Characterization of polyphenolic compounds in cantaloupe melon by-products

Abstract

The Muskmelon (Cucumis melo L.), which includes several crops of great economic importance worldwide, belongs to the Cucurbitaceae family, and it is well recognized for culinary and medicinal purposes. The high fruit consumption produces a large quantity of waste materials, such as peels and seeds that are still rich in molecules like polyphenols, carotenoids, and other biologically active components that possess a positive influence on human health and wellness. A sustainable development in agro-food and agro-industry sectors could come through the reutilization and valorization of these wastes, which in turn, could result in reducing their environmental impact. The current study provides a biochemical characterization of cantaloupe by-products, peels and seeds, through evaluating total polyphenols, ortho-diphenols, flavonoids, and tannins content. Furthermore, the antioxidant activity was assessed in order to understand potential benefits as natural antioxidants. Overall, the peel extract revealed the highest radical's scavenging and reducing activities, moreover, it showed higher polyphenolic content than seed extract as revealed by both cromatographic and spectrophotometric analyses. The results of the present study indicate that the melon residues are a good source of natural phytochemicals useful for many purposes, such as ingredients for nutraceutic, cosmetic, or pharmaceutical industries, development of functional ingredients and new foods, and production of fertilizers and animal feed.

Full text

foods
Article
Characterization of Polyphenolic Compounds in
Cantaloupe Melon By-Products
Filomena Monica Vella 1, Domenico Cautela 2and Bruna Laratta 1, *
1Consiglio Nazionale delle Ricerche (CNR), Istituto di Ricerca sugli Ecosistemi Terrestri (IRET),
via P. Castellino, 111-80131 Napoli, Italy; monica.vella@iret.cnr.it
2Stazione Sperimentale per le Industrie delle Essenze e dei derivati dagli Agrumi (SSEA), Azienda Speciale
della Camera di Commercio di Reggio Calabria, via T. Campanella, 12-89125 Reggio Calabria, Italy;
dcautela@ssea.it
*Correspondence: bruna.laratta@cnr.it; Tel.: +39-081-6132329
Received: 2 April 2019; Accepted: 1 June 2019; Published: 6 June 2019


Abstract:
The Muskmelon (Cucumis melo L.), which includes several crops of great economic
importance worldwide, belongs to the Cucurbitaceae family, and it is well recognized for culinary
and medicinal purposes. The high fruit consumption produces a large quantity of waste materials,
such as peels and seeds that are still rich in molecules like polyphenols, carotenoids, and other
biologically active components that possess a positive influence on human health and wellness. A
sustainable development in agro-food and agro-industry sectors could come through the reutilization
and valorization of these wastes, which in turn, could result in reducing their environmental impact.
The current study provides a biochemical characterization of cantaloupe by-products, peels and seeds,
through evaluating total polyphenols, ortho-diphenols, flavonoids, and tannins content. Furthermore,
the antioxidant activity was assessed in order to understand potential benefits as natural antioxidants.
Overall, the peel extract revealed the highest radical’s scavenging and reducing activities, moreover,
it showed higher polyphenolic content than seed extract as revealed by both cromatographic and
spectrophotometric analyses. The results of the present study indicate that the melon residues are a
good source of natural phytochemicals useful for many purposes, such as ingredients for nutraceutic,
cosmetic, or pharmaceutical industries, development of functional ingredients and new foods, and
production of fertilizers and animal feed.
Keywords: Cucumis melo; polyphenols; flavonoids; antioxidants; by-products; waste valorization
1. Introduction
The Cucurbitaceae family covers several species of great economic importance, including
muskmelon (Cucumis melo L.), which is largely cultivated and consumed in Europe. Muskmelon
encircles a wealth of varietal types, such as smooth-skinned varieties like Honeydew, Crenshaw, and
Casaba (C. melo var. inodorous), rough-skinned varieties like Cantaloupe, Persian melon, and Santa
Claus or Christmas melon (C. melo var. reticulatus), and varieties used when they are immature as
vegetables like Barattiere, Carosello, and Armenian Cucumber (C. melo var. flexuosus). The Cantaloupe
melon is well recognized by its net-like slightly ribbed, gray-to-green or light brown skin. It is one
of the most consumed melons worldwide thanks to its sweetness, juicy taste, pleasing flavor, and
nutritional value [
1
,
2
]. In 2016, about 1.9 million tons of melon were harvested in the Mediterranean
area, with Spain, Italy, and France representing the main European producers, accounting for 35%,
34%, and 13% overall yield, respectively [
3
]. In Italy, Cantaloupe is the most cultivated variety. Its
name is supposed to derive from Italian “Cantalupo in Sabina”, which was formerly a papal county
seat near Rome [4].
Foods 2019,8, 196; doi:10.3390/foods8060196 www.mdpi.com/journal/foods

