Indole: A Promising Scavenging Agent for Methylglyoxal and Related Carbonyls in Tryptophan Containing Maillard Model Systems

Article abstract of DOI:10.1021/acs.jafc.9b02286

In situ generation of efficient carbonyl trapping agents from amino acids during food processing can be considered a useful approach to control the accumulation of harmful Maillard reaction products in food. Tryptophan is one such amino acid that can be used to generate carbonyl trapping agents. Indole, the main thermal degradation product of tryptophan, is known to react with simple aldehydes through electrophilic aromatic substitution type reactions mainly at carbon positions 2 and 3 in addition to the ring nitrogen. The ability of indole to scavenge three moles of reactive aldehydes per mole of indole such as formaldehyde, methylglyoxal, and phenylacetaldehyde was investigated using model systems containing tryptophan or indole. The model systems were either (a) heated in an aqueous solution in stainless steel reactors at specified time and temperatures and analyzed by qTOF-MS/MS or (b) directly pyrolyzed and analyzed by GC/MS using isotope labeling technique. Unlike the other aldehydes, the initial alcohol formed with phenylacetaldehyde was able to dehydrate and form an stable conjugated system with the indole. In general, indole was able to capture three moles of paraformaldehyde, three moles of methylglyoxal and three moles of phenylacetaldehyde and suppress the formation of 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) generated in a model system.

Full text of DOI:10.1021/acs.jafc.9b02286

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Food and Beverage Chemistry/Biochemistry
Indole: A Promising Scavenging Agent for Methylglyoxal and
Related Carbonyls in Tryptophan Containing Maillard Model Systems
Raheleh Ghassemzadeh, and Varoujan A. Yaylayan
J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.9b02286 • Publication Date (Web): 15 May 2019
Downloaded from http://pubs.acs.org on May 15, 2019
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Journal of Agricultural and Food Chemistry
Indole: A Promising Scavenging Agent for Methylglyoxal and Related Carbonyls in
Tryptophan Containing Maillard Model Systems
Raheleh Ghassem Zadeh and Varoujan Yaylayan*
McGill University, Department of Food Science and Agricultural chemistry, 21111 Lakeshore,
Ste. Anne de Bellevue, Quebec Canada
*
Author to whom Correspondence should be addressed
McGill University, Department of Food Science and Agricultural chemistry, 21111 Lakeshore,
Ste. Anne de Bellevue, Quebec Canada
Varoujan.yaylayan@mcgill.ca
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Abstract
In situ generation of efficient carbonyl trapping agents from amino acids during food processing
can be considered a useful approach to control the accumulation of harmful Maillard reaction
products in food. Tryptophan is one such amino acid that can be used to generate carbonyl trapping
agents. Indole, the main thermal degradation product of tryptophan, is known to react with simple
aldehydes through electrophilic aromatic substitution type reactions mainly at carbon positions 2
and 3 in addition to the ring nitrogen. The ability of indole to scavenge three moles of reactive
aldehydes per mole of indole such as formaldehyde, methylglyoxal and phenylacetaldehyde was
investigated using model systems containing tryptophan or indole. The model systems were either
(a) heated in an aqueous solution in stainless steel reactors at specified time and temperatures and
analyzed by qTOF-MS/MS or (b) directly pyrolyzed and analyzed by GC/MS using isotope
labelling technique. Unlike the other aldehydes, the initial alcohol formed with
phenylacetaldehyde was able to dehydrate and form an stable conjugated system with the indole.
In general, indole was able to capture three moles of paraformaldehyde, three moles of
methylglyoxal and three moles of phenylacetaldehyde and suppress the formation of 2-amino-1-
methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) generated in a model system.
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Key words: Tryptophan, indole, carbonyl scavengers, methylglyoxal, formaldehyde,
phenylacetaldehyde and PhIP.
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1. Introduction
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Thermally generated carbonyl compounds in food can play an important role in flavor and aroma
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formation and also in the generation of toxicants . Trapping of such carbonyl compounds is
considered one of the pathways to control the formation of harmful Maillard reaction products.
