Identification of dihydrogalangal acetate in galangal [Alpinia galangal (L.) Swartz] extracts

Article abstract of DOI:10.1021/jf803387z

Dihydrogalangal acetate has been discovered for the first time in galangal roots [Alpinia galangal (L.) Swartz]. The compound has a taste sensation similar to galangal acetatesthe pungent principle of galangalsbut it is more stable in food and beverage applications. Therefore, dihydrogalangal acetate provides many advantages as a flavor ingredient for alcohol enhancement and taste modification. Dihydrogalangal acetate is present in approximately 0.0005% of fresh roots and in about 0.004% of dried roots. (S)-Dihydrogalangal acetate is found as the main optical isomer in galangal roots (98%), while its minor (R)-isomer is less abundant (2%). Enantiomers of galangal acetate and dihydrogalangal acetate were separated and evaluated by sensory analysis. (R)-Galangal acetate has a very faint woody and sweet aroma, and (R)-dihydrogalangal acetate is almost odorless, while (S)-galangal acetate has strong and (S)-dihydrogalangal acetate has weak pungent and woody notes. Although the aroma characters of these optical isomers are different, taste sensations were found to have no significant differences among galangal acetate, dihydrogalangal acetate, and their optical isomers.

Full text of DOI:10.1021/jf803387z

3286 J. Agric. Food Chem. 2009, 57, 3286–3290
Identification of Dihydrogalangal Acetate in Galangal
[Alpinia galangal (L.) Swartz] Extracts
XIAOGEN YANG,* MARTIN ROHR, AND JASON JORDAN
Givaudan Flavors Corporation, Science and Technology, 1199 Edison Drive, Cincinnati, Ohio 45216
Dihydrogalangal acetate has been discovered for the first time in galangal roots [Alpinia galangal
(L.) Swartz]. The compound has a taste sensation similar to galangal acetatesthe pungent principle
of galangalsbut it is more stable in food and beverage applications. Therefore, dihydrogalangal acetate
provides many advantages as a flavor ingredient for alcohol enhancement and taste modification.
Dihydrogalangal acetate is present in approximately 0.0005% of fresh roots and in about 0.004% of
dried roots. (S)-Dihydrogalangal acetate is found as the main optical isomer in galangal roots (98%),
while its minor (R)-isomer is less abundant (2%). Enantiomers of galangal acetate and dihydrogalangal
acetate were separated and evaluated by sensory analysis. (R)-Galangal acetate has a very faint
woody and sweet aroma, and (R)-dihydrogalangal acetate is almost odorless, while (S)-galangal
acetate has strong and (S)-dihydrogalangal acetate has weak pungent and woody notes. Although
the aroma characters of these optical isomers are different, taste sensations were found to have no
significant differences among galangal acetate, dihydrogalangal acetate, and their optical isomers.
KEYWORDS: Dihydrogalangal acetate; galangal acetate; galangal; Alpinia galanga; Alpinia galangal (L.)
Swartz; 1′-acetoxydihydrochavicol acetate; 1′-acetoxychavicol acetate
INTRODUCTION
the gas chromatography (GC) chromatogram. This trace com-
pound has been isolated and identified as dihydrogalangal acetate
by chromatographic techniques and spectroscopic methods. The
discovery will enable development of this compound as a natural
ingredient for food flavors. In this paper, we report the discovery
and the characterization of its optical isomers.
