Identification of novel aroma-active thiols in pan-roasted white sesame seeds

Article abstract of DOI:10.1021/jf100623a

Screening for aroma-active compounds in an aroma distillate obtained from freshly pan-roasted sesame seeds by aroma extract dilution analysis revealed 32 odorants in the FD factor range of 2-2048, 29 of which could be identified. The highest FD factors were found for the coffee-like smelling 2-furfurylthiol, the caramel-like smelling 4-hydroxy-2,5-dimethyl-3(2H)-furanone, the coffee-like smelling 2-thenylthiol (thiophen-2-yl-methylthiol), and the clove-like smelling 2-methoxy-4-vinylphenol. In addition, 9 odor-active thiols with sulfurous, meaty, and/or catty, black-currant-like odors were identified for the first time in roasted sesame seeds. Among them, 2-methyl-1-propene-1-thiol, (Z)-3-methyl-1-butene-1-thiol, (E)-3-methyl-1-butene-1-thiol, (Z)-2-methyl-1-butene-1-thiol, (E)-2-methyl-1-butene-1-thiol, and 4-mercapto-3-hexanone were previously unknown as food constituents. Their structures were confirmed by comparing their mass spectra and retention indices as well as their sensory properties with those of synthesized reference compounds. The relatively unstable 1-alkene-1-thiols represent a new class of food odorants and are suggested as the key contributors to the characteristic, but quickly vanishing, aroma of freshly ground roasted sesame seeds.

Full text of DOI:10.1021/jf100623a

7368 J. Agric. Food Chem. 2010, 58, 7368–7375
DOI:10.1021/jf100623a
Identification of Novel Aroma-Active Thiols in Pan-Roasted
White Sesame Seeds
†
HITOSHI
T
AMURA,*,† AKIRA
IROYUKI
F
UJITA,† MARTIN
†
S
TEINHAUS,‡ EISUKE
‡
T
AKAHISA
,
H
W
ATANABE
,
AND
P
ETER
S
CHIEBERLE
†Technical Research Institute, R&D Center, T. Hasegawa Company, Ltd., 29-7 Kariyado, Nakahara-ku,
‡
€
Kawasaki-shi 211-0022, Japan, and Deutsche Forschungsanstalt fur Lebensmittelchemie,
Lise-Meitner-Strasse 34, D-85354 Freising, Germany
Screening for aroma-active compounds in an aroma distillate obtained from freshly pan-roasted
sesame seeds by aroma extract dilution analysis revealed 32 odorants in the FD factor range of
2-2048, 29 of which could be identified. The highest FD factors were found for the coffee-like
smelling 2-furfurylthiol, the caramel-like smelling 4-hydroxy-2,5-dimethyl-3(2H)-furanone, the coffee-
like smelling 2-thenylthiol (thiophen-2-yl-methylthiol), and the clove-like smelling 2-methoxy-4-
vinylphenol. In addition, 9 odor-active thiols with sulfurous, meaty, and/or catty, black-currant-like
odors were identified for the first time in roasted sesame seeds. Among them, 2-methyl-1-propene-
1-thiol, (Z)-3-methyl-1-butene-1-thiol, (E)-3-methyl-1-butene-1-thiol, (Z)-2-methyl-1-butene-1-thiol,
(E)-2-methyl-1-butene-1-thiol, and 4-mercapto-3-hexanone were previously unknown as food con-
stituents. Their structures were confirmed by comparing their mass spectra and retention indices as
well as their sensory properties with those of synthesized reference compounds. The relatively
unstable 1-alkene-1-thiols represent a new class of food odorants and are suggested as the key
contributors to the characteristic, but quickly vanishing, aroma of freshly ground roasted sesame
seeds.
KEYWORDS: Roasted white sesame seeds; aroma extract dilution analysis; 2-methyl-1-propene-
1-thiol; 2-methyl-1-butene-1-thiol; 3-methyl-1-butene-1-thiol; 4-mercapto-3-hexanone
INTRODUCTION
However, the sensory contribution of the individual compounds
identified to the overall aroma of roasted sesame was addressed
in only a few studies (12-17). A systematic study on the key
aroma compounds of roasted sesame seeds was performed by
one of the authors of the present paper some years ago.
Application of an aroma extract dilution analysis (AEDA)
revealed 41 odor-active volatiles (14). Ten major aroma-active
compounds were subsequently quantified by stable isotope
dilution assays (12-14). According to their high odor activity
values (OAV) calculated on the basis of concentrations and odor
thresholds (20), 2-acetyl-1-pyrroline (popcorn-like), 2-furfur-
ylthiol (coffee-like), 2-phenylethylthiol (rubbery), and 4-hydro-
xy-2,5-dimethyl-3(2H)-furanone (caramel-like) were identified
as key aroma compounds of roasted sesame seeds. However, in
these studies the structures of eight compounds with sulfurous
or catty aroma notes remained open. The aim of the present
research was, therefore, to reinvestigate the aroma-active com-
pounds present in roasted white sesame seeds with special
emphasis on the identification of the presently unknown sulfur-
ous and catty smelling odorants.
Sesame (Sesamum indicum L.) is an important oilseed crop of the
tropics and subtropics. Its cultivation is believed to have begun in
the African savannah ∼3000 B.C. During the period of the so-called
four great civilizations (China, India, Mesopotamia, and Egypt),
sesame was spread out all over the ancient world (1). Sesame seeds
show high linoleic acid levels in combination with a high antiox-
idant capacity and, also, an advantageous amino acid balance.
Raw sesame seeds elicit only a weak odor, but the oil obtained
by pressing is used as a valuable cooking oil, especially in the
Asian cuisine. However, for other sesame products the seeds are
roasted, resulting in a unique and highly attractive odor char-
acterized by sulfurous, roasty, nutty, and meaty notes. In Europe
and the United States the roasted seeds are a popular topping for
bakery products, whereas in Asia the oil isolated from the roasted
seeds is used as a seasoning in many dishes. In Japan, mainly
ground roasted sesame seeds are consumed, and it is preferred to
grind roasted sesame seeds in a small mortar just before con-
sumption to ensure a fresh aroma.
The first attempts to clarify the compounds responsible for the
aroma ofroasted sesameseeds wereperformed inthe 1960s (2-4),
and these authors already assumed that sulfur-containing
compounds may play an important role. Later, the identifica-
tion of more than 300 volatile compounds was reported (5-19).
