Journal of Chromatography A, 1518 (2017) 8–14

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Journal of Chromatography A
journal homepage: www.elsevier.com/locate/chroma

Full length article

The analysis of aroma/flavor compounds in green tea using ice

concentration linked with extractive stirrer
Abdullah H. Alluhayb, Brian A. Logue ∗
Department of Chemistry and Biochemistry, South Dakota State University, Box 2202, Avera Health and Science Center 131, Brookings, SD, 57007, USA

a r t i c l e i n f o a b s t r a c t

Article history: Worldwide, green tea is one of the most popular beverages. It promotes blood circulation, liver function,
Received 3 May 2017 and lowers the risk of cancer and cardiovascular diseases. This drink is characterized by the distinctive
Received in revised form 17 August 2017 odors and flavors produced by its constituent compounds, with its value predicated on the amount and
Accepted 18 August 2017
type of constituents extracted from the tea leaves during brewing. Ice concentration linked with extractive
Available online 25 August 2017
stirrer (ICECLES) is a novel sample preparation technique, especially applicable for the extraction of
relatively polar compounds while retaining excellent extraction efficiencies for non-polar compounds.
Keywords:
In this study, ICECLES was used to prepare green tea for analysis of aroma/flavor compounds by gas
Green tea
Food flavor analysis
chromatography-mass spectrometry (GC–MS). ICECLES performed very well, revealing 301 constituents
Aroma analysis as compared to 245 for SBSE (i.e., 56 more constituents were detected via ICECLES). Moreover, ICECLES
ICECLES produced stronger signal to noise ratios for all except 4 of 301 constituents, with a maximum signal
SBSE enhancement of 19. Of the constituents which were only detectable using ICECLES, some very important
GC–MS aroma/flavor and/or medicinal compounds were easily identified, including furfural, furfural alcohol,
maltol, eugenol, 2-methylpyrazine, phenethyl alcohol, 2,6-dimethoxyphenol, and ␣-terpineol. Overall,
we confirmed that ICECLES sample preparation followed by GC–MS consistently allowed more complete
green tea aroma/flavor analysis, especially for relatively polar compounds, some of which are critical for
flavor quality.
© 2017 Elsevier B.V. All rights reserved.

1. Introduction leaves [7]. These compounds generally consist of non-terpenoids

and terpenoids, including alcohols and aldehydes, as the main
Green tea is the second most consumed beverage worldwide, source of green tea aroma [8]. Approximately 200 volatile com-
following water [1]. It is made from the leaves of the camellia pounds have been identified and about 30 of these compounds
sinensis plant and has been known since ancient times to exhibit contribute to green tea flavor [8,9]. These compounds play an
beneficial medicinal properties [2]. It promotes blood circulation, important role in determining the quality of individual green
improves liver function, promotes metabolism of various toxins, teas [10]. Therefore, the comprehensive analysis of green tea
and is more beneficial than beverages that contain large amounts aroma/flavor compounds is important for researchers and tea pro-
of vitamin C, vitamin E, or ␤-carotene [3]. In addition, numerous ducers to understand the makeup, quality, and identity of green
studies have shown that consumption of green tea is linked to the teas [11].
prevention of certain cardiovascular diseases and some types of Various methods have been used to identify green tea aro-
skin, lung, and liver cancers [4]. The beneficial effects of green tea mas/flavors, including gas and liquid chromatography (GC and
have been attributed to its rich abundance of antioxidant polyphe- LC, respectively) with mass spectrometric detection (MS). For
nolic compounds, mainly flavonoids [5]. Furthermore, green tea this type of analysis, sample preparation is vital but sometimes
contains other compounds that promote human health, including requires lengthy processing times, large sample volumes, and sig-
sterols, vitamins, amino acids, and proteins [6]. nificant organic solvent consumption [12]. The objective of sample
Green tea’s distinctive flavors and aromas are due to the many preparation for aroma/flavor analysis is to efficiently extract as
volatile and semi-volatile compounds extracted from green tea many compounds from brewed green tea as possible. Liquid-
liquid extraction (LLE), simultaneous distillation and extraction
(SDE), dynamic headspace (DHS), supercritical fluid extraction
∗ Corresponding Author. (SFE), ultrasound assisted extraction (UAE), microwave-assisted
E-mail address: Brian.Logue@sdstate.edu (B.A. Logue). extraction (MAE), solid-phase extraction (SPE), solid-phase micro-