Galangal [Alpinia galangal (L.) Swartz] is a popular spice in
Thailand and eastern Asia. Galangal acetate (1′-acetoxychavicol
acetate, Figure 1) has been identified as the pungent principle of
galangal (1, 2). Because of its mild and clean pungent taste, galangal
acetate has found many applications in food, beverages, and
personal care products as an alcohol enhancer, cooling enhancer,
flavor modifier, and pungent impact (3). However, because of the
1,5-oxadiene system, galangal acetate easily undergoes hydrolysis
and isomerization in aqueous media and loses its desirable taste
sensations. The instability limits the applications of galangal acetate
in food and beverages. Studies on the structure and taste relationship
led to the discovery of a series of stable galangal acetate derivatives
(2). It was concluded that the double bond of the vinyl group, which
causes the instability in food applications, is not necessary for the
pungency of galangal acetate. Therefore, a straightforward approach
to stabilize galangal acetate is to hydrogenate the double bond,
yielding dihydrogalangal acetate (1′-acetoxydihydrochavicol ac-
etate, Figure 1). The stability of dihydrogalangal acetate is excellent
in food and beverage applications, while the clean pungency of
galangal acetate is preserved. Recently, dihydrogalangal acetate
has been granted GRAS (generally regarded as safe) status (FEMA
#4555) as a flavor ingredient.
MATERIALS AND METHODS
Materials. Fresh galangal roots were obtained from a local market
in Cincinnati, OH. Dried galangal roots were obtained from Haldin
International (Closter, NJ).Galangal oleoresin was obtained by ethanol
extraction (product of Givaudan Flavors, Cincinnati, OH). All synthetic
reagents were obtained from Aldrich (Milwaukee, WI).
Synthesis of Galangal Acetate (Racemic). A solution of 30.5 g
(0.25 mol) of 4-hydroxybenzaldehyde in 150 mL of tetrahydrofuran
(THF) was added dropwise to a vigorously stirred and chilled solution
of vinylmagnesium bromide (0.8 mol) in THF (800 mL). The mixture
was stirred at room temperature under a nitrogen atmosphere for 5 h
before the reaction was quenched by carefully adding, under ice cooling,
a solution of 100 g of NH4Cl in 350 mL of water. Additional water
was introduced as necessary, and stirring was continued until all solids
had dissolved. Extraction with 1000 mL of methyl tert-butyl ether
(MTBE), washing of the organic layer with water (2 × 1000 mL),
The presence of dihydrogalangal acetate in plants has not
been reported in literature. During our study on galangal extracts,
we found an unknown trace peak close to galangal acetate in
* To whom correspondence should be addressed. Tel: +1-513-948-
4944. Fax: +1-513-948-3582. E-mail: xiaogen.yang@givaudan.com.
Figure 1. Structures of galangal acetate and dihydrogalangal acetate.
10.1021/jf803387z CCC: $40.75  2009 American Chemical Society
Published on Web 03/06/2009

Dihydrogalangal Acetate
J. Agric. Food Chem., Vol. 57, No. 8, 2009 3287
drying over MgSO4, filtration, and solvent removal yielded 35 g of
4-(1-hydroxy-2-propenyl)phenol as a viscous oil, which was acetylated
without further purification.
langal acetate as a colorless liquid (bp 98-100 °C at ca. 0.05 mmHg)
of high chemical purity (99% by GC-FID) and enantiomeric purity
94.8% as determined by chiral HPLC analysis; [R]D20 ) +81.6 ° (c )
5.15, EtOH).
To the stirred and chilled solution of the crude 4-(1-hydroxy-2-
propenyl)phenol in 100 mL of acetic anhydride, 100 mL of anhydrous
pyridine followed by 0.2 g of solid dimethylaminopyridine were added
dropwise. The clear mixture was agitated at room temperature overnight
before excess reagent was removed by repeated evaporation with toluene
(rotary evaporator). A solution of the resulting oily residue in 1000
mL of MTBE was then extracted sequentially with 10% aqueous sodium
metabisulfite (2 × 500 mL) and water (2 × 500 mL). Drying over
MgSO4, filtration, and solvent removal yielded 38 g of crude galangal
acetate as a pale-yellow oil.
Purification by silica gel chromatography (heptane:ethyl acetate in
a ratio of 3:1) and fractional distillation eventually furnished 30 g of
pure [>95% by GC-flame ionization detection (FID)] racemic galangal
acetate as a colorless oil (bp 102-105 °C at 0.05 mmHg) that slowly
solidified with time.