Foods 2019,8, 196 2 of 10
Cantaloupe is an excellent source of vitamin A, vitamin C, and microelements such as potassium
and magnesium [
1
,
4
,
5
]. In recent years, it has been shown to possess useful medicinal properties
such as analgesic, anti-inflammatory, antioxidant, antiulcer, anticancer, antimicrobial, diuretic, and
antidiabetic properties [
2
,
6
,
7
]. Furthermore, it showed a hepato-protective effect, activity against
hypothyroidism and immune-modulator action [6].
Ever-increasing demand for healthy food has stimulated the manufacturing sectors to search for
new natural sources of nutritional and healthful components to be employed as food additives or
supplements, with high nutritional value [
8
,
9
]. As a consequence, the European Union has encouraged
the exploitation of fruit by-products for their use as a source of nutritionally and therapeutically
functional ingredients to utilize for dietary intake, and as active ingredients in pharmaceuticals and
cosmetic industries [10,11].
During fresh consumption and industrial processing of melons (juices, compotes, and salads),
large quantities of peels and seeds are produced, and are considered waste. The complete utilization
of these by-products could minimize the litter volume, so reducing the environmental impact and
the economic costs associated to their disposal. Peels and seeds, in fact, are potential sources of
phytochemicals, such as polyphenols, carotenoids, flavonoids, and other bioactive compounds with
potential health-promoting effects [
12
,
13
]. Among them, polyphenol compounds show antioxidant
activity, delaying or inhibiting the oxidation of lipids and other molecules, thus playing an important
role in defending cells against free radical damage, a very important way of preventing diseases like
cancer and cardiovascular disorders [12–15].
Studies related to melon peels and seeds are scarce; data concerning their whole biochemical
characterization are insufficient. Recently, Mallek-Ayadi et al. [
5
] studied only the phenolic composition
and functional properties of peels, concluding that this by-product could be considered as a rich source
of carbohydrates, proteins, calcium, potassium, and polyphenols. Fundo et al. [
1
] characterized the
edible and the waste parts of cantaloupe melon, only considering the bioactive compounds showing
antioxidant activity. These studies suggested that the valorization of cantaloupe by-products should
be encouraged because they are important sources of healthy compounds for food, cosmetics, and
nutraceutical products.
On this basis, this research aims to examine the peels and seeds from cantaloupe melon, evaluating
total polyphenol, ortho-diphenol, flavonoid, and tannin contents. At the best of our knowledge,
this is the first time that such a comprehensive investigation, by means of spectrophotometric,
chromatographic and
in vitro
assays, is achieved on both extracts from seeds and peels, in order to
explore their potential attitude as natural sources of antioxidants.
2. Materials and Methods
2.1. Reagents and Standards
Sodium carbonate, Folin–Ciocalteu reagent, sodium nitrite, sodium molybdate, aluminum
chloride 6-hydrate, 2,2-diphenyl-1-picrylhydrazyl (DPPH), sodium acetate, iron(III) chloride 6-hydrate,
2,4,6-tripyridyl-s-triazine (TPTZ), bovin serum albumin (BSA), standards phenolic acids (gallic,
caffeic, chlorogenic, syringic, ferulic, and ellagic acids), flavonoids (rutin, quercetin, kaempferol and
isorhamnetin) and the HPLC-grade solvents were purchased from Sigma Chemical Co. (St. Louis,
MO, USA). Sodium hydroxide, hydrochloric acid and ethanol were obtained from Carlo Erba Reagents
(Milan, Italy).
2.2. Extraction of Bioactive Compounds
Three “Prescott” varieties of cantaloupe melons (Cucumis melo L. var. reticulatus) were purchased
in a local market at commercial ripening stage. Peels were manually removed with a knife and seeds
were separated too. Peels and seeds were oven-dried at 37
◦
C, until constant weight. Randomly chosen
samples were utilized for analyses. Both samples were milled with a food mixer (Moulinex, Italy) and

