants [control,
a-tocopherol (500 ppm),
sinapic acid(500 ppm),
4-VS(500 ppm), a-tocopherol
(250 ppm) ? sinapic acid
(250 ppm), a-tocopherol
(250 ppm) ? 4-VS (250 ppm),
4-VS (250 ppm) ? sinapic acid
(250 ppm),] during oxidation at
60 °C in the dark. a PV and
b TBARS value
PV
A
1000
900
800
700
600
500
400
300
200
100
0
SBO-control
SBO-toco
SBO-SA
SBO-VS
SB0-α-toco+SA
SBO-α-toco+VS
SBO-SA+VS
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
Day
TBARS value
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
B
SBO-control
SBO-toco
SBO-SA
SBO-VS
SB0-α-toco+SA
SBO-α-toco+VS
SBO-SA+VS
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
Day
slightly, SBO-VS showed consistently lower TBARS value
than SBO-SA throughout the oxidation process, and the
final TBARS value of SBO-VS (0.5 0.0 mg-1) was
lower than that of SBO-SA (0.7 0.0 mg-1).
were observed in the other combinations of antioxidants.
The antioxidant activity of tocopherol (250 ppm) with
either sinapic acid (250 ppm) or 4-VS (250 ppm) was
lower than 500 ppm of either sinapic acid or 4-VS,
although such combinations showed higher antioxidant
activity than 500 ppm of a-tocopherol. Thus, the syner-
gistic antioxidant effect of tocopherol with sinapic acid or
4-VS was not distinctly observed in this study.
In addition, in Fig. 1a, b, the synergistic antioxidant
effects of two antioxidants were also determined. Among
the combinations of each two antioxidants, sinapic acid
with 4-VS showed the highest antioxidant activity. On day
19, both PV and TBARS values of SBO-SA ? VS (PV:
380.6 27.7 milliequivalents/kg oil; TBARS values:
0.6 0.0 mg-1) were significantly lower than those of
SBO-toco ? SA (PV: 821.3 42.0 milliequivalents/kg
oil; TBARS value: 1.5 0.0 mg-1) and SBO-toco ? VS
(PV: 810.9 9.8 milliequivalents/kg oil; TBARS values:
1.5 0.1 mg-1) (p \ 0.05). However, compared with
SBO-VS (PV: 326.9 26.0 milliequivalents/kg oil;
TBARS value: 0.5 0.0 mg-1) on day 19, SBO-SA ? VS
showed higher peroxide and malondialdehyde formation,
indicating that combination of sinapic acid (250 ppm) and
4-VS (250 ppm) was less effective on retarding the oxi-
dation than 4-VS (500 ppm) in soybean oil. Similar results
1
Monitoring the Oxidation Process by H NMR
1
To further confirm the antioxidant activity of 4-VS, H
NMR was performed to investigate the degradation of
PUFA (polyunsaturated fatty acids), the evolution of pri-
mary oxidation products (conjugated forms), and the for-
mation of secondary oxidation products (aldehydes) in
1
soybean oil. H-NMR signals are directly proportional to
1
proton numbers. By adopting this principle, H NMR was
able to quantify amounts of linolenic acid (C18:3) and
linoleic acid (C18:2) as previously described [20] and the
results are presented in Fig. 2. Figure 2a shows obvious
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J Am Oil Chem Soc
Fig. 2 a The content (molar
percentage) of linoleic acid
(C18:2) in soybean oils
containing different
The content of linoleic acid (C18:2) in soybean oils with different
antioxidants in different oxidation periods
A
60%
50%
40%
30%
20%
10%
0%
SBO-control
antioxidants [control,
a-tocopherol(500 ppm),
sinapic acid(500 ppm) and
4-VS(500 ppm)] in different
oxidation periods. b Contents
(molar percentage) of linolenic
acid (C18:3) in soybean oils
containing different
SBO-toco
SBO-SA
SBO-VS
antioxidants [control,
a-tocopherol(500 ppm),
sinapic acid(500 ppm) and
4-VS(500 ppm)] in different
oxidation periods
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20
Day
The content of linolenic acid (C18:3) in soybean oils with different
antioxidants in different oxidation periods
B
7%
6%
5%
4%
3%
2%
1%
0%
SBO-control
SBO-toco
SBO-SA
SBO-VS
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20
Day