Isolation of Dihydrogalangal Acetate. Natural dihydrogalangal
acetate was isolated from a crude natural galangal extract obtained from
dried galangal roots. The isolation was performed using an Agilent
1100 preparatory HPLC system equipped with a reversed phase column
[Phenomenex Luna C18(2), 21.2 mm i.d., 250 mm length, 5 µm particle
size] and a diode array detector. The mobile phase was composed of
60% methanol and 40% water (isocratic) at a flow rate of 20 mL/min.
For each injection, 300 µL of 10% galangal acetate in methanol was
used. The dihydrogalangal peak was collected in multiple injections.
Methanol of the collected effluent was removed by rotary evaporator,
and the remaining aqueous phase was extracted with hexane. After the
hexane extract was dried under a gentle nitrogen stream, an oily liquid
was obtained. Identification of dihydrogalangal acetate was performed
by NMR, GC-mass spectrometry (MS), and chiral GC analysis.
Synthesis of Dihydrogalangal Acetate (Racemic). To a vigorously
stirred and chilled solution of ethylmagnesium chloride (1 mol) in THF
(750 mL), a solution of 61 g (0.5 mol) of 4-hydroxybenzaldehyde in
750 mL of THF was added dropwise. The mixture was agitated at room
temperature under a nitrogen atmosphere for an additional 2 h before
the reaction was quenched by carefully adding, under ice cooling, a
solution of 130 g of NH4Cl in 750 mL of water. Extraction with 1000
mL of MTBE, washing of the organic layer with water (2 × 1000
mL), drying over MgSO4, filtration, and solvent removal yielded 91 g
of 4-(1-hydroxypropyl)phenol as an orange-colored oil, which was
acetylated without further purification.
To the stirred and chilled solution of the crude 4-(1-hydroxypropyl)-
phenol in 250 mL of acetic anhydride, 300 mL of anhydrous pyridine
followed by 1.0 g of solid dimethylaminopyridine was added dropwise.
The clear mixture was agitated at room temperature overnight before
excess reagent was removed by repeated evaporation with toluene
(rotary evaporator). A solution of the resulting oily residue in 1000
mL of MTBE was then extracted sequentially with 10% aqueous sodium
metabisulfite (2 × 500 mL) and water (2 × 500 mL). Drying over
MgSO4, filtration, and solvent removal yielded 106.5 g of crude
dihydrogalangal acetate as a pale-yellow oil that gradually crystallized
upon standing. Recrystallization from hexane eventually provided 91 g
of racemic dihydrogalangal acetate of high chemical purity (>99% by
GC-FID) with an mp of 41.5-43.5 °C.
Synthesis of (-)-(S)-Dihydrogalangal Acetate. The (S)-configu-
ration of natural galangal acetate isolated from galangal root has
previously been established (4), and reduction of the terminal methylene
group was not expected to affect its chiral center. A solution of 200 g
of galangal root extract (50-60% galangal acetate) in 600 mL of ethanol
was hydrogenated at room temperature under pressure (150-200 psi)
in the presence of Adam’s catalyst (0.4 g) until conversion was complete
(8 h). Filtration and solvent removal provided a crude product that was
purified by silica gel chromatography (heptane:ethyl acetate in a ratio
of 5:1) followed by fractional distillation to yield 102 g of (-)-(S)-
dihydrogalangal acetate as a colorless liquid (bp 95-105 °C at 0.05
mmHg) of high chemical purity (>99% by GC-FID) and enantiomeric
purity 96.9% as determined by chiral high-performance liquid chro-
matography (HPLC) analysis; [R]2D0 ) -89.3° (c ) 5.05, EtOH).