MATERIALS AND METHODS
Materials. White sesame seeds (Egypt) were purchased in a local
supermarket in Garching, Germany. The seeds (250 g) were washed with
tap water (500 mL), filtered with a strainer, and then roasted in a frying
pan with continuous stirring for 15 min at 200 °C. After freezing with
liquid nitrogen, the seeds were ground in a commercial blender.
*Corresponding author (telephone þ81-44-411-0131; fax þ81-44-
434-5257; e-mail hitoshi_tamura@t-hasegawa.co.jp).
pubs.acs.org/JAFC
Published on Web 05/24/2010
© 2010 American Chemical Society

Article
J. Agric. Food Chem., Vol. 58, No. 12, 2010 7369
MS-EI, m/z (%) 88 (Mþ, 65), 60 (39), 59 (10), 55 (26), 54 (38), 53 (15), 47
(100), 46 (28), 45 (26), 41 (16), 39 (42).
2-Methyl-2-propene-1-thiol (Figure 1). The compound was prepared
from 3-chloro-2-methyl-1-propene following the method described above
for 3-butene-1-thiol (yield = 12%).
1H NMR, δ 1.47 (t, J = 8.0 Hz, 1H), 1.85 (s, 3H), 3.14 (d, J = 8.0 Hz,
2H), 4.78 (s, 1H), 4.91 (s, 1H).
13C NMR, δ 20.6, 31.8, 112.1, 144.5.
MS-EI, m/z (%) 88 (Mþ, 98), 73 (18), 60 (15), 59 (11), 55 (100), 54 (46),
53 (34), 51 (10), 50 (10), 47 (20), 45 (31), 41 (13), 39 (66), 29 (22).
3-Butene-2-thiol (Figure 1). The target compound was synthesized in a
two-step procedure as follows:
(a) 3-Buten-2-yl Methyl Dithiocarbonate. NaH (60%, 48.5 g, 1.21 mol,
washed with n-hexane prior to use) was suspended in a solution of
N,N-dimethyl-4-aminopyridine (DMAP, 1.22 g, 10 mmol) in tetrahydro-
furan (THF, 500 mL). Then, 2-buten-1-ol (30.0 g, 416 mmol) in THF (1 L)
was slowly added, and after for 1.5 h of stirring at room temperature,
CS2 (158 g, 2.08 mol) was added to the reaction mixture within 45 min.
After further stirring for 30 min at room temperature, methyl iodide
(285 g, 2.01 mol) was slowly added within 1 h. The mixture was stirred
overnight, and then acetic acid (131 g, 2.18 mol) followed by water (1 L)
was added. The organic layer was separated, and the aqueous layer was
extracted with ethyl acetate. The combined organic layers were succes-
sively washed with water and brine, then dried over anhydrous MgSO4,
filtered, and concentrated under reduced pressure to yield a colored oil
(105.8 g). The crude product was purified by distillation (bp, 69-77 °C/
0.8 kPa), yielding 3-buten-2-yl methyl dithiocarbonate (65.2 g; yield =
97%; purity = 79%) as an oil.
Figure 1. Structures of the 11 thiols prepared by synthesis. Only com-
pounds also identified in sesame seeds are numbered. Numbers of
synthesized reference compounds are italicized to differentiate them from
the sesame odorants.
Reference Odorants. The following compounds were obtained from
the commercial sources given in parentheses: 2-methyl-3-furanthiol,
dimethyl disulfide, 2-ethyl-3,5(6)-dimethylpyrazine, and 2-thenylthiol
(thiophen-2-yl-methylthiol) (Acros Organics, Geel, Belgium); 3-mercap-
to-2-pentanone and 2-methoxy-4-vinylphenol (Alfa Aesar, Karlsruhe,
Germany); 2-phenylethylthiol (Aldrich, Milwaukee, WI); 4-hydroxy-3-
methoxybenzaldehyde (vanillin) (Merck, Darmstadt, Germany); 3-methyl-
thiopropanal (methional), 2-furfurylthiol, and 4-hydroxy-2,5-dimethyl-
3(2H)-furanone (Aldrich, Steinheim, Germany); 3-methyl-1H-indole
(skatole) (Tokyo Chemical Industry Co., Tokyo, Japan). A reference
standard from the product line of T. Hasegawa Co., Ltd., was used in
the case of 1-octen-3-one. The following compounds were synthesized
according to the literature cited: 2-mercapto-3-pentanone (21), 3-mercap-
to-3-methylbutyl formate (22), 2-methyl-3-thiophenethiol (23), 3-methyl-2-
butene-1-thiol (24), 2-acetyl-1-pyrroline (25), and trans-4,5-epoxy-(E)-2-
decenal (26).
MS-EI, m/z (%) 102 (31), 87 (5), 75 (10), 55 (100), 54 (19), 53 (12), 47
(10), 45 (15), 39 (11), 29 (11).
(b) The synthesis of 3-butene-2-thiol was finished following a procedure
as given by Taguchi et al. (27). A mixture of 3-buten-2-yl methyl
dithiocarbonate (20.0 g, 123 mmol), 2-aminoethanol (7.5 g, 123 mmol),
and 2,6-di-tert-butyl-4-methylphenol (BHT, 0.1 g) was heated to 80 °C
with continuous stirring. After a few minutes, the reaction mixture was
distilled under atmospheric pressure (bp, ∼25-47 °C) to yield a colorless
oil (2.0 g). The crude product obtained was further purified by distillation
under atmospheric pressure (bp, ∼79-80 °C) to yield 3-butene-2-thiol
(400 mg; yield = 4%; purity = 89%).
Syntheses. General remark: The structures of all compounds newly
synthesized are given inFigure1. Only compounds thatwerealso identified
in roasted sesame seeds are numbered in bold, but italicized to differentiate
them from the odorants having the same structure.
1H NMR, δ 1.41 (d, J = 7.2 Hz, 3H), 1.66 (d, J = 5.6 Hz, 1H), 3.59
(ddq, J = 5.6, 7.2, 7.2 Hz, 1H), 4.93 (d, J = 10.0 Hz, 1H), 5.09 (d, J = 17.2
Hz, 1H), 5.90 (ddd, J = 7.2, 10.0, 17.2 Hz, 1H).
13C NMR, δ 24.0, 37.4, 112.6, 142.9.