2
Recently, flavonoids and other phenolic compounds have been suggested as natural scavengers
of reactive aldehydes to inhibit the formation of the thermally generated toxicants in food.
Availability of other sources of scavenging agents that do not interfere with color and flavor
3
perception can be similarly used in processed food. Among the essential amino acids, tryptophan
has been shown to have the highest inhibitory activity towards early and advanced glycation of
BSA and highest reduction in the levels of lysine modification compared to the control
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experiments. During thermal processing of foods tryptophan is also known to degrade into indole
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and indole derivatives. Furthermore, it scavenge aromatic aldehydes such as benzaldehyde and
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vanillin and aliphatic aldehydes including sugars through Pictet-Spengler reaction to generate
tetrahydro-β-carboline. Tryptophan therefore appears to play a multifunctional role as a carbonyl
and free radical scavenger and as an antioxidant and could be a useful replacement to other
carbonyl scavenging molecules. Indole, the main volatile thermal degradation product of
tryptophan, is also known to react with simple aldehydes through electrophilic aromatic
substitution type reactions mainly at carbon position 3 and to a certain extant at carbon position 2
in addition to the ring nitrogen, however, this aspect of tryptophan chemistry and its ability to
scavenge three moles of reactive aldehydes per mole of indole, has not been investigated in the
context of Maillard reaction. We therefore investigated the in situ generation of indole from
tryptophan during the Maillard reaction and its reactivity towards selected Maillard generated
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aldehydes or dicarbonyl compounds as a useful approach to control the accumulation of harmful
Maillard reaction products in food.
2. Experimental Procedures
2.1 Materials, Reagents, and Equipment. L-tryptophan (99%), L-tryptamine (98%), D-glucose,
2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole (98%), 3-methylindole (98%), 2,3-dimethylindole
(≥97%), quinoline (98%) and paraformaldehyde were purchased from Sigma-Aldrich chemical
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company (Milwaukee, WI). The [ N ]tryptophan (98%) was purchased from Cambridge Isotope
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Laboratories (Andover, MA, USA). Reactions were carried out in sealed stainless steel reactors
heated in a commercial toaster oven (1200 Watts).
2.2 Synthesis of bis(tryptophanate)copper (II) complex. The synthesis was carried out
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according to published procedures. In summary, tryptophan (0.2g) was dissolved in methanol (10
mL) at room temperature in the presence of KOH (0.05g) followed by addition of 0.5 moles of
CuCl . The resulting blue precipitate was filtered, washed with methanol and dried before analysis
2
by ESI/qTOF/MS.
2.3 Sample Preparation. Model systems (see Table 1) were either (a) heated in methanol/water
o
o
(50%) solutions in a stainless steel reactor at selected temperatures (220 C or 150 C) for 1 or 2h
o
and analyzed by qTOF-MS or (b) directly pyrolyzed at 250 or 300 C and analyzed by GC/MS. All
the samples were analyzed in duplicate.
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2.4 Py-GC/MS analysis. A Varian CP-3800 gas chromatograph coupled to a Saturn 2000 ion trap
detector interfaced to a CDS Pyroprobe 2000 unit through a valved interface (CDS 1500) was used
for the desorption of the volatiles from the model systems. For each analysis, approximately 0.5
mg of sample was weighed into a quartz tube, sealed with glass wool and inserted into the
pyroprobe and pyrolyzed for 20 s at the desired temperature. The separation was performed using
a fused silica DB-5MS column (50-m length x 0.2 mm i.d. x 33 µm film thickness). The GC
method used for the analysis of the volatiles was as follows: GC column flow rate was regulated
by an electronic flow controller (EFC) and set at a pressure pulse of 70 psi for first 4 minutes then
decreased to 33 psi at the rate of 400 psi/min and finally increased to 70 psi at a rate of 1.23 psi/min
for the rest of the run. The GC oven temperature was set at −5°C for first 5 min using CO as the
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cryogenic cooling source and then increased to 50°C at a rate of 50°C/min. Then, the oven
temperature was again increased to 270°C at a rate of 8°C/min and kept at 270°C for 5.87 min.
