J. Pineal Res. 2014; 56:31–38
© 2013 John Wiley & Sons A/S.
Published by John Wiley & Sons Ltd
Molecular, Biological, Physiological and Clinical Aspects of Melatonin
Doi:10.1111/jpi.12093
Journal of Pineal Research
Alcoholic fermentation induces melatonin synthesis in orange
juice
Abstract: Melatonin (N-acetyl-5-methoxytryptamine) is a molecule implicated
in multiple biological functions. Its level decreases with age, and the intake of
foods rich in melatonin has been considered an exogenous source of this
important agent. Orange is a natural source of melatonin. Melatonin synthesis
occurs during alcoholic fermentation of grapes, malt and pomegranate. The
amino acid tryptophan is the precursor of all 5-methoxytryptamines. Indeed,
melatonin appears in a shorter time in wines when tryptophan is added before
fermentation. The aim of the study was to measure melatonin content during
alcoholic fermentation of orange juice and to evaluate the role of the
precursor tryptophan. Identification and quantification of melatonin during
the alcoholic fermentation of orange juice was carried out by UHPLC-QqQMS/MS. Melatonin significantly increased throughout fermentation from day
0 (3.15 ng/mL) until day 15 (21.80 ng/mL) reaching larger amounts with
respect to other foods. Melatonin isomer was also analysed, but its content
remained stable ranging from 11.59 to 14.18 ng/mL. The enhancement of
melatonin occurred mainly in the soluble fraction. Tryptophan levels
significantly dropped from 13.80 mg/L (day 0) up to 3.19 mg/L (day 15)
during fermentation. Melatonin was inversely and significantly correlated with
tryptophan (r = 0.907). Therefore, the enhancement in melatonin could be due
to both the occurrence of tryptophan and the new synthesis by yeast. In
summary, the enhancement of melatonin in novel fermented orange beverage
would improve the health benefits of orange juice by increasing this bioactive
compound.
ndez-Pachón1,
M. S. Ferna
S. Medina2, G. Herrero-Martı́n1,
1,3,
I. Cerrillo1, G. Berna
B. Escudero-López1,
F. Ferreres2, F. Martı́n1,3,
M. C. Garcı́a-Parrilla4 and
A. Gil-Izquierdo2
1
Área de Nutrición y Bromatologı́a,
Departamento de Biologı́a Molecular e
Ingenierı́a Bioquı́mica, Universidad Pablo de
Olavide, Sevilla, Spain; 2Departamento de
Ciencia y Tecnologı́a de Alimentos, CEBASCSIC, Murcia, Spain; 3CIBER de Diabetes y
Enfermedades Metabólicas Asociadas
(CIBERDEM), Universidad Pablo de Olavide,
Sevilla, Spain; 4Área de Nutrición y
Bromatologı́a, Departamento de Nutrición y
Bromatologı́a, Toxicologı́a y Medicina Legal,
Universidad de Sevilla, Sevilla, Spain
Key words: alcoholic fermentation, food
analysis, melatonin, orange juice, tryptophan,
UHPLC-MS/MS
Address reprint requests to Marı́a-Soledad
ndez-Pachón, Área de Nutrición y
Ferna
Bromatologı́a, Departamento de Biologı́a
Molecular e Ingenierı́a Bioquı́mica, Universidad
Pablo de Olavide, Carretera de Utrera Km 1,
E-41013, Sevilla, Spain.
E-mail: msferpac@upo.es
Received July 24, 2013;
Accepted September 6, 2013.
Introduction
In the last two decades, numerous epidemiological and
intervention studies have associated the consumption of
fruits and vegetables with a lower risk of diseases such as
cardiovascular disease, cancer and ageing-related disorders
[1–3]. Citrus fruits have been recognized to be rich sources
of bioactive compounds, and orange juice is known for its
ascorbic acid, carotenoid and flavonoid content [4]. Furthermore, an inverse correlation between moderate alcohol
consumption and the occurrence of coronary heart disease
has been established [5–7]. The health effects of dietary
bioactive compounds and moderate alcohol consumption
could be used as novel commercial beverage of low alcoholic graduation prepared from orange juice by controlled
alcoholic fermentation. Indeed, it is remarkable that beverage developed by alcoholic fermentation of orange juice
continues with increased effort; this has led to the development of fruit wines rich in bioactive compounds [8–10].
Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine synthesized in the pineal gland and many other
organs of animals from L-tryptophan metabolism via sero-
tonin [11]. This indoleamine has been implicated in several
biological processes including the modulation of circadian
rhythm, immune responses, free radical-scavenging activity, activation of antioxidant enzymes, reproductive activity and bone metabolism and improves glucose tolerance,
insulin action and lipid profile being beneficial for diabetes, obesity or dyslipidemia [12–19]. Melatonin is also
present as metabolite in plants and edible products such as
tomatoes, strawberries, grapes, cherries, olive oil, nuts and
cereals [20–25]. Given that the melatonin is absorbed when
melatonin-containing foods are eaten [21, 26], the intake
of these foods could prevent the reduction in melatonin
plasma concentration, which occurs with age [27]. The
orange fruit is a natural source of melatonin. Sae-Teaw
and colleagues [28] analysed the melatonin concentration
in orange extracts and found that it contained 150 pg/g.
Johns and colleagues [29] described the melatonin content
of orange to be 150 pg/g. The beneficial effects of melatonin of orange juice consumption have been shown as it
increased plasma antioxidant capacity after its intake [28].
Moreover, melatonin synthesis by yeast during alcoholic
fermentation in white and red wines [30–33], beer [34] and
31
Fern
andez-Pachón et al.
Table 1. Quality parameters of orange juice before and after fermentation
Days of fermentation
TA (g citric acid/L)
pH
Total glucids (g/L)
TPI (mg/L)
Alcohol (% v/v)
8.48 0.02
8.85 0.02
3.48 0.20
3.43 0.20
78.2 5.64
53.7 4.65
793 0.50
722 12.7
0
0.87 0.01
0
15
Values are expressed as mean DS of four independent alcoholic fermentation processes analysed in triplicate.
TA, titratable acidity; TPI, total polyphenols index.
pomegranate wine [35] production has been observed.
Also, it has been observed that yeasts synthesize melatonin
isomers (ISO) during alcoholic fermentation involved in the
winemaking process [36, 37]. These ISO seem to share also
similar biological functions. Mor and colleagues [38] studied
the antioxidant activity of several melatonin isomers. According to the results of Mor and colleagues [38], Gómez and
colleagues indicated that the isomer which they had identified
in wine was even more potent than melatonin itself [37].
The amino acid tryptophan is the precursor of
all 5-methoxytryptamines (or indoleamines), including
melatonin, and the biosynthetic pathway is via serotonin
(5-hydroxy-tryptamine) in the case of yeasts, plants and
mammals [11, 39, 40]. Taking into account the formation
of melatonin by yeasts during alcoholic fermentation in
grape and pomegranate wines, it was of interest to evaluate whether this indoleamine is also synthesized during the
elaboration process of the new beverage of the fermented
orange juice. Thus, the aim of the present study was to determine, for the first time, whether melatonin and ISO are synthesized during the alcoholic fermentation process of orange
juice. Likewise, the relation between levels of tryptophan,
melatonin and ISO during the process was also evaluated.
The possible enhancement of melatonin and ISO in the new
fermented orange drink could improve the health benefits of
orange juice by increasing its bioactive compounds.
Materials and methods
Chemicals and reagents
N-acetyl-5-methoxytryptamine (melatonin) standard was
purchased from Fluka (Neu-Ulm, Germany). All LC-MSgrade solvents (acetonitrile and methanol) were obtained
from J. T. Baker (Phillipsburg, NJ, USA). Formic acid,
ammonium acetate, sodium hydroxide and dimethyl sulfoxide (DMSO) were purchased from Panreac Quımica S.A.
(Barcelona, Spain). Boric acid was from Probus (Badalona,
Spain). Calcium disodium EDTA, Bis-Tris reagent and
tryptophan standard for derivatization were obtained from
Sigma-Aldrich (Madrid, Spain). The 6-aminoquinolyl-Nhydroxysuccinimidyl carbamate (AQC) reagent was purchased from Chemos GmbH (Regenstauf, Germany). Solutions were prepared by diluting with Milli-Q water
produced using an Elixâ3 Millipore water purification system coupled to a Milli-Q module (model Adventage 10)
(Molsheim, France). All reagents were of analytical grade.
