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July 2018. Horticultural Plant Journal, 4 (4): 144–150.
Horticultural Plant Journal
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Melatonin Treatment Enhances the Polyphenol Content and
Antioxidant Capacity of Red Wine
XU Lili , YUE Qianyu , BIAN Feng’e , ZHAI Heng , and YAO Yuxin
∗
State Key Laboratory of Crop Biology, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (Huang-Huai Region, Ministry of
Agriculture), College of Horticulture Science and Engineering, Shandong Agricultural University, Tai’an, Shandong 271000, China
Received 9 October 2017; Received in revised form 21 November 2017; Accepted 20 April 2018
Available online 7 June 2018
A B S T R A C T
Melatonin and polyphenols are strong antioxidants, and melatonin is also a potential plant growth regulator. The role of melatonin in regulat-
ing polyphenol metabolism is unclear. This study assessed the primary impacts of exogenous melatonin treatment on phenolics accumulation
and antioxidant capacity of the ‘Moldova’ wine. It was found that two times of 100 μmol ·L
−1
melatonin treatment clearly enhanced the en-
dogenous melatonin content of ripened berries and wine. Further experiments indicated that melatonin treatment signicantly increased the
contents of total phenols, avonoids and anthocyanins in wine. Additionally, the contents of most of the 20 detected individual phenolic com-
pounds were signicantly enhanced by melatonin treatment in wine. Particularly, the content of two non-avonoid phenolic compounds (sy-
ringic and coumaric acid) and four anthocyanin compounds [Mv-3-Glu, Mv-3-(6-Coum)Glu-5-Glu, Dp-3-(6-AC)Glu and Dp-3-(6-Coum)Glu-5-Glu]
were largely increased by melatonin treatment. In contrast, only Pn-3-(6-Coum)Glu was signicantly reduced. Moreover, melatonin treatment
signicantly enhanced the antioxidant capacity of wine indicated by DPPH and FRAP assays. In summary, melatonin treatment enhanced the
polyphenol content and antioxidant capacity of wine.
Keywords: grape; red wine; melatonin; phenolics; antioxidant capacity
1. Introduction
Grapes are one of the world’s largest fruit crops, with an
annual production of more than 60 billion kg ( Radovanovi
´
c et
al., 2015 ). Approximately 71% of world grape production is used
for wine, 27% as fresh fruit, and 2% as dried fruit ( Radovanovi
´
c
et al., 2015 ). As an alcoholic beverage of economic relevance,
wine contains a lot of bioactive compounds with antioxidant
properties and makes a signicant contribution to a healthy
diet.
Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine
that is synthesized from L -tryptophan metabolism via serotonin,
and is a proven broad-spectrum antioxidant ( Galano et al., 2011 ).
Melatonin has been shown to occur in grape skin, esh and
seeds ( Murch et al., 2010 ). Its concentration depends on the grape
variety and the phenological stage; the highest concentration of
∗Corresponding author. Tel .: + 86 538 8246258
E-mail address: yaoyx@sdau.edu.cn
Peer review under responsibility of Chinese Society for Horticultural Science (CSHS) and Institute of Vegetables and Flowers (IVF), Chinese
Academy of Agricultural Sciences (CAAS)
melatonin is found at the early stage of veraison in wine grapes
( Murch et al., 2010 ). As expected, further studies identied mela-
tonin in wine. The levels of melatonin vary in wine amongst
different cultivars and also depend on agrochemical treatments
and wine-making processes ( Vitalini et al., 2011 ). Melatonin has
been reported to have many physiological functions in plants,
and credible evidences show that melatonin functions in pre-
venting oxidative damage via direct detoxication of reactive
oxygen and reactive nitrogen species and indirectly by stimu-
lating antioxidant enzymes ( Zhang and Zhang, 2014; Reiter et
al., 2016 ). Additionally, melatonin is indicated to function as a
growth regulator ( Arnao and Hernández-Ruiz, 2015 ). For example,
melatonin can promote plant growth with a considerable auxinic
effect ( Hernández-Ruiz et al., 2004 ), promote tomato ripening
( Sun et al., 2015 ), and increase the size and synchronicity of grape
berries ( Meng et al., 2015 ).
