Antagonism between lipid-derived reactive carbonyls and phenolic compounds in the Strecker degradation of amino acids

Article abstract of DOI:10.1016/j.foodchem.2015.07.126

The Strecker-type degradation of phenylalanine in the presence of 2-pentanal and phenolic compounds was studied to investigate possible interactions that either promote or inhibit the formation of Strecker aldehydes in food products. Phenylacetaldehyde formation was promoted by 2-pentenal and also by o- and p-diphenols, but not by m-diphenols. This is consequence of the ability of phenolic compounds to be converted into reactive carbonyls and produce the Strecker degradation of the amino acid. When 2-pentenal and phenolic compounds were simultaneously present, an antagonism among them was observed. This antagonism is suggested to be a consequence of the ability of phenolic compounds to either react with both 2-pentenal and phenylacetaldehyde, or compete with other carbonyl compounds for the amino acids, a function that is determined by their structure. All these results suggest that carbonyl-phenol reactions may be used to modulate flavor formation produced in food products by lipid-derived reactive carbonyls.

Full text of DOI:10.1016/j.foodchem.2015.07.126

Accepted Manuscript
Antagonism between lipid-derived reactive carbonyls and phenolic compounds
in the Strecker degradation of amino acids
Rosa M. Delgado, Francisco J. Hidalgo, Rosario Zamora
PII:
S0308-8146(15)01160-7
DOI:
http://dx.doi.org/10.1016/j.foodchem.2015.07.126
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25 July 2015
Please cite this article as: Delgado, R.M., Hidalgo, F.J., Zamora, R., Antagonism between lipid-derived reactive
carbonyls and phenolic compounds in the Strecker degradation of amino acids, Food Chemistry (2015), doi: http://
dx.doi.org/10.1016/j.foodchem.2015.07.126
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Antagonism between lipid-derived reactive carbonyls and phenolic
compounds in the Strecker degradation of amino acids
Rosa M. Delgado, Francisco J. Hidalgo, Rosario Zamora *
Instituto de la Grasa, Consejo Superior de Investigaciones Científicas, Carretera de
Utrera km 1, Campus Universitario – Edificio 46, 41013-Seville, Spain
∗
Corresponding author. Tel.: +34 954 611 550; fax: +34 954 616 790. E-mail
address: rzamora@ig.csic.es (R. Zamora)
Abbreviated running title: Antagonism between carbonyls and phenols for amino acid
degradation
1

ABSTRACT
The Strecker-type degradation of phenylalanine in the presence of 2-pentanal and
phenolic compounds was studied to investigate possible interactions that either promote
or inhibit the formation of Strecker aldehydes in food products. Phenylacetaldehyde
formation was promoted by 2-pentenal and also by o- and p-diphenols, but not by m-
diphenols. This is consequence of the ability of phenolic compounds to be converted
into reactive carbonyls and produce the Strecker degradation of the amino acid. When
2
-pentenal and phenolic compounds were simultaneously present, an antagonism among
them was observed. This antagonism is suggested to be a consequence of the ability of
phenolic compounds to either react with both 2-pentenal and phenylacetaldehyde, or
compete with other carbonyl compounds for the amino acids, a function that is
determined by their structure. All these results suggest that carbonyl-phenol reactions
may be used to modulate flavor formation produced in food products by lipid-derived
reactive carbonyls.
Keywords:
Carbonyl-amine reactions; Carbonyl-phenol reactions; Lipid oxidation; Maillard
reaction; Phenolic compounds; Strecker degradation
Chemical compounds studied in this article:
Phenylalanine (PubChem ID: 994); phenylacetaldehyde (PubChem ID: 998); 2-pentenal
(
PubChem ID: 5364752); catechol (PubChem ID: 289); resorcinol (PubChem ID:
054); hydroquinone (PubChem ID: 785); benzoquinone (PubChem ID: 4650);
5
pyrogallol (PubChem ID: 1057); 1,2,4-trihydroxybenzene (PubChem ID: 10787);
phloroglucinol (PubChem ID: 359).
2

