Effect of pH on the maillard reaction of [C]xylose, cystein, and thiamin

Article abstract of DOI:10.1021/jf062874w

The influence of different pH values, ranging from 4.0 to 7.0, on the formation of sulfur volatiles in the Maillard reaction was studied using a model system with [¹³C₅]xylose, cysteine, and thiamin. The use of ¹³C-labeled xylose allowed, by analysis of the mass spectra, volatiles that incorporated xylose carbons in the molecule from other carbon sources to be discerned. For 2-furaldehyde and 2-furfurylthiol, which were favored at low pH, the labeling experiments clearly indicated that xylose was the exclusive carbon source. On the other hand, xylose was virtually not involved in the formation of 3-mercapto-2-butanone, 4,5-dihydro-2-methyl-3- furanthiol, and 5-(2-hydroxyethyl)-4-methylthiazole, which apparently stemmed from thiamin degradation. Both xylose and thiamin seemed to significantly contribute to the formation of 2-methyl-3-furanthiol, 3-mercapto-2-pentanone, and 2-mercapto-3-pentanone, and therefore different formation pathways must exist for each of these molecules. In general, the pH determined strongly which volatiles were formed, and to what extent. However, the relative contribution of xylose to the C-skeleton of a particular compound changed only slightly within the investigated pH range, when both xylose and thiamin were involved in the formation.

Full text of DOI:10.1021/jf062874w

1552 J. Agric. Food Chem. 2007, 55, 1552−1556
13
Effect of pH on the Maillard Reaction of [ C ]Xylose, Cysteine,
5
and Thiamin
CHRISTOPH CERNY* AND MATTHIEU BRIFFOD
Corporate R&D Division, Firmenich SA, P.O. Box 148, CH-1217 Meyrin, Geneva 2, Switzerland
The influence of different pH values, ranging from 4.0 to 7.0, on the formation of sulfur volatiles in
13
5
the Maillard reaction was studied using a model system with [ C ]xylose, cysteine, and thiamin. The
use of 13C-labeled xylose allowed, by analysis of the mass spectra, volatiles that incorporated xylose
carbons in the molecule from other carbon sources to be discerned. For 2-furaldehyde and
2-furfurylthiol, which were favored at low pH, the labeling experiments clearly indicated that xylose
was the exclusive carbon source. On the other hand, xylose was virtually not involved in the formation
of 3-mercapto-2-butanone, 4,5-dihydro-2-methyl-3-furanthiol, and 5-(2-hydroxyethyl)-4-methylthiazole,
which apparently stemmed from thiamin degradation. Both xylose and thiamin seemed to significantly
contribute to the formation of 2-methyl-3-furanthiol, 3-mercapto-2-pentanone, and 2-mercapto-3-
pentanone, and therefore different formation pathways must exist for each of these molecules. In
general, the pH determined strongly which volatiles were formed, and to what extent. However, the
relative contribution of xylose to the C-skeleton of a particular compound changed only slightly within
the investigated pH range, when both xylose and thiamin were involved in the formation.
KEYWORDS: Maillard reaction; xylose; cysteine; thiamin; solid-phase microextraction; mass spectrom-
etry; 13C-labeling; pH
INTRODUCTION
of aroma compounds such as 2-methyl-3-furanthiol. Grosch and
Zeiler-Hilgart (7) found that the formation of 2-methyl-3-
furanthiol from cysteine/ribose drastically increased in model
experiments when thiamin was present. The authors used very
low concentrations of the reactants in order to approach the
conditions in meat. They concluded that thiamin was more
efficient in generating 2-methyl-3-furanthiol than cysteine/ribose
under these conditions. Bolton and co-workers used [ S]cysteine
in a model system comprising, in addition, thiamin, xylose, and
other ingredients, to determine how much sulfur in the 2-methyl-
The Maillard reaction is the main pathway for aroma
generation when meat is cooked. Capitalizing on this fact, the
flavor industry also utilizes the Maillard reaction for the
production of thermally generated flavorings, the so-called
process or reaction flavors (1). Cysteine and thiamin are two
important ingredients for meat-like reaction flavors as they act
as important aroma precursors for meat aroma, in particular for
sulfur-containing odorants (2). Gas chromatography-olfacto-
metry and aroma extract dilution analysis (AEDA) have detected
34
3-furanthiol stemmed from cysteine (8). The reactant concentra-
3-mercapto-2-pentanone, 2-methyl-3-furanthiol, 4,5-dihydro-2-
tions were between 0.2 and 1.1% and simulated process flavor
methyl-3-furanthiol, bis(2-methyl-3-furyl) disulfide, 5-(2-ac-
etoxyethyl)-4-methylthiazole, 5-(2-hydroxyethyl)-4-methylthi-
azole, and others as key odorants in heated thiamin solutions
3
4
conditions. Only a low amount of [ S]-2-methyl-3-furanthiol
8%) was found, indicating that cysteine contributed to only a
small extent to its formation.