Alcoholic fermentation procedure
The company ‘Grupo Hesperides Biotech S.L.’ carried out
the controlled alcoholic fermentation of commercial pas32
teurized juice made from Citrus sinensis L. var. Navel late
(Huelva, Spain) (patent: WO2012/066176A120120524).
The criteria for selecting this orange juice were the compositional homogeneity, microbiological stability and organoleptic quality (data not shown). These aspects are
necessary for adequate development of the fermentation
process and consumer acceptance of final product. The
fermentation was carried out in two parallel PVC tanks
(5 L) at 20°C for 15 days in repose. The yeast strain
Saccharomycetaceae var. Pichia kluyveri was isolated from
the natural microbiota present in the orange fruit and used
for inoculation of the fermentation. The selected yeast
strain ferments only reducing sugars, allowing low alcohol
content in the final product (0.8–1.2% v/v). Before sample
collection, fermentation liquid was agitated and mixed by
using magnetic agitators to promote sample homogenization. Samples were collected every 2 days (day 0 [original
orange juice], day 1, day 3, day 5, day 7, day 9, day 11,
day 13 and day 15) and immediately stored at 20°C until
analysis.
Table 1 provides the quality parameters: titratable acidity (TA), pH, total sugars and alcohol [41], and total
polyphenols index (TPI), determined by Folin-Ciocalteu
method [42].
Melatonin analysis
Samples were processed according to Rodrı́guez-Naranjo
and colleagues [30, 31] with minor modifications. Briefly, a
volume (10 mL) of each sample was centrifuged at 4500 g
for 10 min, and both the supernatant and pellet were separated. The pellet was then extracted with DMSO (500 lL).
Samples were evaporated to dryness under vacuum. The
residues were resuspended in methanol/water (1:1, v/v), up
to a concentration of 3:1 (v/v) and treated with mild ultrasonic for 10 min at room temperature. The reconstituted
extracts were filtered through a 0.45-lm nylon membrane
(Simplepure; Membrane Solutions, Spring View Lane
plano, TX, USA) before the analysis.
Melatonin determination
and quantification was
analysed using a UHPLC-QqQ-MS/MS (UPCL-1290
Series and a 6460 QqQ-MS/MS; Agilent Technologies,
Waldbronn, Germany) with an Acquity BEH C18 column
(2.1 9 150 mm; 1.7 lm; Waters, Milford, MA, USA).
Chromatographic separation was achieved using a binary
gradient consisting of (A) water and (B) methanol as
LC-grade solvents both containing 0.1% formic acid (v/v).
The flow rate was 0.30 mL/min using a linear gradient
(t; %B): (0.00; 40), (1.50; 40), (1.51; 90), (3.50; 90), (3.51;
40). The volume injection was 20 lL. Multiple reaction
monitoring (MRM) in positive mode was carried out. The
MS data obtained were compared with the authentic
Melatonin in fermented orange juice
markers to produce a final melatonin identification and
investigate the ISO present in samples. Melatonin quantification was based on the 233/216 MRM transition [30, 31,
35]. This MRM transition was selected because of its specificity and its better signal-to-noise ratio. Melatonin standard external calibration was used to quantify melatonin
and its ISO in samples. Chromatographic profile is shown
in Fig. 1. Nitrogen was used as the collision gas for the
fragmentation by collision-induced dissociation of the
compounds at the collision cell of the triple quadrupole
mass spectrometer. Mass spectrometer parameters were set
as follows: drying gas flow: 8 L/min; sheath gas flow:
12 L/min; sheath gas temperature: 350°C; nebulizer pressure: 30 psi; capillary voltage: 4000 V and nozzle voltage:
1000 V. MassHunter software version B 04.00 was used
for MS control and data gathering, and MassHunter soft-
(A)
(B)
(C)
Fig. 1. Chromatographic profile recorded using UHPLC-MS/MS
with multiple reaction monitoring (MRM) mode for the 233/216
transition of (A) melatonin (MEL) standard (0.312 lM), (B)
supernatant of orange juice (isomer (ISO) and MEL) and (C)
supernatant of fermented orange juice (day 15) (ISO and MEL).
ware version B 03.01 was used for data processing, peak
integration and linear regression.