Synthesis of (+)-(R)-Dihydrogalangal Acetate. A stirred suspension
of 20 g of lipase acrylic resin from Candida antarctica in a solution of
20 g of racemic 4-(1-hydroxypropyl)phenol in 500 mL of vinyl acetate
was incubated at room temperature for 20 h. Filtration and removal of
vinyl acetate under reduced pressure (rotary evaporator) provided 28 g
of a crude product mixture, which, upon silica gel chromatography
(heptane:ethyl acetate 3:2), yielded 8 g of (R)-4-(1-acetoxypropyl)phe-
nol.
Chiral Separation/Analysis of Galangal Acetate and Dihydro-
galangal Acetate. Solutions of 1% synthetic racemic mixtures were
prepared in hexane for chiral separation. A Perkin-Elmer Series 200
HPLC system equipped with a diode array detector was used. The
enantiomer separation was achieved using a chiral HPLC column
[Whelk-O 1(S,S), 4.6 mm i.d., 250 mm length, 5 µm particle size, Regis
Technologies, Morton Grove, IL] and an isocratic mobile phase,
composed of 95% hexane and 5% methanol, at a flow rate of 1.5 mL/
min. The enantiomer peaks were collected in multiple injections. The
fractions were concentrated by rotary evaporator to a volume of
approximately 20 mL, dried over MgSO4, filtered, and further dried
under a nitrogen stream. All fractions were obtained as an oily liquid.
The identification and purity of the isolated compounds were determined
by chiral HPLC and GC analysis.
Analytical Methods. Standard Addition Extraction. Pure galangal
acetate was dissolved in the solvent mixture (hexane:acetone in a ratio
of 10:1) to make 2, 5, and 10% stock solutions. Pure dihydrogalangal
acetate was dissolved in the solvent mixture at concentrations of 0.02,
0.05, and 0.1%. Fresh galangal root obtained from a local market was
cut into small pieces (ca. 5 mm). The mixture of hexane and acetone
in a ratio of 10:1 was used as the extraction solvent. A sample (2 g of
ground dry galangal root or 15 g of fresh galangal root) was extracted
with 100 mL of solvent (hexane:acetone in a ratio of 10:1). The standard
addition experiments were composed of four extractions, spiked with
2 mL of one of the galangal acetate and dihydrogalangal acetate stock
solutions or a blank solvent mixture, respectively. The mixture was
blended for 5 min using an Omni mixer homogenizer with a grinding
blade. The solids were filtered and extracted again with 100 mL of the
extraction solvent twice. The extract solution was combined and
concentrated to 20 mL by rotary evaporation and a gentle nitrogen
stream. The extraction recovery for both galangal acetate and dihy-
drogalangal acetate was greater than 95%, estimated by the analysis
of the residue solids.
GC-MS Analysis. Galangal root extracts (1-3 µL) were injected into
a GC-MS system with an Agilent 6890 GC equipped with 5973 mass
selective detector and a DB-5 ms capillary column (30 m length, 0.25
mm i.d., and 0.25 µm film, Agilent, Wilmington, DE). Helium was
used as a carrier gas with a flow rate of 30 cm/s. A split mode (50:1)
was used for the sample introduction. The GC oven temperature was
held at 120 °C for 1 min and then programmed to 180 at 3 °C/min and
held for 4 min at 180 °C. The mass selective detector was operated in
positive electron ionization (EI) mode with a mass scan range from
m/z 30 to 350 at 70 eV. Identification of the target analytes by GC-MS
was performed by comparing the full-scan mass spectra and relative
retention indices with the data of authentic reference samples.
GC-FID Analysis of Enantiomers. Analysis of enantiomers of
galangal acetate and dihydrogalangal acetate was achieved using a chiral
column Cyclosil-B (30 m length, 0.32 mm i.d., and 0.25 µm film,
Agilent). A sample of 0.5 µL (0.05-0.1%) in ethyl acetate was analyzed
in an Agilent 6890N GC equipped with a split injector (split ratio 50:
1) and a FID detector. The GC oven temperature was held at 120 °C
for 2 min and then programmed to 170 at 2 °C/min.