The samples were detected by using an ion-trap mass detector. The MS transfer-line temperature
was set at 250°C, manifold temperature was set at 50°C, and the ion-trap temperature was set at
175°C. The ionization voltage of 70 eV was used, and EMV was set at 2000 V. The generated data
was analyzed using the AMDIS 32 version 2.69 and NIST version 2.0 mass spectral research
program.
2.5 Electrospray Ionization/ Quadrupole Time of Flight/ Mass Spectrometric Analysis
(ESI/qTOF/MS). The samples were diluted in methanol (90% v/v) before analyzing by
ESI/qTOF/MS. The system used was a Bruker Maxis Impact quadrupole time-of-flight mass
spectrometer (Bruker Daltonics, Bremen, Germany) operating in positive ion mode. Calibration of
the instrument was carried out by using sodium formate clusters. The diluted samples were infused
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continuously into the detector. The acquisition parameters for electrospray interface were the
following; nebulizer pressure, 0.6 Bar; drying gas, 4.0 l/min, 180 °C; capillary voltage, 4500 V.
Scan range was done from m/z 90 to 1000. The data were analyzed by Bruker Compass Data
Analysis software version 4.2. Tandem mass spectrometry (MS/MS) was carried out in multiple
+
reaction monitoring (MRM) mode using 25 eV collision energy for the ion at [M+Na] = 311.1154
+
+
and 40eV for the ions at [M+H] = 225.1126 and [M+Na] = 284.0893.
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2.6 Structural Identification. Evidence for the proposed structures of non-volatile reaction
intermediates were provided through ESI/qTOF/MS analysis, elemental composition, MS/MS
1
analysis in addition to FTIR and H-NMR (see supporting information). Tentative identification
of volatile compounds was performed by comparison of their retention times with that of
commercial standards and with NIST library search routines in addition to isotope-labeling studies
where possible.
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3. Results and Discussion
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Tryptophan is known to spontaneously scavenge various aldehydes to generate ß-carbolines and
tetrahydro-ß-carboline derivatives in food during storage or under commercial or domestic food
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processing conditions via Pictet-Spengler reaction. Methylglyoxal a well-known and reactive α-
dicarbonyl compound can be scavenged by tryptophan to form 1-acetyl-ß-carboline.10,11 On the
other hand, indole derivatives and indole itself which is the major volatile degradation product of
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tryptophan , is also known to undergo electrophilic substitution reaction with carbonyl compounds
at C-2 position and to a certain extent at the C-3 and ring nitrogen positions. In addition, the
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benzylic position of alkyl substituents of indoles exhibits special reactivity which includes
susceptibility to radical or ionic reactions, because of the stabilization provided by the benzylic
position due to resonance. However, the ability of indole derivatives and specifically indole to
scavenge reactive aldehydes during the Maillard reaction has not been investigated. In order to
examine the potential of tryptophan to generate indole derivatives and their ability to scavenge
Maillard generated aldehydes various model systems containing tryptophan or indole (see Table
1) were either (a) heated in methanolic aqueous solution in sealed stainless steel reactors and
subsequently analyzed by qTOF-MS/MS or (b) directly pyrolyzed and analyzed by GC/MS.