1. Introduction
The Strecker degradation of amino acids is an oxidative decarboxylation reaction by
which these compounds are transformed into decarboxylated deaminated carbonyl
compounds in the presence of a variety of reagents under different reaction conditions
(
Yaylayan, 2003). This reaction is a source of important volatile constituents of food
flavors, including Strecker aldehydes, pyrazines, pyridines, pyrroles, and oxazoles,
among other compounds (see, for example, Kebede et al., 2014; Lu, Bruheim,
Haugsgjerd, & Jacobsen, 2014).
In Maillard chemistry, the Strecker degradation is basically produced between α-
dicarbonyl compounds produced by carbohydrate dehydratation or fragmentation (1- or
3
-deoxyosones, glyoxal, 2,3-butanedione, 2-oxo-propanal, etc.) and amino acids
(
Guerra & Yaylayan, 2013; Zamora & Hidalgo, 2015). In addition, other carbonyl
compounds, or their precursors, are also able to degrade amino acids. Thus, the ability
of lipid-derived reactive carbonyls (Hidalgo & Zamora, 2004), amino acid-derived
reactive carbonyls (Hidalgo, Alcón, & Zamora, 2013), polyphenol-derived quinones
(
Rizzi, 2006), and polyphenols (Delgado, Zamora, & Hidalgo, 2015) for producing the
Strecker degradation of amino acids has also been described.
The fact that reactive carbonyls coming from very different origins, such as
carbohydrates, lipids, amino acids, or polyphenols, can promote amino acid
degradation, suggests the existence of many different alternative reaction pathways that
contribute to the formation of a large variety of flavor compounds in addition to
Strecker aldehydes. This would explain the seemingly endless source of flavor-
significant compounds produced in the course of Strecker degradation (Rizzi, 2008).
Furthermore, the existence of, at present, unknown interactions among all these routes
might be either enhancing or inhibiting the formation of Strecker aldehydes as common
3

products of all these routes. In an attempt to uncover possible interactions that either
promote or inhibit the formation of Strecker aldehydes in food products, this manuscript
studies the amino acid degradation produced in the presence of phenolic compounds or
a lipid-derived reactive carbonyl, as well as in the simultaneous presence of both kinds
of Strecker degradation promoters.
2. Materials and methods
2.1. Materials
Phenylalanine was selected as a model amino acid because its Strecker aldehyde
phenylacetaldehyde has a high boiling point (195 ºC), can be easily determined by gas
chromatography-mass spectrometry (GC-MS), and is a very powerful odorant (Delgado,
Zamora, & Hidalgo, 2015).
2
-Pentenal was employed as a model lipid-derived reactive carbonyl because its
reaction with phenolic compounds, in addition to amino compounds, has been
thoroughly studied (Hidalgo & Zamora, 2014).
Ten simple phenolic compounds having two or three hydroxyl groups at different
positions of the aromatic ring were employed to understand also the role of the relative
positions of hydroxyl groups in the aromatic ring for producing the Strecker degradation
of the amino acid. Some of these compounds also contained one carboxylic group. The
chemical structures of these phenolic compounds are shown in Fig. 1. The selected
phenols included o-diphenols: cathecol (CAT) and 3,4-dihydroxybenzoic acid (3,4-
DHB); m-diphenols: resorcinol (RES) and 2,6-dihydroxybenzoic acid (2,6-DHB); p-
diphenols: hydroquinone (HQ) and 2,5-dihydroxybenzoic acid (2,5-DHB); and
trihydroxyphenols: pyrogallol (PG), 1,2,4-trihydroxybenzene (TH), and phloroglucinol
(
PHL). In addition, although benzoquinone (BQ) is not a phenol derivative, it was
4

