Hydrophilic Carboxylic Acids and Iridoid Glycosides in the
Juice of American and European Cranberries (
Vaccinium
macrocarpon
and V. oxycoccos), Lingonberries (V. vitis-idaea),
and Blueberries (
V. myrtillus)
H
EIDI D. JENSEN,†,‡ KAREN A. KROGFELT,‡ CLAUS CORNETT,§
S. H
ONOREÄ HANSEN,§ AND S. BRØGGER CHRISTENSEN*,†
Department of Medicinal Chemistry, Royal Danish School of Pharmacy, Copenhagen, Denmark,
Department of Gastro-Intestinal Infections, Statens Serum Institut, Copenhagen, Denmark, and
Department of Analytical and Pharmaceutical Chemistry, Royal Danish School of Pharmacy,
Copenhagen, Denmark
Analysis of the hydrophilic fraction of cranberry juice by reversed-phase HPLC using an Aqua LUNA
column with diode array or MS detection revealed the presence of quinic acid, malic acid, shikimic
acid, and citric acid. For the first time, two iridoid glucosides were found in the juice. The two iridoid
glucosides were shown to be monotropein and 6,7-dihydromonotropein by MS and NMR spectroscopy.
A fast reversed-phase HPLC method for quantification of the hydrophilic carboxylic acids was
developed and used for analyses of cranberry, lingonberry, and blueberry juices. The level of
hydrophilic carboxylic acids in cranberries was 2.67
-3.57% (w/v), in lingonberries 2.27-3.05%, and
in blueberries 0.35
-0.75%. In lingonberries both iridoid glucosides were present, whereas only
monotropein was present in blueberries.
KEYWORDS: HPLC; American cranberry (Vaccinium macrocarpon); European cranberry (Vaccinium
oxycoccus); lingonberry (Vaccinium vitis-idaea); blueberry (Vaccinium myrtillus); quinic acid; malic acid;
shikimic acid; citric acid; iridoid glucosides; monotropein; 6,7-dihydromonotropein
INTRODUCTION
Approximately 25% of women will have at least one urinary
tract infection in their lifetime caused by infection by bacteria,
especially
Escherichia coli (1). Many of these will have several
infections (
2). Whereas some clinical trials have shown that
cranberry juice prevents urinary tract infections in women (
3,
4
), other reports still question the beneficial effects (5, 6). In
vitro experiments have revealed that cranberry fruit juice
(
Vaccinium macrocarpon Aiton, family Ericaceae) possesses
an antimicrobial (
7) and an antiadhesive effect (8) on E. coli.
Since lack of sensitivity toward common antibiotics increasingly
complicates treatment of infections, antiadhesion therapy might
become an important alternative to the presently used methods.
Some previous studies have related the antiadhesion effects to
the presence of proanthocyanidins (
9), fructose, and macromolecules
(
8) in the juice, whereas other studies have correlated
the effect to the acidificaton of urine caused by the organic acids
(
5). Despite these hypotheses, only very limited attention has
been paid to the hydrophilic fraction, maybe because of
difficulties in performing such analyses. Reversed-phase column
packing materials applicable for separation of very
hydrophilic compounds have enabled development of the fast
method for analyses of the hydrophilic carboxylic acids presented
in this paper. Previous studies have only elucidated the
structures of the very polar compounds by their retention times
(
10, 11). The present study was undertaken in order to confirm
the structures of the polar acids present in cranberry juice and
to identify possible unknown constituents which might contribute
to the biological activity and to the taste of the juice.
Techniques such as HPLC-MS and HPLC-NMR have facilitated
unequivocal structural determination of the detected
compounds. For comparison the study also includes analyses
of the juices of European cranberries (
Vaccinium oxycoccos L.),
lingonberries (
Vaccinium Vitis-idaea L.), and blueberries (Vaccinium
myrtillus
L.).
EXPERIMENTAL PROCEDURES
Chemicals and Materials.