Tryptophan analysis
Samples were centrifuged at 10,000 g during 10 min
(model EBA 21, Hettich Zentrifugen, Tuttlingen, Germany),
and the supernatant was transferred to a limited-volume
vial. Tryptophan content was determined as previously
described by Salazar and colleagues [43]. An aliquot of
500 lL of the supernatant was mixed with 12.5 lL of
extraction buffer [MeOH/water (50% v/v)] and vortexed
for 30 s on ice followed by incubation on ice for 5 min
and sonicated in an ultrasound bath for 1 min. The
homogenates were then centrifuged (centrifuge 5804 R,
Hamburg, Germany) for 10 min at 17,900 g at 4°C. The
supernatant was transferred to a limited-volume vial.
Extracts were immediately derivatized.
Derivatization of tryptophan was carried out following
a method described previously by Salazar and colleagues
[43] and Nagumo and colleagues [44]. Briefly, 350 lL of
borate derivatization buffer (0.2 M sodium borate, pH 8.8
with 5 mM calcium disodium EDTA), 50 lL of tryptophan standard or sample and 100 lL of reconstituted
AQC (10 mM AQC in acetonitrile) [45, 46] was added in a
2-mL propylene vial. The vial was vortexed for several
seconds, and then was left to rest for 1 min at room temperature. Thereafter, the vial was heated in a heating block for
10 min at 55°C. After this step, it was removed from the
heating block, and the sample was injected in a UHPLCtriple quadrupole mass spectrometer (UHPLC-MS/MS).
Analysis of tryptophan was accomplished by reversed
phase by means of UHPLC-MS/MS technology, as
reported by Salazar and colleagues [43] and Nagumo and
colleagues [44] with slight modifications. Briefly, chromatographic separation was carried out on an AccQ Tag
Ultra BEH column (2.1 9 100 mm; 1.7 lm; Waters,
Dublin, Ireland). The applied solvent system for gradient
separation consisted of two types of eluents: the mobile
phase A consisted of 50 mL of an aqueous solution (acetonitrile, formic acid and acetate ammonium in water (5 mM),
10:6:84, v/v/v) diluted with 950 mL of Mili-Q water, and
the mobile phase B was a mixture of acetonitrile and formic acid (99.9:0.1, v/v). 20 lL of the derivatized tryptophan standard or sample was injected onto the column
and eluted at a flow rate of 0.5 mL/min according to the
gradient profile as follows: 99.9% A at 0–0.5 min, 90.9%
A at 5.7 min, 78.8% A at 7.7 min, 40.4% A at 8–10 min,
10% A at 10.01–12.00 min and 99.9% A at 12.01–
14.00 min. The acquisition time was 12 min for standard
or sample. Concentrated tryptophan was prepared by dissolving in Bis-Tris buffer pH 6.5. Calibration standard
was generated by diluting the stock solution at 1, 0.5,
0.25, 0.12, 0.06 and 0.03 mM. Identification of tryptophan
was achieved using a UHPLC system coupled with a 6460
tandem mass spectrometer (Agilent Technologies). Data
acquisition and processing were performed using the MassHunter software version B.04.00 from Agilent Technologies. The MS analysis was applied in the MRM mode,
which was performed using the positive ionization mode.
The working conditions for the MS parameters were
33
Fern
andez-Pachón et al.
extraction and NMR identification in addition to ion trap
mass spectrometer [31]. Table 2 reports the content of
melatonin and ISO in the soluble and pellet fractions in
orange juice during fermentation, and Fig. 2 shows the
evolution of total melatonin and ISO contents (sum of
supernatant and pellet content).
Melatonin content increased progressively during the
fermentation process in the soluble fraction of orange
juice. From day 7, melatonin content (8.82 ng/mL) was
significantly higher than that of day 0 (2.49 ng/mL).