included for comparison purposes. Phenolic compounds, phenylalanine, 2-pentenal, and
other chemicals were purchased from Aldrich (Milwakee, WI), Sigma (St. Louis, MO),
Fluka (Buchs, Switzerland), or Merck (Darmstadt, Germany), and were of the highest
available quality.
2
.2. Formation of phenylacetaldehyde in binary and ternary mixtures of phenylalanine,
-pentenal, and phenolic compounds
2
Mixtures of phenylalanine (25 µmol), the phenolic compound (0, 25 or 50 µmol),
and/or 2-pentenal (0 or 25 µmol) in 500 µL of 0.3 M citrate buffer, pH 3, were
introduced in closed test tubes and heated at 180 ºC for 1 h. After cooling (10 min at
room temperature) samples were diluted with 1 mL of acetonitrile and 50 µL of internal
standard solution (54.8 mg of methyl heptanoate in 25 mL of ethanol) added. Samples
were analyzed for phenylacetaldehyde formation by GC-MS.
2
.3. Phenylacetaldehyde and 2-pentenal concentration changes in the presence of
phenols
Mixtures of phenylacetaldehyde (25 µmol), 2-pentenal (25 µmol), and the phenolic
compound (25 µmol) in 500 µL of 0.3 M citrate buffer, pH 3, were introduced in closed
test tubes and heated at 180 ºC for 1 h. After cooling (10 min at room temperature),
samples were diluted with 1 mL of acetonitrile and 50 µL of internal standard solution
(
54.8 mg of methyl heptanoate in 25 mL of ethanol) added. Phenylacetaldehyde and 2-
pentenal were determined by GC-MS.
2.4. GC-MS analyses
GC-MS analyses were conducted with a Hewlett-Packard 6890 GC Plus coupled
with an Agilent 5973 MSD (mass selective detector, quadrupole type). A fused-silica
HP5-MS capillary column (30 m × 0.25 i.d.; coating thickness, 0.25 µm) was used, and
5

1
µL of sample was injected in the pulsed splitless mode. Working conditions were as
follows: carrier gas, helium (1 mL/min at constant flow); injector, 250 ºC; oven
temperature programmed from 40 ºC (1 min) to 240 ºC at 5 ºC/min and then to 300 ºC
at 10 ºC/min; transfer line to MSD, 280 ºC; ionization EI, 70 eV; ion source
temperature, 230 ºC; mass range, 28–550 amu.
2.5. Determination of phenylacetaldehyde and 2-pentenal contents
Quantification of phenylacetaldehyde and 2-pentenal was carried out as described
previously for phenylacetaldehyde (Zamora, Gallardo, & Hidalgo, 2007) by preparing
standard curves of both aldehydes in the 1.55 mL of the solution prepared for GC-MS
injection. Then, different concentration levels of both aldehydes were used. Aldehyde
content was directly proportional to the aldehyde/internal area ratio (r = 0.999, p <
0.0001). The coefficients of variation were < 10%.
2
.6. Statistical analysis
All data given are mean or mean ± SD values of, at least, three independent
experiments. Statistical comparisons among different groups were made using analysis
of variance. When significant F values were obtained, group differences were evaluated
by the Tukey test (Snedecor & Cochran, 1980). Statistical comparisons were carried out
using Origin v. 7.0 (OriginLab Corp., Northampton, MA, USA). The significance level
is p < 0.05 unless otherwise indicated.
3. Results
3.1. Phenylacetaldehyde formation in binary and ternary mixtures of phenylalanine, 2-
pentenal and phenolic compounds
As described previously, both lipid-derived reactive carbonyls (Hidalgo & Zamora,
2004) and some phenolic compounds (Delgado, Zamora, & Hidalgo, 2015) are able to
6

produce the Strecker degradation of amino acids. Thus, addition of 2-pentenal,
analogously to other lipid-derived reactive carbonyls, increased phenylacetaldehyde
formation by 274% in relation to the phenylacetaldehyde produced in the absence of an
added carbonyl compound (Table 1). Analogously, addition of o- and p-diphenols also
increased phenylacetaldehyde formation by 68–391% when 25 µmol of the phenolic
compound were added and by 144–397% when 50 µmol of the phenolic compound
were added. An analogous increase in phenylacetaldehyde formation was observed
when either pyrogallol or 1,2,4-trihydroxybenzene were added. Thus,
phenylacetaldehyde content increased by 227–247% when 25 µmol of these trihydroxy
derivatives were added and by 309–322% when 50 µmol of these trihydroxy derivatives
were added. Differently to the increases observed for all these compounds, no
significant increases were observed when m-diphenols were added (Table 1). This
happened for resorcinol, 2,6-dihydroxybenzoic acid, and phloroglucinol.
This different behavior between m-diphenols and o- and p-diphenols is consequence
of the ability of carbonyl compounds, including the quinones formed by oxidation of o-
and p-diphenols, to produce the Strecker degradation of phenylalanine. For that reason,
when benzoquinone was employed in the place of phenolic derivatives,
phenylacetaldehyde was produced to a higher extent than when the phenolic compound
was added (about 500–600% higher than the phenylacetaldehyde produced by
hydroquinone in relation to control reaction).
When both 2-pentenal and phenolic compounds were added simultaneously to
phenylalanine, the obtained results were different to those described above and much
lower increases in the phenylacetaldehyde produced were observed. Thus,
phenylacetaldehyde only increased significantly (p < 0.05) in relation to the control of
phenylalanine and 2-pentenal, when 25 µmol of hydroquinone, benzoquinone,
7