All solvents and reagents were of
analytical grade. Trifluoroacetic acid 99% was from Aldrich, and
acetonitrile and methanol were HPLC-grade. Water was deionized and
filtered through a 0.45
ím poresize Millipore filter (Millipore, Ireland)
before use. Authentic (
-)-quinic acid (1â,3R,4R,5â-tetrahydroxycy-
* Corresponding author. Address: Department of Medicinal Chemistry,
Royal Danish School of Pharmacy, Universitetsparken 2, DK-2100 Copenhagen
Ø, Denmark. Tel.:
+45 35306253. Fax: +45 3530 6040. E-mail:
sbc@dfh.dk.
†
Department of Medicinal Chemistry, Royal Danish School of Pharmacy.
‡
Department of Gastro-Intestinal Infections, Statens Serum Institut.
§
Department of Analytical and Pharmaceutical Chemistry, Royal Danish
School of Pharmacy.
J. Agric. Food Chem.
2002, 50, 6871-6874 6871
10.1021/jf0205110 CCC: $22.00 © 2002 American Chemical Society
Published on Web 10/11/2002
clohexane carboxylic acid) (Aldrich), l-(
-)-malic acid (S-hydroxysuccinic
acid) (Fluka), (
-)-shikimic acid (3R,4S,5R)-3,4,5-trihydroxycyclohexene-
1-carboxylic acid) (Aldrich), and citric acid (2-hydroxy-
1,2,3-propanetricarboxylic acid) (Riedel-de Hae¨n) were used as standards.
Pectinex Ultra SP-L (Novozymes) was used as pectinase. Solidphase
extraction catridges were 500 mg, 3 mL C-18 BondElut (Varian).
RP-18 LiChroprep, 40
-63 ím silylated silica gel (Merck), was used
for preparative removal of the less hydrophilic constituents of the juices.
NMR Apparatus.
The NMR spectra were recorded on a Gemini
2000 spectrometer at 300 and 75 MHz for
1H- and 13C NMR spectra,
respectively. The spectra were recorded in deuterium oxide using
acetonitrile (2.06 ppm) as an internal standard.
HRMS.
The high-resolution mass spectra were recorded on a Q-Tof1
(Micromass) with a 3.6 GHz TDC. Negative ions obtained after electron
spray were detected using a mixture of corn syrup and maltose as
references.
HPLC Apparatus.
The quantitative analyses were performed using
a Water Associates pump Model 510, a Rheodyne 7125 injector valve
with a 20
íL injection loop, and a Shimadzu SPD-10A UV-vis
Detector. Data acquisition and manipulation were performed on a
C-R8A Chromatopac, Shimadzu, Japan. Separation was accomplished
at room temperature on a 150
4.6 mm i.d., 5 ím Aqua LUNA C-18
column (Phenomenex). The preparative isolation of the compounds was
performed on a 150
21.2 mm i.d., 5 ím Aqua LUNA C-18 column
(Phenomenex) and with the same apparatus as for the quantitative
analysis except for a 2 mL loop and a preparative UV detector cell.
HPLC-MS was performed on an 1100 HPLC system equipped with a
diode array and a mass spectrometric detectors (Agilent Technologies,
USA), and HPLC NMR was performed on a Bruker spectrometer
working at 400 MHz using a flow cell.
Berry Samples.
The origins of the berries used in this study are
given in
Table 1. Samples 1, 2, 3, 6, 8, and 9 were purchased in a
grocery store. Sample 4 was a generous gift from Rynkeby A/S,
Denmark. One of the authors collected sample 5 in the fall 2000 in
Bøllemose moor, north of Copenhagen, Denmark, and sample 7 in the
fall 2001 in the Alps near Lausanne, Switzerland. The identities of
samples 5 and 7 were confirmed by Dr. Per Mølgaard, The Royal
Danish School of Pharmacy. All the berries were frozen immediately
after collection or purchase and stored at
-20 °C.
Sample Preparation.