Foods 2019,8, 196 3 of 10
kept at
−
20
◦
C until extractions were performed. For bioactive compounds recovery, 200 mg of fine
powder of cantaloupe peels and seeds were extracted with 10 mL of 95% ethanol (ratio 1:50 w/v) for
6 h at 50
◦
C in a closed vessel using an ultrasonic bath. The extracts were recovered by centrifugation
at 13,000
×
gfor 10 min at 4
◦
C, and dried using a rotary evaporator (IKA RV8, IKA-Werke GmbH &
Co, Staufen, Germany).
2.3. Total Polyphenols Content
Total polyphenols were spectrophotometrically determined according to the Folin–Ciocalteu
method [
16
]. In brief, 150
µ
L of extracts were mixed with 750
µ
L of Folin–Ciocalteu reagent and 600
µ
L
of 7.5% (w/v) Na
2
CO
3
. After incubation, the absorbance was read at 765 nm (UV-Vis spectrophotometer,
model DMS-200, Varian, Leini, Italy). Total phenolic amount was calculated by a six point calibration
curve obtained with different quantities of gallic acid standard solution ranging from 1.5 to 10
µ
g.
(y =0.0768 x; R
2
=0.9909) and the results were expressed as mg of gallic acid equivalents (GAE) per g
of extract.
2.4. Ortho-Diphenols Content
Ortho-diphenols content was evaluated by Arnow assay [
17
]. Briefly, 400
µ
L of extracts were
mixed with 400
µ
L of 0.5 M HCl, 400
µ
L of 1.45 M NaNO
2
—0.4 M Na
2
MoO
4
and 400
µ
L of 1 M NaOH.
The absorbance was recorded at 500 nm and ortho-diphenols were determined by a calibration curve
obtained using caffeic acid as standard. The ortho-diphenolic content was determined by a calibration
curve obtained using a caffeic acid standard solution ranging from 5 to 50
µ
g (y =0.0152 x; R
2
=0.9921),
and the results were expressed as mg of caffeic acid equivalents (CAE) per g of extract.
2.5. Flavonoid Content
Flavonoid content in the extracts was determined according to the colorimetric method based on
the formation of flavonoid-aluminum compounds [
18
]. In the assay, extracts were mixed with distilled
water and NaNO
2
. After 5 min, AlCl
3×
6H
2
O were added and the reaction was stopped by adding
1 M NaOH and distilled water. The absorbance was read at 510 nm and (+)-catechin was used to create
the standard curve. (+)-Catechin, from 5 to 100
µ
g was used to create the calibration curve (y =0.009 x;
R2=0.9940) and the results were expressed as mg of catechin equivalents (CE) per g of extract.
2.6. Tannins Content
Total tannins were assessed as reported by Vella et al. [
19
] incubating extracts with BSA at 30
◦
C for
1 h. The supernatant, representing the non-tannin fraction, was collected by centrifugation at 13,000
×
g
for 10 min at 4
◦
C and was analyzed using the Folin-Ciocalteu method. Tannins were determined
by difference from the amounts of the polyphenols determined before and after BSA precipitation.
Tannins were expressed as mg of gallic acid equivalents (GAE) per g of extract.
2.7. In Vitro Antioxidant Activity
The antioxidant activity of cantaloupe peels and seed extracts were evaluated by means of
two
in vitro
biochemical assays: The Ferric Reducing Antioxidant Power (FRAP) and the DPPH
(2,2-diphenyl-1-picrylhydrazyl) radical-scavenging activity.
As reported by Benzie and Strain [
20
], freshly prepared FRAP reagent were added to the extracts.
The absorbance was recorded after 4 min at 593 nm. The antioxidant activity of samples was calculated
from a calibration curve with L-ascorbic acid ranging from 0.5 to 5
µ
g (y =0.1662 x; R
2
=0.9918) and
the results were expressed as mg of ascorbic acid equivalents (AAE) per g of extract.
The free radical scavenging activity (RSA) of the extracts was assessed according to the procedure
of Blois [
21
]. In brief, different concentrations of peels and seeds extracts were mixed with DPPH
methanolic solution. The absorbance reduction at 517 nm of the DPPH was determined continuously.
The RSA was calculated as a percentage of DPPH discoloration, using the following equation:

Foods 2019,8, 196 4 of 10
%RSA ="[ADPPH −As]
ADPPH #∗100, (1)
where A
S
is the absorbance of the solution when the extract was added and A
DPPH
is the absorbance
of the DPPH solution. The EC
50
value was obtained from the graph of %RSA against the extract
concentrations in mg/mL.
2.8. Cromatographic Analyses
High performance liquid chromatography-photodiode-array-mass spectrometry (HPLC-PDA-ESI-
MS/MS) analyses were performed using a Surveyor LC pump, a Surveyor autosampler, coupled with a
photodiode array detector (PDA) Surveyor and a LCQ Advantage ion trap mass spectrometer (Thermo
Finnigan, Waltham, MA, USA) equipped with Xcalibur 3.1 software (Thermo Fisher Scientific, Waltham,
MA, USA).
A volume of 5
µ
L was employed for the analysis on a Supelco Spherisorb
®
ODS2 HPLC Column
(250
×
4.6 mm), and the column was thermostatically controlled at 35
◦
C. The elution was conducted,
as already reported [
22
], by employing 0.3% acetic acid solution (solvent A) and acetonitrile (solvent B).
A gradient elution was performed as following: the initial solvent was 90% A and 10% B; the gradient
elution was changed from 10% to 20% B in a linear mode for 15 min; this composition was maintained
at isocratic flow for 10 min; the solvent B reached 50% in 10 min and from 50 to 90% B in 10 min.
Elution was performed at a flow rate of 0.5 mL/min with a splitting system of 2:8 to the MS
detector (100
µ
L/min) and PDA detector (400
µ
L/min). Analyses were performed with an electrospray
ionization (ESI) interface in the negative mode. The optimization of the instrumental parameters for
bioactive compounds was performed by continuous infusion (FIA)-ESI MS/MS analyses. Parameters
for analysis were set using negative and positive ion modes, with spectra acquired over a mass range
from m/z50 to 1100. The ionization conditions were optimized, and the parameters used were as
follows: capillary temperature, 210
◦
C; capillary voltage,
−
10.0 V; tube lens offset,
−
50.0 V; sheath gas
flow rate, 60.00 arbitrary units; auxiliary gas flow rate, 20.00 arbitrary units; spray voltage, 4.50 kV;
and scan range of m/z150–1200. In the MS/MS experiments, normalized collision energy of 35.0%
was applied.
PDA data were recorded with 200–600 nm range, and HPLC/UV chromatograms were acquired at
three different wavelengths (226, 284 and 369 nm) according to the absorption maxima of analyzed
compounds. Figure 3 shows the 284 nm absorption data for all compounds. For the quantitative analysis
of phenolic compounds, a calibration curve was obtained by the injection of different concentrations of
each standard. Peak identification of phenolic compounds was performed according to their retention
time, UV-Vis and mass spectra.
For the quantification of phenolic compounds by HPLC-UV, a calibration curve was obtained
through injection of different concentrations of standard mixture, blending aliquots of different stock
individual standards into a 10 mL glass volumetric flask. The standard solutions were prepared in
methanol in the range of 0.0025–0.045 mg/mL. The reproducibility of the detector response at each
concentration level was evaluated by a triplicate injection of standard mix and expressed as percentage
of relative standard deviations (RSD%). The RSDs were expected to be less than 2%. The limits of
detection (LOD) were established at a signal to noise ratio (S/N) of 3. The limits of quantification (LOQ)
were established at a signal to noise ratio (S/N) of 10. LOD and LOQ were experimentally verified by
the nine injections of reference compounds in LOQ concentrations.
2.9. Statistical Analysis
All samples were analyzed in triplicates and the results were expressed as mean
±
standard
deviation (SD). Means, SD, calibration curves and linear regression analyses (R
2
) were determined
using Microsoft Excel 2013 (Microsoft Corporation, Redmond, WA, USA).