http://dx.doi.org/10.1016/j.chroma.2017.08.049
0021-9673/© 2017 Elsevier B.V. All rights reserved.
 A.H. Alluhayb, B.A. Logue / J. Chromatogr. A 1518 (2017) 8–14 9

extraction (SPME) and stir bar sorptive extraction (SBSE) have been (hydroxymethyl)furfural (100 mM) were prepared in 10 mL of
used to prepare green teas for analysis [8,13]. Although most of purified water and stored at 4 ◦ C. The stock solutions were diluted
these techniques are excellent for extracting relatively hydropho- with purified water to the desired concentration for individual
bic molecules, they generally suffer from low extraction efficiencies experiments.
for relatively polar compounds. For the few sample preparation
techniques which are applicable to more polar compounds, they 2.2. Green tea sample preparation
generally extract compounds in a relatively narrow polarity range
[14]. Tea bags were carefully cut and green tea leaves were removed,
ICE Concentration Linked with Extractive Stirrer (ICECLES) is a weighed (1.25 g), and added to 200 mL of boiling water for 5 min.
novel extraction technique that combines freeze concentration (FC) The solution, now yellowish-green, was covered with a watch glass
and SBSE. ICECLES was first reported in 2016 by Maslamani et al. and cooled for one hour at room temperature. The prepared green
[15] and showed the ability to increase the extraction efficiencies tea was then divided into four portions, each placed into a 50-
for each compound tested, but works particularly well for more mL capped vial, and centrifuged for 5 min at 3000 rpm. Carefully,
polar compounds (log Kow < 3; Kow represents the octanol-water a 10-mL aliquot of the supernatant was transferred into a 24-mL
partition coefficient), without sacrificing extraction efficiency for capped glass vial. Prepared green tea samples were then immedi-
less polar compounds (log Kow ≥ 3). Furthermore, because ICECLES ately extracted via ICECLES and/or SBSE.
is performed at the freezing point of the sample, it is excel-
lent for more volatile and thermally labile components. ICECLES
2.3. ICECLES sample preparation
proved to be an excellent sample preparation technique for trace
analysis of pesticides in environmental surface waters and other
ICECLES was performed as previously presented [15] with minor
compounds in aqueous solution, producing enhanced limits-of-
modifications. An aliquot (10 mL) of prepared green tea, a stan-
detection (LODs) and signal enhancements of up to 474 times better
dard solution, or blank was added to a 24-mL glass vial along with
than SBSE [15,16].
a PDMS-coated stir bar. The vial was capped and placed into an
With the inherent advantages of ICECLES (i.e., excellent perfor-
ICECLES apparatus, as shown in Fig. 1. During optimization, ICE-
mance for more polar and more volatile compounds), it should
CLES was performed with coolant temperatures of −7, −5, and
be highly complementary to green tea aroma/flavor analysis.
−3 ◦ C (to modify the freezing rate), while stirring at 1200 rpm.
Therefore, the objective of the current study was to evaluate the
After optimization of the freeze temperature, −5 ◦ C was used for
performance of ICECLES towards green tea aroma/flavor analysis,
the remainder of the study. The green tea sample froze gradually
with direct comparison to SBSE.
from the bottom to the top of the vial until the entire solution was
frozen. After extraction was complete, the stir bar, now located on
2. Materials and methods top of the ice near the top of the vial, was magnetically removed
with a clean Teflon-coated stir bar. Gently, the stir bar was dried
