Characterization of aroma compounds of Chinese "Wuliangye" and "Jiannanchun" liquors by aroma extract dilution analysis

Article abstract of DOI:10.1021/jf052635t

Aroma compounds in Chinese "Wuliangye" liquor were identified by gas chromatography-olfactometry (GC-O) after fractionation. A total of 132 odorants were detected by GC-O in Wuliangye liquor on DB-wax and DB-5 columns. Of these, 126 aromas were identified by GC-mass spectrometry (MS). Aroma extract dilution analysis (AEDA) was further employed to identify the most important aroma compounds in "Wuliangye" and "Jiannanchun" liquors. The results showed that esters could be the most important class, especially ethyl esters. Various alcohols, aldehydes, acetals, alkylpyrazines, furan derivatives, lactones, and sulfur-containing and phenolic compounds were also found to be important. On the basis of flavor dilution (FD) values, the most important aroma compounds in Wuliangye and Jiannanchun liquors could be ethyl butanoate, ethyl pentanoate, ethyl hexanoate, ethyl octanoate, butyl hexanoate, ethyl 3-methylbutanoate, hexanoic acid, and 1,1-diethoxy-3-methylbutane (FD ≥ 1024). These compounds contributed to fruity, floral, and apple- and pineapple-like aromas with the exception of hexanoic acid, which imparts a sweaty note. Several pyrazines, including 2,5-dimethyl-3-ethylpyrazine, 2-ethyl-6-methylpyrazine, 2,6-dimethylpyrazine, 2,3,5-tri-methylpyrazine, and 3,5-dimethyl-2-pentylpyrazine, were identified in these two liquors. Although further quantitative analysis is required, it seems that most of these pyrazine compounds had higher FD values in Wuliangye than in Jiannanchun liquor, thus imparting stronger nutty, baked, and roasted notes in Wuliangye liquor.

Full text of DOI:10.1021/jf052635t

J. Agric. Food Chem. 2006, 54, 2695−2704 2695
Characterization of Aroma Compounds of Chinese “Wuliangye”
and “Jiannanchun” Liquors by Aroma Extract Dilution Analysis
WENLAI FAN AND MICHAEL C. QIAN*
Department of Food Science and Technology, Oregon State University, Corvallis, Oregon 97331
Aroma compounds in Chinese “Wuliangye” liquor were identified by gas chromatography-olfactometry
(GC-O) after fractionation. A total of 132 odorants were detected by GC-O in Wuliangye liquor on
DB-wax and DB-5 columns. Of these, 126 aromas were identified by GC-mass spectrometry (MS).
Aroma extract dilution analysis (AEDA) was further employed to identify the most important aroma
compounds in “Wuliangye” and “Jiannanchun” liquors. The results showed that esters could be the
most important class, especially ethyl esters. Various alcohols, aldehydes, acetals, alkylpyrazines,
furan derivatives, lactones, and sulfur-containing and phenolic compounds were also found to be
important. On the basis of flavor dilution (FD) values, the most important aroma compounds in
Wuliangye and Jiannanchun liquors could be ethyl butanoate, ethyl pentanoate, ethyl hexanoate,
ethyl octanoate, butyl hexanoate, ethyl 3-methylbutanoate, hexanoic acid, and 1,1-diethoxy-3-
methylbutane (FD g 1024). These compounds contributed to fruity, floral, and apple- and pineapple-
like aromas with the exception of hexanoic acid, which imparts a sweaty note. Several pyrazines,
including 2,5-dimethyl-3-ethylpyrazine, 2-ethyl-6-methylpyrazine, 2,6-dimethylpyrazine, 2,3,5-tri-
methylpyrazine, and 3,5-dimethyl-2-pentylpyrazine, were identified in these two liquors. Although further
quantitative analysis is required, it seems that most of these pyrazine compounds had higher FD
values in Wuliangye than in Jiannanchun liquor, thus imparting stronger nutty, baked, and roasted
notes in Wuliangye liquor.
KEYWORDS: GC-olfactometry; AEDA; Wuliangye; Jiannanchun; Chinese liquors; distillate; aroma
compounds; pyrazines
INTRODUCTION
are typically milled and pressed into a mould of different sizes
depending upon the manufacturer. The Daqu is then incubated
under controlled conditions. On the basis of the maximum
temperature at which the Daqu is incubated, the types of Daqu
can be classified into low-temperature Daqu (<45 °C), moder-
ate-temperature Daqu (45-60 °C), and high-temperature Daqu
(>60 °C). Daqu is rich in various microorganisms including
bacteria, yeast, and fungi (1). In addition, complex enzyme
systems are accumulated in the finished Daqu (3).
The grains used for liquor fermentation are first cooked and
then mixed with Daqu powder. The fermentation is typically
carried out at 28-32 °C for 60 days under anaerobic conditions
in a solid state. After fermentation, the liquor is distilled out
with steam and aged in sealed pottery jars to develop the
balanced aroma. While most of the liquors are aged for about
1 year, some of them are aged for more than 3 years. The aged
liquor is diluted with water and blended to yield an ethanol
content of 40-55% (v/v) for constant quality in the finished
product.
Chinese liquor is a traditional distillate fermented from grains.
After the fermentation, the fresh spirit is distilled out and then
aged under controlled conditions. The aged distillate is adjusted
to the designated ethanol concentration and blended to ensure
the quality of finished product (1). Chinese liquor has an annual
consumption of approximately 4 million kiloliters, creating a
sales revenue of 500 billion Chinese Yuan. There is no standard
procedure to make Chinese liquor. The traditional manufacturing
is more of an art than a science. The raw materials for making
Chinese liquor can be quite different depending upon availability
and the economics of the raw materials. In general, Chinese
liquor is made from sorghum or a mixture of sorghum, wheat,
corn, rice, and sticky rice. Rice hull is typically used as the
fermentation aide (1, 2).
The saccharifying and fermentation cultures used for Chinese
liquor are Daqu, Xiaoqu, or other enzyme preparations. Daqu
is the most widely used culture and is made from wheat or a
mixture of wheat, barley, and pea. The raw materials of Daqu
Because of differences in manufacturing practices, the aroma
profiles of various Chinese Daqu liquors are quite different. On
the basis of aroma characteristics, Chinese liquor can be
classified into strong aroma style, light aroma style, soy sauce
aroma style, sweet honey style, and miscellaneous style. Of
* To whom correspondence should be addressed: Department of Food
Science and Technology, 100 Wiegand Hall, Oregon State University,
Corvallis, OR 97331-6602. Telephone: 541-737-9114. Fax: 541-737-1877.
E-mail: michael.qian@oregonstate.edu.
10.1021/jf052635t CCC: $33.50
© 2006 American Chemical Society
Published on Web 03/03/2006

2696 J. Agric. Food Chem., Vol. 54, No. 7, 2006
Fan and Qian
hexanoate, hexyl hexanoate, 2-methylpropyl acetate, 2-methylpropyl
hexanoate, and 3-methylbutyl pentanoate were obtained from K and K
Laboratories (Plainview, NY). 2-Pentanol and ethyl 2-hydroxypro-
panoate were from Matheson Coleman and Bell (East Rutherford, NJ).
Ethyl benzoate was obtained from EKC, Inc. (Rosemont, IL). Phenol
was purchased from EMD Chemical, Inc. (Gibbstown, NJ). The rest
of the aroma standards were obtained from Sigma-Aldrich (St. Louis,
MO). Pentane was from Mallinckrodt Baker, Inc. (Phillipsburg, NJ).
Diethyl ether was obtained from Burdick and Jackson (Muskegon, MI).