Foods 2019,8, 196 5 of 10
3. Results and Discussion
The phenolic composition and functional activity of melon residues, peels and seeds, were
studied in order to explore their beneficial properties in sight of potential industrial applications.
In this contribution, a biochemical characterization was obtained through the evaluation of total
polyphenols, ortho-diphenols, flavonoids, tannins, and antioxidants by means of photometric assays
and by HPLC profiling.
In Figures 1and 2polyphenol, ortho-diphenol, flavonoid, and tannin contents in cantaloupe peels
and seeds, respectively, are reported.
Figure 1. Polyphenol, ortho-diphenol, flavonoid, and tannin contents in cantaloupe peels.
Figure 2. Polyphenol, ortho-diphenol, flavonoid, and tannin contents in cantaloupe seeds.
In peels, the polyphenol content was 25.48
±
1.44 mg GAE/g, which is 6- and 8-fold higher than
that reported by Isamil et al. [
2
] and Mallek-Ayadi et al. [
5
], respectively. This gap could be attributed
to several factors, including cultivar, degree of ripening, and environmental elements, such as climatic
conditions and geographical origin [
4
,
19
,
22
]. Conversely, cantaloupe seeds content of polyphenols
was 1.50
±
0.02 mg GAE/g, and this result matches with the range reported in literature data [
1
,
2
].
Polyphenols are commonly found in both edible and non-edible plant parts, being essential compounds
for their growth and reproduction pathways. They also play an important role in modulating the

Foods 2019,8, 196 6 of 10
defense response against insects, pathogens, and microorganisms. Moreover, they take an active part
in determining color, flavor, taste, and appearance of fruits. Among phenolics, ortho-diphenols are
recognized as the most important in relation to their antioxidant activity, since they are able to improve
radical stability by forming an intra-molecular hydrogen bond between the hydrogen and phenoxyl
radicals. As reported in Figures 1and 2,ortho-diphenols content was 17.86
±
1.43 and 0.92
±
0.04 mg
CAE/g in peels and seeds, respectively. To the best of our knowledge, data on ortho-diphenols have
never been reported in cantaloupe until now.
Considering flavonoids, they are the most common and widely distributed group of plant
phenolics, being very effective antioxidants [
23
]. Cantaloupe peels showed the highest flavonoid
content of 15.19
±
1.88 mg CE/g, meanwhile seeds had 0.74
±
0.03 mg CE/g, as shown in Figures 1
and 2, respectively. In addition, these components scored higher content values, as well for the total
phenolic compounds, than those reported in the literature [
2
,
5
]. Moreover, similarly to polyphenols,
flavonoid content has many sources of variation such as genotype, fruit ripening, plant phenotypic
state and pedoclimatic conditions [4,19,22].
Tannins have been considered health-promoting components of plants, since possessing
anti-carcinogenic and anti-mutagenic potentials, as well as antimicrobial, antioxidant and antiradical
properties [
24
–
27
]. In the present study, tannins content was higher in peels than in seeds, displaying
11.83
±
1.44 and 0.92
±
0.03 mg GAE/g, respectively. The literature reports many studies comparing
polyphenolic and flavonoid contents of different parts of cantaloupe [
1
,
2
,
5
] but tannins were
never assessed.
As the phenolic compounds are known to protect cellular components against free radicals, the
antioxidant properties of cantaloupe peels and seed extracts were estimated by means of the FRAP
assay and by the DPPH radical scavenging activity, whose results are shown in Table 1. As reported by
Benzie and Strain [
20
], the FRAP assay measures the reduction of a ferric 2,4,6-tripyridyl-s-triazine
complex (Fe
3+
-TPTZ) to the ferrous form (Fe
2+
-TPTZ) in the presence of an antioxidant compound.
The antioxidant ability, measured by the FRAP assay, indicated a higher value in peels as compared to
seeds, with values of 12.27 ±1.22 mg AAE/g and 0.31 ±0.02 mg AAE/g, respectively.
Table 1. Antioxidants content and activity in cantaloupe peels and seeds.
Antioxidant Power (mg AAE/g) * EC50 (mg/mL) **
Peels 12.27 ±1.22 6.65
Seed 0.31 ±0.02 55.03
* The antioxidant power was measured by FRAP assay; ** EC50 was calculated by DPPH assay.
The scavenging activity was studied by means of the DPPH assay, based on the evaluation of the
reduction of the DPPH radical to hydrazine as a consequence of the antiradical activity of the extracts.
Similarly to the results of the FRAP assay, scavenging activity in the peels extracts was stronger since
the EC
50
after 15 min was 6.65 mg/mL, while seed extracts showed a value of 55.03 mg/mL, thus
indicating a lower antioxidant activity of this latter cantaloupe by-product. These results were in
agreeance with literature data: in particular, the cantaloupe peels extract in our experiment proved
to be 1.4 fold more active when compared to the results published by Isamil et al. [
2
]. Conversely,
seed extract showed an activity that was half than that observed and reported by Isamil et al. [
2
]. The
results of the DPPH assay suggest that extracts are capable of scavenging free radicals via electron or
hydrogen-donating mechanisms. Moreover, DPPH activity of these cantaloupe by-products showed
similar behavior with the polyphenols, ortho-diphenols, flavonoids, and tannins content, thus indicating
that radical scavenging activity of cantaloupe peels and seeds extracts is related to the amount of
phenolic compounds.
Nowadays, synthetic antioxidants are widely used as additives in food, pharmaceuticals, and
cosmetics, but their uses have been questioned because of their possible toxic or carcinogenic activities
due to some components formed during their degradation occurring in industrial processing [
28
].