(
(3, 4). 2-Methyl-3-furanthiol, its disulfide bis(2-methyl-3-furyl)
13
disulfide, and 3-mercapto-2-pentanone were also found to be
important aroma compounds in thermally treated solutions of
cysteine and ribose (3, 5), together with 2-furfurylthiol, 2-me-
thyltetrahydrothiophen-3-one, 3-mercapto-2-butanone, 5-acetyl-
In a recent study (9), we heated a solution of [ C5]xylose,
cysteine, and thiamin (molar ratio 3:1:1) in phosphate buffer
(pH 5.0) at 145 °C for 20 min. Analysis of the mass spectra
revealed that 2-furaldehyde and 2-furfurylthiol were exclusively
13
13
2,3-dihydro-1,4-thiazine, 2-acetyl-2-thiazoline, 2-thenylthiol, and
C5-labeled, indicating that the carbon atoms stem from [ C5]-
ethyl mercaptan.
xylose. On the other hand, other volatiles such as 3-mercapto-
2-butanone, 4,5-dihydro-2-methyl-3(2H)-furanone, and 4,5-
dihydro-2-methyl-3-furanthiol were found to be virtually
unlabeled, suggesting their origin was thiamin. Finally a
balanced mixture of unlabeled and C5-labeled 2-methyl-3-
furanthiol and 3-mercapto-2-pentanone, respectively, was formed,
indicating that thiamin and xylose were equally important as
carbon source. If cysteine was omitted from the reaction, all
When both thiamin and cysteine/pentose are present as
precursors, for example, when meat is boiled or a process flavor
is prepared (6), the question arises concerning the relative
contribution of each of the precursor systems to the formation
1
3
*
Author to whom correspondence should be addressed (telephone +41
2
2 780 22 16; fax +41 22 780 27 35; e-mail christoph.cerny@firmenich.com).
1
0.1021/jf062874w CCC: $37.00
© 2007 American Chemical Society
Published on Web 01/23/2007

Maillard Reaction of [13
J. Agric. Food Chem., Vol. 55, No. 4, 2007 1553
5
C ]Xylose, Cysteine, and Thiamin and pH Effect
Table 1. Model Reactionsa
A
B
C
D
E
F
G
H
I
pH
4.00
6.25
22.50
5.00
6.25
22.50
6.00
6.25
22.50
7.00
6.25
22.50
4.00
6.25
5.00
6.25
5.50
6.25
6.00
6.25
7.00
6.25
b
cysteine
13
b
[
C
5
]xylose
b
xylose
thiamin hydrochloride
22.50
16.85
22.50
16.85
22.50
16.85
22.50
16.85
22.50
16.85
b
16.85
16.85
16.85
16.85
a
°
C (20 min). b Amount (mg).
Reaction in phosphate buffer (0.5 mol/L; 1.00 mL) at 145
Table 2. Influence of the pH on the Formation of Sulfur Volatiles from Xylose, Cysteine, and Thiamin (GC-TIC Peak Areas
×
106)
no.
compounda
RIb
pH 4.0
pH 5.0
pH 5.5
pH 6.0
pH 7.0
1
2
3
4
5
6
7
8
9
4,5-dihydro-2-methyl-3(2H)-furanone
3-mercapto-2-butanone
2-furaldehyde
800
807
831
871
901
911
915
939
950
17
69
208
415
145
0
431
226
14
0
0
0
525
18
81
158
336
141
0
368
43
12
0
18
83
165
371
147
0
364
41
11
0
94
59
0
539
62
19
185
18
11
372
75
117
161
104
73
0
391
12
5
0
7
0
470
82
240
80
2-methyl-3-furanthiol
3-mercapto-2-pentanone
2-mercapto-3-pentanone
c
2-furfurylthiol
4,5-dihydro-2-methyl-3-furanthiol
c
2-methyl-3-(methylthio)furan
10
11
12
13
4,5-dihydro-2-methyl-3(2H)-thiophenone
988
c
3-methyl-1,2-dithian-4-one
3-acetyl-1,2-dithiolane
1162
1201
1261
0
0
54
0
0
43
c
5-(2-hydroxyethyl)-4-methylthiazole
a
If not indicated otherwise, compounds were identified in the corresponding reaction between xylose, cysteine, and thiamin by comparing the mass spectra and retention
b
c
indices with those of authentic reference compounds. Retention index on HP-5MS. The compound was tentatively identified by comparing the mass spectra and retention
index with literature data (11 14).