https://doi.org/10.1016/j.hpj.2018.05.004
2468-0141/© 2018 Chinese Society for Horticultural Science (CSHS) and Institute of Veget abl es and Flowers (IVF), Chinese Academy of Agricultural
Sciences (CAAS). This is an open access article under the CC BY-NC-ND license. ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )
Melatonin Treatment Enhances the Polyphenol Content and Antioxidant Capacity of Red Wine 145
Red wine contains a large amount of diverse phenolic com-
pounds; a bottle of red wine contains a total of 1.8 g ·L
−1 of
polyphenols ( Fernández-Mar et al., 2012 ). Red grape and red wine
polyphenols are mainly avonoid (anthocyanins, avonols and
avanols, proanthocyanidins) and non-avonoid compounds
(phenolic acids), all known for their strong biological actions
( Monagas et al., 2005 ). Polyphenols represent the paradigm of
the health-promoting effects ascribed to grape products, and
polyphenols as strong antioxidants play a key role in prevent-
ing oxidative damage ( Monagas et al., 2005 ) . Additionally, in-
creasing evidence shows that the in vivo antioxidant effects of
polyphenols arise from their ability to modulate cellular sig-
naling transduction ( Zhang and Tsao, 2016 ). A high correlation
between phenolic composition and the antioxidant capacity of
wine has been described, and anthocyanins are the main com-
position with signicant contributions to antioxidant capacity
( Lingua et al., 2016a ). Additionally, synergism between phenolic
compounds makes a positive contribution to antioxidant capac-
ity ( Lingua et al., 2016b ).
To date, it is largely unknown whether melatonin treatment
can modify the composition and content of phenolic compounds
and thereby alter the antioxidant capacity of red wine. In this
study, the wine made from ‘Moldova’ grape, which is widely
planted as a table or wine grape cultivar due to its high resistance
to downy mildew in China, was used to explore the key changes
in phenolics upon melatonin treatment. This research will pro-
mote the application of melatonin for quality improvements of
red wine.
2. Materials and methods
2.1. Plant materials and experimental design
The present experiment was undertaken at an experimental
vineyard in Tai ’ a n City, Shandong Province, China. Six-year-old
self-rooted ‘Moldova’ vines were used in 2016. When the berries
reached early veraison (6th July), the berries were subjected to
the rst melatonin treatment. Each grape cluster on the vine
was gently put into a 2-L plastic beaker containing different
concentrations of melatonin solutions and soaked for 10 s. The
melatonin solutions were prepared at concentrations of 0, 10,
100 and 1 000 μmol ·L
−1 plus 0.05% (v/v) Triton X-100. Eight
days later, the second melatonin treatment was performed for
the 100- μmol ·L
−1 melatonin treated berries using the same
concentration and method. The ripened berries, at 77 days after
veraison, were collected and used for small-scale winemaking.
The experiment was a randomized block design with three repli-
cations. Each replication consisted of 12 vines. Each vine had 15
vertical fruiting shoots on the horizontal cordon. Each fruiting
shoot was controlled to produce two clusters. For each cluster, 15
berries were randomly sampled from the shoulder, middle, and
tail.
2.2. Extraction of total phenols, phenolic compounds and
melatonin
Tota l phenols and phenolic compounds were extracted from
wine according to Xu et al. (2011) with some modications. One
milliliter of wine was mixed with 8 mL acidied methanol (0.1%
HCl, v/v) and sonicated in an ultrasonic bath for 15 min. After
the supernatants had been poured out, the precipitate was ex-
tracted two more times. The supernatants were combined and
centrifuged at 5 000 r ·min
−1 for 15 min. The supernatants were
then ltered on a lter paper, and the ltrate was evaporated to
dryness at 30 °C in a rotary evaporator. The residue was dissolved
in 5 mL methanol. Extractions were performed in three replicates.