Foods 2019,8, 196 7 of 10
Therefore, the application of natural plant-based substances may be a suitable alternatives to replace
artificial molecules, not only because of their safety, but also since they protect food, feed, and
derivatives from the deleterious effects of natural oxidation.
The two extracts from melon peels and seed were also analyzed by HPLC to evaluate the real
composition of the phenolic profiles (Figure 3).
Figure 3.
HPLC chromatograms of melon peel and seed extracts, monitored at 284 nm. (
A
) Standard
mixture of bioactive compounds. (
B
) Melon peels ethanolic extract. (
C
) Melon seeds ethanolic extract.
Gallic acid (Gal), Chlorogenic acid (Clo), Caffeic acid (Caf), Syringic acid (Sir), Rutin (Rut), Ferulic acid
(Fer), Ellagic acid (Ell), Quercetin (Que), Kaempferol (Kae), Isorhamnetin (Iso).

Foods 2019,8, 196 8 of 10
Phenolic acids and flavonoids were quantified according to HPLC-PDA data recorded at 284 nm,
where gallic acid (2.45
±
0.08 mg/g), ellagic acid (0.57
±
0.01 mg/g), and kaempferol (0.32
±
0.03 mg/g)
were the main bioactive compounds found in the peels extract (Table 2; Figure 3B). In seed extract, the
richest phytochemicals were ferulic acid (1.51
±
0.02 mg/g), followed by kaempferol (
0.54 ±0.02 mg/g
),
and gallic acid (0.07
±
0.02 mg/g), as reported in Table 2and in Figure 3C. Peak identification of phenolic
compounds was performed according to their retention time, UV-Vis and mass spectra (Table 2).
Table 2. Bio-active contents in melon peel and seed extracts (UV-Vis, HPLC and MS data).
Bioactive Compound Retention
Time (min)
Parent Ion
[M-H]-(m/z)
Transitions
(m/z)
Peel Extract
(mg/g)
Seed Extract
(mg/g) λ(max)
Gallic acid (Gal) 7.39 169.0 125.1 2.45 ±0.08 0.07 ±0.02 272
Chlorogenic acid (Clo)
14.62 353.0 191.1 0.08 ±0.03 0.03 ±0.01 243,328
Caffeic acid (Caf) 17.52 179.0 135.1 <LOD <LOD 287,324
Syringic acid (Sir) 18.33 198.1 153.1 <LOD <LOD 276
Rutin (Rut) 26.15 609.0 299.9 0.06 ±0.01 nd 258,356
Ferulic acid (Fer) 27.58 193.0 176.9 0.09 ±0.01 1.51 ±0.02 287,312
Ellagic acid (Ell) 29.86 301.3 229.0 0.57 ±0.01 nd 254,364
Quercetin (Que) 38.61 301.0 150.9 0.02 ±0.01 nd 255,372
Kaempferol (Kae) 39.96 285.0 185.0 0.32 ±0.03 0.54 ±0.02 266,366
Isorhamnetin (Iso) 40.51 315.0 286.0 <LOD <LOD 268,342
LOD =limit of detection S/N: 3 (n=9) LOD =0.02 µg/mL.
Gallic acid, ellagic acid and kaempferol have been reported to have antiviral, anti-mutagenic,
anticancer, antioxidant and cytotoxic effects [
29
–
31
]. Ferulic acid is a ubiquitous natural phenolic
compound in seeds; it exhibits a wide variety of biological activities such as antioxidant,
anti-inflammatory, antimicrobial, antiallergic, hepatoprotective, anticarcinogenic, antithrombotic,
antiviral and vasodilatory actions, increase sperm viability, metal chelation, modulation of enzyme
