Trapping Effects of Green and Black Tea Extracts on
Peroxidation-Derived Carbonyl Substances of Seal
QIN ZHU,†CHIA-PEI LIANG,§KA-WING CHENG,†XIAOFANG PENG,†
CHIH-YU LO,#FEREIDOON SHAHIDI,⊥FENG CHEN,†CHI-TANG HO,*,§AND
School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong,
People’s Republic of China; Department of Food Science, Rutgers University, 65 Dudley Road,
New Brunswick, New Jersey 08901; Department of Food Science, National Chiayi University,
Chiayi 600, Taiwan; and Department of Biochemistry, Memorial University of Newfoundland,
St. John’s, Newfoundland, Canada A1B 3X9
Green and black tea extracts were employed to stabilize seal blubber oil at 60 °C for 140 h. On the
basis of the headspace SPME-GC-MS analysis, with the addition of green/black tea extracts, the
contents of acetaldehyde, acrolein, malondialdehyde, and propanal, four major lipid peroxidation
products, were reduced. The inhibition rates of acrolein formation by green tea and black tea extracts
were 98.40 and 96.41% respectively, and were 99.17 and 98.16% for malondialdehyde, respectively,
much higher than the inhibition of the formation of acetaldehyde and propanal. Because malondial-
dehyde and acrolein are reactive carbonyl species (RCS) and recent studies have suggested that
phenolics can directly trap RCS, this study also investigated whether green tea polyphenols can trap
acrolein or not. Acrolein was reduced by 90.30% in 3 h of incubation with (-)-epigallocatechin-3-
gallate (EGCG). Subsequent LC-MS analysis revealed the formation of new adducts of equal molars
of acrolein and EGCG. The reaction site for acrolein was elucidated to be the A ring of EGCG as
evidenced by LC-MS/MS analysis and by testing of the acrolein-trapping capacities of the analogous
individual A, B, and C rings of EGCG. Thus, EGCG’s direct trapping of RCS may also contribute to
the significant reduction of acrolein and other aldehydes in the peroxidation of seal blubber oil.
KEYWORDS: Tea extracts; seal blubber oil; SPME; acrolein; EGCG
The intake of ω-3 polyunsaturated fatty acids (PUFAs) has
been positively related to human health. Mounting epidemio-
logical and interventional trials showed the beneficial effects
of ω-3 PUFAs on the prevention and treatment of cardiovascular
diseases, psychiatric disorders, immune deficiency, and cancers
(1). Dietary marine oils are considered to be a rich source of
ω-3 fatty acids, including eicosapentaenoic acid (EPA; 20:5 n-3)
and docosahexaenoic acid (DHA; 22:6 n-3). Many countries
have allowed formulating them in food products to achieve an
adequate intake of ω-3 PUFAs (2). As a result, a wider variety
of food products such as bread, milk, ice cream, and others that
usually are not associated with marine origins are fortified with
ω-3 PUFAs (3). However, ω-3 PUFAs of marine origin, such
as fish and algae oils, are susceptible to rapid oxidative
deterioration during storage and processing with the generation
of undesirable rancid flavors and reduced nutritional quality (4).
The stability of PUFAs varies widely according to their degree
of unsaturation, position of PUFAs in the triacylglycerol
molecule, and composition of minor components (5, 6).
Many strategies have been employed to avoid the potential
pro-oxidation factors that may initiate and/or accelerate lipid
peroxidation. Addition of antioxidants is one of the effective
ways to inhibit lipid peroxidation and preserve food quality.
Synthetic antioxidants, including butylated hydroxyanisole
(BHA), butylated hydroxytoluene (BHT), tert-butylhydroquino-
ne (TBHQ), and propyl gallate (PG), have commonly been used
in several countries (7). However, with the trend toward the
elimination of the utilization of synthetic food additives,
considerable interest has been focused on natural antioxidants,
which commonly exist in plants, microorganisms, fungi, or even
animal tissues (8). The application of some plant polyphenols,
such as phenolic compounds from grape and olive oil, as
inhibitors of lipid peroxidation has been well documented (9, 10).
It is reasonable to employ tea polyphenols, which are demon-
* Authors to whom correspondence should be addressed [e-mail
(M.W.) email@example.com, (C.-T.H.) firstname.lastname@example.org].
†The University of Hong Kong.
#National Chiayi University.
⊥Memorial University of Newfoundland.
J. Agric. Food Chem. 2009, 57, 1065–1069
10.1021/jf802691k CCC: $40.75
2009 American Chemical Society
Published on Web 01/20/2009
strated to be effective antioxidants for scavenging of reactive
oxygen species in vitro and in vivo, in the preservation of
unsaturated lipid-containing foods (11).