Melatonin was extracted according to the method of Sun
et al. (2015) with some modications, and the process was similar
to polyphenol extraction but with the following changes: extrac-
tion was carried out under dim green light, acidied methanol
was replaced by methanol, and the nal extracts were passed
through a C
18 solid phase extraction (SPE) cartridge (ProElut
TM
,
DIKMA, China) with the help of a vacuum pump at a ow rate of
1 mL ·min
−1
for the purication of melatonin.
2.3. Photometric determination of total phenols, avonoids,
proanthocyanidins and anthocyanins
Tota l phenols and proanthocyanidins were determined us-
ing the Folin-Ciocalteu method with gallic acid as the standard
( Dewanto et al., 2005 ) and the vanillin assay with vanillin as the
standard ( Sun et al., 1998 ), respectively. Tota l avonoids and an-
thocyanins were photometrically measured according the meth-
ods published previously ( Dewanto et al., 2005; Li et al., 2013 ).
2.4. Identication of anthocyanin compounds and melatonin by
UPLC-QToF-MS
Anthocyanins and melatonin were identied by Ultra-
Performance Liquid Chromatography (UPLC) equipped with au-
tosampler injection and pump systems (Waters, Milford, MA,
USA). The chromatographic separation was performed on a
reverse-phase C
18
analytical column (Acquity UPLC BEH C
18
, Wa-
ters) of 100 mm ×2.1 mm and 1.7 μmol ·L
−1 particle size. Mass
spectrometry analysis was performed using a QTof-Micro mass
spectrometer (Waters, Milford, MA, USA). The injection volume
was set as 5 μL. The parameters and conditions were set accord-
ing to the methods described by Machado et al. (2015) and Gomez
et al. (2012) for anthocyanins and melatonin, respectively. The
amount of anthocyanin was calculated with reference to the ex-
ternal calibration curve of malvidin-3- O -glucoside.
2.5. Identication of non-avonoid phenolic compounds and
avanols by HPLC
Phenolic compounds were analyzed on a HPLC system (Wa-
ters 600, Wate rs, Milford, MA, USA) equipped with a Water s 2487
dual λabsorbance detector. Determination was performed as de-
scribed by Katalini
´
c et al. (2010) with some modications. The
extracts were ltered through 0.22- μm syringe lters and di-
rectly injected through a 10 μL xed loop into a C
18 guard col-
umn. Phenolic compounds were separated on a XDB-C
18
column
(4.6 mm ×250 mm, 5 μm, Kromasil, Sweden) maintained at 30 °C.
A gradient consisting of solvent A (water/acetic acid, 98:2) and
solvent B (acetonitrile) was applied at a ow rate of 1.0 mL ·min
−1
as follows: 0 min, 90% A and 10% B; 30 min, 65% A and 35% B;
42 min, 90% A and 10% B; 45 min, 90% A and 10% B. The signal was
monitored at 280 nm. The phenolic compounds were quantied
from the areas of their peaks at 280 nm using external standard
calibration curves.
146 XU Lili et al.
2.6. Assays of antioxidant properties
Free radical scavenging activity was assessed by the DPPH as-
say ( Katalini
´
c et al., 2010 ) and ABTS assay ( Re et al., 1999 ). For the
DPPH assay, antiradical activity was dened as the amount of an-
tioxidant necessary to decrease the initial DPPH concentration by
50% (EC
50
). EC
50
was calculated with gallic acid as equivalent; for
reasons of clarity, the results were provided as antiradical power
(ARP = 1/EC
50
). The determination of ferric reducing antioxidant
power (FRAP assay) was performed according to the method of
Sun et al. (2011) . For ABTS and FRAP assays, the radical scaveng-
ing activities of the samples were expressed as Trolox equivalent
antioxidant capacity.