Moreover, the highest melatonin content (day 15: 20.0 ng/
mL) was observed at the end of fermentation (Table 2). A
major portion of the melatonin content was present in the
supernatant, but small amounts were identified in the
pellet fraction. Additionally, melatonin concentration underwent a significant increase in the pellet after alcoholic
fermentation from day 0 (0.66 ng/mL) to day 7 (1.45
ng/mL). Thereafter, the content increased until day 15
(1.85 ng/mL), but this evolution was not significant. The
results indicate that the increase in melatonin content
along orange juice alcoholic fermentation is mainly due to
the increase in the soluble fraction. Total melatonin
content (sum of supernatant and pellet content) during
fermentation is presented in Fig. 2A. It is observed that
total melatonin underwent a marked 7-fold increase from
day 0 (3.15 ng/mL) until maximal value at day 15
(21.9 ng/mL) (P < 0.001). The significant difference was
also found after day 7 (P < 0.05).
Several studies of melatonin levels have been based on
fresh fruits (grapes, cherries and tomatoes) [22, 48, 49]. In
recent years, the enhancement of melatonin after fermentation processes has been studied. The rise in melatonin in
wines is due to its synthesis during alcoholic fermentation
by Saccharomyces cerevisiae [30–32, 35, 50]. Accordingly,
an enrichment of melatonin content during the production
of beer by yeast contribution was also observed [34]. Melatonin level in fermented orange juice (21.9 ng/mL) is
higher than that found for fresh fruits. Johns and
colleagues [29] measured melatonin concentrations in pineapple (302 pg/g), banana (8.9 pg/g), mango (699 pg/g) and
papaya (241 pg/g). Fermented orange juice reached similar
values to other fermented products. Melatonin content
varied depending on wine variety from 5.1 to 130 ng/mL
optimized for this device, and they were set as follows: gas
flow: 9 L/min, nebulizer: 40 psi, capillary voltage: 4000 V,
nozzle voltage: 1000 V, gas temperature: 325°C, sheath
gas temperature: 390°C, and jetstream gas flow: 11 L/min.
The MS parameters for fragmentor (ion optics; capillary
exit voltage) and collision energy were optimized. The
allocation of these parameters along with preferential
MRM transition of the analyte generated the most abundant product ions. In this sense, the preferential MRM
transition obtained for tryptophan corresponded to the
AMQ moiety (171+), a result from the collision-induced
cleavage at the ureide bond of AMQ adduct of amino acid
[43, 47].
Statistical analysis
Fermentation was performed in quadruplicate, and all
analyses were in triplicate. The analysis of variance (oneway ANOVA; Duncan) was applied to establish significant
differences between the means obtained during the fermentation process. A probability value of P < 0.05 was
adopted as the criteria for significant differences. Pearson’s
correlation coefficient (r) was used to determinate the correlation between the parameters evaluated. A P < 0.05
was adopted as the criteria for significant correlation.
These analyses were performed with SPSS version 15
software (SPSS Inc., Chicago, IL, USA).
Results and discussion
Melatonin has been identified in orange [28, 29]. However,
this is the first time that alcoholic fermentation influences
melatonin formation in orange juice. Melatonin analysis
during alcoholic fermentation of orange juice was carried
out by UHPLC-QqQ-MS/MS as it has been validated as a
selective and sensitive method for an appropriate identification and quantification of melatonin in wine samples
[31]. As the authentic maker is not available to identify the
current isomer detected by UHPLC-QqQ-MS/MS, tentative identification by comparing relative abundance of
minority fragment ions to identify position isomer is
adequate. However, the total identification of a novel
compound requires the isolation by previous solid phase
Table 2. Melatonin (MEL) and MEL isomer (ISO) contents of orange juice during the alcoholic fermentation process
MELa (ng/mL)
Days of
fermentation
Supernatant
0
1
3
5
7
9
11
13
15
2.49
2.38
3.31
6.67
8.82
13.7
14.9
18.8
20.0
0.03a
0.16a
0.43a
1.10ab
0.67b
1.30c
1.42cd
1.50de
2.02e
ISOb (ng/mL)
Pellet
0.66
0.48
0.95
0.98
1.45
1.46
1.98
1.93
1.85
0.00a
0.00a
0.24ab
0.15ab
0.10bc
0.03bc
0.13c
0.27c
0.16c
Supernatant
8.28
8.52
8.58
9.20
9.71
9.83
10.3
10.4
10.5
0.73a
0.53a
0.72ab
0.66abc
0.46abc
0.50abc
0.48bc
0.30bc
0.32c
Pellet
3.31
2.79
2.86
3.15
3.34
2.89
3.70
2.48
3.66
0.58a
0.51a
0.50a
0.51a
0.28a
0.46a
0.41a
0.42a
0.16a
Results are expressed as mean S.E.M. of four independent alcoholic fermentation processes analysed in triplicate. Values with different
roman letters (a–e) in the same column indicate means significantly different at P < 0.05.
a
Melatonin was measured by UHPLC-MS/MS.
b
ISO amount calculated by use of MEL standard.