(E)-2-Butene-1-thiol and (Z)-2-Butene-1-thiol (Figure 1). A mixture of
(E)- and (Z)-2-buten-1-ol (96:4, 21.5 g, 300 mmol) was dropwise added to a
solution of thiourea (29.5 g, 390 mmol) in hydrochloric acid (6 mol/L,
65 mL) kept at room temperature during 15 min. After further stirring for
4 h at 45 °C, sodium hydroxide (10% in water, 158 g) was added. The
reaction mixture was heated to 100 °C, and the crude product was distilled
off together with the water. The organic layer was separated, dried over
anhydrous Na2SO4, and distilled under atmospheric pressure (bp, 101 °C)
to yield an oil consisting of (E)- and (Z)-2-butene-1-thiol (5.1 g; yield =
19%). The (E)/(Z) ratio was determined by GC to be 93:7.
MS-EI, m/z (%) 88 (Mþ, 50), 73 (10), 59 (17), 55 (100), 54 (26), 53 (22),
51 (10), 45 (20), 39 (29), 29 (19).
4-Mercapto-3-hexanone (15). The target compound was synthesized in
a three-step procedure starting from 4-hydroxy-3-hexanone (Figure 2).
(a) 4-(Methanesulfonyloxy)-3-hexanone. 4-Hydroxy-3-hexanone (5.0 g,
43.0 mmol) and triethylamine (13.0 g, 129.0 mmol) were dissolved in
diethyl ether (43 mL), and methanesulfonyl chloride (5.9 g, 51.6 mmol) in
diethyl ether (10 mL) was added to the solution at 0 °C. After 5.5 h of
stirring, water was added, and the organic layer was separated and
successively washed with citric acid (10% in water), brine, an aqueous
sodium bicarbonate solution (10%), and again with brine and was finally
dried over anhydrous MgSO4. The organic phase was filtered and
concentrated under reduced pressure to yield crude 4-(methanesulfonyl-
oxy)-3-hexanone (7.3 g), which was directly used in the next step.
MS-EI, m/z (%) 137 (7), 136 (6), 79 (13), 69 (3), 59 (11), 58 (4), 57 (100),
55 (4), 41 (7), 29 (18).
MS-EI (E), m/z (%) 88 (Mþ, 91), 73 (10), 55 (100), 54 (43), 53 (24), 47
(11), 45 (21), 39 (31), 29 (24).
MS-EI (Z), m/z (%) 88 (Mþ, 89), 73 (10), 55 (100), 54 (58), 53 (25), 47
(11), 45 (21), 39 (36), 29 (25).
3-Butene-1-thiol (Figure 1). Thiourea (6.8 g, 88.9 mmol) and 4-bromo-
1-butene (10.0 g, 74.1 mmol) were dissolved in ethanol (95%, 50 mL)
under an atmosphere of nitrogen. After stirring for 8 h at 80 °C, the
reaction mixture was cooled to room temperature, and sodium hydroxide
(50% in water, 12 g) was added. After a further 8 h of stirring at 80 °C, the
reaction mixture was cooled to 0 °C, acidified to pH ∼3 with citric acid
(27% in water, 35.5 g), and extracted with n-pentane. The organic phase
was dried over anhydrous MgSO4, and the solvent was removed under
atmospheric pressure. The crude product was then distilled under atmo-
spheric pressure (bp, ∼70-80 °C) to yield 3-butene-1-thiol (560 mg;
yield = 9%).
(b) 4-Acetylthio-3-hexanone. Potassium thioacetate (9.1 g, 80.0 mmol)
was dissolved in N,N-dimethylformamide (DMF, 100 mL), and 4-(meth-
anesulfonyloxy)-3-hexanone (14.0 g, 80.0 mmol) in DMF (140 mL) was
added to the solution at 20-30 °C within 1 h. After stirring for 3 h at 35 °C,
the reaction mixture was extracted with diethyl ether. The organic layer
was washed with an aqueous sodium bicarbonate solution (10%) and
brine, dried over anhydrous MgSO4, filtered, and concentrated under
reduced pressure to obtain 4-acetylthio-3-hexanone, which was purified by
distillation (bp, ∼55-58 °C/0.4 kPa) to yield 4-acetylthio-3-hexanone
(10.0 g; yield = 80%; purity > 99%).
1H NMR, δ 1.43 (t, J = 7.6 Hz, 1H), 2.38 (dt, J = 7.2, 7.2 Hz, 2H), 2.59
(dt, J = 7.2, 7.6 Hz, 2H), 5.07-5.13 (m, 2H), 5.77 (ddt, J = 7.2, 10.0, 17.2
Hz, 1H).
13C NMR, δ 23.9, 37.9, 116.8, 136.0.
MS-EI, m/z (%) 174 (Mþ, 5), 132 (16), 131 (24), 117 (20), 99 (5), 75 (25),
74 (5), 58 (5), 57 (100), 55 (7), 45 (6), 43 (94), 41 (12), 39 (6), 29 (18).

7370 J. Agric. Food Chem., Vol. 58, No. 12, 2010
Tamura et al.
Figure 2. Synthetic approach used in the preparation of 4-mercapto-3-hexanone (15).
Figure 3. Synthetic approach used in the preparation of (A) 2-methyl-1-propene-1-thiol (1), (B) (E)-2-methyl-1-butene-1-thiol (5) and (Z )-2-methyl-1-
butene-1-thiol (4 ), and (C) (E )-3-methyl-1-butene-1-thiol (3) and (Z )-3-methyl-1-butene-1-thiol (2).
(c) To obtain the thiol, an aqueous solution of NaOH (5%, 140.0 g,
175.0 mmol) was added to a solution of 4-acetylthio-3-hexanone (8.7 g,
50.0 mmol) in diethyl ether (62.0 g) at ∼0-10 °C within 30 min. After
stirring for 2 h, the reaction mixture was separated, and the aqueous layer
was acidified to pH 4.0 with citric acid (10% in water) and extracted with
diethyl ether. The combined organic layers were washed with brine, dried
over anhydrous MgSO4, filtered, and concentrated under reduced pres-
sure. The residue (9.0 g) was distilled (bp, ∼45-46 °C/0.8 kPa) to yield the
target compound (3.9 g; yield = 59%; purity > 99%).
1H NMR, δ 0.98 (t, J = 7.2 Hz, 3H), 1.11 (t, J = 7.2 Hz, 3H), 1.70 (ddq,
J = 7.2 Hz, 7.2, 14.4, 1H), 1.71 (d, J = 10.4 Hz, 1H), 1.95 (ddq, J = 7.2,
Figure 4. NOE observed for synthesized (E)-2-methyl-1-butene-1-thiol
7.2, 14.4 Hz, 1H), 2.53 (dq, J = 7.2, 17.2 Hz, 1H), 2.74 (dq, J = 7.2,
(5 ) and (Z )-2-methyl-1-butene-1-thiol (4 ).