−
2-methyl-3-furanthiol and 3-mercapto-2-pentanone were found
to be unlabeled, showing that xylose was an effective precursor
for these compounds only when cysteine was present.
The present study is designed to elucidate the influence of
1
3
the pH on the reaction between thiamin, cysteine, and [ C5]-
xylose. The pH value was varied between 4.0 and 7.0, peaks of
selected volatiles were integrated in the total ion chromatogram
(TIC) obtained from GC-MS, and the corresponding mass
spectra were analyzed to assess the relative contribution of
thiamin to their formation.
MATERIALS AND METHODS
Chemicals. Chemicals were of analytical grade. L-Cysteine, xylose,
dipotassium hydrogenphosphate and potassium dihydrogenphosphate
13
5
were from Fluka (Buchs, Switzerland), [ C ]xylose (99% enrichment)
was from Cambridge Isotope Laboratories (Andover, MA), and thiamin
hydrochloride (aroma grade) was from Firmenich.
Reactions. The reagents in Table 1 were dissolved in 1.00 mL of
potassium phosphate buffer (0.5 mol/L). Different buffers with pH
values from 4.0 to 7.0 were used. The mixtures were heated while
stirring in Teflon vials (Infochroma, Zug, Switzerland) in a heated metal
block (Reactitherm, stirring/heating module, Pierce Chemical Co.,
Rockford, IL) for 20 min at 145 °C. Trials with unlabeled xylose (E-
I) were carried out in triplicate.
Figure 1. Identified volatiles from the reactions of xylose, cysteine, and
thiamin.
RESULTS AND DISCUSSION
Small-scale reactions between cysteine (50 µmol), thiamin
50 µmol), and xylose (unlabeled and C5-labeled, respectively;
13
(
Analysis. All samples were analyzed by headspace solid-phase
microextraction in tandem with gas chromatography coupled to mass
spectrometry (HS-SPME-GC-MS) as previously described (10). Ab-
sorption was carried out at 40 °C for 35 min. The oven temperature
was 40 °C during 5 min, then raised by 5 °C/min to 260 °C and finally
1
50 µmol) were effected in phosphate buffer at 145 °C for 20
min. The pH value for the different experiments varied between
.0 and 7.0 (Table 1). The analysis was carried out after transfer
4
of the reacted solutions to 20-mL headspace vials, by SPME-
GC-MS at 40 °C. The identified volatiles in Table 2 include
the major sulfur-containing compounds in the gas chromato-
gram. Their chemical structures are shown in Figure 1. The
identification is based on the comparison of the mass spectrum
and the retention index with reference compounds. No com-
mercial reference compounds exist for 2-mercapto-3-pentanone
13
5
by 15 °C/min to 280 °C. The isotopomer ratios in the trials with [ C ]-
xylose were calculated using the relative signal intensities of the
analyzed ions (m/z) in the mass spectrum of the respective compound.
Peak areas were integrated using the TIC signals from the experiments
with unlabeled xylose and expressed as mean values from triplicates.
The standard deviation did not exceed 23%.