2.1. Materials and standards using a clean lab wipe and then placed into a glass thermal des-
orption (TD) tube. It should be noted that the sorptive stir bars can
2.1.1. Materials be damaged if rounded bottom vials are used because of the high
Bigelow green tea classic brand bagged tea (CT, USA) was pur- stir rate [15]. Therefore, care must be used in sample vial selec-
chased from a local market. All tea samples in this study were tion. When SBSE was compared with ICECLES, the same sample of
stored in their original tea bags at room temperature before anal- green tea was extracted with SBSE performed at room temperature
ysis. Acetic acid (C2 H4 O2 , ≥99.7%), 2-propanol (C3 H8 O, ≥99.9%), alongside the ICECLES extraction. SBSE was performed for the same
2-furaldehyde (C5 H4 O2 , 99%), indole (C8 H7 N, 99 +%), benzyl alco- amount of time as ICECLES for each individual sample.
hol (C7 H8 O, 99%), 2,6-dimethoxyphenol (C8 H10 O3 , 99%), eugenol
(C10 H12 O2 , 99%), 2-methylpyrazine (C5 H6 N2 , 99 +%), phenethyl 2.4. m ICECLES sample preparation
alcohol (C8 H10 O, 99%), ␣-terpineol (C10 H18 O, 96%), trans,trans-
2,4-hexadienal (C6 H8 O, 95%), and toluene (C6 H5 -CH3 , 99.5%) In this study, a multiple-stir bar (m ICECLES) method was used
were purchased from Fisher Scientific (Fair Lawn, NJ, USA). to provide increased signals for some compounds, which gen-
1-pentanol (C5 H12 O, 99%), cis-2-penten-1-ol (C5 H10 O, ≥96%), theo- erally afforded easier identification of green tea components.
bromine (C7 H8 N4 O2 , ≥98), ␥-undecalactone (C11 H20 O2 , ≥98%), 5- For m ICECLES, five individual green tea samples were prepared
(hydroxymethyl)furfural (C6 H6 O3 , ≥99%), maltol (C6 H6 O3 , ≥99%), via ICECLES as described above and analyzed via TD-GC–MS in
furfuryl alcohol (C5 H6 O2 , 98%), benzyladehyde (C7 H6 O, 99.5%), multi-desorption mode. In multi-desorption mode, each stir bar is
and a mixed alkane standard (C7-C40) were purchased from sequentially desorbed in the thermal desorption unit (TDU), with
Sigma-Aldrich (St. Louis, MO, USA). Purified water was obtained the desorbed compounds transferred to the cooled injection sys-
from a water PRO PS polisher (Labconco, Kansas City, KS, USA) tem (CIS). The CIS was cooled with liquid N2 and used to collect
at a resistivity of 18.2 M-cm. Stir bars (10 mm length) coated the compounds desorbed from all five stir bars prior to injection
with polydimethylsiloxane (PDMS; 0.5 mm film thickness) were into the GC. Therefore, theoretically, the amount of each compound
obtained from Gerstel, Inc. (Baltimore, MD, USA). injected into the GC–MS (as described below) is five times that of a
single ICECLES analysis.
2.1.2. Standard solutions
Stock solutions of acetic acid (1 M), benzyl alcohol (1 M), benzy- 2.5. Gas chromatography-mass spectrometry
ladehyde (1 M), toluene (1 M), 1-pentanol (1 M), cis-2-penten-1-ol
(1 M), ␥-undecalactone (1 M), maltol (10 mM), furfuryl alco- Each prepared stir bar was desorbed using a TDU equipped
hol (10 mM), theobromine (10 mM), and indole (10 mM) were with a multiple position system (MPS) 2 auto-sampler and a CIS
prepared in 10 mL of purified water and stored at room tem- 4 programmed temperature vaporization (PTV) inlet (Gerstel, Bal-
perature. 2-furaldehyde (1 M), phenethyl alcohol (1 M), eugenol timore, MD, USA). The Gerstel autosampler was coupled to an
(1 M), trans,trans-2,4-hexadienal (1 M), 2-methylpyrazine (1 M), Agilent Technologies 7890A GC and a 5975C inert XL electron ion-
␣-Terpineol (10 mM), 2,6-dimethoxyphenol (10 mM), and 5- ization (EI)/chemical ionization (CI) mass selective detector with
10 A.H. Alluhayb, B.A. Logue / J. Chromatogr. A 1518 (2017) 8–14