17.2 Hz, 1H), 3.24 (ddd, J = 7.2, 7.2, 10.4 Hz, 1H).
13C NMR, δ 8.2, 11.9, 27.7, 33.3, 48.6, 208.8.
MS-EI, m/z (%) 132 (Mþ, 20), 130 (5), 75 (45), 74 (32), 73 (12), 57 (100),
55 (7), 47 (17), 41 (33), 39 (11), 29 (26).
MS-EI, m/z (%) 88 (Mþ, 78), 69 (5), 60 (15), 59 (20), 55 (100), 53 (37), 45
(54), 39 (45), 29 (17).
2-Methyl-1-propene-1-thiol (1; Figure 1). The target compound
was prepared in a two-step synthesis starting from methylpropanal
(Figure 3A).
(Z)-2-Methyl-1-butene-1-thiol and (E)-2-Methyl-1-butene-1-thiol (4 and
5; Figure 1). The target compounds were synthesized starting from
2-methylbutanal as reported above for compound 1 following the reaction
scheme detailed in Figure 3B.
(a) 2-Methylbutane-1,1-dithiol. 2-Methylbutanal was treated with H2S
using the method described above for the synthesis of 1 (yield = 24%;
purity = 97%).
(a) 2-Methylpropane-1,1-dithiol. Pyrogallol(0.5 g, 4 mmol) and dimethyl
sulfoxide (DMSO, 400 g) were added to 2-methylpropanal (132.3 g, 1835
mmol) at room temperature, and the mixture was slowly cooled to 10 °C.
H2S (102.1 g, 2996 mmol) was passed through the solution for 2 h while the
temperature was maintained below 20 °C. Then, the reaction mixture was
poured into ice water (600 g) and extracted with diethyl ether. The
combined organic phases were washed with water and brine, dried over
anhydrous MgSO4, and concentrated under reduced pressure. The residue
(77.8 g) was subjected to vacuum distillation, and the distillate was washed
with aqueous sodium bicarbonate (10%), dried over anhydrous MgSO4,
and filtered to yield a pale yellowish oil of 2-methylpropane-1,1-dithiol
(36.7 g; yield = 16%; purity = 97%).
1H NMR, δ 0.92 (t, J = 7.2 Hz, 3H), 1.04 (d, J = 6.4 Hz, 3H), 1.32
(ddq, J = 7.2, 7.2, 15.2 Hz, 1H), 1.51-1.61 (m, 1H), 1.71-1.80 (m, 1H),
2.14 (d, J = 6.4 Hz, 1H), 2.29 (d, J = 6.4 Hz, 1H), 4.23 (ddd, J = 3.6, 6.4,
6.4 Hz, 1H).
13C NMR, δ 11.6, 14.8, 26.7, 43.7, 44.2.
MS-EI, m/z (%) 136 (Mþ, 22), 103 (81), 102 (70), 87 (33), 79 (30), 69
(100), 61 (46), 53 (23), 47 (23), 45(53), 41 (81), 39 (27).
(b) The target compounds 4 and 5 were prepared by FVP of 2-methyl-
butane-1,1-dithiol using the parameters described above for the synthesis
of 1 (yield = 72%; purity = 92%). The (E)/(Z) ratio was determined by
GC to be 60:40. The correct assignment of the GC peaks was achieved by
NOESY-NMR of the mixture (Figure 4).
1H NMR, δ 1.03 (d, J = 6.8 Hz, 6H), 2.01 (double septuplet, J = 4.4,
6.8 Hz, 1H), 2.20 (d, J = 6.8 Hz, 2H), 4.08 (dt, J = 4.4, 6.8 Hz, 1H).
13C NMR, δ 18.8, 37.2, 45.7.
MS-EI, m/z (%) 122 (Mþ, 25), 89 (69), 88 (40), 79 (28), 73 (17), 59 (15),
55 (100), 47 (16), 45 (41), 41 (17), 39 (23).
1H NMR (5), δ 1.00 (t, J = 7.6 Hz, 3H), 1.72 (s, 3H), 2.07 (q, J = 7.6
Hz, 2H), 2.54 (d, J = 7.2 Hz, 1H), 5.71 (d, J = 7.2 Hz, 1H).
1H NMR (4), δ 1.00 (t, J = 7.6 Hz, 3H), 1.75 (s, 3H), 2.16 (q, J = 7.6
Hz, 2H), 2.51 (d, J = 7.2 Hz, 1H), 5.67 (d, J = 7.2 Hz, 1H).
13C NMR (5), δ 12.4, 22.4, 32.1, 106.4, 140.6.
(b) To obtain 1, 2-methylpropane-1,1-dithiol (1.1 g, 9.0 mmol) was
subjected to flash vacuum pyrolysis (FVP, 380 °C/0.4 kPa) (28,29) over 20
min, and a yellowish oil of 2-methyl-1-propene-1-thiol (0.6 g; yield = 78%;
purity = 86%) was collected.
1H NMR, δ 1.73 (s, 3H), 1.77 (s, 3H), 2.52 (d, J = 6.8 Hz, 1H), 5.69 (d,
J = 6.8 Hz, 1H).
13C NMR (4), δ 11.4, 17.0, 25.8, 106.6, 141.1.
MS-EI (5), m/z (%) 102 (Mþ, 100), 85 (12), 73 (22), 69 (77), 59 (29), 53
(63), 47 (26), 45 (67), 41 (100).
13C NMR, δ 18.8, 25.3, 107.3, 135.8.

Article
J. Agric. Food Chem., Vol. 58, No. 12, 2010 7371
MS-EI (4), m/z (%) 102 (Mþ, 63), 85 (17), 73 (22), 68 (61), 59 (15), 53
(33), 47 (13), 45 (37), 41 (100).
in four equal portions (fractions A-D), and each fraction was concen-
trated to 200 μL.
For selective enrichment of thiols, fractions A and B were concentrated
to 5 mL and thiols were isolated by affinity chromatography on mercu-
rated agarose gel (31).
(Z)-3-Methyl-1-butene-1-thiol and (E)-3-Methyl-1-butene-1-thiol (2 and
3; Figure 1). The target compounds were synthesized by a two-step
synthesis as outlined in Figure 3C.