In this study, we adopted headspace solid-phase microex-
traction (SPME) coupled with GC-MS (12) to monitor the major
oxidation end products from ω-3 fatty acids in peroxidized seal
blubber oil and evaluated the protective effects of green and
black tea extracts against peroxidation of PUFAs. Compared
to traditional analytical methods, SPME presents an attractive
alternative for its solvent-free process, which combines sam-
pling, extraction, concentration, and instrument introduction into
a single step, eliminating complicated sample-preparation
procedures (13). This method is sensitive and precise for the
differentiation of various aldehydes according to their retention
times and molecular weights.
Unsaturated aldehydes such as 4-hydroxy-trans-2-nonenal
(HNE), malondialdehyde (MDA), and acrolein (ACR) are
released from the peroxidation of PUFAs. They not only
contribute to the aroma of oxidized oils but also are regarded
as causative agents in the cytotoxic process initiated by the
exposure of biological systems to oxidizing agents or free
radicals (14). These simple aldehydes produced from the
breakdown of PUFAs are termed as harmful reactive carbonyl
species (RCS), and so far, a few inhibitors have been evaluated
to quench them before they react with protein, DNA, to form
advanced lipoxidation end products (ALEs) (15). However, little
information is available on whether phenolic compounds can
be potential candidates of RCS-sequestering agents or not. In
this study, tea polyphenols’ capacity to directly trap ACR (one
RCS released from the peroxidation of seal blubber oil) was
MATERIALS AND METHODS
Chemicals and General Procedures. Acetaldehyde, propanal,
acrolein, 1,1,3,3-tetramethoxypropane, O-(2,3,4,5,6-pentafluorobenzyl)
hydroxylamine hydrochloride (PFBHA), corn oil, hexane, phosphate-
buffered saline (PBS), pH 7.4, 1,3,5-trihydroxybenzene, 1,2,3-trihy-
droxybenzene, and methyl gallate were purchased from Sigma-Aldrich
(St. Louis, MO). Poly(dimethylsiloxane)/divinylbenzene SPME fiber,
fiber holder, and crimp-top amber glass vials were all purchased from
Supelco (Bellefonte, PA). All analytical GC and HPLC grade solvents
used were obtained from BDH Laboratory Supplies (Poole, U.K.).
Malondialdehyde standard solution (10 mM) was prepared by dissolving
160 µL of 1,1,3,3-tetramethoxypropane into 5 mL of 1 M HCl and
heated in a water bath at 95 °C for 3 min. Seal blubber oil was a
Newfoundland product obtained from Atlantis Marine Inc. (St. John’s,
NL, Canada). Green tea and black extracts were gifts from Shenzhen
Bannerbio Inc. (Shenzhen, China).
SPME On-Fiber Derivatization. PFBHA solution (1 mL, 17 mg/
mL) was placed into 4 mL amber Teflon-capped vials with a 1-cm
stirring bar. A SPME fiber was inserted into the vial headspace for 2
min to adsorb the volatile PFBHA. The fiber was then inserted into
the headspace of each seal blubber oil-containing vial for 5 min. During
the process, the PFBHA and sample solutions were stirred at 600 rpm.
The fiber was then removed and inserted into GC.
GC-MS Analysis of PFBHA Oximes. An Agilent 6890 gas
chromatographic analysis system equipped with an Agilent 5973 MS
detector (EI mode) and an HP-5 MS 5% phenylmethylsiloxane column
(30.0 m × 250 µm × 0.25 µm) was used. The injection port was kept
at 250 °C. The oven temperature was held at 45 °C for 1 min, then
increased to 200 at 10 °C/min, and held there for 8.5 min. The MS
detector was operated in the electron ionization mode. The ionization
voltage was held at 70 eV, and the ion temperature was 280 °C.
n-Dodecane was used as an internal standard to adjust the peak
Effect of Solvent on Propanal On-Fiber Derivatization. Hexane,
methanol, or ethanol (200 µL) was mixed with 2.5 ppm of propanal in
5 mL of corn oil, respectively. After loading PFBHA, the SPME fiber
was inserted into the headspace of each vial for 2 min and then removed
and inserted into the GC.