Frozen berries were thawed at 5 °C overnight,
and 1 kg of the berries blended with 0.7 L of deionized water for five
minutes in a Waring Commercial Blendor. The pulp was centrifuged
at 420
g for 15 min in a SIGMA 3 centrifuge. The supernatant was
filtered to give 1 L of juice.
Pectinase Treatment.
The large amount of pectin in blueberries
(samples 8 and 9) necessitated treatment with a pectinase (Pectinex
Ultra) before centrifugation. The pectinase (0.1% v/v) was added to
the pulp, and the pulp was stirred for 60 min at 35
°C. Further sample
preparation was performed as described above.
Quantitative Analysis of the Hydrophilic Carboxylic Acids.
A
BondElut cartridge was activated by washing with 10 mL of acetonitrile
-
water (1:1) and dried by sucking 10 mL of air through the
cartridge. Two portions of 5 mL of the fresh juice were sucked through
the cartridge. The first 5 mL of eluate was discarded and the following
5 mL collected. After filtration through 0.45
ím poresize Whatman
filter, 200
íL of the filtrate was diluted to 5000 íL, and 100 íL of the
diluted sample was injected into the HPLC system using water
containing 0.06% of trifluoroacetic acid as the mobile phase, flow 1.0
mL/min, detection 214 nm. Quantification was based on linear
regression analysis of the ratio between the peak areas in the
chromatograms of the juice and the peak areas of the standards.
Linearity.
Standard solutions of authentic samples of quinic acid,
malic acid, shikimic acid, and citric acid were prepared in mobile phase.
The standard curves were based on five or six concentrations each
analyzed in triplicate. The final concentrations of the acids in the
solutions were as follows: quinic acid, 0.125, 0.167, 0.215, 0.301,
0.378, and 0.501 mg/mL; malic acid, 0.064, 0.128, 0.171, 0.205, and
0.256 mg/mL; shikimic acid, 2.35, 3.10, 4.70, 6.27, and 7.50
íg/mL;
and citric acid, 0.124, 0.165, 0.212, 0.247, 0.297, 0.371, and 0.495
mg/mL. Quality control samples were analyzed before an analysis. Both
standard solutions and samples were stored at 5
°C. Good linearity for
quinic acid and citric acid was achieved between 0.124 and 0.495 mg/
mL with correlation coefficients of 0.9992 and 0.9818, respectively,
for malic acid between 0.064 and 0.256 mg/mL with a correlation
coefficient of 0.9982, and for shikimic acid between 2.4 and 9.4
íg/
mL with a correlation coefficient of 0.9991.
Recovery.
The extraction efficiency (recovery) was determined by
adding authentic standards to the juice and comparing the found
amounts of acids with the amounts in unspiked juice. The recovery
data for quinic acid, malic acid, shikimic acid, and citric acid were
103%, 91%, 97%, and 95%, respectively, with coefficients of variation
between 6 and 8.
Stability Studies.
No changes in the contents of the carboxylic acids
could be observed after freezing and thawing of the juice, as revealed
by comparison of the chromatograms of a freshly prepared juice and a
juice which had been frozen at
-20 °C.
Preparative Isolation of Iridoid Glycosides and Carboxylic Acids.
Frozen berries (1020 g) were thawed at 5
°C, and water (700 mL) was
added. The mixture was blended and the pulp centrifuged at 420
g for
15 min. A 200 mL sample of the supernatant was applicated with a
FMI LAB pump model QD (Fluid Metering, Inc. USA) on 20 g of
RP-18 silylated silica gel in a 300
20 mm column activated with
methanol and washed with deionized water. The column was eluted
with 300 mL water, and the eluates were pooled and evaporated in
vacuo at 40
°C to the volume of the applied juice (200 mL). For the
preparative HPLC, the compounds eluted with a flow of 10 mL/min
were collected and the fractions lyophilized. Detection and mobile phase
were as in the quantitative analysis of the compounds. The
1H and 13C
NMR spectra of quinic acid, malic acid, shikimic acid, citric acid, and
monotropein were superimposable to those of authentic samples and
the expected peaks for (M-1) were found in all the mass spectra.