Gas Chromatography-Mass Spectrometry (GC-MS). For com-
pound identification, mass spectra were generated using a sector field mass
spectrometer typeMAT 95 S (Finnigan, Bremen, Germany) inthe electron
impact mode (EI mode) at 70 eV using the columns and the temperature
programs detailed above.
(a) 3-Methylbutane-1,1-dithiol. The target compound was prepared by
treatment of 3-methylbutanal with H2S as described above for compound
1 (yield = 18%; purity = 98%).
1H NMR, δ 0.92 (d, J = 6.4 Hz, 6H), 1.74 (dd, J = 7.2, 7.2 Hz, 2H),
1.79-1.93 (m, 1H), 2.36 (d, J = 6.4 Hz, 2H), 4.11 (tt, J = 6.4, 7.2 Hz, 1H).
13C NMR, δ 21.9, 26.7, 37.2, 52.6.
When coeluting compounds did not allow unequivocal mass spectra of
the target compounds to be obtained, a two-dimensional heart-cut
technique using a GC-O/GC-O/MS system was used. This system con-
sisted of a GC Mega 2 (Fisons Instruments, Egelsbach, Germany)
equipped with an FFAP column and a GC 5160 (Carlo Erba, Hofheim,
Germany) equipped with a DB-5 column (both columns 30 m ꢀ 0.32 mm,
0.25 μm film thickness) (J&W Scientific, Waldbronn, Germany). The first
GC housed a moving column stream switching system (MCSS) leading the
effluent of the first column either to an FID and a sniffing port or via a
deactivated fused silica transfer line to the column in the second oven. The
end of the second column was simultaneously connected to an ion trap
ITD 800 (Finnigan, Bremen, Germany) and a second sniffing port via a
Y-shaped glass splitter. To obtain a mass spectrum of an unknown
odorant, at its elution time from the first column, which was determined
by GC-O in a preliminary run, the MCSS was switched to the transfer line.
While collecting the effluent of the first column, a trap section of the
transfer line was held at -80 °C. After the collection was stopped, the trap
was heated to 250 °C to flush the target compound onto the second
column. Elution of the target compound from the second column was
monitored at the second sniffing port, and its mass spectrum was
simultaneously recorded.
Mass spectra of the synthesized reference odorants and the intermedi-
ates were obtained using an Agilent 6890 gas chromatograph connected
to a 5973 mass selective detector equipped with a TC-1 capillary column
(60 m ꢀ 0.25 mm, 0.25 μm film thickness) (GL Sciences Co., Tokyo,
Japan). Samples were applied in the split mode (1:50) at 250 °C, and helium
at a flow rate of 1.8 mL/min served as the carrier gas. The initial oven
temperature was 40 °C. It was held for 2 min, and then the temperature was
raised at 3 °C/min to a final temperature of 280 °C. Mass spectra were
generated in the EI mode at 70 eV.
MS-EI, m/z (%) 136 (Mþ, 21), 103 (65), 102 (58), 87 (40), 69 (100), 61
(42), 60 (36), 59 (27), 45(40), 43 (46), 41 (62), 39 (22).
(b) The 1-butene-1-thiol isomers were prepared by FVP of 3-methylbu-
tane-1,1-dithiol (yield = 60%; purity = 96%). The (E)/(Z) ratio was
determined by GC to be 55:45. The correct assignment of the GC peaks
was achieved by 1H NMR of the mixture using the coupling constants of
the neighboring olefinic protons at a chemical shift of δ 5.74 and 5.48,
respectively.
1H NMR (3), δ 0.98 (d, J = 6.8 Hz, 6H, (CH3)2), 2.61 (double septuplet,
J = 6.8, 9.2 Hz, 1H, CH(Me)2), 2.62 (d, J = 9.2 Hz, 1H, SH), 5.48 (dd,
J= 9.2, 9.2 Hz, 1H, i-Pr;CHdR), 5.87 (dd, J=9.2Hz, 1H, RdCH;SH).
1H NMR (2), δ 0.97 (d, J = 6.4 Hz, 6H, (CH3)2), 2.30 (double septuplet,
J = 6.4, 6.4 Hz, 1H, CH(Me)2), 2.68 (d, J = 6.4 Hz, 1H, SH), 5.74 (dd,
J = 6.4, 15.2 Hz, 1H, i-Pr;CHdR), 5.76 (dd, J = 6.4, 15.2 Hz, 1H,
RdCH;SH).
13C NMR (3), δ 22.1, 31.9, 111.0, 141.4.
13C NMR (2), δ 22.0, 27.8, 112.0, 138.5.
MS-EI (3), m/z (%) 102 (Mþ, 76), 87 (83), 85 (24), 69 (100), 59 (30), 53
(65), 47 (22), 45 (67), 41 (79), 39 (33).
MS-EI (2), m/z (%) 102 (Mþ, 81), 87 (90), 85 (24), 69 (100), 59 (32), 53
(64), 47 (24), 45 (69), 41 (80), 39 (31).
Isolation of the Volatiles. Roasted, ground white sesame seeds (2.5 g)
were extracted with dichloromethane (50 mL) at room temperature for 1 h.
After filtration, the residue was twice extracted for 30 min with dichloro-
methane (total volume = 100 mL). The organic phases were combined,
and the volatiles were isolated by solvent assisted flavor evaporation
(SAFE) (30). The SAFE distillate was concentrated to 200 μL at 45 °C
using a Vigreux column (60 cm ꢀ 1 cm).
Gas Chromatography-Olfactometry (GC-O). GC-O was per-
formed using a Trace GC (Thermo Scientific, Dreieich, Germany) and
the following fused silica capillary columns: DB-5, DB-1701, and DB-
FFAP (all 30 m ꢀ 0.32 mm, 0.25 μm film thickness) (J&W Scientific,
Waldbronn, Germany). Samples (0.5 μL) were applied by cold-on-column
injection at an oven temperature of 40 °C. Helium at a flow rate of 2.5 mL/
min was used as the carrier gas. After 2 min, the temperature was raised at
a rate of 6 °C/min to 250 °C (DB-5) or 240 °C (DB-1701) or 230 °C (DB-
FFAP), respectively. The column effluent was split 1:1 by volume at the
end of the capillary column using a glass splitter and two deactivated fused
silica capillaries (50 cm ꢀ 0.20 mm). The first was connected to a flame
ionization detector (FID) and the second to a heated (250 °C) sniffing port.
Linear retention indices (RI) were calculated from the retention times of
n-alkanes.