3.1 Proposed mechanism of tryptophan degradation and formation of indole derivatives
The potential of tryptophan containing model systems to generate indole derivatives was verified
through both pyrolysis experiments and under heating in an aqueous methanolic solution. Both
modes of heating generated indole and its derivatives, however, under pyrolytic conditions the
parent indole was the major volatile product of tryptophan containing model systems followed by
3-methylindole. Their structures were verified by comparison of their retention times with those
of the commercial standards and through NIST library searches under GC/MS conditions. The
mechanism of indole generation from tryptophan is not reported in the literature and it requires
breaking of a covalent bond to an aromatic system. The proposed mechanism shown in Figure 1
is based on the observation that tryptophan undergoes thermal decarboxylation to generate
tryptamine and tryptamine in turn is degraded into indole and 3-methylindole as evidenced by the
presence of both indoles in the heated tryptamine model systems. Furthermore, the importance of
decarboxylation step in the generation of indoles was verified when tryptophan was replaced with
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bis(tryptophanate)copper (II) complex or when tryptophan was pyrolyzed in the presence of CuCl2,
the intensity of the indole peaks increased more than fifty fold due to the catalytic effect of metal
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salts on the decarboxylation of amino acids. According to Figure 1, tryptamine formed from
decarboxylation of tryptophan, can undergo conjugated retro-aldol type reaction to generate 3-
methylindole with the loss of methanimine molecule, alternatively, it can lose ammonia to generate
3-ethenyl-2H-indole, the acrylamide counterpart of tryptophan. The formation of this intermediate
was verified only through its mass spectrum (EI) and through the presence of a single nitrogen
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atom in the ion at m/z 144 when [ N ]tryptophan was used in the model system. Furthermore, the
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released ammonia was captured as hexamethylenetetramine when tryptophan or [ N ]tryptophan
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was co-pyrolyzed with paraformaldehyde with the observation of a M+4 peak in the labelled model
system in the hexamethylenetetramine peak. The benzylic position in 3-ethenyl-2H-indole is
particularly reactive towards addition of water due to the stabilization of the carbocation formed
during the addition of water. The resulting alcohol after water addition, undergoes retro-aldol type
degradation using the imine moiety as the electron sink instead of a carbonyl and with the loss of
acetaldehyde generates indole. Furthermore, tryptamine at m/z 161.1069 (6.0 ppm) and 1,2,3,4-
+
tetrahydro-9H-pyrido[3,4-b]indole at [M+H] 173.1066 (7.3 ppm) were detected in the heated
aqueous reaction mixture of tryptophan alone indicating the formation of formaldehyde from
tryptamine and its eventual capture by tryptophan via Pictet-Spengler reaction to form the 1,2,3,4-
tetrahydro-9H-pyrido[3,4-b]indole.
3.2 Scavenging of carbonyl moieties. Selected aldehydes such as formaldehyde, methylglyoxal
and phenylacetaldehyde were reacted with indole to confirm the ability of indole to scavenge these
aldehydes and identify the specific adducts formed. The selected aldehydes represented common
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aldehydes or dicarbonyl compounds formed during the Maillard reaction. All carbonyl compounds
were captured through electrophilic substitution reactions at positions C-2, C-3 and the ring
nitrogen of indole as shown in Figure 2.
3.3 Formaldehyde represents a simple aldehyde that is usually formed from sugar or tryptamine
degradation or as Strecker aldehyde of glycine during the Maillard reaction. When indole was
reacted with paraformaldehyde in an aqueous methanolic solution, the expected adduct 2-
methylidene-2H-indole was not detected due to the instability of the exocyclic double bond,
however its thermal ring-expansion12 product quinoline was observed at [M+H]+ 130.0651
indicating the capture of formaldehyde. The identity of the peak in the pyrolysis experiment was
confirmed through matching of its the retention time with commercial standard and NIST library
searches and in the reaction mixture through its elemental composition by qTOF-MS. Furthermore,
analysis of the indole/paraformaldehyde methanolic aqueous reaction mixture have indicated that
(2H-indole-2-yl)methanol can further react with a second mole of formaldehyde to form (3H-
indole-2,3-diyl)dimethanol as evidenced by the observation of its dehydration product (3-
+
methylidene-3H-indol-2-yl)methanol at [M+H] = 160.0762 and its further reaction with a third
+
mole of formaldehyde to form (1H-indole-1,2,3-triyl)trimethanol at [M+Na] = 230.0794 (see
Table 2).
On the other hand, indole at [M+H] 118.0645 (9.94 ppm) generated from tryptamine or tryptophan
+
degradation can capture formaldehyde to form quinoline (C H N) at [M+H] 130.0644 (9.8 ppm)
9
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after ring expansion as shown in Figure 2 and as verified by library search and by matching the
retention time (21.7 min) with the commercial available quinoline standard.