LC-MS Analysis.
An isocratic elution mode with 0.1% (v/v) aqueous
formic acid as an eluent was used at a flow rate of 0.5 mL/min. The
same HPLC column as for the UV detection was used, and the injection
volume was 50
íL. The mass spectrometric detection was performed
using API-ES in the negative mode.
Molecular Analysis Data.
Quinic acid, shikimic acid, and citric
acid were obtained as a colorless solid. Monotropein (16 mg) was
Table 1.
Sample Number, Origin, and Concentration of Four Organic Acids in the Hydrophilic Fractions of Cranberry, Lingonberry, and Blueberry
Juices (% W/V
± RSD %)
sample
a (4) species origin quinic acid (1) malic acid (2) shikimic acid (3) citric acid
1
V. macrocarpon USAa 1.14 ± 0.01 0.82 ± 0.01 0.041 ± 0.0003 1.20 ± 0.01
2
V. macrocarpon USAa 1.180 ± 0.003 0.80 ± 0.01 0.0293 ± 0.0002 1.14 ± 0.01
3
V. macrocarpon Holland
(Thershellingen)
0.892
± 0.003 0.626 ± 0.004 0.059 ± 0.001 1.10 ± 0.01
4
V. macrocarpon Czech Republic 0.605 ± 0.001 1.052 ± 0.002 0.01092± 0.00004 1.863 ± 0.001
5
V. oxycoccos Denmark 0.55 ± 0.01 0.95 ± 0.01 0.00670 ± 0.00004 1.63± 0.01
6
V. vitis-idaea Sweden 0.88 ± 0.03 tr.b 0.0040 ± 0.0002 1.391 ± 0.003
7
V. vitis-idaea Switzerland 1.530 ± 0.001 tr. 1.52 ± 0.01
8
V. myrtillus Germany tr. tr. tr. 0.75 ± 0.01
9
V. myrtillus Argentina tr. tr. tr. 0.350 ± 0.003
a
The two samples were obtained from different suppliers. b tr., trace amounts.
6872
J. Agric. Food Chem., Vol. 50, No. 23, 2002 Jensen et al.
isolated from 200 mL juice as an amorphous colorless solid, corresponding
to 0.01% w/v in single strength cranberry juice. [
R]25
D
)
-
132.1° (c 0.165, H2O). ìmax (measured with a diode array detector,
which prevented measurement of
) (H2O) 239 nm. 1H NMR (D2O,
300 MHz)
ä 7.47 (1H, d, J3,5 ) 1.0 Hz, H-3), 6.29 (1H, dd, J5,6 ) 2.7
Hz,
J6,7 ) 6.0 Hz, H-6), 5.73 (1H, dd, J5,7 ) 1.5, J6,7 ) 6.0 Hz, H-7),
5.67 (1H, d,
J1,9 ) 1.8 Hz, H-1), 4.82 (1H, d, J1¢,2¢ ) 8.1 Hz, H-1¢),
3.94 (1H, dd,
J6¢a,6¢b ) 12.3, J6¢,5¢ ) 2.4 Hz, H-6¢a), 3.75 (1H, dd, J6¢b,6¢a
)
12.3, J6¢b,5¢ ) 5.7 Hz H-6¢b), 3.72 (1H, d, J10a,10b ) 11.4 Hz, H-10a),
3.66 (1H, d,
J10b,10a ) 11.4, H-10b), 3.52 (1H, ddd, J4¢,5¢ ) 9.9 Hz,
J
6a¢,5¢ ) 2.4 Hz, J6¢b,5¢ ) 5.7 Hz, H-5¢), 3.57-3.60 (1H, m, H-5), 3.51
(1H, t,
J2¢,3¢ ) 9.3 Hz, J3¢,4¢ ) 9.0 Hz, H-3’), 3.40 (1H, t, J3¢,4¢ ) 9.0 Hz,
J
4¢,5¢ ) 9.9 Hz, H-4’), 3.28 (1H, dd, J1¢,2¢ ) 8.1 Hz, J2¢,3¢ ) 9.3 Hz,
H-2’), 2.74 (1H, dd,
J1,9 ) 1.8 Hz, J5,9 ) 8.7 Hz, H-9).13C NMR (D2O,
75.5 MHz)
ä 95.38 (C-1), 153.04 (C-3), 111.53 (C-4), 37.73 (C-5),
133.32 (C-6), 138.70 (C-7), 85.81 (C-8), 44.73 (C-9), 67.34 (C-10),
172.33 (C-11), 99.38 (C-1
¢), 73.61 (C-2¢) 76.60 (C-3¢), 70.51 (C-4¢),
77.29 (C-5
¢), 61.55 (C-6¢). MS API-ES negative [M - 1]- m/z ) 389.0.