Sodium sulfate anhydrous was from EMD Chemicals, Inc. (Gibbstown,
NJ). Sodium chloride, sodium bicarbonate, and sulfuric acid were
obtained from Sigma-Aldrich (St. Louis, MO). Ethanol, absolute-200
proof, was purchased from AAPER Alcohol and Chemical Co.
(Shelbyville, KY).
Synthesis of Esters. 3-Methylbutyl butanoate, 3-methylbutyl pen-
tanoate, 3-methylbutyl octanoate, pentyl 3-methylbutanoate, heptyl
hexanoate, 2-phenylethyl butanoate, and 2-phenylethyl hexanoate were
individually synthesized by reacting their respective acids and alcohols
(6). Each acid (600 µL) was mixed with 2 mL of alcohol in a 20 mL
vial. The reactions were catalyzed by acid (1 N H2SO4, 500 µL) at 100
°C for 1 h, after which the mixture was cooled and mixed with 5 mL
of saturated NaCl solution. The esters were extracted with 5 mL of
Freon 11 in a separatory funnel, and 1 µL of extract was analyzed by
GC-mass spectrometry (MS) (split ratio of 100:1) for confirmation
of ester identity.
these, the strong aroma style accounts for about 70% of total
liquor production. Strong aroma style liquors typically have
strong fruity, pineapple- and banana-like aromas (4). Within
this category, “Wuliangye” and “Jiannanchun” are two of the
most famous brands, followed by “Yanghe Daqu” and a few
others.
The volatile composition of Chinese liquor has been studied
extensively. Esters, alcohols, acids, aldehydes, ketones, acetals,
and heterocyclic compounds are the major classes of com-
pounds. These compounds are largely from the fermentation,
distillation, and aging processes. Fan and Xu (5) quantified the
volatile compounds of Wuliangye and Yanghe Daqu liquors.
Among the compounds quantified, the content of ethyl hex-
anoate was the highest, with a concentration of more than 2
g/L. Several other esters such as ethyl acetate, ethyl butanoate
and ethyl 2-methylpropanoate also had high concentrations. In
addition to esters, acids such as hexanoic, acetic, butanoic, and
2-hydroxypropanoic acids were also found at high concentra-
tions, along with 1,1-diethoxyethane. 3-Methylbutanol, 2-meth-
ylpropanol, 1-butanol, and propanol were the main alcohols.
Aldehydes such as acetaldehyde, 1-propanal, 2-methylpropanal,
1-hexanal, and 3-methylbutanal were also detected, but their
concentrations were relatively low in these liquors.
Synthesis of Acetals. 1,1-Diethoxy-2-methylpropane, 1,1-diethoxy-
2-methylbutane, 1,1-diethoxy-3-methylbutane, 1,1-diethoxypropane,
1,1-diethoxyhexane, 1,1-diethoxynonane, and 1,1-diethoxy-2-phenyl-
ethane were synthesized by reacting 2-methylpropanal, 2-methylbutanal,
3-methylbutanal, propanal, hexanal, nonanal, and phenylacetaldehyde,
respectively, with ethanol under acidic conditions (6, 8). Each aldehyde
(600 µL) was mixed with 2 mL of ethanol plus 2 mL of 1 N H2SO4.
The mixture was stirred at 58 °C for 1 h. After cooling, 50 mL of
saturated NaCl solution was added to the reaction mixture, and the
product was extracted with 10 mL of Freon 11 in a separatory funnel.
Each acetal solution (1 µL) was analyzed by GC-MS (split ratio of
100:1) for identification.
Liquors. Wuliangye liquor (500 mL, 52% ethanol by volume) was
bottled on September 7, 2004, at Wuliangye Co. Ltd. in Yibin City,
Sichuan Province, China. Jiannanchun liquor (500 mL, 52% ethanol
by volume) was bottled on October 26, 2004, at Jiannanchun Chiew
Distillery Co. Ltd. in Mianzhu City, Sichuan Province, China. Both
samples were procured commercially in China and shipped to the US,
where the samples were stored at -15 °C until analysis.
Identification of Aroma Compounds in Wuliangye Liquor by
Fractionation and GC-O Analysis. Aroma Extraction. Wuliangye
liquor was extracted using the same procedure as described previously
(6). A total of 100 mL of liquor sample was diluted to 14% ethanol by
volume with deodorized water (deionized water was boiled for 5 min
and then cooled to room temperature). The diluted liquor sample was
saturated with analytical-grade sodium chloride and extracted 3 times
with 100 mL aliquots of freshly distilled diethyl ether in a separatory
funnel. All extracts were combined and slowly concentrated to 50 mL
under a gentle stream of nitrogen. This was labeled as “extract 1”.
Acidic/Water-Soluble Fractionation. To facilitate GC-O and GC-
MS analysis, the aroma extract of liquor was separated into acidic/
water-soluble, neutral, and basic fractions, using a modified method
of Qian and Reineccius (9). Freshly distilled pentane and deodorized
water, 50 mL each, were added to “extract 1”. The aqueous phase was
adjusted to pH 9.0 with sodium bicarbonate solution (10%, w/v), then
separated in a separatory funnel, and saved. The organic phase was
washed twice with 10 mL of deodorized water. The washings were
combined with the aqueous phase. The organic phase was labeled
“extract 2”.
Very few studies have reported the aroma compounds in
Chinese liquor that are odor-active or present at concentrations
above the sensory threshold. Using the gas chromatography-
olfactometry (GC-O) technique, Fan and Qian (6, 7) have
identified more than 70 odor-active compounds in Yanghe Daqu
liquor. The results show that Yanghe Daqu liquor aroma is
mainly contributed by esters and fatty acids. Ethyl butanoate,
ethyl pentanoate, ethyl hexanoate, ethyl octanoate, and 3-meth-
ylethyl hexanoate are the most important aroma compounds in
Yanghe Daqu liquor. In addition, methyl hexanoate, ethyl
heptanoate, ethyl benzoate, and butyl hexanoate are also very
important because of their high flavor dilution (FD) values.
Although Wuliangye and Jiannanchun are the two most
popular liquors in China, the aroma compounds in these liquors
have not been investigated yet. Compared to Yanghe Daqu
liquor, Wuliangye and Jiannanchun liquors have more soy sauce
and roasted characters. The flavor difference can be caused by
many factors such as the raw ingredients used in the fermenta-
tion, fermentation conditions, distillation practices, and aging
processes. Although Wuliangye, Jiannanchun, and Yanghe Daqu
liquors are all made from sorghum, rice, sticky rice, wheat, and
corn, the proportion of these raw materials will vary for each
liquor. The key fermentation starter, Daqu, is also made
differently. The Daqus of Wuliangye and Jiannanchun are
produced from wheat, while the Daqu of Yanghe is made from
a mixture of wheat, barley, and peas. Furthermore, differences
in the environment, especially temperature and humidity, play
an important role in the selection of microorganisms used for
fermentation. As a result of these multiple variations, Wuliangye,
Jiannanchun, and Yanghe Daqu all have unique aroma profiles
(1, 5). The objective of this study was to identify the odor-
active compounds in Wuliangye liquor by normal-phase frac-
tionation and GC-O and to examine the most important aroma
compounds in both Wuliangye and Jiannanchun liquors using
aroma extract dilution analysis (AEDA). It is expected that the
findings of this research will help to better understand the aroma
chemistry of these two famous Chinese liquors.
The aqueous phase was further adjusted to pH 2 with 2 N H2SO4,
saturated with NaCl, and then extracted twice with 20 mL aliquots of
freshly distilled diethyl ether. The extracts were combined and dried
with 5 g of anhydrous sodium sulfate overnight. The dried solution
was filtered and then slowly concentrated to a final volume of 200 µL
under a gentle stream of nitrogen. This concentrate was labeled as the
“acidic/water-soluble fraction” for further GC-O analysis.