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3.4 Methylglyoxal a well-known and reactive α-dicarbonyl compound can be scavenged by
tryptophan via Pictet-Spengler reaction to form 1-acetyl-ß-carboline.10,11 To confirm the ability of
o
indole to scavenge methylglyoxal, the aqueous methanolic mixture was reacted at 150 C for 1.5 h
and analyzed by qTOF/MS as indicated in the experimental section. The analysis of the data
indicated the ability of indole to capture up to three methylglyoxal moieties at C-3, C-2 and N
positions. The initial indole adduct of MG the 1-hydroxy-1-(2H-indol-2-yl)propan-2-one [M+Na]+
212.0676 (see Figure 2) is assumed to form at the C-2 position of indole, this adduct reacted further
with another mole of indole to generate 1,2-di(2H-indol-2-yl)propan-1-one, the most intense peak
+
in the reaction mixture that was detected in its potassiated [M+K] 327.0893 and sodiated forms
+
[M+Na] 311.1154. The structure of this adduct was further confirmed through observation in its
+
MS/MS spectrum of the predicted acylium ion at [M+H] = 172 generated from the carbonyl
+
moiety and its daughter ion at [M+H] = 144 (see Figure 3). Furthermore, the 1,2-di(2H-indol-2-
yl)propan-1-one reacted further with another mole of indole to eventually form the tri-indolyl
+
derivative at [M+K] 444.1486. More importantly, the 1-hydroxy-1-(2H-indol-2-yl)propan-2-one
+
at [M+Na] = 212.0676 can further scavenge two more molecules of methylglyoxal one at C-3
+
position to form 1,1'-(2H-indole-2,3-diyl)bis(1-hydroxypropan-2-one) at [M+Na] = 284.0893 and
the other at N to form 1,1',1''-(1H-indole-1,2,3-triyl)tris(1-hydroxypropan-2-one) at [M+Na]+
+
356.1111 as shown in Figure 2 (see also Table 2). The proposed structure of [M+Na] = 284.0893
was further confirmed through analysis of its MS/MS spectrum shown in Figure 3. In addition,
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H-NMR and FTIR spectral data are also provided for the structure of the ion at [M+Na] =
212.0676 (see Supporting Information).
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3.5 Scavenging of phenylacetaldehyde by indole and tryptophan. To illustrate the potential of
tryptophan and indole to capture phenylacetaldehyde; an important precursor of thermally
generated carcinogens such as PhIP (2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine), indole
o
or tryptophan were reacted with phenylacetaldehyde at 220 C in methanol/water for 2h and
analyzed by qTOF-MS. The results indicated the formation of various adducts in both systems as
major peaks (see Figure 2). Indole reacted with up to three moles of phenylacetaldehyde and in
addition, tryptophan containing model system showed Pictet-Spengler adduct of
+
phenylacetaldehyde at [M+H] 259.1225 (see Table 2). The mechanism of the adduct formation
with phenylacetaldehyde differs slightly from that of MG by the fact that the initial alcohol formed
+
can dehydrate and form an extended conjugated system at [M+H] 220.1120. In the case of MG
the molecule can stabilize by forming an enediol structure without undergoing dehydration. The
initial adduct 2-[2-phenylethenyl]-1H-indole at [M+H]+ 220.1120 can react at C-3 position with
a second mole of phenylacetaldehyde to form 2,3-bis[(2-phenylethenyl]-1H-indole at [M+Na]+
+
380.1626 which can dehydrate and form the ion at [M+H] 322.1590. Finally, the indole nitrogen
can capture a third mole of phenylacetaldehyde to form 1,2,3-tris[(2-phenylethenyl]-1H-indole at
[M+H]+ 424.2066 (see Table 2).