6,7-Dihydromonotropein (22 mg) was isolated from 200 mL juice as
an amorphous colorless solid, corresponding to 0.01% w/v in single
strength cranberry juice. [
R]25
D
) -204.6° (c 0.100, H2O). ìmax
(measured with a diode array detector, which prevented measurement
of
) (H2O) 239 nm. 1H NMR (D2O, 300 MHz) ä 7.55 (1H, br s, H-3),
5.54 (1H, d,
J1,9 ) 3.6 Hz, H-1), 4.82 (1H, d, J1¢,2¢ ) 8.4 Hz, H-1¢),
3.92 (1H, br d,
J6¢a,6¢b ) 12.3, H-6¢b), 3.74 (1H, dd, J6¢b,6¢a ) 12.3, J6¢b,5¢
)
5.7 Hz H-6’b), 3.62 (1H, d, J10a,10b ) 17.5 Hz, H-10a), 3.56 (1H, d,
J
10b,10a ) 17.5, H-10b), 3.54-3.48 (1H, m, H-5¢), 3.51 (1H, t, J3¢,4¢ )
9.1 Hz, H-3
¢), 3.41 (1H, t, J3¢,4¢ ) J4¢,5¢ ) 9.1 Hz, H-4¢), (1H, d, J1¢,2¢ )
8.1 Hz, H-1
¢), 3.29 (1H, t, J2¢,3¢ ) 9.1 Hz, J1¢,2¢ ) 8.1 Hz, H-2¢), 2.95
(1H, m, H-5), 2.34 (1H, dd,
J1,9 ) 3.6 Hz, J5,9 ) 9.3 Hz, H-9), 2,08-
1.63 (4H, m, 2H-6, 2H-7).
13C NMR (D2O, 75.5 MHz) ä 95.6 (C-1),
153.4 (C-3),112.4 (C-4), 32.5 (C-5), 30.1 (C-6), 35.7 (C-7), 82.8
(C-8), 45.7 (C-9), 68.2 (C-10), 172.0 (C-11), 99.4 (C-1
¢), 73.3 (C-2¢),
76.3 (C-3
¢), 70.1 (C-4¢), 77.0 (C-5¢), 61.3 (C-6¢). MS API-ES negative
[M
- 1]- m/z ) 391.1 and exact mass ES negative [M - 1]- m/z )
391.1228, cald for C
16H23O11 391.1240.
RESULTS AND DISCUSSION
Chromatographic Data.
Isocratic elution using aqueous
trifluoroacetic acid (0.06%) as an eluent afforded good separation
of a series of carboxylic acids in the most hydrophilic
fraction of the juice (
Figure 1).
Structural Elucidation.