MATERIALS AND METHODS
Chemicals. Methyl hexanoate, ethyl octanoate, ethyl nonanoate, ethyl
decanoate, heptanoic acid, and octanoic acid were from Eastman
(Rochester, NY). Ethyl 2-methylpropanoate, propyl hexanoate, pentyl

Aroma Compounds of Chinese Liquors
J. Agric. Food Chem., Vol. 54, No. 7, 2006 2697
Basic Fraction. A total of 50 mL of deodorized water was added to
“extract 2”. The aqueous phase was adjusted to pH 1.3 with 2 N H2-
SO4, saturated with NaCl, and then separated in a separatory funnel.
The organic phase was labeled “extract 3” and saved. The aqueous
phase was then adjusted to pH 10 with sodium bicarbonate solution
(10%, w/v) and then extracted twice with 30 mL of freshly distilled
diethyl ether. The organic phase was combined and dried with 5 g of
anhydrous sodium sulfate overnight. The extract was filtered and slowly
concentrated to 200 µL under a gentle stream of nitrogen. This extract
was labeled as the “basic fraction”.
was achieved by comparing mass spectra, aromas, and RIs of the
standards. Tentative identification was achieved by comparing aroma
or mass spectra only.
RESULTS AND DISCUSSION
Synthesis of Some Esters and Acetals. Several esters and
acetals were not available commercially; therefore, they were
synthesized to provide a reference for positive identification.
Esters were synthesized from corresponding alcohols and acids
under acidic condition. After the reaction, the excess alcohols
were washed out with water and the esters were extracted with
Freon 11. Similarly, the acetals were synthesized by reacting
excess ethanol with corresponding aldehydes under acidic
conditions and then extracted with Freon 11. The synthesized
esters and acetals were analyzed by GC-MS. The retention
index and mass spectra of synthesized compounds are listed in
Table 1.
Aroma Fractionation and GC-O of Wuliangye Liquor.
To facilitate the identification of aromas, the extract of
Wuliangye liquor was separated into three fractions: acidic/
water-soluble, basic, and neutral. GC-O and GC-MS were
performed on each fractionation. Because only one person
performed the GC-O analysis, this approach cannot provide
accurate odor intensity results. However, it can provide informa-
tion of the aroma quality of the compounds, as well as positive
MS identification because the fractionation process greatly
reduced the complexity of each fraction. A total of 126 aroma
compounds from Wuliangye liquor (15 in the basic fraction,
77 in the neutral fraction, and 44 in the acidic/water-soluble
fraction) were identified by GC-O and GC-MS (Tables 2-4).
In addition, 6 aroma compounds, unknown, were detected by
GC-O but could not be identified by GC-MS.
The acidic/water-soluble fraction mainly consisted of fatty
acids, alcohols, and phenolic compounds (Table 2). Hexanoic
acid could be an important aroma contributor in this fraction
based on its GC-O intensity of very strong. Among the
alcohols, 3-methylbutanol had the highest aroma intensity
detected by GC-O on the DB-wax column and was also
identified in the basic and neutral fractions (intensity of moderate
and strong, respectively) because of its high concentration and
incomplete fractionation. 1-Pentanol, 2-phenylethanol, butanoic
acid, 3-methylbutanoic acid, phenol, and 2-furancarboxaldehyde
(furfural) had moderate intensities. Several alcohols, acids, and
phenolic compounds identified in the acidic/water-soluble
fraction had weaker intensities, including 1-butanol and acetic,
propanoic, pentanoic, 4-methylpentanoic, heptanoic, and nonano-
ic acids (all with weak intensities), along with 4-ethylguaiacol,
4-methylphenol, 4-ethylphenol, and benzoic, phenylacetic, and
phenylpropanoic acids (all with very weak intensities). Phenol
and 4-methylphenol were also identified in this fraction.
The basic fraction mainly consisted of alkylpyrazines. In this
fraction, only one alkylpyrazine, 2-ethyl-6-methylpyrazine, had
a moderate intensity (Table 3). 2,3,5-Trimethylpyrazine had a
weak intensity. Others had very weak intensities, including 2,6-
dimethylpyrazine, 2,6-diethylpyrazine, 2,5-dimethyl-3-ethylpyra-
zine, 2,3,5,6-tetramethylpyrazine, 2,3,5-trimethyl-6-ethylpyra-
zine, 5-ethyl-2,3-dimethylpyrazine (tentatively identified), 3,5-
dimethyl-2-butylpyrazine (tentatively identified), and 3,5-
dimethyl-2-pentylpyrazine (tentatively identified). 2-Furan-
methanol, although not a basic compound, was identified in this
fraction and had a moderate intensity. In addition, 2-acetyl-6-
methylpyridine was detected in this fraction, which is the first
report of this compound in Chinese liquor.
Neutral Fraction. The “extract 3” was dried with 5 g of anhydrous
sodium sulfate overnight. The extract was filtered and slowly concen-
trated to 200 µL under a gentle stream of nitrogen. This extract was
labeled as the “neutral fraction”.
GC-O Analysis. GC-O analysis was performed on a Hewlett-
Packard 5890 GC equipped with a flame ionization detector (FID) and
an olfactometer. The column carrier gas was nitrogen, at a constant
pressure (2 mL/min, column flow measured at 25 °C). Half of the
column flow was directed to the FID, while the other half was directed
to the olfactometer. The samples were analyzed on a DB-wax column
(30 m × 0.32 mm i.d., 0.25 µm film thickness; J&W Scientific, Folsom,
CA) and on a DB-5 column (30 m × 0.32 mm i.d., 1 µm film thickness;
J&W Scientific). Each concentrated fraction (1 µL) was injected with
a split ratio of 1:1. The oven temperature was held at 40 °C for 2 min,
then raised to 230 °C at a rate of 4 °C/min, and held at 230 °C for 15
min on the DB-wax column, while the final temperature was 250 °C
for 15 min on the DB-5 column. Injector and detector temperatures
were 250 °C.
All of the fractionations were analyzed in duplicate by a well-trained
panelist. Both the aroma descriptor and intensity were recorded. The
perceived aroma intensity was relatively scaled as “very strong”,
“strong”, “moderate”, “weak”, and “very weak”. Aroma intensity was
reported as “strong” if one of the two analyses detected it as “strong”.
AEDA of Wuliangye and Jiannanchun Liquors. A total of 40
mL of liquor sample of either Wuliangye or Jiannanchun was diluted
to 14% ethanol by volume with deodorized water to reduce the
extraction of ethanol. The diluted liquor sample was saturated with
NaCl and extracted with diethyl ether as described previously. The
aroma extract was fractionated into the acidic/water-soluble fraction
and the neutral/basic fraction. Both fractions were dried with 5 g of
anhydrous sodium sulfate overnight. The extract was filtered and then
concentrated to a final volume of 200 µL under a gentle stream of
nitrogen.
Each concentrated fraction was diluted stepwise with diethyl ether
using a series of 1:1 dilution, and each dilution was then analyzed by
AEDA using the same GC conditions as above. The FD factors were
determined for the odor-active compounds in each sample (10). Two
panelists (both male), were selected for the AEDA study. One panelist
had more than 5 years of sensory analysis experience in Chinese liquor,
and the other was a student in the Department of Food Science and
Technology at Oregon State University. Both panelists had previous
GC-O experience and completed more than 30 h of training for GC-O
analysis of Chinese liquors prior to the AEDA analysis. Each sample
was analyzed in duplicate where the aroma descriptors and correspond-
ing retention times were recorded by each panelist for each GC column.