A solution of the above intermediate in 30 mL of acetic anhydride
and 40 mL of anhydrous pyridine was agitated at room temperature
overnight in the presence of a catalytic amount of dimethylaminopy-
ridine (0.1 g). Removal of excess reagent by repeated stripping with
toluene (rotary evaporator) gave 10 g of crude product as an orange-
colored oil. Silica gel chromatography (heptane:ethyl acetate, 4:1)
followed by flash distillation then provided 6 g of (+)-(R)-dihydroga-

3288 J. Agric. Food Chem., Vol. 57, No. 8, 2009
Yang et al.
Figure 2. HPLC chromatogram of galangal root extract. Column, Phenomenex Luna C18(2), 21.2 mm × 250 mm, 5 µm; mobile phase, 60% methanol,
40% water, isocratic; flow rate, 20 mL/min; and detection, λ ) 280 (green), 254 (red), and 210 nm (blue).
NMR Spectroscopy. NMR experiments [1H, 13C, distortionless
enhancement by polarization transfer (DEPT), correlation spectroscopy
(COSY), heteronuclear multiple quantum coherence (HMQC), hetero-
nuclear multiple bond correlation (HMBC)] were performed for
structure elucidation using a Bruker DRX 500 spectrometer equipped
with a 5 mm inverse probe and a 5 mm BBO probe.
Optical Rotation Measurements. Optical rotation measurements were
conducted on a Rudolph Research Analytical Autopol IV system.
Samples were prepared in ethanol solutions, and specific rotation values
were recorded using a sample cell of 50 mm length and 1.0 mL volume.
Sensory Methodology. The objective of this experiment was to
determine whether 15 ppm galangal acetate in 40 proof cordial base
and 15 ppm dihydrogalangal acetate in 40 proof cordial base are
different from one another in strength of alcohol intensity. Twenty
milliliters of each solution was presented in random order to 30 panelists
from the discriminator database. Panelists were asked to select the
solution that was perceived as having a stronger alcohol intensity. The
data were subject to a binomial test to determine significance. The same
methodology was used to evaluate the optical isomers of galangal
acetate and dihydrogalangal acetate.
RESULTS AND DISCUSSION
Isolation and Structure Elucidation. During the investiga-
tion of the pungent principles of galangal, we observed that
there was a trace peak after galangal acetate in the GC
chromatograms of galangal extracts. No match was found for
the mass spectrum of the GC peak from our in-house and
commercial mass spectra libraries. For structure identification,
this unknown compound was isolated from galangal extracts
by semiprep HPLC (Figure 2).
The high-resolution chemical ionization mass spectrum of
the isolated compound showed an ammonium adduct of the
molecule ion at m/z 254.1379, corresponding to the element
+
composition of C13H16O4 ·NH4 (exact mass, 254.1392). As
compared with the formula of galangal acetate, C13H14O4, the
double bond equivalent of the unknown was reduced from 7 to
6.
NMR experiments (1H, 13C, DEPT, COSY, HMQC, and
HMBC) were conducted for chemical structure elucidation.
It is obvious by the comparison of the 13C spectra that the
unknown has some similar patterns as galangal acetate: two
carbonyl groups with chemical shifts at around 170 ppm and
a benzene ring with para-substitution. The large difference
is that the two aliphatic double bond carbons in galangal
acetate are shifted from 117 (dCH2) and 136 ppm (-CHd)
to 9.93 (-CH3) and 29.26 ppm (-CH2-), which strongly
indicates that the unknown compound is a derivative of
galangal acetate with the aliphatic double bond saturated.
Further analysis of the couplings and connectivity of carbon
and proton atoms in the NMR correlation spectra confirmed
that the unknown has the structure of dihydrogalangal acetate
(1′-acetoxydihydrochavicol acetate).