activity, activation of transcriptional factor [
31
]. Peel and seed HPLC profiles showed some differences
from what was reported by Mallek-Ayadi et al. [
5
] and Zeb [
32
]. We suppose that these differences
might be due to variation relating to different cultivar, environmental conditions during plant growth
and fruiting, plant phenotypic state, and possibly due to extraction conditions too [4,19,22].
Altogether, HPLC analysis confirms a higher level of phenolic acids and flavonoids in melon
peel than in seed extract. The diverse tissue distribution of bioactive compounds may be attributed to
different metabolic roles and networks active in peels and seeds due to their different roles in plant
architecture and physiology. Furthermore, it is important to underline that in this study ethanol was
used for chemical extraction of peels and seeds and, since it is a GRAS (Generally Recognized As Safe)
solvent, it can be utilized safely for bioactive compound recovery, to be used in the food industry.
4. Conclusions
Normally, the non-edible parts of the melon (seeds and peels) are discarded during production
processes, reaching approximately 8 to 20 million tons of waste per year worldwide [
33
]. The
extracts of melon exhibit valuable functional and nutraceutical properties, in the light of all the data,
spectrophotometry, HPLC profiling and biological activity, obtained in the course of the present study.
With the aim of developing new nutraceuticals, such as supplements, dietary and nutritional
products, these cantaloupe by-products seem to be very promising, opening up new perspectives
for their use, mainly due to the solubility in water and the stability of their extracts. Therefore, the
melon extracts could be used in the production of functional waters, greatly demanded by markets
and consumers all over the world, or in food and cosmetic products. Indeed, it has been observed
that these by-products act against the oxidation process, thus suggesting their possible future uses
as natural colorants and antioxidants in yogurt, biscuits, cupcakes, jellies, sweets and bread, and
in anti-wrinkle creams, soaps and bathroom foams, as reported in the literature [
33
]. Moreover, in
this study the reduction to a minimum of the waste volumes and the possibility of developing new

Foods 2019,8, 196 9 of 10
products, with the recovery of biomolecules with high added value, may contribute to the sustainable
management of waste biomasses that otherwise imply environmental and economic costs.
Author Contributions:
Conceptualization, B.L.; formal analysis, F.M.V., D.C. and B.L.; investigation, F.M.V. and
D.C.; writing—original draft, F.M.V. and B.L.
Funding: This research received no external funding.
Conflicts of Interest: The authors declare no conflict of interest.
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