When a volatile compound was detected at least twice, this analyte
was determined to be an aroma compound. These aroma compounds
were cross-referenced with fractionation results for confirmation.
GC-MS Analysis. Identification was carried out using an Agilent
6890 GC coupled to an Agilent 5973 mass selective detector (MSD).
Each concentrated fraction (1 µL) was analyzed on a DB-wax column
(30 m × 0.25 mm i.d., 0.25 µm film thickness; J&W Scientific) and
on a DB-5 column (30 m × 0.32 mm i.d., 0.25 µm film thickness;
J&W Scientific). The oven and injector temperatures were identical to
those of GC-O and AEDA analysis, described above. The column
carrier gas was helium at a constant flow rate of 2 mL/min. The electron
impact energy was 70 eV, and the ion source temperature was set at
230 °C. Mass spectra of unknown compounds were compared with
those in the Wiley 275.L Database (Agilent Technologies, Inc.).
Retention indices (RIs) of unknown compounds were calculated in
accordance with a modified Kovats method (11). Positive identification
The neutral fraction had the most complexity among the three
fractions. It consisted of esters, acetals, sulfur-containing

2698 J. Agric. Food Chem., Vol. 54, No. 7, 2006
Fan and Qian
Table 1. Retention Indices and Mass Spectra of Synthesized Aroma Compounds
synthesized compounds
RIwax
969
RIDB
mass spectrum (m/z %)
-
5
1,1-diethoxy-2-methylpropane
859
953
103 (100), 47 (94), 73 (79), 75 (68), 101 (50), 57 (47), 29 (40), 43 (39),
55 (35), 27 (23), 28 (23), 31 (23), 41 (19), 45 (19), 72 (16), 100 (13)
103 (100), 47 (72), 75 (60), 20 (47), 45 (44), 71 (43), 28 (40), 41 (37),
1,1-diethoxy-2-methylbutane
1063
115 (37), 57 (30), 43 (25), 31 (20), 70 (19), 69 (17), 27 (16), 87 (16),
55 (14), 99 (12), 59 (12), 114 (10)
1,1-diethoxy-3-methylbutane
1,1-diethoxypropane
1068
950
955
812
47 (100), 103 (94), 75 (63), 69 (56), 115 (41), 43 (28), 71 (25), 41 (24),
29 (22), 87 (10)
59 (100), 29 (97), 31 (68), 47 (64), 87 (60), 27 (60), 103 (43), 75 (33),
28 (26), 45 (20), 57 (18), 41 (17), 58 (14), 26 (13), 43 (12)
1,1-diethoxyhexane
1238
1498
1690
1255
1346
1350
1092
1382
1328
1056
1152
1155
103 (100), 47 (44), 129 (42), 75 (38), 83 (37), 55 (28), 29 (21), 57 (13),
41 (10), 43 (10)
103 (100), 57 (34), 85 (27), 75 (25), 171 (23), 69 (21), 47 (21), 29 (19),
43 (13), 55 (13), 83 (13), 41 (12)
103 (100), 91 (59), 75 (54), 47 (52), 29 (28), 121 (20), 31 (16), 120 (15),
149 (15), 27 (13), 65 (13), 148 (12)
57 (100), 85 (77), 56 (76), 43 (62), 41 (55), 29 (55), 103 (43), 27 (23),
60 (22), 39 (13), 87 (12), 42 (12), 55 (12), 28 (11), 15 (10), 61 (10)
70 (100), 85 (58), 43 (53), 57 (42), 55 (37), 41 (31), 29 (20), 71 (19),
1,1-diethoxynonane
1,1-diethoxy-2-phenylethane
3-methylbutyl butanoate
3-methylbutyl pentanoate
pentyl 3-methylbutanoate
42 (12), 103 (11)
43 (100), 85 (92), 70 (89), 57 (76), 41 (75), 103 (75), 42 (49), 29 (41),
55 (33), 27 (30), 87 (24), 60 (22), 39 (21), 61 (18), 71 (16), 69 (12),
56 (10), 102 (10)
3-methylbutyl octanoate
heptyl hexanoate
1606
1683
1446
1482
70 (100), 99 (54), 43 (48), 71 (42), 55 (24), 117 (14), 41 (13), 42 (10)
43 (100), 117 (96), 56 (80), 99 (76), 57 (73), 70 (67), 41 (61), 98 (61),
55 (48), 29 (38), 69 (37), 28 (36), 71 (32), 61 (29), 42 (28), 27 (23),
73 (15), 60 (14), 39 (13), 68 (10)
2-phenylethyl butanoate
2-phenylethyl hexanoate
1958
2160
1447
1649
104 (100), 43 (15), 71 (11), 105 (8)
104 (100), 43 (47), 105 (40), 99 (27), 71 (22), 91 (5)
compounds, lactones, pyrrole derivatives, aldehydes, and ketones
(Table 3). In this fraction, ethyl butanoate, ethyl pentanoate,
ethyl hexanoate, and 1,1-diethoxy-3-methylbutane had very
strong intensities by GC-O. Several other aroma compounds
had strong intensities, including ethyl 2-methylpropanoate, ethyl
3-methylbutanoate, 3-methylbutanol, and butyl hexanoate. Ethyl
acetate, ethyl heptanoate, ethyl octanoate, ethyl cyclohexan-
ecarboxylate, ethyl 3-phenylpropanoate, methyl hexanoate, hexyl
hexanoate, 2-methylpropyl acetate, 2-furancarboxaldehyde,
2-furanmethanol, 1,1-diethoxyethane, and 1,1-diethoxy-2-meth-
ylbutane had moderate aroma intensities. Three sulfur-containing
compounds, which had weak intensities, were detected in this
fraction: dimethyl sulfide (tentatively identified), dimethyl
disulfide, and dimethyl trisulfide. A few aldehydes were detected
in this fraction, but they had weak or very weak intensities.
γ-Octalactone, γ-nonalactone, γ-decalactone, and γ-dodeca-
lactone, along with 2-acetylpyrrole, were also identified and had
very weak intensities.
its very high FD value (FD g 1024). Butanoic, 3-methylbu-
tanoic, and pentanoic acids were very important (FD g 128)
while acetic, propanoic, 4-methylpentanoic, and heptanoic acids
had moderate FD values (FD g 16). Acetic and propanoic acids
gave acidic and vinegar odors, while butanoic, 3-methylbutanoic,
pentanoic, 4-methylpentanoic, hexanoic, and heptanoic acids
contributed to cheesy, rancid, sweaty, and sour aromas. These
acids also exist in Yanghe Daqu liquors (6, 7). Wuliangye,
Jiannanchun, and Yanghe liquors are produced through solid-
state fermentation; the fermentor is made of clay, and the inside
is usually coated with a layer of mud comprised of clay, spent
grains, and bean cake powder. After repeated use, the fermentors
gradually mature and will contain a diversity of microorganisms,
including butanoic and hexanoic acid-producing bacteria, on the
inside of the fermentor (5, 12). These microorganisms will
effectively produce organic acids. In addition, the cooked grains
are fermented in an open system, allowing for extensive
generation of short-chain free fatty acids (4, 6).
AEDA Analysis of Wuliangye and Jiannanchun Liquors.
The aroma extracts were fractionated into acidic/water-soluble
and neutral/basic fractions for AEDA analysis. Because the basic
fraction had only a few aroma compounds and they had been
positively identified by both GC-O and GC-MS, it was
combined with the neutral fraction. The two fractions were
diluted stepwise with diethyl ether using a series of 1:1 dilution,
and each dilution was analyzed by GC-O. The acidic/water-
soluble fraction was analyzed on the DB-wax column, while
the neutral/basic fraction was analyzed on both the DB-wax
and DB-5 columns because of the complex composition of
Chinese liquors. The FD factors were determined for the odor-
active compounds in each sample as described by Grosch (10).