Nuclear Magnetic Resonance (NMR) Spectra. 1H and 13C NMR
spectra were recorded in CDCl3 by means of a JEOL JNM-LA400
spectrometer (JEOL Ltd., Tokyo, Japan) at 400 or 100 MHz, respectively.
Chemical shift was recorded in parts per million (ppm) using tetramethyl-
silane as the internal standard (δ = 0.00 ppm). Coupling constants J are
denoted in hertz.
RESULTS AND DISCUSSION
Characterization of Aroma-Active Compounds in Roasted Se-
same Seeds. Application of the AEDA on a distillate eliciting the
typical aroma of roasted sesame seed, when checked on a strip of
filter paper, revealed 32 odor-active compounds in the FD factor
range of 2-2048. On the basis of our previous study (14), the
structures of 16 odorants could readily be assigned and confirmed
by means of reference compounds (Table 1). In agreement with
the earlier results (14), 2-furfurylthiol (10, coffee-like) and 4-hy-
droxy-2,5-dimethyl-3(2H)-furanone (21; caramel-like) showed
the highest FD factors, followed by 2-thenylthiol (24; thiophen-
2-yl-methylthiol; coffee-like) and 2-methoxy-4-vinylphenol (29;
clove-like). With somewhat lower odor activities, dimethyl tri-
sulfide (13), 2-ethyl-3,5-dimethylpyrazine (23), and trans-4,5-
epoxy-(E)-2-decenal (30) were identified. However, the structures
of 14odorants could not beassigned onthe basis ofprevious data,
although 8 of them (1, 5-7, 9, 15, 19, 20) had already been
detected as odor-active compounds in roasted sesame before (14),
but remained unidentified. Due to their meaty, catty, and/or
black-currant-like odors, it can, however, be assumed that these
odorants might play a crucial role in the characteristic sulfurous
Aroma Extract Dilution Analysis (AEDA). The SAFE distillate
(200 μL) was stepwise diluted with dichloromethane to prepare dilutions of
1:2, 1:4, 1:8, 1:16, ..., etc. of the original extract. GC-O of the diluted
extracts was performed on capillary DB-5, and dilution was continued
until no odor was detected during the whole run. Each single odorant was,
thus, assigned a flavor dilution factor (FD factor) representing the highest
dilution in which the odorant was detected at the sniffing port.
Fractionation of Volatiles by Column Chromatography. For the
identification experiments, roasted white sesame seeds (2.5 kg) were
extracted with dichloromethane (2.5 L) at room temperature for 1 h.
After filtration, the residue was further extracted for 30 min with two more
portions of dichloromethane (1.25 L). The combined extracts were
concentrated to 2 L, and the volatiles were isolated by SAFE distillation.
The distillate was concentrated to 2 mL and applied onto a water-cooled
glass column (39 cm ꢀ 2.5 cm i.d.) filled with a slurry of purified silica gel
(75 g, 7% water) in n-pentane (26). Elution was performed using four
n-pentane/diethyl ether mixtures of increasing polarity (100:0, 90:10,
70:30, 50:50, v/v, 450 mL each; fractions A-D). The eluate was collected

7372 J. Agric. Food Chem., Vol. 58, No. 12, 2010
Tamura et al.
Table 1. Odor-Active Compounds (FD g 2) in the Aroma Distillate Obtained from Roasted White Sesame Seeds
RI on
no.
odoranta
odor qualityb
DB-5
FFAP
fractionc
FD factor
1
2-methyl-1-propene-1-thiol
(Z)-3-methyl-1-butene-1-thiol
(E)-3-methyl-1-butene-1-thiol
(Z)-2-methyl-1-butene-1-thiol
(E)-2-methyl-1-butene-1-thiol
2-methyl-3-furanthiol
3-mercapto-2-pentanone
3-(methylthio)propanal (methional)
2-mercapto-3-pentanone
2-furfurylthiol
sulfurous, meaty
sulfurous, meaty
sulfurous, meaty
sulfurous, meaty
sulfurous, meaty
meaty
718
770
788
807
818
865
895
902
905
911
924
932
967
978
987
996
1019
1013
ndd
A
A
A
A
A
A
B
C
B
B
B
D
A
B
B
C
C
4
4
2
3
ndd
16
4
4
1098
1105
1300
1344
1452
1361
1426
1326
1422
1370
1295
1405
nd
5
64
256
4
6
7
catty, black-currant-like
potato-like
8
32
2
9
catty, black-currant-like
coffee-like
nutty
10
11
12
13
14
15
16
17
2048
16
128
256
128
4
2-acetyl-1-pyrroline
4-methyl-3-thiazolinee
dimethyl trisulfide
1-octen-3-one
earthy, burnt
sulfurous, onion-like
mushroom-like
catty, black-currant-like
roasty
4-mercapto-3-hexanone
unknown
2-acetylthiazolee
16
16
popcorn-like
1611
18
19
unknown
3-mercapto-3-methylbutyl formate
roasty
sulfurous, catty
1032
1032
nd
1517
C
B
} 256
20
21
22
23
24
25
26
27
28
29
30
31
32
2-methyl-3-thiophenethiol
4-hydroxy-2,5-dimethyl-3(2H)-furanone
2-ethyl-3,6-dimethylpyrazine
2-ethyl-3,5-dimethylpyrazine
2-thenylthiol
meaty, sulfurous
caramel-like
earthy, potato-like
earthy, potato-like
coffee-like
roasty
1054
1059
1079
1086
1088
1126
1177
1198
1296
1315
1383
1391
1404
1556
2029
1449
1449
1676
nd
A
D
D
D
B
B
B
B
B
C
C
D
D
64
1024
64
256
512
128
64
unknown
2-phenylethylthiol
rubber-like
fatty
fatty
1611
1507
1763
2193
1997
2497
2569
2-pentylpyridinee
32
(E,Z)-2,4-decadienalf
128
512
256
64
2-methoxy-4-vinylphenol
trans-4,5-epoxy-(E)-2-decenal
3-methyl-1H-indole (skatole)
4-hydroxy-3-methoxybenzaldehyde (vanillin)
clove-like
metallic
fecal
vanilla-like
128
a The odorant was identified by comparing it with the reference compound on the basis of the following criteria: retention indices on the stationary phases detailed in the table,
odor quality perceived at the sniffing port, and mass spectrum obtained by MS-EI. b Odor quality perceived at the sniffing port. c Silica gel fractions (n-pentane/diethyl ether, v/v): A,
100:0; B, 90:10; C, 70:30; D, 50:50. d Due to bad chromatographic behavior a retention index on FFAP could not be determined. Identification was based on the remaining criteria
given in footnote a. nd, not determined. e Tentative identification based on published data (14). f No unequivocal mass spectrum was obtained. Identification was based on the
remaining criteria given in footnote a.
aroma of roasted sesame seeds, in particular in the freshly ground
state.
by affinity chromatography on mercurated agarose gel was
applied to fraction A. A further increase in sensitivity was
achieved by using a GC-O/GC-O/MS system with a heart-cut
interface to monitor their mass spectra. Using this approach
allowed the identification of 6 as 2-methyl-3-furanthiol and that
of 20 as the corresponding 2-methyl-3-thiophenethiol (Table 1).