Seal Blubber Oil Purification and Aging Study. The oil (100 mL)
was added into a separation funnel and mixed with a suitable amount
of sodium hydroxide solution to remove free fatty acids. The oil was
rinsed with 80 mL of distilled water three times. The oil layer was
dried with anhydrous sodium sulfate and further purified by passing
through a silica gel column. The oil collection process was accelerated
by vacuum. The purified oil was transferred to an amber glass bottle,
and the headspace was flushed with nitrogen before storing at -21 °C
for further analysis. Aging studies were conducted at 60 °C. Purified
seal oil (5 mL) was placed into a 10-mL crimp top amber glass vial
with a TFE starburst stirring head of 9.5-mm diameter. Aldehydes
formed from seal blubber oil peroxidation were collected every 24 h
from different batches of samples.
Effect of Antioxidant Mixtures on Aldehyde Formation. Two
hundred microliters of antioxidant mixture (1% lecithin, 0.25% green
or black tea extract) was dissolved in 200 µL of hexane and added
into 5-mL seal oil samples. The aldehydes formed from seal blubber
oil were monitored by SPME-GC-MS with on-fiber derivatization.
Trapping Effects of EGCG and Three Simple Phenolic Com-
pounds on Acrolein. This experiment was designed and conducted in
a buffer system. ACR and EGCG were dissolved in pH 7.4 phosphate
buffer (0.01 mol/L). The buffer (5 mL) containing 1 mM EGCG and
0.5 mM ACR was added to the amber crimp-top vial with a TFE
starburst stirring head (diameter ) 9.5 mm) and was incubated in a 37
°C water bath with shaking at 120 rpm. The amount of ACR in the
samples was measured using the SPME-GC-MS or SPME-GC method
with on-fiber derivatization every 1.5 h using different batches of
samples and controls (each sample/control is measured only one time).
The effects of 1,3,5-trihydroxybenzene, 1,2,3-trihydroxybenzene, and
methyl gallate on ACR were evaluated under the same conditions as
LC-MS Analysis of Reaction Products. Samples were analyzed
on an LC-MS/MS instrument equipped with an electrospray ionization
source interfaced to an Applied Biosystems Q-trap LC-MS/MS mass
spectrometer. Liquid chromatography was carried out on an Agilent
HPLC system with a degasser (G1379A), a quaternary pump (G1311A),
a thermostated autosampler (G1329A), and a diode array detector
(G1315B). Separation of reaction products was carried out on a Varian
Inertsil ODS C-18 column (3 µm, 15 × 4.6 mm). The mobile phase
was composed of 0.1% formic acid (solvent A) and acetonitrile (solvent
B) with the following gradients: 0 min, 5% B/95% A; 25 min, 35%
B/65% A; 28 min, 80% B/20% A; and 30 min, 5% B/95% A. Effluent
from the UV detector was split 4:1, and only one part (200 µL/min)
was directed to the MS for spectrometric analysis with the remaining
discharged as waste. The MS operation parameters were as follows:
negative ion mode; spray voltage, 4 kV; scan range, 200-1000 Da;
capillary temperature, 300 °C. LC-MS/MS conditions: negative ion
mode; precursor ion m/z 513; collision energy, 40 eV.
Statistical Analysis. Statistical analyses were performed with the
SPSS statistical package (SPSS Inc., Chicago, IL). Paired sample t test
was applied to determine whether there was significant difference.
RESULTS AND DISCUSSION
To evaluate the protective effects of green/black tea extracts
against peroxidation of PUFAs, a sensitive analytical method
was first to be established. In the present study, four major
aldehydes, including acetaldehyde, propanal, acrolein, and
malondialdehyde, were identified and quantified as their PFBHA
carbonyl-oxime isomers with the application of headspace
SPME-GC-MS. A derivatization reagent was used to ensure
binding of aldehydes to fiber because without a strong chro-
mophore, volatile polar aldehydes are difficult to analyze directly
(16) and the binding affinity of short-chain aldehyde to SPME
fiber is low. PFBHA is an excellent choice for derivatization
of aldehydes under mild reaction conditions with good perfor-
mance in this study.