Many compounds were identified including various acids,
alcohols, esters, acetals, pyrazines, and many others. Fatty acids
were detected by AEDA in the acidic/water-soluble fraction on
the DB-wax column (Table 2). Hexanoic acid was probably
the most important compound among the fatty acids based on
As expected with any alcoholic beverage, alcohols were
among the major volatile compounds. During fermentation, yeast
can form alcohols from sugars under aerobic conditions and
from amino acids under anaerobic conditions (13). A small
amount of alcohols can also be made by yeast through the
chemical reduction of corresponding aldehydes (14). Although
alcohols are typically separated into the neutral fraction, their
high concentrations in alcoholic beverages interfere with the
identification of other neutral compounds. Therefore, it is
desirable to separate them into the acidic/water-soluble fraction
to be analyzed simultaneously with the acids (9) (Table 2). Most
alcohols have high sensory thresholds and impart fruity, floral,
and alcohol-like aromas. 3-Methylbutanol, with a fruity and nail-
polish-like odor, could be the most important among alcohols
because of its FD value (FD g 128). However, because of its
high concentration, 3-methylbutanol could not be completely
fractionated into the acidic/water-soluble fraction and could be
smelled in the neutral/basic fraction where its FD was greater

Aroma Compounds of Chinese Liquors
J. Agric. Food Chem., Vol. 54, No. 7, 2006 2699
−O on a DB-Wax Column
Table 2. Aroma Compounds in Acidic/Water-Soluble Fraction Detected by GC
FD factora
RI
aroma compounds
2-butanol
1-propanol
2-methylpropanol
2-pentanol
1-butanol
3-methylbutanol
2-hexanol
1-pentanol
3-hydroxy-2-butanone
2-heptanol
descriptor
fruity
alcoholic, fruity
wine, solvent
fruity, alcoholic
pungent, alcoholic
fruity, nail polish
fruity
fruity, balsamic
buttery
fruity
floral, green
acidic, vinegar
roasted
fruity, alcoholic
sweet, almond
rosy, green
vinegar
basic of identificationb
GC−
O intensityc
WLY
1
JNC
ND
1020
1035
1087
1114
1137
1201
1210
1268
1304
1318
1341
1424
1442
1443
1456
1474
1525
1539
1555
1602
1647
1655
1659
1727
1764
1820
1846
1872
1906
1914
1955
2007
2031
2060
2080
2168
2185
2282
2449
2550
2603
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIL
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIL
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma
VW
VW
VW
VW
W
S
VW
M
VW
VW
VW
W
VW
VW
M
VW
W
VW
VW
M
VW
M
VW
W
VW
W
VS
VW
M
4
8
64
1
ND
128
128
256
128
128
2
8
32
2
32
8
1-hexanol
acetic acid
2-(diethoxymethyl)furand
1-heptanol
2-furancarboxaldehyde
2-ethyl-1-hexanol
propanoic acid
1-octanol
2-methylpropanoic acid
butanoic acid
2-furanmethanol
3-methylbutanoic acid
2-methylbutanoic acid
pentanoic acid
2-methylpentanoic acid
4-methylpentanoic acid
hexanoic acid
benzenemethanol
2-phenylethanol
5-methylhexanoic acidd
heptanoic acid
phenol
128
8
16
2
16
8
fruity
acid, rancid
rancid, cheesy
burnt sugar
rancid, acidic
cheesy, rancid
sweaty, rancid
sweaty, rancid
sweat, sour
sweaty, cheesy
floral
rosy, honey
cheesy, sweaty
sweaty
phenol, medicinal
clove, spicy
sweaty, cheese
animal, phenol
fatty
2
512
8
2
512
ND
256
128
64
128
16
512
8
1024
128
128
VW
W
M
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma
64
128
1
2
4
8
32
64
8
4-ethylguaiacol
octanoic acid
4-methylphenol
nonanoic acid
4-ethylphenol
decanoic acid
VW
VW
VW
VW
VW
VW
VW
VW
VW
32
smoky
fatty
fruity, cherry
fruity, rosy
floral, fruity
2
8
benzoic acid
phenylacetic acid
phenylpropanoic acidd
a WLY, Wuliangye liquor; JNC, Jiannanchun liquor; and ND, not detected by GC O. b MS, compounds were identified by MS spectra; aroma, compounds were identified
−
by the aroma descriptors; RI, compounds were identified by a comparison to the pure standard; and RIL, compounds were identified by a comparison with the retention
index from the literatures. c VS, very strong; S, strong; M, moderate; W, weak; and VW, very weak. d Tentatively identified.
than 128 (Table 3). 1-Butanol and 1-pentanol had very high
FD values (FD g 128), while 1-hexanol and 2-ethyl-1-hexanol
also contributed to the overall aroma because of their moderate
FD values (FD g 16). 2-Ethyl-1-hexanol, with a rosy green
odor, has also been detected in freshly distilled Calvados and
Cognac (8). 2-Phenylethanol was detected in both liquors (FD
g 128). This compound gave rosy and honey aromas and can
be produced by yeast (13, 15). Benzenemethanol was also
detected by GC-O, but it had a very low intensity.
Esters, which were found in the neutral/basic fraction, were
the most abundant aroma compounds in the Wuliangye and
Jiannanchun liquors, with ethyl esters dominating this class. On
the basis of the FD values detected on the DB-wax and DB-5
columns (Tables 3 and 4), ethyl butanoate, ethyl pentanoate,
ethyl hexanoate, ethyl octanoate, ethyl 3-methylbutanoate, and
butyl hexanoate could be extremely important odorants (FD g
1024) in both liquors. These esters have also been identified as
the most potent aromas in Yanghe Daqu liquors (6, 7). Ethyl
acetate, ethyl heptanoate, ethyl 2-methylpropanoate, methyl
hexanoate, propyl hexanoate, hexyl hexanoate, and 2-methyl-
propyl acetate were of high importance because of their high
FD values (FD g 128) in the Wuliangye and Jiannanchun
liquors. Ethyl propanoate, ethyl decanoate, ethyl 2-methylbu-
tanoate, hexyl acetate, 3-methylbutyl butanoate, 3-methylbutyl
hexanoate, and 2-methylpropyl hexanoate could also contribute
to the aroma of both liquors but to a lesser degree (FD g 16).
All of these esters have been detected in Yanghe Daqu liquors
(6, 7). In addition, some long-chain esters were identified by
GC-MS in these liquors, including ethyl hexadecanoate, ethyl
9-octadecenoate, and ethyl 9,12-octadecadienoate, all of which
had high concentrations but were not detected by GC-O. Esters
seemed to be the most important aroma compounds for strong
aroma style Chinese liquor and contributed to the pleasant fruity,
floral, pineapple-, apple-, and banana-like aromas.