2.7. Small-scale wine making
Control and melatonin-treated berries (35 kg for each repli-
cate) were squeezed in a squeezing roller and the grape must
was transferred to 50-L stainless steel fermentation tanks. The
must was treated with sulfur dioxide (80 mg ·L
−1
) prior to
undergoing fermentation at 25 °C. The cap of the wine was
punched down twice daily until it remained submerged. Af-
ter 10 days of maceration when fermentation was nished,
the wine residue was pressed. Free-run and press wines were
combined and stored in vessels at 15 °C. After one month
of storage, sulfur dioxide (30 mg ·L
−1
) was added a second
time and the wines were cold-stabilized for one month at
4 °C. Finished wines were ltered and bottled for subsequent
storage.
2.8. Statistical analysis
All statistical analysis was performed by SPSS (V19.0) soft-
ware. A One-way analysis of variance (ANOVA) followed by
Duncan’s multiple range test was employed, standard devia-
tion ( SD ) was calculated from three replicates. The differences
between individual means were deemed to be signicant at
P < 0.05.
3. Results
3.1. Effects of different concentrations of melatonin treatments
on endogenous melatonin content in berry and wine
The content of melatonin was determined in the ripened
berries and wine ( Fig. 1 , A). The content of melatonin in berries,
treated once with melatonin at early veraison, was continu-
ously increased with the enhancement of the applied mela-
tonin concentration, and the increments under 100- and 1 000-
μmol ·L
−1 melatonin conditions reached statistically signicant
levels compared to the control. Additionally, there was no sig-
nicant difference between 100- and 1 000- μmol ·L
−1
melatonin
treatments ( Fig. 1 , B). On the other hand, it was found that the
berries treated twice with 100- μmol ·L
−1 melatonin contained
Fig. 1 Changes of endogenous melatonin in berry and wine under melatonin treatments
A, the berries at veraison and ripened stages and wine under melatonin treatment; B, the melatonin content of berries under
different concentrations of melatonin treatments; C, the melatonin content in berries and wine after two times of 100- μmol ·L
−1
melatonin treatment.
Melatonin Treatment Enhances the Polyphenol Content and Antioxidant Capacity of Red Wine 147
Table 1 Contents of total phenols, avonoids, anthocyanins and proanthocyanidins in wine
Treatment Phenols/(mg ·mL
−1
) Total flavonoids/(mg ·mL
−1
) Total anthocyanins/(OD ·mL
−1
) Total proanthocyanins/(mg ·mL
−1
)
Control 317.62 ±18.75 0.84 ±0.12 7.68 ±0.62 8.05 ±0.76
Melatonin (100 μmol ·L
−1
) 375.56 ±27.11
∗1.06 ±0.05
∗9.24 ±0.68
∗8.41 ±0.64
Note: Va lue s are reported as the means ±SD .
∗Signicant difference, P < 0.05.
Table 2 Modications of non-avonoid phenolic compounds and avanols in wine under melatonin treatment mg ·L
−1
Treatment Chlorogenic acid Gallic acid Caffeic acid Syringic acid Coumaric acid
Control 5.75 ±1.30 9.50 ±1.00 4.52 ±0.47 4.85 ±0.85 1.54 ±0.33
Melatonin (100 μmol ·L
−1
) 11.15 ±1.02
∗∗ 13.33 ±1.58
∗∗ 7.00 ±0.49
∗∗ 13.88 ±1.02
∗∗ 4.32 ±0.63
∗∗
Treatment Ferulic acid Phloretin Cinnamic acid Trans-resveratrol (-) Epicatechin ( + ) Catechin
Control 1.68 ±0.07 0.19 ±0.03 1.02 ±0.17 0.77 ±0.01 36.27 ±1.32 31.22 ±0.95
Melatonin (100 μmol ·L
−1
) 2.09 ±0.30
∗0.23 ±0.03 2.03 ±0.16
∗∗ 1.22 ±0.09
∗∗ 44.91 ±2.23
∗36.48 ±1.38
∗
Note: values are reported as the means ±SD .
∗Signicant difference, P < 0.05;
∗∗Highly signicant difference, P < 0.01.