Compound 19 was found to coelute with a roasty smelling
odorant (18), but could be separated from 18 in fraction B
(Table 1). Finally, a mass spectrum was obtained, and the structure
of 19 could be assigned as 3-mercapto-3-methylbutyl formate.
Identification of Odorant 1. Using the GC-O/GC-O/MS sys-
tem, a mass spectrum of odorant 1 was obtained by isolating all
thiols from fraction A using the mercurated agarose gel
(Figure 5A). However, no reference spectrum could be found in
the literature. The mass spectrum suggested a formula weight of
88 and the additional fragment m/z 90, amounting to 4.3% of the
intensity of m/z 88, proposed the presence of one sulfur atom in
the molecule. In addition, the fragment ion m/z 55 indicated the
cleavage of an SH group (Mþ - 33) and, also, the presence of a
butenyl moiety. Thus, the structure of odorant 1 was proposed to
be a butenethiol.
Identification of New Aroma Compounds. GC-MS analysis of
the SAFE distillate did not allow mass spectra of several
unknown odorants to be obtained due to coeluting substances.
Therefore, fractionation of the distillate was done to avoid
coelutions and to obtain unequivocal mass spectra of the target
compounds.
First, column chromatography on silica gel using n-pentane/
diethyl ether mixtures of different polarities was performed. The
eluate was separated into four fractions, and in all fractions the
odorants were located by GC-O (Table 1).
Identification of Odorants 7 and 9. Compounds 7 and 9, both
showing catty, black-currant-like odors at the low FD factors of 4
and 2, respectively, could be detected in fraction B (Table 1).
Enrichment from a total of 2.5 kg of sesame seeds succeeded in
obtaining a mass spectrum, and finally, by means of the respective
reference odorants, these compounds could be identified as
3-mercapto-2-pentanone (7) and 2-mercapto-3-pentanone (9).
The latter was recently also reportedby Takeda and co-workers (19)
as a volatile constituent of ground roasted sesame seeds.
Identification of Odorants 6, 19, and 20. The meat-like smelling
compound 6, showing the highest FD factor among the pre-
viously unknown odorants, and, also, compound 20 were en-
riched in fraction A. Because the odor qualities suggested that
these compounds were also thiols, selective enrichment of thiols
To check this assumption, five possible butenethiol isomers were
synthesized, namely (E)- and (Z)-2-butene-1-thiol, 3-butene-1-
thiol, 3-butene-2-thiol, and 2-methyl-2-propene-1-thiol (Figure 1).
First, their retention indices and odor qualities were compared to
those of 1. Due to their clearly different retention indices as

Article
J. Agric. Food Chem., Vol. 58, No. 12, 2010 7373
Table 2. Odor Qualities and Retention Indices of the Synthesized Thiols
RIb on
no.
compound
3-butene-2-thiol
odor qualitya
sulfurous
sulfurous
DB-5 FFAP
677
689
700
717
718
721
770
788
807
818
987
<900
996
2-methyl-2-propene-1-thiol
3-butene-1-thiol
(E)-2-butene-1-thiol
rotten
sulfurous
980
1006
1013
1014
nd
1
2-methyl-1-propene-1-thiol
(Z)-2-butene-1-thiol
(Z)-3-methyl-1-butene-1-thiol
sulfurous, meaty
sulfurous
sulfurous, meaty
2
3
(E)-3-methyl-1-butene-1-thiol sulfurous, meaty
(Z)-2-methyl-1-butene-1-thiol sulfurous, meaty
(E)-2-methyl-1-butene-1-thiol sulfurous, meaty
4-mercapto-3-hexanone catty, black-currant-like
nd
4
1098
1105
1405
5
15
a Odor quality perceived at the sniffing port. b RI, retention index correlated to a
homologous series of n-alkanes.
elimination leading to the target compound 2-methyl-1-propene-
1-thiol (1).
The analytical data of 1, such as retention indices (Table 2), the
mass spectrum (Figure 5D), and the odor quality, were identical
with those of 1, and thus, this compound was identified as
2-methyl-1-propene-1-thiol (Table 1).
Identification of Odorants 2-5. Odorant 5 (Table 1) was first
suggested to be 3-methyl-2-butene-1-thiol, because its retention
indices (DB-5, 818; DB-FFAP, 1105) were very similar to those of
the reference compound (DB-5, 820; DB-FFAP, 1101). In addi-
tion, both exhibited a sulfurous, meaty odor quality. However,
GC-O/GC-O/MS analysis yielded a mass spectrum (Figure 6A)
which differed in the intensities from that of 3-methyl-2-butene-1-
thiol (Figure 6B). Furthermore, the mass spectra of odorants 2, 3,
and 4, obtained by GC-O/GC-O/MS analysis of the thiol isolate
of fraction A, exhibited similar fragmentation patterns and, also,
the same molecular ion (m/z 102; data not shown), indicating that
all four compounds might be isomers of a similar structure.
A comparison of the mass spectrum of 5 (Figure 6A) to that of
2-methyl-1-propene-1-thiol (1; Figure 5D) showed similar clea-
vage patterns, but indicated a skeleton consisting of five instead
of four carbon atoms. Thus, odorant 5 was proposed to be either
(E)-2-methyl-1-butene-1-thiol or (Z)-2-methyl-1-butene-1-thiol
or (E)-3-methyl-1-butene-1-thiol or (Z)-3-methyl-1-butene-1-thiol,
respectively, because all fragments in 5 were shifted by 14 mass
units as compared to 1.
Figure 5. Mass spectra (MS-EI) of odorant 1 (A), (E)-2-butene-1-thiol
(B), (Z)-2-butene-1-thiol (C), and 2-methyl-1-propene-1-thiol (D; 1).