Some hydroxy fatty acid esters were identified in both liquors
(Tables 3 and 4). Among these esters, ethyl 2-hydroxypro-
panoate, ethyl 2-hydroxyhexanoate, and ethyl 2-hydroxy-3-
methylbutanoate gave fruity, floral, and jasmine aromas and
could have some importance to the aroma because of their FD
values (FD g 16). These hydroxy esters have been detected in
Chinese liquor (6, 7) and freshly distilled Calvados and Cognac
(8, 14). Hydroxy esters are formed from the esterification of
corresponding hydroxy fatty acids, which could be produced
from the reduction of keto acids. 2-Hydroxypropanoic acid

2700 J. Agric. Food Chem., Vol. 54, No. 7, 2006
Fan and Qian
FD factora
Table 3. Aroma Compounds in Neutral/Basic Fraction Detected by GC
−O on a DB-Wax Column
RI
aroma compounds
ethyl acetate
1,1-diethoxylethane
2-methylbutanal
descriptor
pineapple
fruity
green
green, malty
cooked onion, sulfur
fruity
banana, fruity
fruity, sweet
fruity
fruity
floral, fruity
pineapple
berry, fruity
apple
onion, cabbage
fruity
fruity
apple, green grass
apple
basic of identificationb
GC
−
O intensityc
WLY
JNC
892
892
911
915
929
950
953
961
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
aroma, RI
M(N)
M(N)
VW(N)
W(N)
W(N)
VW(N)
W(N)
S(N)
VW(N)
VW(N)
M(N)
VS(N)
W(N)
S(N)
W(N)
M(N)
VS(N)
VW(N)
VS(N)
VW(N)
VW(N)
M(N)
256
256
256
256
3-methylbutanal
16
32
8
2
dimethyl sulfided
1,1-diethoxypropane
ethyl propanoate
ethyl 2-methylpropanoate
1,1-diethoxy-2-methylpropane
2-pentanone
2-methylpropyl acetate
ethyl butanoate
ethyl 2-methylbutanoate
ethyl 3-methylbutanoate
dimethyl disulfide
1,1-diethoxy-2-methylbutane
1,1-diethoxy-3-methylbutane
1-hexanal
ethyl pentanoate
3-methylbutyl acetate
1-butanol
methyl hexanoate
unknown
3-methylbutanol
ethyl hexanoate
hexyl acetate
3-methylbutyl butanoate
unknown
1,1,3-triethoxypropane
propyl hexanoate
ethyl heptanoate
MS, aroma, RIS
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIS
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIS
MS, aroma, RIS
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
64
512
2
8
32
32
969
972
988
256
2048
32
512
16
8
2048
64
1024
8
1031
1045
1060
1061
1063
1068
1073
1128
1102
1137
1178
1182
1201
1235
1254
1255
1288
1291
1293
1310
1330
1334
1341
1360
1368
1373
1375
1384
1388
1397
1399
1400
1404
1409
1415
1429
1430
1445
1456
1460
1489
1491
1498
1501
1509
1523
1527
1555
1583
1583
1593
1603
1603
1610
1620
1640
1647
1649
1655
1676
1683
1690
1768
32
4096
8
1024
2048
512
fruity
pungent, alcoholic
floral, fruity
fruity, floral
fruity, nail polish
fruity, floral, sweet
fruity, floral
floral, fruity
fruity
fruity, vegetal
pineapple, sweet
fruity
nutty
fruity
floral, green
sulfur, rotten cabbage
floral, fruity
apple, sweet
nutty, roasted
pineapple, fruity
fruity
roasted, nutty
floral
fruity, floral
fruity, floral
fruity
nutty, baked
fruity, apple, green
roasted, baked
baked
sweet, almond
baked
sweet, caramel
baked
fruity
128
64
128
8192
4
16
32
16
32
32
64
32
4096
32
16
32
2
128
256
32
W(N)
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIS
S(N), M(B)
VS(N)
VW(N)
W(N)
W(N)
W(N)
W(N)
M(N)
VW(B)
W(N)
VW(N)
W(N)
VW(N)
W(N)
M(B)
S(N)
VW(N)
W(B)
W(N)
VW(N)
M(N)
MS, aroma, RIL
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIL
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIL
MS, aroma, RIL
MS, aroma, RIL
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIL
MS, aroma
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIS
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIL
MS, aroma, RIL
MS, aroma, RI
MS, aroma, RI
MS, aroma
32
2
32
2,6-dimethylpyrazine
ethyl 2-hydroxypropanoate
1-hexanol
16
dimethyl trisulfide
64
64
2-hydroxy-3-pentanone
2-methylpropyl hexanoate
2-ethyl-6-methylpyrazine
butyl hexanoate
32
128
1024
64
4
2048
hexyl butanoate
2,3,5-trimethylpyrazine
ethyl 2-hydroxy-3-methylbutanoate
ethyl 2-hydroxybutanoate
ethyl cyclohexanecarboxylate
ethyl octanoate
2,6-diethylpyrazine
3-methylbutyl hexanoate
2,5-dimethyl-3-ethylpyrazine
5-ethyl-2,3-dimethylpyrazined
2-furancarboxaldehyde
2,3,5,6-tetramethylpyrazine
2-acetylfuran
2,3,5-trimethyl-6-ethylpyrazine
1,1-diethoxynonane
benzaldehyde
ethyl nonanoate
furfuryl acetate
64
32
8
8
256
512
256
1024
M(N)
VW(B)
VW(N)
M(B)
VW(B)
M(N)
VW(B)
VW(N)
VW(B)
VW(N)
W(N)
VW(N)
W(N)
W(N)
VW(N)
M(N)
VW(B)
VW(N)
VW(N)
VW(B)
VW(N)
W(N)
W(N)
M(B), N(W)
W(N)
VW(N)
VW(B)
VW(N)
VW(N)
W(N)
1
256
16
8
128
32
2
2
32
1
fruity, berry
floral, fruity
caramel, sweet
floral, jasmine
green, roasted
apple, peach
baked, roasted
roasted
16
2
16
16
1
256
8
8
16
8
64
1
ethyl 2-hydroxyhexanoate
5-methyl-2-furfural
hexyl hexanoate
3,5-dimethyl-2-butylpyrazined
2-acetyl-5-methylfuran
ethyl 2-furoate
MS, aroma, RI
MS, aroma, RI
MS, aroma
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIL
MS, aroma, RI
MS, aroma, RI
MS, aroma
2
8
16
8
balsamic
2-acetyl-6-methylpyridined
ethyl decanoate
roasted, baked
fruity, grape
floral, rose
fruity
burnt sugar
sweet, caramel, fruity
fruity, sweet
nutty, baked
sweet, fruity
fruity
8
32
64
64
64
1
16
16
32
32
8
phenylacetaldehyde
ethyl benzoate
2-furanmethanol
furfuryl butanoate
diethyl butanedioate
3,5-dimethyl-2-pentylpyrazined
heptyl hexanoate
1,1-diethoxy-2-phenylethane
ethyl phenylacetate
8
16
1
MS, aroma, RIS
MS, aroma, RIS
MS, aroma, RI
8
64
64
128
rosy, honey

Aroma Compounds of Chinese Liquors
J. Agric. Food Chem., Vol. 54, No. 7, 2006 2701
Table 3. (Continued)
FD factora
RI
aroma compounds
2-phenylethyl acetate
ethyl dodecanoate
furfuryl hexanoate
descriptor
rosy, floral
sweet, fruity
caramel, fruity
fruity, floral
coconut, fruity
rosy, honey
fruity
herbal, medicine
phenol, medicinal
sweet, coconut
coconut
basic of identificationb
GC
−
O intensityc
WLY
JNC
1801
1828
1857
1872
1886
1906
1958
1972
2007
2018
2110
2160
2273
2365
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIS
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIS
MS, aroma, RIL
MS, aroma, RI
W(N)
32
8
1
128
32
64
8
8
32
2
VW(N)
VW(N)
M(N)
ethyl 3-phenylpropanoate
γ
-octalactone
W(N)
2-phenylethanol
2-phenylethyl butanoate
2-acetylpyrrole
phenol
VW(N)
VW(N)
VW(N)
VW(N)
VW(N)
VW(N)
VW(N)
VW(N)
VW(N)
1
8
2
ND
γ
γ
-nonalactone
-decalactone
8
64
2-phenylethyl hexanoate
ethyl 2-hydroxy-3-phenylpropanoate
fruity
smoky
sweet, coconut
γ
-dodecalactone
a WLY, Wuliangye liquor; JNC, Jiannanchun liquor; and ND, not detected by GC O. b MS, compounds were identified by MS spectra; aroma, compounds were identified
−
by the aroma descriptors; RI, compounds were identified by a comparison to the pure standard; RIL, compounds were identified by a comparison with the retention index
from the literatures; and RIS, compounds were identified by a comparison with the retention index from the synthesized compounds. c VS, very strong; S, strong; M,
moderate; W, weak; and VW, very weak. In the parenthesis, N, neutral fraction; B, basic fraction. d Tentatively identified.