Fig. 1. Green tea extraction via ICECLES sample preparation. The schematic and photographs show sample preparation before (A), during (B), and after (C) ICECLES. The green
tea solution in (A) is clearly concentrated in a small volume of solution as the solution is progressively frozen from the bottom of the vial (B + C). After performing ICECLES,
green tea components are concentrated in a sorptive stir bar (C) and analyzed by TD-GC–MS.

triple-axis detector. Separation was performed on an HP-5MS cap- by setting the peak threshold to 16.1, initial area reject at 1, peak
illary column (30 m x 250 ␮m x 0.25 ␮m). Following ICECLES, the width to 0.02 min, with shoulder detection off. The Kovats reten-
glass TDU tube containing the stir bar was placed into the TDU. tion indices of green tea components were obtained using direct
All prepared stir bars were thermally desorbed by performing a liquid injection of the mixed alkane standard.
temperature gradient from 40 ◦ C (held for 1 min) to 250 ◦ C (held To consider a green tea constituent “identified”, the retention
for 1.5 min) at 720 ◦ C/min in splitless mode. After desorption, com- time (±0.1 s) and the ion masses of the target green tea compound
pounds were cryo-trapped onto a deactivated CIS glass liner (filled and an aqueous standard of the proposed compound the standard
with quartz wool) at −100 ◦ C via liquid nitrogen. The PTV-CIS tem- were compared. All peaks which were not identified were classified
perature was increased from −100 ◦ C (held for 0.20 min) to 250 ◦ C based on their probability of a spectrum match via the NIST refer-
(held for 1.5 min) at 12◦ C/s using PTV solvent vent mode with a ence database as follows: if the probability range was between 0
purge flow of 50 mL/min (held for 1.5 min) to transfer compounds and 40, the compound classified was as unknown, if the probabil-
to the analytical column. The GC oven was held constant at 40 ◦ C ity range was between 41 and 70, the compound was classified as
for 1 min and slowly increased to 250 ◦ C (held for 3 min) at 5 ◦ C/min a medium probability, if the probability range was between 71 and
with a 46-min chromatographic runtime. The mass spectrometer 100 the match was classified as a high probability. Additionally, for
was operated in EI mode at 70 eV and a scan range from 35 to those compounds initially identified as medium or low probability,
550 m/z. The mass spectrometer source temperature was 230 ◦ C if all fragments from the experimental mass spectrum at ≥15% of
◦
and the quadrupole temperature was 150 C. Helium was used as the base peak (minus those present in the blank mass spectrum at
the carrier gas at a flow rate of 1 mL/min and a pressure of 7.07 psi. that retention time) were also present in the NIST library spectrum
and the relative abundance of each of these peaks were within 1%
of the NIST library MS, the matches were classified as “tentatively
2.6. Identification of green tea components
identified”.
Each peak in the ICECLES chromatogram was analyzed by com-
paring the mass spectrum of the compound with those of the 3. Results and discussion
National Institute of Standards and Technology (NIST) mass spec-
tra reference database (the NIST/EPA/NIH Mass Spectral Library, 3.1. ICECLES sample preparation
Version 2.0d, 2005). Where possible, identification was supported
by comparison of the mass spectra in m ICECLES and/or SBSE. Fur- ICECLES is an elegant sample preparation technique where sam-
thermore, some green tea compounds were definitively confirmed ples are frozen while rapidly stirred with a sorptive stir bar to
by ICECLES analysis of an aqueous solution spiked with a stan- concentrate the sample components in the remaining aqueous
dard compound. The retention time and mass spectra of the spiked layer and stir bar for follow-on analysis. As more of the liquid
standards were compared to those of the unknown green tea com- sample is frozen, concentration factors and extraction efficien-
pounds to confirm their identity. In this study, all standards were cies can be become greatly enhanced. The advantages of ICECLES
prepared and analyzed alongside green tea samples to eliminate (i.e., higher extraction efficiencies, especially for more polar com-
day-to-day differences in retention times. To avoid run-to-run pounds, and the ability to analyze more volatile and thermally
error, bias, and sorptive stir bar variability, green tea sample anal- labile compounds) are well-aligned with the main goal of green
ysis via both ICECLES and SBSE was performed in nonuplicate tea aroma/flavor analysis: comprehensive identification of green
under the same conditions (besides temperature) and the total ion tea components.
chromatograms were averaged. Automated peak selection was per- In this study, ICECLES successfully preconcentrated the green
formed using Chemstation software from Agilent Technologies, Inc tea components into a sorptive stir bar. Before performing ICECLES,
 A.H. Alluhayb, B.A. Logue / J. Chromatogr. A 1518 (2017) 8–14 11