The carboxylic acids, quinic acid
(peak 2), malic acid (peak 3), shikimic acid (peak 4), and citric
acid (peak 5), had previously been stated to be present in the
juice (
10, 11), but no verification of the structures had been
given. HPLC-NMR and HPLC-MS was used in this study to
establish the structures. The above four carboxylic acids were
isolated by preparative HPLC and comparison of their
1H NMR
spectra with those of authentic samples unequivocally established
their structures. In addition to these four carboxylic acids,
two additional peaks at 10.9 and 16.3 min were observed in
the chromatogram. The characteristic signal at 7.5 ppm and the
presence of a glucopyranosyl moiety as revealed by the signal
pattern in the HPLC-
1H NMR spectrum indicated that both of
these compounds were iridoid glucosides. After isolation by
preparative HPLC, the
1H NMR and 13C NMR spectra of the
more hydrophilic iridoid glucoside were found to be superimposable
to the spectra of monotropein (
12). The spectra of the
less polar iridoid glucoside were very similar to those of
monotropein except for the missing signals originating in the
nuclei at the 6,7 double bond. Instead, a complex pattern was
found at 2.08
-1.63 ppm in the 1H NMR spectrum and two
signals at 30.1 and 35.7 ppm in the
13C NMR spectrum. MS
revealed that the molecular weight of the compound was two
units higher than that of monotropein. Consequently the
compound was concluded to be 6,7-dihydromonotropein. The
methyl ester of 6,7-dihydromonotropein (splendoside) has
previously been isolated from
Fouquieria splendens (13), but
this is the first report of natural occurrence of the free acid.
The structures of the compounds isolated from the cranberry
juice are given in
Figure 2. Monotropein is proven to be present
in all the analyzed
Vaccinium species by LC-MS. 6,7-Dihydromonotropein
was proven to be present in cranberries and
lingonberries by LC-MS, but absent in blueberries. A compound
with the
Rf values of monotropein on TLC and PC has
previously been demonstrated in the green parts of
V. oxycoccos
L. (European cranberries), in the stem and fruit of
V. myrtillus
L. (blueberry), and in the leaves and stem of
V. Vitis-ideae L.
(lingonberry) (
14).
Quantification of Quinic, Malic, Shikimic, and Citric Acid.
The amounts of the four carboxylic acids (
1-4) in cranberry,
Figure 1.
Chromatogram of the hydrophilic fraction of cranberry juice
(
Vaccinium macrocarpon). Peak at 2.4 min quinic acid (1), 2.9 min malic
acid (
2), 3.2 min shikimic acid (3), 5.0 min citric acid (4), 10.9 min
monotropein (
5), and 16.3 min 6,7-dihydromonotropein (6). Detection at
240 nm.
Figure 2.
Structures of the isolated acids and iridoid glucosides,
(
-)-quinic acid (1), (-)-shikimic acid (2), L-malic acid (3), citric acid (4),
monotropein (
5), and 6,7-dihydromonotropein (6).
Hydrophilic Acids in Cranberries
J. Agric. Food Chem., Vol. 50, No. 23, 2002 6873
lingonberry, and blueberry juices are given in
Table 1, which
reveals that no major differences in the concentrations of the
acids are found in the different samples of juices. The results
are in agreement with previous finding in juice from
V.
macrocarpon
(10, 11, 14). The analyses were extended to a
series of juices prepared from berries of other
Vaccinium species
such as European cranberries, lingonberries and blueberries
(
Table 1). Preliminary studies revealed that the two iridoid
glucosides do not contribute to the antiadhesive effect of the
juice, but the presence of acids and iridoid glucosides contributes
to the taste of the products. Consequently analyses of the
contents of such compounds are important for making products
with similar tastes. The new analytical protocol facilitates
quantification of the carboxylic acids and has revealed the
presence of iridoid glucosides in cranberry, lingonberry, and
blueberry juices.
ACKNOWLEDGMENT
We thank Carina Jensen, Rynkeby A/S, Denmark for European
cranberries (
V. oxycoccus), Eva Langhoff, NovoZymes for
Pectinase, S. Rosendal Jensen, The Technical University of
Denmark, for a sample of monotropein, students Inge Lise,
Finne´ Nielsen, and Christina Fischer for helping in the
preliminary studies, and Bruker for lending us a flow probe.
Gustav Bojesen (The University of Copenhagen) recorded the
HRMS spectra. The Danish Medical Research Council is
thanked for financial support (grant 9800 989) to K.A.K.
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Received for review May 1, 2002. Revised manuscript received August
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JF0205110
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