34
Melatonin in fermented orange juice
25
(A)
***
MEL (ng/mL)
20
***
***
***
15
*
10
5
0
0
1
3
5
7
9
11
13
15
Time (days of fermentation)
20
(B)
Fig. 2. Evolution in the total content
(supernatant and pellet) of melatonin
(MEL) (A) and isomer (ISO) (B) of
orange juice during the alcoholic
fermentation process. Symbols represent
mean values and error bars the S.E.M.
*P < 0.05, ***P < 0.001 as compared
with day 0.
ISO (ng/mL)
18
16
14
12
10
8
6
0
[31] or 18 ng/mL [50]. Mena and colleagues [35] obtained
the maximum melatonin content of 8.78 ng/mL during
fermentation of pomegranate. These differences among
fermented products can be explained by the basal concentration of melatonin before fermentation onset, growth
phase and type of yeast [32], which determine the concentration of melatonin in the final product.
Melatonin has up to nine known ISO (including itself)
[51]; nomenclature for these has been recently proposed
[36]. Possible appearance of ISO can occur during the
winemaking process as single compounds or together with
melatonin [31]. ISO content was also evaluated during
alcoholic fermentation of orange juice. Analyses of ISO
fractions separately showed that ISO content gradually
increased in the soluble fraction during the orange juice
fermentation process. This improvement was significant
between day 0 (8.28 ng/mL) and day 11 (10.3 ng/mL).
Thereafter, the increase was not significant, but at day 15
(10.5 ng/mL), the maximum value was achieved. Before
fermentation, ISO concentration in the supernatant was
higher than the melatonin content, but the augmentation
in ISO during fermentation was lower. So ISO values from
day 0 to day 15 underwent a 1.26% increase, while the
melatonin rise was 8%. Therefore, the final concentration
of melatonin was twofold higher than ISO final value in
the supernatant fraction. Conversely, ISO concentration in
the pellet fraction remained unchanged during alcoholic fermentation from day 0 (3.31 ng/mL) to day 15
(3.66 ng/mL). Similar to melatonin, ISO level in pellet was
higher (3.31 ng/mL) than the melatonin content (0.66 ng/
mL) before fermentation, but the increment in melatonin
value from day 0 to day 15 of fermentation process was
2.8%. The final content of ISO in the insoluble fraction
1
3
5
7
9
11
13
15
Time (days of fermentation)
was twofold higher than melatonin content. The total ISO
content (sum of supernatant and pellet fractions) remained
stable during the 15 days of orange juice fermentation, with a
minor and nonsignificant increase between day 0 (11.6 ng/
mL) and day 15 (14.2 ng/mL) (Fig. 2B). ISO content of
fermented orange juice was similar to that reported by
Rodrıguez-Naranjo and colleagues [31] and Gómez and
colleagues [37], who reported values of ISO in different
types of wines after winemaking process: 5.2–21.9 ng/mL
and 15 ng/mL, respectively. Gómez and colleagues [37]
observed an enhancement of ISO content during fermentation in wines. In contrast, in the current study, ISO content did not rise during fermentation. These results
indicate that ISO is not synthesized during the orange
juice fermentation process. This could be explained by the
type of yeast used. In this regard, Tan and colleagues [36]
mentioned that yeasts producing elevated levels of ISO
might be able to produce higher levels of alcohol.
Fermented orange juice has a low alcoholic grade.
Melatonin has a number of biological functions: glucose
tolerance, circadian rhythm regulation, antioxidant
defence or immune system action. We hypothesized that
the consumption of fermented orange juice could induce
higher beneficial effects than orange juice alone, and the
difference between both beverages would be caused by the
higher melatonin as ISO content does not significantly
change during alcoholic fermentation.