ICECLES
SBSE

Fig. 2. Average total ion chromatograms of nonuplicate ICECLES and SBSE analyses of prepared green tea samples. As clearly shown in the first 15–20 min, ICECLES extracts
the vast majority green tea components more efficiently than SBSE. (For interpretation of the references to colour in this figure legend, the reader is referred to the web
version of this article.)

Fig. 3. Example of the definitive identification of furfural. A) GC–MS chromatogram of furfural extracted via ICECLES and confirmed with its standard, B) mass spectrums of
furfural in green tea sample and furfural standard. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

the components of green tea, including polar and nonpolar compo- ages green tea components, even more polar ones, to concentrate
nents, were distributed throughout the sample solution (Fig. 1A). into the PDMS-coated stir bar.
Green tea components initially equilibrate with the PDMS-stir bar,
which is the same as with SBSE. The affinity of a PDMS-coated
3.2. Extraction of green tea components
stir bar for nonpolar components leads the hydrophobic compo-
nents (i.e., generally log Kow ≥ 3) to prefer the PDMS-coated stir
ICECLES was performed at different temperatures (or freeze
bar over the aqueous green tea solution, whereas the more polar
rates) to determine the temperature that produced the best green
components prefer the aqueous environment of the sample. Dur-
tea extraction. The extraction efficiency increased as the tempera-
ing ICECLES, the sample is concentrated in progressively smaller
ture increased from −7 ◦ C to −3 ◦ C. Although −3 ◦ C produced better
aqueous volumes (Fig. 1B and C). When the sample becomes almost
extraction, sample preparation took 14 h (overnight). Therefore,
completely frozen, the green tea components, including more polar
since ICECLES sample preparation at −5 ◦ C gave very similar extrac-
ones, are concentrated into a very small volume at the top of the vial.
tion efficiencies to −3 ◦ C, but was complete within 5.5 h, −5 ◦ C
This is clearly demonstrated in Fig. 1C by the dark ring at the top of
was used for the remainder of the study. Fig. 2 shows the aver-
the prepared green tea sample and the almost clear ice below. This
age total ion chromatograms comparing ICECLES and SBSE from
concentration leads to a change in the equilibrium which encour-
nine samples each (nonuplicate). Log Kow s of the green tea com-
12 A.H. Alluhayb, B.A. Logue / J. Chromatogr. A 1518 (2017) 8–14

Fig. 4. Extracted ion chromatograms for green tea components detectable via ICECLES, but undetectable via SBSE (when evaluating TICs). A) furfural, B) 5-
(hydroxymethyl)furfural, C) E,E-2,4-hexadienal, and D) methylpyrazine. (For interpretation of the references to colour in this figure legend, the reader is referred to the
web version of this article.)