Table 3 Modications of the anthocyanin proles in wine induced by melatonin treatment mg ·L
−1
Treatment Mv-3,5-Glu Mv-3-Glu Mv-3-(6-Coum) Glu-5-Glu Mv-3-(6- Coum)Glu
Control 2 160.12 ±172.05 250.45 ±21.36 113.94 ±7.25 Undetectable
Melatonin (100 μmol ·L
−1
) 2 109.54 ±333.37 345.61 ±32.84
∗∗ 366.30 ±17.51
∗∗ 22.34 ±3.14
Treatment Pn-(6-Caff) Glu Pn-3-Glu Pn-3-(6-Coum) Glu Dp-3-(6-AC) Glu Dp-3-(6-Coum) Glu-5-Glu
Control 492.57 ±23.65 55.26 ±6.74 133.28 ±21.03 304.12 ±20.17 124.50 ±6.99
Melatonin (100 μmol ·L
−1
) 541.67 ±22.38 63.22 ±5.31 64.49 ±4.06
∗∗ 397.11 ±38.82
∗∗ 377.52 ±13.54
∗∗
Note: values are reported as the means ±SD . Mv, malvidin; Glu, glucoside; Coum, coumaroyl; Pn, peonidin; Caff, caffeoyl; AC, acetyl; Dp, delphinidin;
∗∗ Highly signicant difference, P < 0.01.
Table 4 Changes of the antioxidant activities in wine induced by melatonin treatment
Treatment DPPH/(mg gallic acid ·mL
−1
) ABTS/(mg Tro lox ·mL
−1
) FRAP/(mg Tro lox ·mL
−1
)
Control 2.38 ±0.32 6.70 ±0.41 6.32 ±0.61
Melatonin (100 μmol ·L
−1
) 3.16 ±0.15
∗∗ 7.10 ±0.75 8.20 ±0.76
∗
Note: values are reported as the means ±SD .
∗Signicant difference, P < 0.05;
∗∗Highly signicant difference, P < 0.01.
16.9% higher melatonin content than the berries treated once.
Consistently, two times of 100- μmol ·L
−1
melatonin signicantly
enhanced melatonin levels of wine. Therefore, two times of 100-
μmol ·L
−1
melatonin treatments were applied to evaluate the ef-
fects of melatonin on polyphenol content and antioxidant capac-
ity in the following sections ( Fig. 1 , C).
3.2. Melatonin treatments enhanced the content of total
phenols, avonoids, anthocyanins and proanthocyanidins in
wine
There was no visual distinguishable color difference between
the control and melatonin-treated berries and wine ( Fig. 1 , A), but
the content of total anthocyanin was increased 20.3% by mela-
tonin treatment ( Table 1 ). Additionally, melatonin treatment sig-
nicantly enhanced the contents of total phenols and avonoids,
compared to the control, with the increments of 18.2% and 26.2%,
respectively. In contrast, only a 4.47% increment in the content of
proanthocyanins was produced by melatonin treatment ( Table 1 ).
3.3. Melatonin treatment modies content of phenolic
compounds in wine
To investigate the changes in the phenolic compound con-
tents between the control and melatonin-treated wine, 20 phe-
nolic compounds were determined ( Ta b l e 2 and 3 ). A total of nine
non-avonoid phenolic compounds were detected, including
chlorogenic acid, gallic acid, caffeic acid, syringic acid, coumaric
acid, ferulic acid, phloretin, cinnamic acid and resveratrol
( Tabl e 2 ). Gallic acid exhibited the highest concentration, followed
by chlorogenic, syringic and caffeic acids. In contrast, phloretin
was at low concentrations in the wine. Melatonin treatment sig-
nicantly enhanced the content of the detected phenolic com-
pounds except for phloretin and hence generated an 85.8% in-
crease in total compounds in the wine. In particular, the con-
tents of syringic and coumaric acids were increased 1.86- and
1.81-folds by melatonin treatment. The increments for chloro-
genic and cinnamic acids neared one fold.