Among amino acids, specially tryptophan could be a
pivotal factor as it is a precursor of melatonin in yeast [30,
39]. Rodrı́guez-Naranjo and colleagues [30] and Gómez
and colleagues [37] evaluated an increase in the melatonin
of wines when tryptophan was added during the fermentation process. To evaluate the influence of tryptophan on
35
Fern
andez-Pachón et al.
Tryptophan (mg/L)
20
16
12
*
8
*
*
**
**
4
0
0
1
3
5
7
9
11
13
15
Tryptophan (mg/L)
Time (days of fermentation)
16
14
12
10
8
6
4
2
0
y = –0.48x + 12.665
r = –0.907 **
0
5
10
15
MEL (ng/mL)
melatonin synthesis, tryptophan content was analysed during alcoholic fermentation of orange juice (Fig. 3). The
tryptophan concentration of orange juice was 13.8 mg/L
before fermentation (day 0) and significantly decreased by
day 7 (6.47 mg/L). At the end of the fermentation process
(day 15), tryptophan content reached a minimal value of
3.19 mg/L.
Mercolini and colleagues [25] also observed a drop in
tryptophan content during grape must fermentation from
117 to 82 ng/mL. There is some controversy among
authors related to factors involved in the synthesis of
melatonin during fermentation. Rodrı́guez-Naranjo and
colleagues [32] indicated that melatonin synthesis depends
on the growth phase of the yeast and the concentration of
tryptophan. However, Tan and colleagues [36] pointed to
melatonin production without the presence of tryptophan
and observed that the production of melatonin and ISO
was independent of external tryptophan during wine
fermentation, suggesting that yeasts can still synthesize
this indoleamine without tryptophan in the medium.
In the present study, the drop of tryptophan level during fermentation could be related to the simultaneous synthesis of melatonin. In addition, the correlation between
content of tryptophan and melatonin of orange juice
during fermentation was studied, and the results are presented in Fig. 4. Total melatonin concentration inversely
and significantly correlated with tryptophan values
(r = 0.907). Taking these results into account, we hypothesize that the enhancement in melatonin content of orange
juice during fermentation could be due to both the presence of its precursor, tryptophan, and the new synthesis
by yeast.
This study reports for the first time the influence of
alcoholic fermentation on melatonin and ISO formation in
36
Fig. 3. Evolution in the tryptophan
content of the orange juice during the
alcoholic fermentation process. Symbols
represent mean values and error bars the
S.E.M. *P < 0.05, **P < 0.01 as compared
with day 0.
20
25
Fig. 4. Correlation between total melatonin (MEL) content (ng/mL) and tryptophan concentration (mg/L) present in
fermented orange juice. Pearson’s correlation coefficient (r) is significant at the
** 0.01 level.
orange juice. According to our results, fermentation of
orange juice induces a gradual synthesis of melatonin with
a rise from day 7 to day 15 of alcoholic fermentation.
When comparing melatonin amounts in fermented orange
juice with the content in other fruits, it is suggested that
this beverage is a promising source of this bioactive compound. However, ISO content remains stable during the
process. Moreover, to optimize the conditions for melatonin synthesis, it is important to know the factors involved
in this process. In this study, the enhancement of the melatonin content may have been dependent on tryptophan as
this precursor decreases during orange juice fermentation.
Fermented orange juice could be a new functional food,
and its consumption could exert a potentially positive
effect on health. Subsequent intervention studies are necessary to evaluate the health effects of this novel orange
beverage and to verify whether any benefits observed may
be, at least in part, due to melatonin and its isomers, possibly
acting synergistically with other bioactive compounds present
in the fruit such as flavanones and carotenoids.
Acknowledgements
The authors are grateful to the company ‘Grupo
Hesperides Biotech S.L.’ for providing the samples of fermented orange juice. The authors also gratefully acknowledge the support of Junta de Andalucı́a through the
Project P09-AGR4814M and of National funding agencies
through the Projects AGL2011-23690, CSD007-0063
(CONSOLIDER-INGENIO 2010 ‘Fun-C-Food’) and
CSIC 201170E041. The authors are also grateful to the
Fundación Seneca – CARM ‘Group of Excellence in
Research’ 04486/GERM/06 and the Ibero-American
Programme for Science, Technology and Development
Melatonin in fermented orange juice
(CYTED) – Action 112RT0460 CORNUCOPIA. The
Research Project grant of BEL is supported by Junta de
Andalucı́a.
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