J. Agric. Food Chem., Vol. 57, No. 3, 2009 Zhu et al.
The direct addition of plant extracts into the oil was not
practical as the phenolic extracts used in this research are
hydrophilic compounds, whereas oils are hydrophobic. Some
dispersing solvents have to be used, which may affect the
accuracy of aldehyde analysis by SPME-GC. When methanol,
ethanol, and hexane were evaluated as dispersing reagents with
propanal as the aldehyde, it was found that the formation of
propyl-oximes in methanol- or ethanol-containing samples was
reduced to 8.77 and 19.30%, respectively, compared with the
control, whereas in hexane it was much better (Figure 1). This
might be addressed by the fact that the high concentration of
polar solvent in the headspace of sample vials interfered with
the binging rate of propanal to PFBHA. In addition, methanol
or ethanol could not act as a good dispersing reagent, and the
plant extracts tend to remain at the surface of the oil. To address
this concern, green or black tea extract was first dispersed into
the oil using soy lecithin and hexane to achieve best dispersion
of hydrophilic antioxidants into the oil and to minimize the
Compared with the control, after incubation at 60 °C for
140 h, the addition of green tea and black tea extracts in purified
seal blubber oil exhibited strong inhibitory effects on the
formation of aldehydes. The inhibition rates of ACR by green
tea and black tea extracts were 98.40 and 96.41%, respectively,
and those for MDA were 99.17 and 98.16%, respectively
(Figure 2). A significant reduction in the formation of secondary
oxidation products by tea catechins of seal blubber oil at 65 °C
for 144 h, measured by TBARS method, has already been
reported (17). However, the TBA test is intrinsically nonspecific
for MDA because some MDA-like substances can interfere with
the test (18). It has been found that non-lipid-related materials
as well as fat peroxide-derived decomposition products other
than MDA, such as 2-alkenals, 2,4-alkadienals, 4-hydroxyalk-
enals, or protein-bound MDA are TBA positive (19). The on-
fiber derivatization SPME-GC-MS analysis of headspace volatile
compounds provides a more specific analysis for the separation
and identification of four major aldehydes in this study. There
were also decreases in the amount of propanal and acetaldehyde
by 58.44 and 59.40%, respectively, by green tea compared with
corresponding values of 24.81 and 24.76% by black tea. This
could be explained by the higher antioxidant power of green
tea extract compared with black tea extract as we showed
The primary purpose of adding green or black tea extract to
seal blubber oil was to evaluate their effects on delaying the
onset of lipid peroxidation and accumulation of peroxidation
products. The reduced accumulation of aldehydes can mainly
be explained by the polyphenols’ capability to scavenge free
radicals and their metal-chelating activities (21, 22). By trapping
free radicals in different stages of lipid peroxidation, polyphenols
spare PUFAs from deterioration. However, it was interesting
to find the inhibitory ratios by tea extracts for these four
aldehydes were different. Green/black tea polyphenols could
extensively decrease the amount of ACR and MDA, whereas
the inhibitory activity on propanal and acetaldehyde was much
lower. Alternative mechanisms other than antioxidant activity
might, in part, be responsible for the significant reduction of
ACR and MDA released to the headspace. Green/black tea
polyphenols might directly trap ACR and MDA as direct
trapping of methylglyoxal (also a kind of RCS) by green tea
and black tea polyphenols has recently been reported (23, 24).
To further clarify the relationship between polyphenols and
reactive aldehydes, the direct co-incubation of ACR and EGCG
was studied, and significant decreases in the amount of ACR
of up to 71.60% in 1.5 h and 90.30% in 3 h compared to the
control were observed (Figure 3). In previous studies, ACR
was proven to be a potent electrophile with high reactivity
toward nucleophiles such as glutathione and amino groups
through Michael addition reaction (25). As to its addition to
polyphenols, the LC-MS analysis of the products of ACR and
EGCG indicated the existence of significant amounts of potential
adducts with predicted molecular ion peak [M - H]-at 513,
which could be the direct combination products of ACR and
EGCG at a mole ratio of 1:1. There are peaks of stereoisomers
ranging from the retention time of 15.91 to 17.99 min on the
HPLC chromatogram (Figure 4). For detailed positions of the
electrophilic substitution, structural elucidation of the adducts
into 5 mL of corn oil).
Figure 2. Inhibition percentage of aldehydes in the vial headspace of
seal blubber oil incubated with/without tea extracts at 60 °C for 140 h.
Eachvalueisexpressedasmean( standarderror of threereplications.
Figure 3. SPME-GC quantification of decreased ACR with the co-
incubationof EGCGfor 1.5and3hwithACR. Eachvalueis expressed
as mean ( standard error of three replications. The remaining amount
of ACR after both 1.5 and 3 h of incubation was significantly different
fromcontrol (P < 0.01).