1
554 J. Agric. Food Chem., Vol. 55, No. 4, 2007
Cerny and Briffod
5
C ]Xylose, Cysteine, and Thiamin, Reacted at Different pH Values
Table 3. Isotope Ratios (Percent) of Sulfur Volatiles Formed from [13
[12
m/z
5
C ] a
pH 4
pH 5
pH 6
pH 7
m/z
[12
C
5
] a
pH 4
pH 5
pH 6
pH 7
2-methyl-3-furanthiol (4)
3-mercapto-2-pentanone (5)
112
113
114
115
116
117
118
119
120
121
0.6
0.5
13.3
53.6
3.9
2.7
0.7
5.8
18.2
0.5
0.6
15.1
61.0
4.5
3.1
0.5
3.5
10.8
0.3
0.5
<0.1
14.2
57.7
4.2
2.9
0.5
4.7
14.7
0.4
116
117
118
119
120
121
122
123
125
126
0.5
1.0
<0.1
67.1
4.6
3.4
0.6
1.4
20.4
0.3
1.3
<0.1
75.9
4.9
3.9
0.4
0.8
12.1
0.2
3.1
2.1
17.8
72.4
5.4
3.6
0.2
<0.1
<0.1
<0.1
<0.1
16.1
65.3
4.7
3.2
0.4
2.3
7.0
0.2
0.3
<0.1
89.1
5.6
4.3
0.3
<0.1
<0.1
<0.1
<0.1
<0.1
75.5
6.5
4.0
1.0
0.7
8.2
0.4
0.6
<0.1
76.0
4.6
4.3
0.5
1.3
10.2
0.2
0.8
0.6
0.7
1.2
0.5
0.8
4,5-dihydro-2-methyl-3-furanthiol (8)
5-(2-hydroxyethyl)-4-methylthiazole (13)
114
115
116
117
118
119
120
121
122
123
0.7
6.1
83.3
5.6
4.1
0.3
<0.1
<0.1
<0.1
<0.1
1.4
6.1
82.4
5.8
3.8
0.5
<0.1
<0.1
<0.1
<0.1
1.3
6.0
82.4
5.9
3.9
0.5
<0.1
<0.1
<0.1
<0.1
1.3
6.3
83.0
5.3
3.7
0.4
<0.1
<0.1
<0.1
<0.1
nab
na
na
na
na
na
na
na
na
na
141
142
143
144
145
146
147
148
149
150
0.2
<0.1
91.3
5.0
3.3
0.2
<0.1
<0.1
<0.1
<0.1
<0.1
0.4
<0.1
88.3
6.6
4.2
0.3
0.3
<0.1
88.5
6.7
4.3
0.2
<0.1
<0.1
<0.1
<0.1
<0.1
0.2
<0.1
87.6
6.9
4.6
0.5
<0.1
0.2
<0.1
<0.1
<0.1
<0.1
<0.1
88.4
6.7
4.4
0.3
<0.1
0.2
<0.1
<0.1
<0.1
0.2
<0.1
<0.1
<0.1
<0.1
151
a
Isotope ratio (percent) for the unlabeled compound from the reaction with unlabeled xylose at pH 4. b Not analyzed.
(
4
6), 4,5-dihydro-2-methyl-3-furanthiol (8), 3-methyl-1,2-dithian-
-one (11), and 3-acetyl-1,2-dithiolane (12). Their mass spectra
and retention indices were compared only with literature data
demonstrating its origin from xylose. Compounds 4 and 5
13
consisted of a mixture of C5-labeled and unlabeled compounds
1
3
with a lower share of the labeled isomer ([ C5]4, 10-25%;
1
3
(11-14), and thus the identification is only tentative.
[ C5]5, 10-23%). According to their mass spectra, the other
volatiles in Table 2 revealed also either unlabeled, fully 13C-
labeled, or a mix of nonlabeled and fully labeled isotopomers
for the reactions at pH 4.0-7.0 (Table 4). The thio ether 9 was
an exception, because it was composed of four isotope molecules
with molecular masses of 128, 129, 133, and 134, indicating
that both the 2-methyl-3-furyl and the thiomethyl fragment can
The data in Table 2 represent integrated peak areas and are
not corrected by MS response factors or taking into account
the different partition coefficients of volatiles between the
sample matrix and the SPME fiber. Also, for certain compounds,
the pH might have an effect on the partition coefficient.
Nonetheless, Table 2 illustrates to a certain extent the influence
of the pH on the formation of the respective volatiles.
Compounds 6, 11, 12, and 4,5-dihydro-2-methyl-3(2H)-
thiophene (10) were detected only when the reaction was carried
out at pH 6.0 and 7.0, and not under more acidic conditions;
the formation of 4,5-dihydro-2-methyl-3(2H)-furanone (1) was
also favored at higher pH values. On the other hand, 2-fural-
dehyde (3), 2-furfurylthiol (7), and 2-methyl-3(methylthio)furan
1
3
be either nonlabeled or fully C-labeled, resulting in four
possible combinations. The unlabeled 2-methyl-3-furyl part
supposedly stems from thiamin, whereas the unlabeled thiom-
ethyl fragment probably originates from cysteine degradation.