Dihydrogalangal acetate was synthesized, and the mass
spectrum and GC retention indices were measured. The synthetic
dihydrogalangal acetate has the same GC retention index (1651
on a DB-5 column) and mass spectrum as that of the unknown
peak. A standard solution of synthetic dihydrogalangal acetate
was spiked into the galangal extract and then analyzed by GC,
resulting in a higher intensity at the same retention time of the
unknown trace peak.
Analytical Data. Melting Point and Boiling Point. Dihydrogalangal
acetate isolated from galangal root is present in the form of oily liquid.
Synthetic (-)-(S)-dihydrogalangal acetate has a bp 95-105 °C at 0.05
mmHg, and synthetic (+)-(R)-dihydrogalangal acetate has a bp 98-100
°C at ca. 0.05 mmHg. The racemic mixture of dihydrogalangal acetate
can be crystallized in hexane, mp 41.5-43.5 °C.
20
Optical Rotation. Galangal acetate from galangal roots, [R]D
20
-55.337 (c ) 0.550, EtOH); purified (S)-galangal acetate, [R]D
-58.760 (c
) 0.535, EtOH); purified (R)-galangal acetate
[R]D20 +59.699 (c ) 0.540, EtOH); purified (S)-dihydrogalangal acetate,
20
[R]D -93.822 (c ) 0.51, EtOH); and purified (R)-dihydrogalangal
20
acetate, [R]D +92.340 (c ) 0.49, EtOH).
Spectroscopic Data. 1′-Acetoxydihydrochavicol acetate (dihydro-
galangal acetate): 1H NMR (500 MHz, CDCl3, δ ppm): 7.33 (2H, d, J
) 8.6 Hz, H3,5), 7.05 (2H, d, J ) 8.6 Hz, H2,6), 5.66 (1H, t, J ) 6.9
Hz, H1′), 2.28 (3H, s, H8), 2.06 (3H, s, H5′), 1.91 (1H, m, H2′a), 1.79
(1H, m, H2′b), 0.88 (3H, t, J ) 7.4 Hz, H3′). 13C NMR (125.7 MHz,
CDCl3, δ ppm): 170.35 (C, C4′), 169.40 (C, C7), 150.17 (C, C1), 138.11
(C, C4), 127.76 (2CH, C3,5), 121.47 (2CH, C2,6), 76.71 (CH, C1′), 29.26
(CH2,C2′), 21.25 (CH3, C5′), 21.15 (CH3, C8), 9.93 (CH3, C3′). IR (neat):
2972 m, 2939 m, 2880 w, 1734 s, 1609 w, 1510 s, 1458 w, 1434 w,
1371 s, 1239 s, 1196 s, 1167 s, 1086 m, 1043 m, 1017 s, 966 m, 912 s,
852 m, 339 w, 557 w, 544 w cm-1. UV absorption maxima (in hexane):
217 nm (intensive), 261 nm (weak). MS (EI), m/z 39 (11), 43 (100),
65 (9), 77 (16), 95 (10), 107 (16), 123 (71), 133 (16), 134 (18), 135
(11), 165 (25), 194 (17), 236 (2).
The contents of dihydrogalangal acetate in fresh and dried
galangal roots were determined by standard addition extraction

Dihydrogalangal Acetate
J. Agric. Food Chem., Vol. 57, No. 8, 2009 3289
Figure 4. Chiral HPLC chromatograms of galangal acetate. Column,
Whelk-O 1(S,S), 4.6 mm × 250 mm, 5 µm; mobile phase, 95% hexane,
5% methanol, isocratic; flow rate, 1.5 mL/min; and detection, λ ) 210
nm.
Figure 3. Chiral HPLC chromatograms of dihydrogalangal acetate.
Column, Whelk-O 1(S,S), 4.6 mm × 250 mm, 5 µm; mobile phase, 95%
hexane, 5% methanol, isocratic; flow rate, 1.5 mL/min; and detection, λ
) 210 nm.