(lactic acid) is formed by lactic acid bacteria, which is found to
be the dominant species in the fermentation culture (5). One
cyclic ester, ethyl cyclohexanecarboxylate, was detected in both
liquors in this work. It had a high FD value (FD g 128) and
gave fruity and floral aromas. This compound has been identified
in Yanghe Daqu liquor (7). Several aromatic esters were also
detected in this study. Ethyl 3-phenylpropanoate and ethyl
2-phenylacetate had high FD values (FD g 128), while ethyl
benzoate and 2-phenylethyl acetate had moderate FD values (FD
g 16). These esters contributed rosy, honey, floral, and fruity
odors and have been identified in Chinese liquors previously
(6, 7). One binary acid ester, diethyl butanedioate, was detected
in the liquors, but it had a relative low FD value (FD e 8);
therefore, it is probably not important to the aroma.
Esters are formed mostly through esterification of alcohols
with fatty acids during the fermentation, distillation, and aging
processes (6, 7, 14). Yeast and other microorganisms can
synthesize esters during fermentation. Strong aroma style
Chinese liquors use Daqu powder as the saccharifying and
fermentation agent. Daqu has high esterase activities (16) and
can catalyze ester synthesis during the fermentation. Ester
formation can be influenced by many factors such as fermenta-
tion temperature, oxygen availability, and fermentation strains.
A higher temperature leads to a greater loss of esters because
of the increased rates of hydrolysis and volatilization. In the
fermentation processes of the Chinese liquors in this study, a
relatively low temperature was maintained, thus favoring the
formation of short-chained esters (17). Esters can also be formed
during the aging process (2). A comparison of aged and young
Yanghe Daqu liquors has shown that some esters in the aged
liquor had higher FD values than in the young liquor, possibly
because of higher concentrations in the aged liquor (7).
However, their formation during the aging process is probably
limited because the ester content was also relatively high in
the young liquor.
cherry odors. Although acetaldehyde was determined to have a
relatively high FD value in Yanghe Daqu liquor (7), it was not
found in this work probably because of the methodology used
in this study. Acetaldehyde has an extremely low boiling point
and can be easily lost during aroma concentration. Most
aldehydes are probably formed by yeast metabolism (18).
Aldehydes can be converted into other compounds during the
liquor-aging process (19, 20).
Acetals were found to have high FD values in both liquors
(Tables 3 and 4). 1,1-Diethoxy-3-methylbutane was one of the
most important aroma compounds (FD g 1024), while 1,1-
diethoxyethane (FD g 128) was also of high importance in both
liquors. 1,1-Diethoxy-2-methylpropane, 1,1-diethoxy-2-meth-
ylbutane, 1,1-diethoxyhexane (detected only on a DB-5 column),
1,1,3-triethoxypropane, and 1,1-diethoxy-2-phenylethane were
all detected by GC-O in this work (FD g 16). Most of these
acetals have been identified in Yanghe Daqu liquors (6, 7) and
in freshly distilled Calvados and Cognac (8, 14, 21). It seemed
that Wuliangye liquor had much higher levels of acetals than
Jiannanchun because of the higher FD values, although quan-
titative analysis is needed to confirm this. Acetals are formed
from the condensation of aldehydes with alcohols.
The importance of pyrazines to the aroma of Chinese liquor
is poorly understood (1, 3). On the basis of the FD values,
pyrazines could be very important for Wuliangye and Jiannan-
chun liquors. 2,5-Dimethyl-3-ethylpyrazine and 2-ethyl-6-meth-
ylpyrazine had high FD values (FD g 128). 2,6-Dimethylpyra-
zine, 2,3,5-trimethylpyrazine, and 3,5-dimethyl-2-pentyl-
pyrazine (tentatively identified) had moderate FD values (FD
g 16). These alkylpyrazines impart nutty, baked, and roasted
notes. Although several pyrazines have been identified in
Yanghe Daqu liquor, many more pyrazines were identified in
the Wuliangye and Jiannanchun liquors in this study. While this
could be due to different methodologies used for aroma isolation,
it is likely that Wuliangye and Jiannanchun liquors may contain
more pyrazines. This could be due to differences involved in
liquor manufacturing. Daqu is not only the starter, but it is also
the fermentation material because it typically accounts for 25%
of the total amount of grains used in the fermentation. The Daqu
used for making Wuliangye and Jiannanchun liquors was
exposed to 58-60 °C for 10-12 days, while the Daqu used
for Yanghe Daqu liquor was only exposed to 54-56 °C for
5-7 days (3). The fermentation temperature of Wuliangye and
Aldehydes had relatively low FD values (Tables 3 and 4)
and contributed to green, grass, and malt aromas. 3-Methylbu-
tanal and 2-methylpropanal both had moderate FD values (FD
g 16), where the latter was only detected on the DB-5 column.