pyrogallol or 1,2,4-trihydroxybenzene, or 50 µmol of 3,4-dihydroxybenzoic acid,
benzoquinone or pyrogallol were added (Table 1). In addition, there was not a clear
difference in the amount of phenylacetaldehyde formed when either 25 or 50 µmol of
phenolic compound was employed. On the other hand, addition of 2,6-
dihydroxybenzoic acid or phloroglucinol at 25 µmol or phloroglucinol at 50 µmol,
significantly reduced the phenylacetaldehyde produced.
3.3. Phenylacetaldehyde and 2-pentenal disappearance in the presence of phenols
To understand this different behavior in the presence and in the absence of 2-
pentenal, the disappearance of phenylacetaldehyde and 2-pentenal in the presence of
phenolic compounds was studied. Four phenols were selected as model compounds for
these studies. They included resorcinol, hydroquinone, 1,2,4-trihydroxybenzene, and
phloroglucinol, as model m-diphenol, p-diphenol, triphenol having ortho and para
substitutions, and triphenol having meta substitutions, respectively.
2
-Pentenal was quite stable after 1 h heating at 180 ºC in sodium citrate buffer, pH 3
(
Fig. 1A). About 80% of original 2-pentenal was recovered, and this recovering was
independent of the presence of phenylacetaldehyde in the reaction mixture. 2-Pentenal
recovering was fairly constant in the presence of resorcinol, hydroquinone, and 1,2,4-
trihydroxyphenol. However, it decreased significantly (p < 0.05) in the presence of
phloroglucinol. In fact, only 56% of the original 2-pentenal was recovered when heated
in the presence of this phenolic compound, and this percentage was similar when 2-
pentenal was heated only with the phenolic compound (binary mixture) or when the
mixture also contained phenylacetaldehyde (ternary mixture).
Differently to 2-pentenal, phenylacetaldehyde was less stable, and only 50% of
original phenylacetaldehyde was recovered after 1 h heating at 180 ºC in sodium citrate
8

buffer, pH 3 (Fig. 1B). This percentage was similar for phenylacetaldehyde heated in
the presence or in the absence of 2-pentenal. However, it decreased when heated in the
presence of most phenols. Thus, resorcinol, hydroquinone, and 1,2,4-trihydroxybenzene
decreased slightly the amount of phenyalcetaldehyde recovered (the phenylacetaldehyde
recovered in the presence of these phenols was 39–47%), and there were not significant
differences when 2-pentenal was, or not, present. The decrease in the amount of
phenylacetaldehyde recovered after heating was much higher in the presence of
phloroglucinol. In the presence of this phenolic compound, only 7–9% of the original
phenylacetaldehyde was recovered at the end of the heating process.
3.2. Antagonism between 2-pentenal and phenolic compounds for phenylacetaldehyde
formation in ternary mixtures of phenylalanine, 2-pentenal and phenolic compounds.
Although 2-pentenal and phenolic compounds converted phenylalanine into
phenylacetaldehyde, the simultaneous presence of both kinds of compounds usually
reduced the amount of phenylacetaldehyde that should have been produced considering
the phenylacetaldehyde produced by both kinds of compounds when added
independently. This antagonism was calculated from the data shown in Table 1
according to the following equation
͙
͙͙ͬͤ͗ͨ͘ꢀ͙͕͙͕͙͙ͤͭ͗ͨͭ͘͘͜͢͜͠͠ Ǝ ͙ͤͦͣͩ͗͘͘ꢀ͙͕͙͕͙͙ͤͭ͗ͨͭ͘͘͜͢͜͠͠
͕
͕ͨ͛ͣͧ͢͢͝͡ꢀʚ$ʛ Ɣꢀ
dz SRR
͙͙͙ͬͤ͗ͨ͘ꢀ͙͕͙͕͙͙ͤͭ͗ͨͭ͘͘͜͢͜͠͠
where the produced phenylacetaldehyde was the phenylacetaldehyde determined
experimentally in the ternary mixtures and the expected phenylacetaldehyde was
calculated by adding the phenylacetaldehyde produced by each component in the binary
mixtures.
The exhibited antagonism is shown in Fig. 3. In general, most of the determined
antagonisms between 2-pentenal and the assayed phenols was about 25%. This occurred
9