decreases in C18:2 levels in the SBO-control and SBO-toco
while SBO-SA and SBO-VS showed only slight degrada-
tion of C18:2 throughout the oxidation process. After
19 days of oxidation at 60 °C in dark, 70.9, 56.3, and
12.2 % of C18:2 were lost in the SBO-control, SBO-toco,
and SBO-SA, respectively. Meanwhile, only 4.2 % of
C18:2 decreased in SBO-VS. On the other hand, the
decomposition of C18:3 in these soybean oils (Fig. 2b)
showed that 86.5, 74.5, 15.4, and 4.4 % of C18:3 were
degraded after 19 days of oxidation in the SBO-control,
SBO-toco, SBO-SA, and SBO-VS, respectively. The sig-
nificantly lower degradation rate of PUFA in SBO-VS
showed that soybean oil containing 4-VS was more resis-
tant to autoxidation than soybean oil containing
a-tocopherol or sinapic acid.
of oxidation. Figure 3b shows that the concentrations of
conjugated forms in SBO-control and SBO-toco decreased
after 7 and 12 days of storage, respectively. However, both
SBO-SA and SBO-VS showed gradual increases in con-
jugated forms until the 19 days of the oxidation. These
results suggest that conjugated forms in SBO-control and
SBO-toco decomposed into secondary oxidation products
[24] while SBO-SA and SBO-VS still in the primary oxi-
dation stage by 19 days of oxidation. Compared with sin-
apic acid, its decarboxylation product (4-VS) was more
useful at preventing the formation of conjugated forms.
From day 0 to day 5, 13.6 0.4 mM oil of the conjugated
forms were formed in SBO-SA, while the conjugated forms
1
in SBO-VS remained undetectable by H NMR over the
same period. From day 5 to day 19, conjugated forms
increased consistently in SBO-SA and SBO-VS, but the
formation rate in SBO-VS was lower. On day 19, the
concentration of conjugated forms in SBO-VS
(44.9 3.0 mM oil) was significantly lower than that in
SBO-SA (111.4 2.5 mM oil) (p \ 0.05).
Finally, although the TBARS assay was used to
evaluate amounts of secondary oxidation products, it can
only detect malondialdehyde generated during lipid
Furthermore, the peroxidation of PUFA is accompanied
by the formation of conjugated diene structures [21]. Thus,
several signals in the region between 5.4 and 6.7 ppm
newly appeared in the 1H-NMR spectra. As Fig. 3a shows,
Z,E-conjugated form and E,E-conjugated form were iden-
tified in oxidized soybean oils, as has been previously
1
reported [22, 23]. In addition, H-NMR quantitative ana-
lysis of conjugated forms was performed to evaluate levels
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J Am Oil Chem Soc
Fig. 3 Primary oxidation
products (conjugated forms):
1
a assignments and the H-NMR
A
spectra of conjugated forms
(obtained from soybean oil
containing a-tocopherol after
7 days of oxidation). b The
concentrations of total
conjugated forms in soybean
oils containing different
antioxidants [control,
a-tocopherol (500 ppm),
sinapic acid (500 ppm), or 4-VS
(500 ppm)] after oxidation at
60 °C in the dark
Concentrations of total conjugated forms in soybean oils with different
B
antioxidants
300
250
200
150
100
50
SBO-control
SBO-toco
SBO-SA
SBO-VS
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20
Day
oxidation, and malondialdehyde is neither the sole end
product nor a substance generated exclusively by lipid
oxidation [25]. Therefore, the molar concentrations of
total aldehydes in soybean oils containing different
antioxidants were also determined by 1H NMR. In this
study, six types of aldehydes, namely (I) n-alkanal, (II)
4-hydroperoxy-(E)-2-alkenal, (III) 4-hydroxy-(E)-2-alke-
nal, (IV) 4,5-epoxy-(E)-2-alkenal, (V) (E,E)-2,4-alkadie-
nal, and (VI) (E)-2-alkenal, were identified (Fig. 4a) [22,
26]. As is shown in the Fig. 4b, 4-VS and its corre-
sponding hydroxycinnamic acid (sinapic acid) showed
obviously higher antioxidant activity than a-tocopherol.