pounds [15,17–27], retention times, and signal enhancements are low polarity, ICECLES and SBSE show similar extraction efficiencies.
also reported in Table S1. It is evident that signals for most com- It is interesting to note that some green tea components present
ponents of the ICECLES prepared samples are larger than for SBSE, only in the ICECLES chromatogram have log Kow ≥ 3 (Table S2). This
especially over the first 15–20 min of the chromatograms. More- is likely because of their relatively small concentrations, necessi-
over, when using automated integration, the average number of tating the high concentration factors, afforded by ICECLES, to be
components found with ICECLES was 301 peaks, not counting those detected.
peaks attributable to components in the blank, while the average
number of peaks for SBSE was 245 peaks. Many green tea compo-
nents observed in ICECLES (i.e., 56) were not detected in the SBSE 3.3. Compound identification
prepared sample. All green tea components that were detected via
only ICECLES are reported in the supporting information (Table S2). Green tea components were initially identified using the NIST
Excluding four components (107, 296, 297, and 300; see sup- mass spectra library. Where possible, components of green tea were
porting information, Table S1), signal enhancements were above definitively confirmed by analysis of aqueous solutions spiked with
1 for each green tea compound. As observed in Fig. 2 and Table pure standards (Table S1). Fig. 3 shows an example of the defini-
S1, high signal enhancements in ICECLES are primarily seen for tive identification of furfural. Both furfural’s retention time and
higher polarity compounds, log Kow < 3. When components have mass spectra from the standard match the furfural detected using
ICECLES. m ICECLES was used to increase signals by preparing five
 A.H. Alluhayb, B.A. Logue / J. Chromatogr. A 1518 (2017) 8–14 13

Table 1
Some important green tea components only detected via ICECLES.

Peak No./Category Name Odor Log BPa

Kow (◦ C)

Alcohol
14 1-Pentanol Fruit 1.33 137.5
15 2-Penten-1-ol, (Z) Rubber 0.9* 138
84 Phenylethyl Alcohol Rose 1.57 218
105 ␣-Terpineol (a,a4-trimethyl 3-Cyclohexene-1-methanol) Floral 3.28 218-221
Heterocyclic
21 Methyl pyrazine Nut 0.49 135
38 2,5-dimethyl pyrazine Nut 1.03 155
Aldehyde
22 Furfural Caramel 0.83 161
37 (E,E)-2,4-Hexadienal Citrus 1.37c 174
111 5-(hydroxymethyl) furfural (5-(hydroxmethyl)-2-Furancarboxaldehyde) Carmel -0.09c 114-116
Ketone
82 Maltol Caramel 0.02 93
91 Ketoisophorone (2,6,6-Trimethyl-2-cyclohexene-1,4-dione) Floral 1b 222
Ester
95 Benzyl acetate Fruit 1.96b 213
66 ␥-Undecalactone (5-heptyldihydro-2-(3H)-Furanone) Fruit 0.7b 219
Phenol
136 Syringol (2,6-dimethoxy phenol) Phenol 1.1b 261
138 Eugenol Clove 2.49 254
a
Boiling point.
b
log Kow values were calculated by using the difference between a log Kow value of known compound and the query compound then estimated by an additive model with
well-defined correction factors [26].
c
log Kow values were calculated by using an atom/fragment contribution method via KOWWINTM program [27].