for catechol, resorcinol, 2,6-dihydroxybenzoic acid, hydroquinone, benzoquinone, and
,2,4-hydroxybenzene. However, three of the assayed phenols clearly exhibited a
1
reduced antagonism. They were 3,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid,
and pyrogallol. On the other hand, the antagonism exhibited between 2-pentenal and
phloroglucinol was clearly higher: around 70%.
4. Discussion
Strecker-type degradation of amino acids is produced by a number of carbonyl
compounds, including carbohydrates (Guerra & Yaylayan, 2013), lipid-derived reactive
carbonyls (Hidalgo & Zamora, 2004), amino acid-derived reactive carbonyls (Hidalgo,
Alcón, & Zamora, 2013), polyphenol-derived quinones (Rizzi, 2006), and polyphenols
(
Delgado, Zamora, & Hidalgo, 2015), among others. A pathway for phenylalanine
degradation in the presence of 2-pentenal is suggested in Fig. 4. This pathway is based
on the studies of amino acid degradation in the presence of carbonyl compounds
discussed by Rizzi (2008). As can be observed, the first step is the formation of the
corresponding imine between the amino group of the amino acid and the carbonyl
group. This imine undergoes then a thermally induced, irreversible decarboxylation.
The reason for this decarboxylation can be better understood from the zwitterionic form
of the imine. Finally, the produced azomethine ylide undergoes addition of water to
produce the Strecker aldehyde (phenylacetaldehyde) and an unstable enamine. The
easiness of the imine decarboxylation in relation to the analogous decarboxylation of
the amino acid is the responsible for the much higher yield of phenylacetaldehyde
produced in phenylalanine/2-pentenal mixtures than in phenylalanine heated alone
(
Table 1).
The presence of phenolic compounds introduces alternative routes in this reaction
pathway. Fig. 4 shows the reactions with resorcinol, but analogous reactions also take
1
0

place with other m-di- or triphenol derivatives (Salazar, Arámbula-Villa, Hidalgo, &
Zamora, 2014). m-Diphenols are able to react with both 2-pentenal and
phenylacetaldehyde. The reaction with 2-pentenal was studied by Hidalgo & Zamora
(
2014). These authors found that a number of carbonyl-phenol adducts are produced,
including 2H-chromenols, chromandiols, chromanols, and dihydropyrano[3,2-
g]chromenes, some of which are only intermediates in the formation of polymeric
structures. Fig. 4 shows only the structures of two of the simplest produced adducts:
2
H-chromenols and chromandiols.
Phenylacetaldehyde also reacts with phenolic compounds. This reaction was studied
by Chen et al. (2009). The reaction takes place by addition of the aromatic CH group in
ortho to one of the hydroxyl groups of the phenolic compound to the carbonyl carbon of
the aldehyde. The produced adduct can suffer then a dehydration to produce the
conjugated structure shown in Fig. 4.
Therefore, m-diphenols should inhibit the reaction between phenylalanine and 2-
pentenal by scavenging either the initial aldehyde or the final phenylacetaldehyde. For
that reason, when the reaction between phenylalanine and 2-pentenal was carried out in
the presence of resorcinol, 2,6-dihydroxybenzoic acid and phlorogucinol, the amount of
phenylacetaldehyde determined was lower than when the phenolic compounds were
absent (Table 1). In particular, the phenylacetaldehyde formed in the presence of
phloroglucinol was similar to the phenylacetaldehyde formed by phenylalanine in the
absence of carbonyl compounds (Table 1). The reason for that was the high carbonyl-
scavenging power of phloroglucinol. As shown in Fig. 2, phloroglucinol exhibited a
significant 2-pentenal-scavenging power, but it was especially good for removing
phenylacetaldehyde, which almost disappeared when mixtures of phenylacetaldehyde
and phloroglucinol were heated either in the presence or in the absence of 2-pentenal.
1
1