Aromatic aldehydes seemed to be important in these liquors,
where phenylacetaldehyde had a high FD value (FD g 256 on
DB-5) and gave a floral aroma, while benzaldehyde had a
moderate FD value (FD g 16) and contributed to fruity and

2702 J. Agric. Food Chem., Vol. 54, No. 7, 2006
Fan and Qian
Table 4. Aroma Compounds in Neutral/Basic Fraction Detected by GC−O on a DB-5 Column
FD factora
RI
aroma compounds
2-methylpropanal
ethyl acetate
3-methylbutanal
descriptor
green
fruity, ester
green, malt
sweet, fruity
fruity
fruity, sweet
cooked onion
strawberry, fruity
nail polish, rancid
green, grass
sweet, fruity
fruity
sweet, fruity, floral
berry, sweet
apple
burnt sugar
fruity
fruity
fruity
green, fruity
fruity
fruity, green
rotten cabbage
ester, fruity
floral, fruity
fruity
basic of identificationb
WLY
JNC
534
584
629
705
726
754
756
770
783
797
800
815
831
849
852
854
859
875
900
924
955
963
976
1010
1015
1047
1056
1062
1076
1089
1092
1093
1097
1136
1150
1152
1155
1163
1171
1175
1176
1183
1189
1191
1196
1215
1247
1260
1287
1294
1328
1353
1357
1368
1385
1394
1401
1446
1456
1482
1556
1563
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIL
MS, aroma, RIS
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIS
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIS
MS, aroma, RIL
MS, aroma, RIL
MS, aroma, RIL
MS, aroma, RIS
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIL
MS, aroma, RI
MS, aroma, RIS
MS, aroma, RIS
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
2
64
4
16
256
128
4
64
128
ND
1024
1
64
64
256
64
16
8
1024
64
2048
64
16
8192
32
256
8
64
128
ND
8
256
32
4
8
32
8
ethyl propanoate
1,1-diethoxyethane
ethyl 2-methylpropanoate
dimethyl disulfide
2-methylpropyl acetate
3-methylbutanol
1-hexanal
ethyl butanoate
1024
8
ethyl 2-hydroxypropanoate
2-furancarboxaldehyde
ethyl 2-methylbutanoate
ethyl 3-methylbutanoate
2-furanmethanol
1,1-diethoxy-2-methylpropane
3-methylbutyl acetate
ethyl pentanoate
methyl hexanoate
1,1-diethoxy-3-methylbutane
benzaldehyde
dimethyl trisulfide
ethyl hexanoate
32
128
1024
32
16
4
2048
8
1024
16
64
4096
64
64
32
2
8
128
8
256
256
128
64
8
8
16
2
16
32
8
256
16
1024
8
128
64
32
16
4
hexyl acetate
phenylacetaldehyde
3-methylbutyl butanoate
ethyl 2-hydroxyhexanoate
1,1,3-triethoxypropane
2,5-dimethyl-3-ethylpyrazine
1,1-diethoxyhexane
propyl hexanoate
fruity
fruity, jasmine
vegetal, fruity
roasted, baked
floral
fruity
fruity
4
64
128
64
16
64
256
16
4
16
4
16
64
2
2
32
1
1024
ND
32
16
2
ethyl heptanoate
ethyl cyclohexanecarboxylate
2-methylpropyl hexanoate
3-methylbutyl pentanoate
pentyl 3-methylbutanoate
2,3,5-trimethyl-6-ethylpyrazine
furfuryl butanoate
ethyl benzoate
diethyl butanedioate
unknown
fruity
floral, fruity
fruity, floral
fruity
baked, nut
fruity, sweet
floral
fruity, wine
nut, roasted
fruity
floral, fruity
fruity
sweet, coconut
rosy, honey
rosy, honey
fruity
fruity
fruity
butyl hexanoate
hexyl butanoate
ethyl octanoate
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
MS, aroma, RIS
MS, aroma, RI
MS, aroma, RIL
MS, aroma, RI
MS, aroma, RI
MS, aroma, RI
γ
-octalactone
ethyl phenylacetate
2-phenylethyl acetate
pentyl hexanoate
ethyl nonanoate
4
1
1,1-diethoxy-2-phenylethane
ethyl 3-phenylpropanoate
3,5-dimethyl-2-pentylpyrazine
furfuryl hexanoate
hexyl hexanoate
ethyl decanoate
fruity
128
64
4
256
16
4
4
16
2
64
2
baked, roasted
caramel, fruity
apple, peach
green, fruity
roasted, nut
fruity, pineapple
goaty, smoky
fruity
16
128
32
32
8
4
8
32
8
unknown
3-methylbutyl octanoate
ethyl 2-hydroxy-3-phenylpropanoate
heptyl hexanoate
unknown
ethyl dodecanoate
MS, aroma, RIS
MS, aroma, RIL
MS, aroma, RIS
baked, roasted
fruity
1
2
MS, aroma, RI
a WLY, Wuliangye liquor; JNC, Jiannanchun liquor; and ND, not detected by GC O. b MS, compounds were identified by MS spectra; aroma, compounds were identified
−
by the aroma descriptors; RI, compounds were identified by a comparison to the pure standard; RIL, compounds were identified by a comparison with the retention index
from the literatures; and RIS, compounds were identified by a comparison with the retention index from the synthesized compounds.
Jiannanchun liquors was also higher than Yanghe Daqu (5).
Because pyrazines are mostly formed through the Maillard
reaction between saccharides and amino residues (22, 23), a
high temperature would benefit the Maillard reaction, and
produce more pyrazines. On the basis of the FD values,
Wuliangye liquor could have more pyrazines with higher
concentrations than Jiannanchun liquor.
Similar to pyrazines, a high temperature also facilitates furan
formation through nonenzymic browning of sugars (24). Several
furan derivatives were identified in this study. Among these,

Aroma Compounds of Chinese Liquors
J. Agric. Food Chem., Vol. 54, No. 7, 2006 2703
LITERATURE CITED
2-furancarboxaldehyde (furfural), with its sweet and almond-
like aroma, could be very important because of a high FD value
(FD g 128). 2-Acetylfuran (sweet, caramel odor), 2-acetyl-5-
methylfuran (green, roasted odor), and 2-furanmethanol (burnt
sugar odor) were also important based on their FD values (FD
g 16). 5-Methyl-2-furfural (green, roasted odor) had a low FD
value (FD g 8). 2-Furancarboxylic acid was found in the acidic/
water-soluble fraction of both liquors, and although it could not
be detected by GC-O, its ester form, ethyl 2-furancarboxylate,
was detected by GC-O in both liquors on the DB-wax column
(FD g 8). Ethyl 2-furancarboxylate imparts a balsamic note
and has been identified in Calvados (8) and tequila (25).
2-Furanmethanol fatty acid esters were also identified in these
two liquors including furfuryl acetate (FD g 16), furfuryl
butanoate (FD g 16), and furfuryl hexanoate (FD g 8), all
contributing to sweet, fruity, and caramel aromas. Furfuryl
hexanoate has been found in Yanghe Daqu liquors (7). Similar
to pyrazines, it seems that Wuliangye liquor had a much higher
concentration of furan derivatives than Jiannanchun liquor.
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Among the lactones identified in this study, γ-octalactone
had the highest FD value (FD g 16), while γ-nonalactone had
a lower FD value (FD e 8). γ-Decalactone and γ-dodecalactone
were identified by GC-MS, but they had very weak or no aroma
in this study. γ-Lactones contribute to sweet, nut, coconut, and
fruity odors, and these lactones have also been detected in
Calvados and Cognac (8).
Sulfur-containing compounds often have very low sensory
thresholds (26), and it is usually difficult to detect and identify
them. Dimethyl trisulfide, dimethyl disulfide, and dimethyl
sulfide (tentatively identified) could contribute to the aroma
based on their moderate FD values (FD g 16). They contributed
to cooked onion, sulfur, fresh cabbage, and rotten cabbage odors.
These three sulfur compounds have been found by GC-O in
Yanghe Daqu liquors (6, 7). The presence of these sulfur
compounds is from the degradation of sulfur-containing amino
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Several phenolic compounds were identified on the DB-wax
column (Table 2). Among them, phenol could be very important
(FD g 128), providing phenolic and medicinal aromas. 4-Eth-
ylguaiacol (4-ethyl-2-methoxyphenol) and 4-methylphenol had
moderate FD values (FD g 16). 4-Ethylguaiacol contributed to
clove and spicy odors, while 4-methylphenol gave animal and
medical aromas. 4-Ethylphenol had a very low FD value (FD
e 8) and gave a smoky odor. Phenolic compounds have been
detected in Chinese liquor (6, 7), Calvados and Cognac (8),
and tequila (25). Phenolic compounds belong to the secondary
plant constituents and can be formed from lignin degradation
in Chinese liquors because high levels of rice hull or sorghum
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In summary, fractionation is an effective technique to simplify
composition for the identification of aroma compounds in a
complex sample. Alcohols and acids can be separated into the
acidic/water-soluble fraction to minimize their interference with
other constituents during GC-O and GC-MS analysis. Simi-
larly, the separation of alkylpyrazines to the basic fraction makes
for easier identification. AEDA results showed that esters could
be very important in Chinese liquors, especially ethyl esters.
Pyrazines and furans were identified in Wuliangye and Jian-
nanchun liquors, and these two classes are probably responsible
for the nutty, toasty, and soy-sauce-like aroma perceived in these
liquors. Both GC-O and AEDA are useful techniques to
identify the most important compounds that contribute to aroma,
although quantitative analysis is often needed for a more direct
comparison.

2704 J. Agric. Food Chem., Vol. 54, No. 7, 2006
Fan and Qian
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Received for review October 24, 2005. Revised manuscript received
February 2, 2006. Accepted February 5, 2006.
JF052635T