samples via ICECLES simultaneously, thermally desorbing each in 3.5. Important medicinal compounds detected by ICECLES
sequence, trapping the desorbed compounds from all the stir bars
in a CIS liner, and analyzing these compounds via GC-MS. m ICECLES Beside components important for aroma/flavor, green tea con-
allowed easier identification of many green tea components. More- tains medicinal components, including antimicrobial agents and
over, it allowed detection of some components which were not potent antioxidants. Green tea contains several terpenoid and phe-
detectable in single green tea samples. Comprehensive analysis of nolic compounds which were extracted via ICECLES. Terpenoids,
the green tea extracts allowed designation of 19 compounds as such as ␣-terpineol (Table 1), have been shown to have antibac-
identified, 11 compounds as tentatively identified, 76 compounds terial effects against periodontal diseases and cariogenic bacteria
as high probability, and 9 compounds as medium probability (Table [34]. Eugenol is a phenolic compound that acts as an antioxidant
S1). and an anti-inflammatory agent. It inhibits lipid-peroxidation, and
can treat many diseases caused by the presence of hydroxyl rad-
icals, such as atherosclerosis, cancer and neurological disorders
3.4. Important aroma/flavor compounds detected by ICECLES
[35,36]. In addition, both ␣-terpineol and eugenol have been used
as natural antifungal agents [37,38]. Syringol is an antioxidant
ICECLES detected many compounds which were not detectable
compound which was also detected by ICECLES alone. Syringol is
by SBSE when initially evaluating total ion chromatograms (i.e., 56
one of the main components of pyroligneous acid complex (i.e.,
compounds). Extracted ion chromatograms of four examples are
pyroligneous acid is a complex mixture of syringol, sugar, water,
shown in Fig. 4. Aldehydes like furfural, 5-(hydroxymethyl)furfural
aldehydes, ketones, and carboxylic acids) and has been used as
(5-HMF), and (E,E)-2,4-hexadienal (Fig. 4A, B, and C, respectively)
sterilizing agent and antimicrobial agent [39]. Although pyrazine
make up a major group of compounds which proved difficult
derivatives are used as food additives, some medicinal research
to detect via SBSE, but can be readily seen via ICECLES. This
proved these compounds to have pharmacological actions. For
group of compounds contributes heavily to green tea’s distinctive
example, methyl pyrazine has a beneficial pharmacological effect,
aroma/flavor [28]. Furfural and 5-HMF have a caramel flavor and are
especially for tuberculosis [40,41]. Phenylethyl alcohol is also an
present in the Maillard reaction as an intermediate, likely adding
effective inhibiting agent for Gram-negative bacteria [42].
to the flavor quality of green tea [29]. Furfuraldehydes have been
Although most green tea components with pharmacolog-
used for assessing food quality to test the misuse of temperature
ical effects are beneficial, some have shown toxicity. For
and poor storage conditions in drinks such as juices and infant milk
example, according to the Flavor and Extract Manufacturers
products [29]. Another aldehyde, (E,E)-2,4-hexadienal has a citrus
Association (FEMA) and the National Cancer Institute of the
odor and is used as a food additive and a fragrance agent [30]. Fig. 4D
National Institutes of Health (NIH), (E,E)-2,4-hexadienal is carcino-
shows the detection of methyl pyrazine by ICECLES, with pyrazine
genic (LD50 = 270 ␮L kg−1 ) [30,43]. Furthermore, maltol can cause
derivatives contributing a nutty-like odor/flavor.
headaches, nausea, vomiting, and impacts the functions of liver and
Some other important aroma/flavor compounds detected via
kidney at high concentrations (above 200 mg kg−1 ) [32,33].
ICECLES and not SBSE (not shown) are phenylethyl alcohol and
maltol (reported in Table S2). Phenylethyl alcohol is widely con-
sumed in food as a flavor component and is also used as ingredient 4. Conclusion
for perfumes to produce a rose smell [31]. Maltol does not have
a remarkable odor/flavor at small concentrations, but it is widely ICECLES proved to be well-suited for food aroma/flavor analysis
consumed as a food additive due to its potent flavor enhancing abil- of green tea and was more efficient for aroma/flavor analysis than
ity [32] and can be used in combination with other components to SBSE for extraction of most green tea components, especially more
produce a caramel smell [33]. polar compounds (log Kow < 3). Signal enhancements were above 1
14 A.H. Alluhayb, B.A. Logue / J. Chromatogr. A 1518 (2017) 8–14

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