3.6 Scavenging of phenylacetaldehdye in PhIP generating model systems. To confirm the
ability of indole to scavenge phenylacetaldehyde the important precursor of PhIP in a model
o
system, a mixture of creatinine, serine and phenylalanine (1:1:1 molar ratio) was heated at 220 C
for 2h in a water methanol solution to generate PhIP. In this mixture, the formation of PhIP was
+
confirmed through the observation of a peak at [M+H] = 225.1126 (C H N ; 6 ppm error)
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consistent with the elemental composition of PhIP and through its MS/MS profile (loss of CH and
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CH N ) as shown in Figure 3. When indole was added to this mixture prior to the heating, not only
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+
the ion at [M+H] = 225.1126 disappeared but also two of the indole/phenylacetaldehyde adducts
+
observed above at [M+H]+ 424.2066 and at [M+Na] 380.1626 appeared, indicating the ability of
indole to scavenge phenylacetaldehyde formed in the model system and supress the formation of
PhIP.
Acknowledgments
The authors acknowledge funding for this research from Natural and Engineering Research
Council of Canada (NSERC).
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References
(1) Hellwiga, M.; Gensberger-Reiglb, S.; Henlea, T.; Pischetsriederb, M. Food-derived 1,2-
dicarbonyl compounds and their role in diseases. Sem. Cancer Biol. 2018, 49, 1–8.
(2) Wu, C.-H.; Huang, S.-M.; Lin, J.-A.; Yen, G.-C. Inhibition of advanced glycation endproduct
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(3) Colahan-Sederstrom, P. M.; Peterson, D. G. Inhibition of key aroma compounds generated
during ultrahigh-temperature processing of bovine milk via epicatechin addition. J. Agric. Food
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(4) Awasthi, S.; Saraswathi, N. T. Carbonyl scavenging and chemical chaperon like function of
essential amino acids attenuates nonenzymatic glycation of albumin. RSC Adv. 2016, 6, 24557-
24564.
(5) Kato, S.; Kurata, T.; Fujimaki, M. Thermal degradation of aromatic amino acids. Agric. Biol.
Chem. 1971, 35 (13), 2106-2112.
(6) Herraiz, T.; Papavergou, E. Identification and occurrence of tryptamine- and tryptophan-
derived tetrahydro-β-carbolines in commercial sausages. J. Agric. Food Chem. 2003, 51,
2168−2173.
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(8) Nashalian, O; Yaylayan, V. Thermally induced oxidative decarboxylation of copper complexes
of amino acids and formation of Strecker aldehdyes. J. Agric. Food Chem. 2014, 62, 8518-8523.
(9) Nemet, I.; Varga-Defterdarovic ́, L. Methylglyoxal-derived ß-carbolines formed from
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(10) Rönner, B.; Lerche, H.; Bergmüller, W.; Freilinger, C.; Severin, T.; Pischetsrieder, M.
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(11) Nemet, I.; Varga-Defterdarovic, L. The role of methylglyoxal in the non-enzymatic
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Table 1 Composition of model systems
Models systems analyzed by Py-GC/MSa
Model systems analyzed by qTOF/MSb
Tryptophan
Tryptophan
1
5
Tryptamine or Tryptophan[ N ]
Tryptamine
2
Tryptophan/glucose
Tryptophan/glucose
Tryptophan/paraformaldehyde
Tryptophan/phenylacetaldehyde
Indole/phenylacetaldehyde
Indole/methylglyoxal
1
5
Tryptophan[ N ]/paraformaldehyde
2
Tryptamine/paraformaldehdye
Indole/paraformaldehyde
Indole/paraformaldehyde
Creatinine/serine/phenylalaninec
Bis(tryptophanate)copper (II)
a
All model systems were prepared in a 1:2 molar ratio and pyrolyzed via GC/MS at 250 or 300°C.
The model systems were prepared at 1:1 molar ratio, analyzed by qTOF-MS after heating in
b
water/methanol between 150 to 220°C for 1 to 2 h.
c
The model system was prepared at 1:1:1 molar ratio, analyzed by qTOF-MS after heating in
water/methanol at 220°C for 2 h.