To corroborate this assumption, first (E)-2-methyl-1-butene-1-
thiol (5) and (Z)-2-methyl-1-butene-1-thiol (4) were synthesized
following the synthetic approach used for 2-methyl-1-propene-1-
thiol, but using 2-methylbutanal instead as the starting material
(Figure 3B). Because the aldehydes were converted via the dithiols
into 2-methyl-1-butene-1-thiol, the compound was obtained as
mixture of (E)- and (Z)-isomers. The two GC peaks obtained in
the synthesis of 2-methyl-1-butene-1-thiol were assigned the
correct stereochemistry according to data obtained by NOESY-
NMR (Figure 4).
Comparison of the retention indices, the mass spectra, and the
olfactory properties of synthesized (E)-2-methyl-1-butene-1-thiol
(5; Figure 1) and (Z)-2-methyl-1-butene-1-thiol (4) identified 4 as
(Z)-2-methyl-1-butene-1-thiol and 5 as (E)-2-methyl-1-butene-
1-thiol.
compared to 1(DB-5, 718; FFAP, 1013), 3-butene-1-thiol, 3-butene-
2-thiol, and 2-methyl-2-propene-1-thiol could be excluded (Table 2).
On the other hand, (E)- and (Z)-2-butene-1-thiol showed
similar retention indices, but differed somehow in the mass
spectrometric fragmentation patterns (Figure 5B,C) as well as
in their odor qualities (Table 2).
At this point it was considered that the thiol group in 1 might be
directly bound to the double bond. Because the fragment ion m/z 73
(Mþ - 15), indicating the cleavage of a methyl group (Figure 5A),
was more abundant in the mass spectrum of 1 than in the mass
spectra of the 2-butene-1-thiols (Figure 5B,C), a branched carbon
skeleton was assumed. Consequently, the structure of 1 was
proposed to be 2-methyl-1-propene-1-thiol (1; Figure 1).
Approaches to synthesize 2-methyl-1-propene-1-thiol have
already been reported (32-34), but these were far from practical.
Thus, a new synthetic route leading from the corresponding
aldehydes to 1-alkene-1-thiols via the alkane-1,1-dithiols was
developed (Figure 3A). First, 2-methylpropanal was converted
to 2-methylpropane-1,1-dithiol by treatment with H2S, which was
then submitted to flash vacuum pyrolysis (FVP) to induce H2S
The mass spectra of compounds 2 and 3 were quite identical
and also showed similarities to compounds 4 and 5 (data not
shown). It was, thus, suggested that these odorants might be (Z)-
and (E)-3-methyl-1-butene-1-thiol. Following the approach
shown in Figure 3C, both compounds were synthesized starting
from 3-methylbutanal. The two peaks obtained during synthesis

7374 J. Agric. Food Chem., Vol. 58, No. 12, 2010
Tamura et al.
Figure 7. Mass spectrum (MS-EI) of odorant 15 (4-mercapto-3-
hexanone).
Figure 8. Chemical structures of the compounds identified for the first time
in roasted sesame or in foods (1-5, 15), respectively.
identified for the first time in a food product. In particular, the
1-alkene-1-thiols might play an important role in the character-
istic and intense aroma of freshly ground sesame. Their instability
and their high volatility might explain the fact that the aroma of
roasted sesame quickly loses its freshness after grinding (35) and
may also account for their relatively low FD factors found in
AEDA. To unequivocally evaluate the aroma impact of these
novel odorants, their quantitation by stable isotope dilution
assay, followed by calculation of odor activity values (OAV:
ratio of concentration to odor threshold), is underway.
Figure 6. Mass spectra (MS-EI) of odorant 5 (A), 3-methyl-2-butene-1-
thiol (B), and (E)-2-methyl-1-butene-1-thiol (C; 5).
wereassigned the correct stereochemistry according tothe (E)/(Z)
1
ratio, which was determined by H NMR on the basis of the
different coupling constants of the protons at the doublebond. By
comparing the mass spectra, the retention indices, and the odor
properties (Table 2) of synthesized (Z)-3-methyl-1-butene-1-thiol
(2; Figure 1) and (E)-3-methyl-1-butene-1-thiol (3; Figure 1), 2
was identified as (Z)-3-methyl-1-butene-1-thiol and 3 as the
corresponding (E)-isomer.
ABBREVIATIONS USED
Identification of Odorant 15. GC-O/GC-O/MS analysis of the
thiol isolate of fraction B yielded a mass spectrum for the catty,
black-currant-like smelling odorant 15 (Figure 7). The identical
odor quality suggested that 15 might be a homologue of 3-mer-
capto-2-pentanone or 2-mercapto-3-pentanone, respectively. Be-
cause the retention indices and the molecular mass of 132 pointed
to a C-6 compound and the fragment m/z 57 suggested a
propionyl moiety in the molecule, the structure was proposed
to be 4-mercapto-3-hexanone.
AEDA, aroma extract dilution analysis; BHT, 2,6-di-tert-butyl-
4-methylphenol; DMAP, N,N-dimethyl-4-aminopyridine; FD fac-
tor, flavor dilution factor; FID, flame ionization detector; FVP,
flash vacuum pyrolysis; GC-O, gas chromatography-olfactome-
try; MCSS, moving column stream switching system; NOESY,
nuclear Overhauser effect correlated spectroscopy; OAV, odor
activity value; RI, retention index; SAFE, solvent assisted flavor
evaporation; SIDA, stable isotope dilution assay.
ACKNOWLEDGMENT
To check this assumption, 4-mercapto-3-hexanone was syn-
thesized following a three-step synthesis (15, Figure 2). Because
the reference compound exhibited the same odor quality as
odorant 15 and yielded the same mass spectrum as well as the
same retention indices, 15 was finally identified as 4-mercapto-3-
hexanone.
We thank Dr. Michael Czerny for helpful advice and Petra
Bail, Anja Mialki, Magdalena Uzunova, and Jorg Stein for
skillful technical assistance.
€
LITERATURE CITED
In summary, nine odor-active thiols with sulfury, meaty, and/
or catty, black-currant-like odor qualities, so far unknown in
roasted sesame seeds, were identified in this study (Figure 8).
Among them, to the best of our knowledge, 2-methyl-1-propene-
1-thiol (1), (Z)-3-methyl-1-butene-1-thiol (2), (E)-3-methyl-1-
butene-1-thiol (3), (Z)-2-methyl-1-butene-1-thiol (4), (E)-2-meth-
yl-1-butene-1-thiol (5), and 4-mercapto-3-hexanone (15) were
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Received for review February 16, 2010. Revised manuscript received
May 11, 2010. Accepted May 12, 2010.