Sensory Evaluation. It was reported that the optical isomer
of galangal acetate with (R)-configuration has no odor by GC
sniffing (7). The odor characters of the purified optical isomers
(>99%) were evaluated by flavorists at Givaudan. (R)-Dihydroga-
langal acetate is odorless, and the corresponding (S)-isomer has
very weak pungent and woody notes. (R)-Galangal acetate has a
faint woody and sweet odor, while (S)-galangal acetate has a
stronger pungent and woody aroma.
method, although the results vary depending on the quality of
galangal products. The fresh galangal roots contain approxi-
mately 0.0005% dihydrogalangal acetate, and the dried roots
contain about 0.004%.
The taste attributes of galangal acetate and dihydrogalangal
acetate are probably of higher commercial interest as flavor
ingredients. One of the potential applications of these com-
pounds is to enhance alcohol sensation in beverages. Odorless
or low aroma intensity is advantageous for such applications.
Sensory experiments were performed to compare the enhance-
ment potency of galangal acetate vs dihydrogalangal acetate.
A nonsignificant difference of evaluations (14 of 30) selected
galangal acetate as having a stronger alcoholic enhancement
than dihydrogalangal acetate. Therefore, galangal acetate and
dihydrogalangal acetate possess practically the same alcoholic
enhancement effect. The same sensory procedure was conducted
for the two optical isomers of dihydrogalangal acetate. A
nonsignificant majority of evaluations (23 of 40) selected (R)-
dihydrogalangal acetate as having a stronger alcohol intensity
than that of (S)-dihydrogalangal acetate. The dihydrogalangal
acetate isomers were also not significantly different in alcohol
enhancement.
Chiral Separation and Determination. To compare the
sensory properties of the enantioisomers of galangal acetate and
dihydrogalangal acetate, the racemic mixtures underwent chiral
separation. The purified enantiomers have above 99% purity
by chiral GC analysis.
To determine the enantiomer configuration of the naturally
occurring dihydrogalangal acetate, the purified isolate, synthetic
racemic, and synthetic (-)-(S)-dihydrogalangal acetate and (+)-
(R)-dihydrogalangal acetate have been analyzed by chiral GC
and chiral HPLC (Figure 3). The results showed that the natural
dihydrogalangal acetate has mainly the (S)-configuration (98%).
The (R)-configuration of dihydrogalangal acetate was also found
in galangal extracts in a minor amount (2%) by chiral HPLC
anlaysis, confirmed by retention time and UV spectrum. Optical
rotation values of the purified chiral isomers were determined.
Dihydrogalangal acetate isolated from galangal extract has a
negative rotation value.
It is known that the (S)-configuration of galangal acetate
is the major optical isomer presented in galangal roots (4-6).
The (R)-galangal acetate is also present in galangal extract.
The ratio of (S)- and (R)-isomers is about 95:5 by chiral GC
analysis. The two enantiomers of synthetic racemic galangal
acetate and those of synthetic dihydrogalangal acetate were
separated by a chiral HPLC column for sensory evaluation
(Figures 3 and 4).
ACKNOWLEDGMENT
We thank Amanda Warnock, sensory department at Givaudan
Flavors, for the taste evaluation experiments of galangal acetate
and dihydrogalangal acetate and Dr. Xinping Liu for the high-
resolution MS measurements. We appreciate Givaudan officials’
permission to publish this paper.
Stability as Flavor Ingredient. Under hydrolytic conditions,
galangal acetate is not stable. After 1 h of reflux in aqueous
solution, it is completely converted to 1′-hydroxychavicol
acetate, p-acetoxycinnamic alcohol, and p-coumaryl diacetate
(1). Hydrogenation of the double bond of galangal acetate makes
dihydrogalangal acetate more stable. Under the same conditions
described above, a practical 100% recovery of dihydrogalangal
acetate was achieved after the reflux, determined by solvent
extraction and GC-MS analysis. Stability in aqueous solution
and even at elevated temperature provides many advantages as
a flavor ingredient in food and beverage applications.
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