The effect of o- and p-diphenols was different. These compounds are oxidized upon
heating and the formed quinones are able to produce the Strecker degradation of amino
acids (Delgado, Zamora, & Hidalgo, 2015). As shown in Fig. 5, catechol, as an example
of o-diphenol, is converted into 1,2-benzoquinone upon heating and this quinone reacts
with amino acids analogously to other carbonyl compounds. Thus, it forms the
corresponding imine, which can be decarboxylated through the zwitterionic form of the
imine. Finally, the produced azomethine ylide undergoes addition of water to produce
the Strecker aldehyde (phenylacetaldehyde) and an aminophenol. Therefore, o- and p-
diphenols and analogous triphenols increased the formation of phenylacetaldehyde in
comparison to the aldehyde produced by decomposition of phenylalanine in the absence
of carbonyl compounds (Table 1).
The differences observed in the phenylacetaldehyde produced in either the presence
of phenols or 2-pentenal is likely related to both the stability of the azomethine ylide
formed and the yield of the conversion of the phenol into quinone. Thus, the azomethine
ylide produced in the reaction with quinones is highly delocalized because of the
aromatic ring, and should be more stable than the corresponding azomethine ylide
formed from 2-pentenal. For that reason, it should be expected that the decarboxylation
of the imine would be easier with quinones than with 2-pentenal. In fact,
phenylacetaldehyde was produced to a lower extent in phenylalanine/2-pentenal
mixtures (43.7 µmol of phenylacetaldehyde/mmol of phenylalanine) than in
phenylalanine/benzoquinone mixtures (105.4 µmol of phenylacetaldehyde/mmol of
phenylalanine). However, when reactions were carried out with phenols and not with
the quinone, the yields were lower more likely because of the limited conversion of the
phenol into the corresponding quinone (Table 1). In fact, the phenylacetaldehyde
1
2

produced in phenylalanine/2-pentenal mixtures was quite similar to the
phenylacetaldehyde produced in mixtures of phenylalanine with o- and p-diphenols.
Independently of the positions of the hydroxyl groups, when phenols and 2-pentenal
were added simultaneously, an antagonism was mostly observed (Fig. 3). The reason for
this antagonism is clear in the case of m-diphenols because they remove the carbonyl
compounds responsible for amino acid degradation from the media. This effect was
clearly observed for phloroglucinol, which, according to the results shown in Fig. 2, is a
powerful phenylacetaldehyde scavenger and, to a lower extent, also a 2-pentenal
scavenger. For that reason, antagonism was very high between 2-pentenal and
phloroglucinol (66-72% as shown in Fig. 3). Contrarily to the antagonism between 2-
pentenal and m-di- and triphenols, the reason for the antagonism exhibited by o- and p-
diphenols is not so clear. This antagonism does not seem to be related to an inhibition of
the conversion of the phenolic compounds into quinones because hydroquinone and
benzoquinone exhibited a similar antagonism. On the contrary, it seems to be related to
a promotion of phenylacetaldehyde disappearance as observed in Fig. 2B. This
promotion of phenylacetaldehyde disappearance was similar for resorcinol,
hydroquinone, and 1,2,4-trihydroxybenzene. For that reason, cathecol, resorcinol,
hydroquinone, and 1,2,4-trihydroxybenzene exhibited a similar antagonism with 2-
pentenal (Fig. 3). Different to these phenolic derivatives, 3,4-dihydroxybenzoic acid,
2,5-dihydroxybenzoic acid, and pyrogallol, exhibited a reduced antagonism with 2-
pentenal (Fig. 3), which remains to be clarified.
All these results confirm that the Strecker degradation of amino acids is produced by
different carbonyl compounds. However, when several of them are present
simultaneously, there are interactions among them that mostly produce a reduction of
the amount of Strecker aldehyde that should have been produced. This reduction is
1
3

particularly important for m-diphenols, which are able to scavenge both the carbonyl
compounds responsible for the Strecker degradation of the amino acid and also the
produced Strecker aldehydes. These results are in agreement with the reduction of off-
flavor development in Maillard chemistry produced when using phenols (Kokkinidou &
Peterson, 2014) and with the aromas developed during cooking of vegetables with
different culinary techniques due to the large amount and variety of phenolic
compounds and the possible interactions with other food components (Kebede at al.,
2013). They also point out to carbonyl-phenol reactions as a way to modulate flavor
formation produced by lipid-derived carbonyl compounds in food products.
Acknowledgments
We are indebted to José L. Navarro for technical assistance. This study was
supported in part by the European Union (FEDER funds) and the Plan Nacional de I +
D of the Ministerio de Economía y Competitividad of Spain (project AGL2012-35627).
1
4