Tw o avanols, catechin and epicatechin, were determined
( Tabl e 2 ). Catechin and epicatechin were present at a high con-
centration compared to non-avonoid phenolic compounds in
the wine. Melatonin treatment led to more than 16.8% and 23.8%
increases in the content of catechin and epicatechin, respectively.
The anthocyanin proles of the detected samples primar-
ily consisted of malvidin (Mv), peonidin (Pn), and delphinidin
(Dp) ( Ta b l e 3 ). Mv-3,5-glucose (Glu) was the most abundant an-
thocyanin and accounted for more than 59.4% and 49.2% of
the detected total anthocyanins in the control and melatonin-
treated wine. In contrast, the other anthocyanin compounds
and especially Pn-3-Glu were present at relatively low levels
( Tabl e 3 ). When comparing anthocyanin content between the
148 XU Lili et al.
control and melatonin-treated wine, the most primary antho-
cyanin compound Mv-3,5-Glu was not clearly altered by mela-
tonin treatment; in contrast, melatonin signicantly enhanced
the contents of Mv-3-Glu, Mv-3-(6-Coum)Glu, Dp-3-(6-AC)Glu,
Mv-3-(6-Coum)Glu-5-Glu and Dp-3-(6-Coum)Glu-5-Glu; particu-
larly, Mv-3-(6-Coum)Glu-5-Glu and Dp-3-(6-Coum)Glu-5-Glu were
increased 2.2 and 2.0-folds, respectively. In contrast, the con-
tent of Pn-3-(6-Coum)Glu was largely reduced by melatonin treat-
ment. As a result, the melatonin treatment enhanced four antho-
cyanin compounds signicantly and generated a 17.2% increase
in the sum of anthocyanins in wine.
3.4. Melatonin treatment enhances the antioxidant capacity of
wine
The in vitro antioxidant activities of the control and
melatonin-treated wine were evaluated by DPPH, ABTS and
FRAP assays ( Table 4 ). Melatonin treatment enhanced the values
of DPPH, ABTS and FRAP to varying extents. The values for
DPPH and FRAP were increased 32.8% and 29.7% in a statistically
signicant manner.
4. Discussion
In this paper, melatonin treatment was indicated to enhance
phenolics content of red wine. It was also reported that mela-
tonin treatment up-regulates the expression levels of the genes
involved in anthocyanin biosynthesis and increases total antho-
cyanin production in cabbages and tomatoes ( Sun et al., 2015;
Zhang et al., 2016 ). In contrast, the mechanism of melatonin
to regulate phenolics accumulation remains poorly understood.
The published data indicates that melatonin acts as a signal
molecular itself ( Lee et al., 2014 ), affects the levels of ABA and
GA in seeds or leaves ( Zhang et al., 2014 ), and increases ethy-
lene production and inuences the ethylene signaling pathway
in climacteric tomato fruits ( Sun et al., 2015 ). In addition, ABA and
ethylene play key roles in regulating grape berry ripening, includ-
ing the regulation of polyphenol metabolism ( Sun et al., 2010; Be-
catti et al., 2014 ). Therefore, melatonin might regulate polyphenol
metabolism as a signal molecular itself and/or via the interplay
with other ripening-related signaling molecule such as ABA and
ethylene.
Assays of DPPH, ABTS and FRAP showed that melatonin treat-
ment conferred wine with high free radical scavenging capacity
and reducing antioxidant power. Similarly, the enhanced antiox-
idant capacity conferred by melatonin treatment was also found
in peach fruits ( Gao et al., 2016 ). Up to now, the precise mecha-
nism underlying the melatonin-induced enhancement in antiox-
idant capacity remains largely unknown; however, several path-
ways are likely to participate in this process.
On the one hand, melatonin can directly scavenge ROS. It
was reported that melatonin directly scavenges the highly toxic
·OH, H
2
O
2
, and O
2
·-
( Tan et al., 1993; Herraiz and Galisteo, 2004 ).