After 19 days of oxidation, aldehydes were not detect-
able in SBO-VS and only n-alkanal and (E)-2-alkenal
were generated in SBO-SA. However, in SBO-control
and SBO-toco, all six aldehydes were detected. On day
19, the concentrations of total aldehydes in SBO-control,
SBO-toco, and SBO-SA were 52.0 3.7, 38.0 0.4,
and 2.7 0.2 mM oil, respectively (Fig. 4b). Further-
more, Figs. 2, 3 and 4 suggest that the degradation of
PUFA, the evolution of conjugated forms, and the for-
mation of aldehydes in soybean oils are somewhat
related. In SBO-toco, for example, the obvious increase
of aldehydes was first observed between day 7 and 10
(Fig. 4), during which PUFA degradation (Fig. 2) and
formation of conjugated forms (Fig. 3) were obviously
fast. In SBO-SA, this phenomenon may be observed
between day 12 and day 17. These results suggest that
significant oxidation of SBO-toco, and SBO-SA started
after 10 days, and 17 days of storage, respectively.
However, changes in fatty acid composition and primary
and secondary oxidation products were almost undetect-
able in SBO-VS even after 19 days of oxidation.
Conclusion
Generally, 4-VS exists in small amounts in crude rapeseed
oil [27] and no side-effects on human health have been
reported. Our results are in agreement with previous studies
[9, 11], in which 4-VS showed greater antioxidant activity
than sinapic acid in meat and emulsion oxidation. In the
present study, 4-VS was obtained from decarboxylated
sinapic acid, and exhibited the highest antioxidant activity
in bulk oil, followed by sinapic acid and a-tocopherol. The
results indicated that 4-VS appears to have potential as an
antioxidant for oil applications. Furthermore, as compared
with sinapic acid, 4-VS (the decarboxylation product of
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J Am Oil Chem Soc
Fig. 4 Secondary oxidation
products (aldehydes):
1
a assignments and the H-NMR
A
spectra of aldehydes obtained
from soybean oil containing
different antioxidants after
oxidation for 19 days.
b Concentrations of total
aldehydes in soybean oils
containing different
antioxidants [control,
a-tocopherol(500 ppm), sinapic
acid (500 ppm), or 4-VS
(500 ppm)] after oxidation at
60 °C in the dark
Concentrations of total aldehydes in soybean oils with different
antioxidants
B
60
50
40
30
20
10
0
SBO-control
SBO-toco
SBO-SA
SBO-VS
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
Day
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sinapic acid) had higher solubility in oil. All the above
findings imply that there is a possibility of further utilization
of sinapic acid which was abundant in rapeseed oil cake. To
the best of our knowledge, the use of rapeseed oil cake has
been limited due to the antinutritional effects of compounds
such as glucosinolates [28]. Therefore, the potential anti-
oxidant activity of 4-VS in this study may allow us to
extend the applications of the by-products of rapeseed oil
processing. Further studies on the antioxidant activities of
4-VS at different concentrations will be performed.
Acknowledgments This work was carried out with the support of
‘‘The Cooperative Research Program for Agriculture Science &
Technology Development (Project No.PJ 009164)’’ Rural Develop-
ment Administration, Republic of Korea.
¨
¨
9. Vuorela S, Salminen H, Makela M, Kivikari R, Karonen M,
Heinonen M (2005) Effect of plant phenolics on protein and lipid
oxidation in cooked pork meat patties. J Agric Food Chem
53:8492–8497
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