Cysteine can be considered as a precursor for the thiomethyl
13
group of 9, because in the reaction product between [ C5]xylose
and cysteine about 36% of 9 was found to be 5 times labeled,
highlighting the origin of the unlabeled methyl carbon from
cysteine (9). The pH during the reaction had no major influence
on the isotopomer distribution of the volatiles (Table 4), in
contrast to the strong effect on the pattern of volatiles and the
pH-dependent formation of most compounds (Table 2).
Few studies have systematically investigated the influence
of the pH value on the formation of volatiles from thiamin
degradation and/or Maillard reaction between cysteine and
pentoses. G u¨ ntert and co-workers (17) have heated thiamin
solutions at different pH values at 130 °C for 6 h. The main
compounds at pH 1.5 were 1-methyl-2,4-dithia-8-oxabicyclo-
[3.3.0]octane, 2-methyl-3(2H)furanone, 1, 8, 1-methyl-2,8-dioxa-
4-thiabicyclo[3.3.0]octane, and 4-acetyl-5-methyl-1,3-dithiolane.
The highest yields at neutral pH 7.0 were obtained for 13, its
formate and acetate esters, 1, 1-methyl-2,8-dioxa-4-thiabicyclo-
[3.3.0]octane, and 4. The treatment under basic conditions
produced the most complex mixture, and also the highest yield
of volatiles. The most prominent ones were 10, 4,5-dimeth-
ylthiazole, 2-methyl-2-hydroxytetrahydrothiophene, (E/Z)-3-
penten-1-ol, 4,5-dihydro-2-methylthiophene, 3-hydroxy-2-pen-
tanone, and 2-methyl-3-thiophenethiol. The authors remarked
that elemental sulfur and the generation of relatively high
(9) were formed only at acidic pH, and no traceable amounts
were detected at pH 7.0. Peak areas decreased with increasing
pH value for 8 and 3-mercapto-2-pentanone (5). The pH had
no obvious influence on the formation of 3-mercapto-2-butanone
(2), 2-methyl-3-furanthiol (4), and 5-(2-hydroxyethyl)-4-meth-
ylthiazole (13).
13
The mass spectra of the compounds from [ C5]xylose,
cysteine, and thiamin were analyzed on the basis of the mass-
to-charge ratios (m/z) of the molecular ions of the isotopomers.
Table 3 compares the isotope ratios of 4, 5, 7, 8, and 13. No
other compounds coeluted with them under the chromatographic
conditions of the study, thus allowing an unequivocal analysis
of their mass spectra. They were either unlabeled, fully C-
labeled, or a mixture of unlabeled and fully labeled isotopomers.
Other isotopomers, singly, doubly, triply, or quadruply C-
labeled, were virtually absent, indicating that the molecules did
not consist of a mixture of labeled and unlabeled carbon
fragments. The carbon skeletons of 8 and 13 were unlabeled
1
3
1
3
(
[
m/z 116 and 143, respectively) and hence derived not from
1
3
C5]xylose, but rather from thiamin, because both volatiles
are known thiamin degradation products (15, 16). On the other
hand, 7 was exclusively 5 times labeled (m/z 119), clearly

Maillard Reaction of [13
J. Agric. Food Chem., Vol. 55, No. 4, 2007 1555
5
C ]Xylose, Cysteine, and Thiamin and pH Effect
Table 4. Proportion of Isotopomers Formed from [13
−7
5
C ]Xylose, Cysteine, and Thiamin at pH 4
pH 4.0
[13C]b
(%)
<1
pH 5.0
[13C]
(%)
<1
pH 6.0
[13C]
(%)
<1
pH 7.0
m/z
analyzed
ions)
labeled
carbon
atoms
(
[12C]a
(%)
[12C]
(%)
[12C]
(%)
[12C]
(%)
[13C]
(%)
no.