The antioxidant role of melatonin in grape fruits is also sug-
gested by monitoring melatonin uctuation during day/night
cycle ( Boccalandro et al., 2011 ). Additionally, melatonin indi-
rectly scavenges radicals by stimulating protective antioxidant
enzymes ( Zhang and Zhang, 2014 ). It was reported that appli-
cation of melatonin alleviates oxidative injury via enhancing
the activity of antioxidant enzymes, such as glutathione per-
oxidase, superoxide dismutase and glutathione reductase ( Gao
et al., 2016 ). The transcript levels of the genes encoding SOD,
APX, CAT and peroxidase are also up-regulated by melatonin
( Rodriguez et al., 2004 ). Therefore, the enhanced melatonin con-
tent in wine contributes positively to scavenge ROS directly as
an antioxidant and/or via promoting the activity of antioxidant
enzymes.
On the other hand, melatonin enhances antioxidant capac-
ity via promoting polyphenol accumulation. In grape berries, the
content of total phenols, total avonoids, total anthocyanins and
proanthocyanidins exhibits a signicant correlation with antiox-
idant properties ( Xu et al., 2010 ). Those compounds were sig-
nicantly increased in the melatonin-treated wine. Additionally,
the large changes in non-avonoid, avanol and anthocyanin
compounds were found in the melatonin-treated wine. Epicat-
echin, catechin and gallic acid were the three highest levels of
non-avonoid polyphenols and avanol in ‘Moldova’ wine. It was
reported that the free radical scavenging activity of gallic acid,
catechin and epicatechin are high and they show high corre-
lations with antioxidant activities compared to other phenolic
compounds ( Alvarez-Casas et al., 2016 ). Therefore, the signicant
increases in the three above compounds might contribute posi-
tively to the enhancement of antioxidant capacity. In contrast,
anthocyanins are described as main contributors to in vivo an-
tioxidant capacity in wine ( Lingua et al., 2016a ). Anthocyanins are
glycosides of anthocyanidins, and six different anthocyanidins
are found in nature; i.e., pelargonidin, cyaniding, delphinidin, pe-
onidin, petunidin and malvidin. Malvidin possesses great antiox-
idant capacity with excellent free radical scavenging properties in
vitro and in cells ( Huang et al., 2016 ). In contrast, cyaniding and
delphinidin have a higher antioxidant activity than malvidin, pe-
onidin and others ( Clifford, 2000 ). Therefore, the large increases
in two delphinidin compounds and three malvidin compounds
might contribute positively to the increased antioxidant capac-
ity. Taken together, melatonin enhances the antioxidant capacity
of wine by widely modifying the content and/or composition of
phenolic compounds.
Moreover, the antioxidant capacity is the result of synergis-
tic or antagonistic effects from interactions between different
polyphenol compositions among each other and with other com-
ponents of the food matrix or organism. It was also reported that
Mv-3-glu shows a synergistic antioxidant effect with catechin
on free radical-initiated peroxidation of linoleic acid in micelles
( Rossetto et al., 2002 ). Melatonin can have a synergistic effect with
other antioxidants, such as resveratrol ( Kwon et al., 2011 ). There-
fore, the enhancement of antioxidant capacity induced by mela-
tonin is associated not only with the increased endogenous mela-
tonin and polyphenolic constituents but also with their compli-
cated reactions.
In conclusion, this report elucidated the impacts of mela-
tonin treatment on the polyphenol content in wine. We found
that two melatonin treatments of veraison grape berries in-
creased the contents of total phenols, avonoids and antho-
cyanins in wine. Meanwhile, the melatonin-induced increases
in individual phenolic compounds were observed, including
syringic acid, coumaric acid, Mv-3-Glu and so on. Addition-
ally, melatonin treatment enhanced the antioxidant capacity of
wine.
Melatonin Treatment Enhances the Polyphenol Content and Antioxidant Capacity of Red Wine 149
Acknowledgments
This work was supported by Natural Science Foundation of
Shandong Province ( ZR2015CM014 ), Funds of Shandong “Double
Tops ” P r o g r a m ( SYL2017YSTD10 ), Chinese Agricultural Research
System ( CARS-30-ZT-06 ).
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