References
Chen, K.-W., Wong, C. C., Chao, J., Lo, C., Chen, F., Chu, I. K., Che, C.-M., Ho, C.-T.,
&
Wang, M. (2009). Inhibition of mutagenic PhIP formation by epigallocatechin
gallate via scavenging of phenylacetaldehyde. Molecular Nutrition and Food
Research, 53, 716–725.
Delgado, R. M., Zamora, R., & Hidalgo, F. J. (2015). Contribution of phenolic
compounds to food flavors: Strecker-type degradation of amines and amino acids
produced by o- and p-diphenols. Journal of Agricultural and Food Chemistry, 63,
3
12–318.
Guerra, P. V., & Yaylayan, V. A. (2013). Cyclocondesation of 2,3-butanedione in the
presence of amino acids and formation of 4,5-dimethyl-1,2-phenylendiamine. Food
Chemistry, 141, 4391–4396.
Hidalgo, F. J., & Zamora, R. (2004). Strecker-type degradation produced by the lipid
oxidation products 4,5-epoxy-2-alkenals. Journal of Agricultural and Food
Chemistry, 52, 7126–7131.
Hidalgo, F. J., & Zamora, R. (2014). 2-Alkenal-scavenging ability of m-diphenols. Food
Chemistry, 160, 118–126.
Hidalgo, F. J., Alcón, E., & Zamora, R. (2013). Cysteine- and serine-thermal
degradation products promote the formation of Strecker aldehydes in amino acid
reaction mixtures. Food Research International, 54, 1394–1399.
Kebede, B. T., Grauwet, T., Palmers, S., Vervoort, L., Carle, R., Hendrickx, M., & Van
Loey, A. (2014). Effect of high pressure high temperature processing on the volatile
fraction of differently coloured carrots. Food Chemistry, 153, 340–352.
1
5

Kebede, B. T., Grauwet, T., Tabilo-Munizaga, G., Palmers, S., Vervoort, L., Hendrickx,
M., & Van Loey, A. (2013). Headspace components that discriminate between
thermal and high pressure high temperature treated green vegetables: Identification
and linkage to possible process-induced chemical changes. Food Chemistry, 141,
1
603–1613.
Kokkinidou, S., & Peterson, D. G. (2014). Control of Maillard-type off-flavor
development in ultrahigh-temperature-processed bovine milk by phenolic chemistry.
Journal of Agricultural and Food Chemistry, 62, 8023–8033.
Lu, F. S. H., Bruheim, I., Haugsgjerd, B. O., & Jacobsen, C. (2014). Effect of
temperature towards lipid oxidation and non-enzymatic browning reactions in krill
oil upon storage. Food Chemistry, 157, 398–407.
Rizzi, G. P. (2006). Formation of Strecker aldehydes from polyphenol-derived quinones
and α-amino acids in a nonenzymic model system. Journal of Agricultural and Food
Chemistry, 54, 1893–1897.
Rizzi, G. P. (2008). The Strecker degradation of amino acids: Newer avenues for flavor
formation. Food Reviews International, 24, 416–435.
Salazar, R., Arámbula-Villa, G., Hidalgo, F. J., & Zamora, R. (2014). Structural
characteristics that determine the inhibitory role of phenolic compounds on 2-amino-
1
4
-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) formation. Food Chemistry, 151,
80–486.
Snedecor, G. W., & Cochran, W. G. (1980). Statistical methods (7th ed.). Ames, IA:
Iowa State University Press.
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6