compound
1
2
3
4
5
6
7
8
9
4,5-dihydro-2-methyl-3(2H)-furanone
3-mercapto-2-butanone
100; 105
104; 108
96; 101
>99
>95
<1
75
77
>99
>98
<1
85
86
>99
>98
>99
>95
<1
<5
5
4
5
5
5
5
5
5
<5
>99
25
<2
>99
15
<2
2-furaldehyde
2-methyl-3-furanthiol
114; 119
118; 123
118; 123
114; 119
116; 121
128; 129; 133; 134
116; 121
148; 153
148; 153
143; 149
90
90
6
<1
>99
40
>99
91
>99
>99
10
10
94
>99
<1
2; 9; 49
<1
9
<1
<1
80
88
<5
20
12
>95
3-mercapto-2-pentanone
2-mercapto-3-pentanone
2-furfurylthiol
4,5-dihydro-2-methyl-3-furanthiol
2-methyl-3-(methylthio)furan
4,5-dihydro-2-methyl-3(2H)-thiophenone
3-methyl-1,2-dithian-4-one
3-acetyl-1,2-dithiolane
23
14
<1
>99
35
>99
<1
3; 8; 54
<1
>99
39
>99
<1
3; 8; 50
>99
<1
1; 5; 6
10
11
12
13
>98
92
<2
8
5
5
5
6
>99
>99
<1
<1
5-(2-hydroxyethyl)-4-methylthiazole
>99
<1
>99
<1
a
Unlabeled carbon atoms (percent). b Labeled carbon atoms.
amounts of hydrogen sulfide played a more important role under
alkaline conditions and that more thiophenes and no furans were
formed. They also speculated that, in reaction mixtures contain-
ing xylose, cysteine, and thiamin, some of the compounds are
probably formed via two different pathways. Our results can
confirm this assumption, because the different isotopomers of
11 at pH 4-5.5, but only at pH 6.0 and 7.0. We suggest that,
in the presence of thiamin, the formation pathway from xylose
and cysteine to 4, 5, and 11 played only a minor role under the
experimental conditions, because the majority (75-92%) of
these molecules were found to be unlabeled and likely arose
from thiamin degradation.
4, 5, 6, 9, and 11 indicate different formation pathways with
The formation of the R-mercaptocarbonyl compounds 5 and
appears to follow different pathways. Whereas 5 was formed
and without involving xylose as precursor. In the present study,
the thiophene 10, as well as the two compounds 11 and 12,
both bearing two sulfur atoms in the ring, were formed only at
the higher pH values of 6.0 and 7.0. This finding is in agreement
with the stronger involvement of hydrogen sulfide at higher pH,
and a formation pathway involving its reaction with 5-hydroxy-
6
throughout the whole pH range, 6 was formed only at pH 6
and 7. The majority of 5 was found to be unlabeled (Table 3),
and consequently thiamin appears to be the main precursor under
the experimental conditions, whereas 6 was >94% 13C-labeled
and thus originated mainly from xylose. Previous studies on
the reaction between ribose and cysteine revealed both 5 and 6
as volatile products at pH 5.0 (22) and pH 5.6 (23), respectively,
with predominantly 5. Both mercaptoketones have been previ-
ously found in reactions between 2,3-pentanedione and hydrogen
sulfide (14, 24). Another study detected only 5 in the reaction
product between xylose and cysteine (25), and consequently a
different formation pathway via 5-hydroxy-2,3-pentanedione as
intermediate and hydrogen sulfide was proposed, as the forma-
tion of 5 via 2,3-pentanedione and hydrogen sulfide without
the concurrent generation of 6 appeared to be unlikely.
3
-mercapto-2-pentanone (17), which is generally accepted as a
key intermediate of thiamin degradation (16).
Dwivedi and Arnold (18) heated solutions of radiolabeled
S]thiamin in phosphate buffer ranging from pH 3.5 to 8.0
[35
and analyzed the TLC radiochromatograms. At pH 6.0 or below,
the principal sulfur compound from thiamin degradation was
13, whereas at pH 7.0 and 8.0 other sulfur compounds
dominated, and hydrogen sulfide appeared to be the main
volatile (18, 19). In our study 13 was the major peak in the
TIC for the reaction at pH 4.0. At pH 5.0-7.0 it generated a
major peak, but was not dominant.
Shu and co-workers (20) studied the degradation of cysteine
in aqueous solution at pH 2.2, 5.1, and 7.1. Strong formation
of volatiles occurred at pH 5.1, but only a low yield was
obtained at pH 2.2 and even less at 7.1. The main volatile at
pH 2.2 was 1,2,3-trithia-5-cycloheptene; at pH 5.1 acetone and
Not only do the pH, reaction temperature, and time have an
influence on the reaction pathways to 4 and 5, but also the
concentration of the precursor molecules may play a crucial
13
role. In a previous study (9) the reaction between [ C5]xylose,
cysteine, and thiamin at pH 5.0 was carried out at exactly the
same reaction conditions, but with twice the precursor concen-
tration as compared to the present study. Inspection of the results
3
,5-dimethyl-1,2,4-trithiolane were formed; and at pH 7.1, 3,5-
dimethyl-1,2,4-trithiolane was the main volatile. None of the
compounds that have been found by Shu and co-workers were
identified in the present study, but Maillard reaction products
and thiamin degradation products dominated (Table 2).