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Table 2. Elemental composition of carbonyl-indole adducts and degradation products of
tryptophan shown in Figures 1 & 2
Ion
Elemental composition
Error (ppm)
Model system
+
[
M+K] 444.1486
C
C
27
19
H
H
23KN
16KN
3
2
O
O
1.7
1.13
1.18
4
Indole/methylglyoxal
Indole/methylglyoxal
Indole/methylglyoxal
Indole/methylglyoxal
Indole/methylglyoxal
Indole/methylglyoxal
+
[
M+K] 327.0893
+
[
M+Na] 311.1154
C
19
19
H
16
N
2
NaO
+
[
M+H] 289.1329
C
H
17
N
2
O
+
[
[
[
M+Na] 356.1111
C
C
C
17
14
11
H
H
H
19NNaO
15NNaO
11NNaO
6
4
2
0.26
3.1
+
M+Na] 284.0893
+
M+Na] 212.0679
4
3
Indole/methylglyoxal
Indole/methylglyoxal
+
[
M+K] 228.042
C
11
22
17
H
11KNO
2
+
[
M+Na] 401.1474
C
H
22
N
2
NaO
4
0.8
4.2
6
Indole/methylglyoxal
Indole/methylglyoxal
+
[
M+Na] 342.1303
C
H
21NNaO
5
+
[
M+H] 220.1112
C
16
H
14
N
Tryptophan or
Indole/Phenylacetaldehyde
Indole/Phenylacetaldehyde
+
[
M+Na] 260.102
C
16
16
24
32
32
24
H
15NNaO
12
6
+
[
M+Na] 242.0932
C
H
13NNa
19NNa
Indole/Phenylacetaldehyde
Indole/Phenylacetaldehyde
Tryptophan /Phenylacetaldehyde
Tryptophan /Phenylacetaldehyde
Tryptophan /Phenylacetaldehyde
Tryptophan /Phenylacetaldehyde
Tryptophan /Phenylacetaldehyde
Tryptophan/Phenylacetaldehyde
Tryptophan or Tryptamine
Tryptophan
+
[
M+Na] 344.1405
C
H
3
+
[
M+H] 424.2066
C
H
26
N
0.18
6.2
0.12
0.08
7.6
3.9
4.8
9.9
7.3
7
+
[
M+Na] 446.1857
C
H
25NNa
+
[
M+Na] 380.1626
C
H
23NaNO
2
+
[
M+H] 322.1596
C
24
24
18
10
H
20
N
+
[
M+Na] 344.1389
C
H
19NNa
[
M+H]+ 259.1225
C
H
15
N
2
+
[
M+Na] 183.0907
C
H
12
N
2
Na
+
[
M+H] 118.0645
8 8
C H N
+
[
M+H] 173.1066
C
11
H
13
N
2
Tryptophan
+
[
M+Na] 166.0621
C
10
H
9
NNa
Tryptophan
+
[
M+H] 132.0799
C
9
H
10
10
13
N
10.8
4.3
2.9
1.8
Tryptophan
+
[
M+H] 144.0807
C
10
10
10
H
N
Tryptophan
+
[
M+H] 161.1074
C
H
N
2
Tryptamine or Tryptophan
Tryptamine
+
[
M+K] 199.0634
C
H
12KN
10NO
2
+
[
M+H] 160.0762
C
10
H
0.2
4.4
Tryptamine
+
[
M+H] 130.0651
C
9
H
8
N
Tryptamine or Tryptophan or
tryptophan or Indole/Formaldehyde
+
[
M+Na] 230.0794
C
11
H
13NNaO
3
0.37
Indole/ formaldehyde
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Figure 1
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Figure 2
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Figure captions
Figure 1. Proposed mechanism of formation of indole and 3-methyl-indole from tryptophan based
on both Py-GC/MS (Library search and retention times) and qTOF/MS data (elemental
composition).
Figure 2. Proposed mechanism of scavenging of methylglyoxal (MG), formaldehyde and
phenylacetaldehyde (Ph-acet) by indole.
+
+
Figure 3. MS/MS fragments generated from the ions at [M+Na] = 311.1154, [M+H] = 255. 1131
+
and [M+Na] = 284.0893
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