Yaylayan, V. A. (2003). Recent advances in the chemistry of Strecker degradation and
Amadori rearrangement: Implications to aroma and color formation. Food Science
and Technology Research, 1, 1–6.
Zamora, R., & Hidalgo, F. J. (2015). 2-Amino-1-methyl-6-phenylimidazo[4,5-
b]pyridine (PhIP) formation and fate: an example of the coordinate contribution of
lipid oxidation and Maillard reaction to the production and elimination of processing-
related food toxicants. RCS Advances, 5, 9709–9721.
Zamora, R., Gallardo, E., & Hidalgo, F. J. (2007). Strecker degradation of
phenylalanine initiated by 2,4-decadienal or methyl 13-oxooctadeca-9,11-dienoate in
model systems. Journal of Agricultural and Food Chemistry, 55, 1308–1314.
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Figure legends
Fig. 1. Chemical structures of phenolic compounds, and analogous compounds,
employed in this study.
Fig. 2. 2-Pentenal and phenylacetaldehyde recovered from mixtures of 2-pentenal,
phenylacetaldehyde, and phenolic compounds heated for 1 h at 180 ºC. 2-Pentenal
recovering (panel A) was determined in binary mixtures of 2-pentenal and phenolic
compounds (striped bars) and in ternary mixtures of 2-pentenal, phenylacetaldehyde
and phenolic compounds (open bars). Phenylacetaldehyde recovering (panel B) was
determined in binary mixtures of phenylacetaldehyde and phenolic compounds
(
striped bars) and in ternary mixtures of phenylacetaldehyde, 2-pentenal and phenolic
compounds (open bars).
Fig. 3. Antagonism among 2-pentenal and phenolic compounds in the formation of
phenylacetaldehyde in ternary mixtures of phenylalanine, 2-pentenal, and phenolic
compounds heated for 1 h at 180 ºC. Two amounts of phenolic compounds were
employed in the mixtures: 25 µmol (striped bars) and 50 µmol (open bars).
Fig. 4. Reaction pathway for phenylacetaldehyde formation by phenylalanine
degradation in the presence of 2-pentenal and inhibition by m-diphenols.
Fig. 5. Competitive reaction pathways for phenylacetaldehyde formation by
phenylalanine degradation in the presence of 2-pentenal and o- and p-diphenols.
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Table 1
Phenylacetaldehyde formation in binary and ternary mixtures of phenylalanine, 2-pentenal and phenolic compounds
2
5 µmol of phenol
50 µmol of phenol
Without 2-pentenal
11.7 ± 1.4
Phenol tested
None
Without 2-pentenal
11.7 ± 1.4
With 2-pentenal
43.7 ± 7.4
With 2-pentenal
43.7 ± 7.4
Catechol
26.0 ± 6.0 *
19.7 ± 6.6
44.8 ± 11.5
28.6 ± 5.4 **
36.2 ± 1.5 ***
16.1 ± 2.9
44.7 ± 9.6
3
,4-Dihydroxybenzoic acid
Resorcinol
,6-Dihydroxybenzoic acid
Hydroquinone
,5-Dihydroxybenzoic acid
51.9 ± 12.7
61.8 ± 15.1 *
36.5 ± 1.0
11.2 ± 2.1
33.9 ± 8.0
2
12.9 ± 3.0
31.0 ± 6.6 *
68.1 ± 15.3 **
52.2 ± 4.8
12.0 ± 2.7
40.4 ± 10.8
56.1 ± 9.6
57.4 ± 7.9 ***
27.0 ± 1.7 **
105.4 ± 17.8 ***
38.3 ± 4.5 ***
40.6 ± 10.2 **
12.8 ± 3.4
58.1 ± 1.4 ***
29.2 ± 1.0 ***
126.3 ± 12.2 ***
47.9 ± 11.7 **
49.4 ± 9.1 **
12.6 ± 2.9
2
57.3 ± 14.2
106.0 ± 4.1 ***
74.9 ± 11.8 **
50.9 ± 12.9
12.3 ± 2.7 ***
Benzoquinone
Pyrogallol
103.2 ± 19.0 ***
84.5 ± 7.7 ***
57.2 ± 9.6 *
15.2 ± 2.0 ***
1
,2,4-Trihydroxybenzene
Phloroglucinol
Values are mean ± SD (in µmol of phenylacetaldehyde/mmol of phenylalanine) for, at least, three independent experiments. Means in the same
column with an asterisk are significantly different from its control: * (p < 0.05), ** (p < 0.01), *** (p < 0.001). Reaction mixtures contained 25
µmol of phenylalanine, 25 µmol of 2-pentenal, and the indicated amount of phenolic compound. Benzoquinone is not a phenol, but it was
assayed for comparison purposes.
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Highlights
Z 2-Pentenal and some phenols promote the Strecker degradation of amino acids
Z When both kinds of compounds are present simultaneously, an antagonism is observed
Z The antagonism with m-diphenols is due to their carbonyl-scavenging ability
Z The antagonism with o- and p-diphenols is due to the competence for the amino acid
Z These reactions can modulate flavor formation by lipid-derived reactive carbonyls
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