(
Table 5) reveals that a higher precursor concentration (A)
13
affords a higher proportion (54 and 60%, respectively) of C-
labeled 4 and 5, indicating that xylose is the predominant
precursor. At lower precursor concentration (B), the unlabeled
molecules dominate and xylose becomes less important. Zeiler
Meynier and Mottram (21) investigated the model reaction
between cysteine and ribose at pH 4.5 to 6.5. Seven of 20
identified compounds, namely, 1, 3, 4, 5, 7, 10, and 11, have
also been found in the present work. The authors observed that
the concentrations were pH-dependent and that the quantities
of 4, 5, and 7 were highest at pH 4.5 and decreased with
increasing pH. For the dithiane derivative 11 the opposite effect
was observed with slightly increasing quantities at higher pH
values. Our results show a similar trend for 5 and 7, whereas
the peak areas for 4 remained relatively constant over the pH
range from 4.0 to 7.0. However, in our study thiamin was an
additional reagent with xylose and cysteine. We could not detect
(26) showed that the degradation of a thiamin solution (120
mmol/L) at pH 5.7 produced 13 times more 4 (45 vs 3.4 µg/L)
than the reaction of ribose and cysteine (both 120 mmol/L) under
the same conditions. She also showed that thiamin generates
1500 times more 4 than the reaction between ribose and cysteine
when the reagent concentrations are as low as in meat (27).
Further studies are necessary to elucidate the role of the reactant
concentration, as well as small pH changes between 5.5 and
6.0, on the formation of sulfur odorants.

1556 J. Agric. Food Chem., Vol. 55, No. 4, 2007
Cerny and Briffod
Table 5. Proportion of Isotopomers from the Reaction of [13
Cysteine, and Thiamin (pH 5) at Different Precursor Concentrations
(12) Hartman, G. J.; Scheide, J. D.; Ho, C. T. Volatile products formed
from a flavor model system at high and low moisture. Lebensm.
Wiss. Technol. 1984, 17, 222-225.
5
C ]Xylose,
m/z
unlabeled:labeled (%)
(
13) G u¨ ntert, M.; Br u¨ ning, J.; Emberger, M.; K o¨ psel, M.; Kuhn, W.;
Thielmann, T.; Werkhoff, P. Identification and formation of some
selected sulfur-containing flavor compounds in various meat
model systems. J. Agric. Food Chem. 1990, 38, 2027-2041.
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meatlike aroma compounds from the reactions of alkanediones
with hydrogen sulfide and furanthiols. J. Agric. Food Chem.
(
analyzed
ions)
no.
compound
Aa
Ba
4
5
2-methyl-3-furanthiol
3-mercapto-2-pentanone
114; 119
118; 123
54:46
60:40
85:15
86:14
(
a
Precursor concentrations: A, xylose (0.3 m), cysteine (0.1 m), thiamin (0.1
m); B, xylose (0.15 m), cysteine (0.05 m), thiamin (0.05 m).
1
995, 43, 189-193.
(
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1
ABBREVIATIONS USED
1
and its related compounds. XIV. Behaviour of vitamin B in
water (in Japanese). Yakugaku Zasshi 1951, 71, 369-371.
DVB/CAR/PDMS, divinylbenzene/carboxen/polymethylsi-
loxane; GC-MS, gas chromatography-mass spectrometry;
SPME, solid-phase microextraction; TIC, total ion chromato-
gram; TLC, thin-layer chromatogram.
(
16) Van der Linde, L. M.; van Dort, J. M.; de Valois, P.; Boelens,
H.; de Rijke, D. Volatile components from thermally degraded
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2
24.
ACKNOWLEDGMENT
(17) G u¨ ntert, M.; Br u¨ ning, J.; Emberger, R.; Hopp, R.; K o¨ psel, M.;
Surburg, H.; Werkhoff, P. Thermally degraded thiaminesa
potent source of interesting flavor compounds. In FlaVor
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Received for review October 6, 2006. Revised manuscript received
December 5, 2006. Accepted December 7, 2006.
5
01-505.
JF062874W