Trapping Effects of Tea Extracts on Carbonyl SubstancesJ. Agric. Food Chem., Vol. 57, No. 3, 2009
was achieved using LC-MS/MS with collisionally activated
dissociation (CAD) of the parent ion m/z [M - H]-513 (Figure
5). The daughter ion of m/z 387 [M - 126 - H]-could be
generated from the loss of a pyrogallol moiety of EGCG’s B
or C ring. The daughter ion of m/z 361 [M - 152 - H]-
suggested the typical loss of a galloyl moiety of EGCG’s C
ring. Therefore, the conjugation of ACR to EGCG most likely
involved the A ring of EGCG at the C-8 or C-6 position, but
not the less nucleophilic rings B and C. This is in agreement
with the findings that C-8 and C-6 positions of the EGCG A
ring could be active sites to react with RCS such as methylg-
lyoxal (MGO) and glyoxal (GO) (23, 24). In other studies, it
was reported that certain flavonoids, especially green tea
catechins, could react with some of the aldehydes including
acetaldehyde and glyoxylic acid to form (+)-catechin-aldehyde
condensation products, leading to bridged dimers in a winelike
model solution. The nucleophilic substitution also occurred at
C-6 or C-8 of the A ring of monomeric flavanols (26, 27).
To further demonstrate the trapping sites of EGCG on ACR,
three simple phenolic compounds, 1,3,5-trihydroxybenzene,
1,2,3-trihydroxybenzene, and methyl gallate, were employed as
the analogous individual A, B, and C rings of EGCG to evaluate
their effects on ACR trapping, and SPME-GC/MS was used to
quantify ACR. It was discovered that 1,2,3-trihydroxybenzene
and methyl gallate showed a low activity, whereas 1,3,5-
trihydroxybenzene was very active with only 13.20% ACR
remaining after 1.5 h of incubation (Figure 6). The possible
new product of ACR and 1,3,5-trihydroxybenzene was identified
using LC-MS, which showed one molecule of ACR (MW 56)
was attached to 1,3,5-trihydroxybenzene (MW 126), and a final
product of MW 182 (m/z [M - H]-at 181) was easily identified
(Figure 7). This result further supported the hypothesis that the
C-8 or C-6 position of the EGCG A ring could serve as the
trapping site for ACR. This can be explained by three electron-
donating hydroxyl groups in the meta configuration on a benzene
ring of 1,3,5-trihydroxybenzene, which activate the ortho and
para positions and result in a pronounced reactivity of the
benzene ring for electrophilic aromatic substitution reactions
at the three unsubstituted carbon sites (28).
Figure 4. HPLC chromatogram of the reaction products of ACR and
EGCGdetectedat thewavelengthof 254nm. Thepeak at 14.12minis
the remaining EGCG. The peaks at 15.91-17.99 min are possible new
products fromthe reaction.
Figure 5. LC-MS/MS analysis of the precursor ion of m/z [M- H]-at
Figure 6. SPME-GC-MS quantification of decreased ACR with the co-
incubation of 1,2,3-trihydroxybenzene, methyl gallate, and 1,3,5-trihy-
droxybenzene for 1.5 h with ACR. Each value is expressed as mean (
standard error of three replications. The remaining amount of ACR
fromcontrol (P < 0.01).
Figure7. (A) HPLCchromatogramof thereactionproductsof ACRand
1,3,5-trihydroxybezene detected at the wavelength of 254 nm. (B) Mass
and its molecular weight is 182 with [M- H]-at 181.2.
J. Agric. Food Chem., Vol. 57, No. 3, 2009 Zhu et al.
From a physiological point of view, there are aldehyde-
sequestering agents (such as aminoguanidine, pyridoxamine,
OPB-9195) that deactivate or degrade cytotoxic carbonyls by
behaving as sacrificial nucleophiles (29). The discovery of the
ACR-quenching capability of EGCG could justify adding this
polyphenol as a possible intervention agent for the inhibition
Overall, this study demonstrated the inhibitory effects of tea
extracts on ω-3 PUFA peroxidation of seal blubber oil by
targeting the major aldehydes formed. EGCG, a major phenolic
component in green tea, could also act as a nucleophile to trap
ACR. A close examination of the reactive sites of EGCG in
trapping reaction was unraveled by LC-MS/MS analysis and
by using analogous individual A, B, and C rings of EGCG.
However, the complicated relationship between natural phenolic
compounds and lipid peroxidation requires further investigation.
Beyond traditional consideration of tea polyphenols as antioxi-
dants in lipid peroxidation systems, their potential as direct
eliminating agents of lipid peroxidation-derived RCS should also
be taken into consideration.
ACR, acrolein; EGCG, (-)-epigallocatechin-3-gallate; MDA,
malondialdehyde; PBS, phosphate-buffered saline; PFBHA,
O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride;
PUFAs, polyunsaturated fatty acids; RCS, reactive carbonyl
species; SPME, solid-phase microextraction.
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Received for review September 1, 2008. Revised manuscript received
December 15, 2008. Accepted December 16, 2008.
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