The Effectiveness of Ultrasound-Assisted Extraction on Antioxidative Properties of Bract Leaves of Globe Artichoke

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European Journal of Biology
Eur J Biol 2023
DOI: 10.26650/EurJBiol.2023.1304325
RESEARCH ARTICLE
The Effectiveness of Ultrasound-Assisted Extraction on Antioxidative
Properties of Bract Leaves of Globe Artichoke
Doruk Akdogan1,2, Aysegul Peksel1
1Yıldız Technical University, Faculty of Science and Arts, Department of Chemistry, Istanbul, Turkiye
2Istanbul Nisantasi University, Departments of Pharmacy Services, Vocational School of Health Services, Istanbul, Turkiye
ABSTRACT
Objective: The antioxidant-rich artichoke bracts leaves are a particularly waste of the food industry. Thus, it would be possible to
utilize a cheap and natural material, which is industrial waste, instead of synthetic antioxidants. The present study aimed to extract
from the bract leaves of globe artichoke by ultrasound-assisted extraction and to evaluate their antioxidant activities.
Materials and Methods: In this study, the effect of ultrasound-assisted extraction (UAE) on antioxidative properties was studied.
The extracts were obtained from the leaves of the head part of the artichoke by using UAE and evaluated for their antioxidative
properties. For this purpose, antioxidant activity methods were investigated for different extraction times. The results obtained
were compared with standard antioxidants.
Results: The results obtained from this study showed that the shorter extraction time resulted in higher antioxidative properties.
Accordingly, in plant extracts prepared by UAE-1, the highest total phenolic content value (193.80 μg pyrocathecol equivalent/mg
extract), the highest total flavonoid content value (254.13 μg catechin equivalent/mg extract), the highest total chlorophyll content
value (10.68 μg/mL) and carotenoid (0.57 μg/mL) were found. Similarly, UAE-1 extracts showed the best results in terms of
free radical scavenging activity. Also, the 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity of UAE-1 (89.09%) was
determined to be higher than the standard antioxidant α-Tocopherol (85.68%) and very close to another standard antioxidant
butylated hydroxyanisole (91.98%).
Conclusion: UAE could be preferred instead of the traditional method (Soxhlet) as a shorter, eco-friendly, and low energy cost.
Keywords: Antioxidative properties; Ultrasound-assisted extraction; Plant extract; Cynara scolymus L.; Radical scavenging
INTRODUCTION
The increasing interest in the replacement of synthetic antioxi-
dants with natural ones has opened the door to much research,
particularly to the study plant sources and new antioxidants
contained in these sources.1,2
Plant extracts are a generous source of bioactive compounds
with medical features.3Reactive oxygen species are produced
continuously during special metabolic events in the organism,
especially various sources such as lipid peroxidation and mi-
tochondrial cytochrome oxidase, or the result of exogenous
sources including ultraviolet light, environmental toxins, and
anticancer drugs.4
It is known that antioxidants have the feature of delaying or
preventing bitter and other taste deterioration caused by oxida-
tion when used in foods other than protecting the cell with its
defense mechanism.5Flavonoids, polyphenolics, tocopherols,
and ascorbic acid are the most important natural antioxidant
groups. It is known that phenolic compounds have high antiox-
idant activity and their most important sources are found in
plants.
In particular, the extraction of phenolic compounds from
agricultural and industrial organic wastes has been one of the
most important issues that many researchers are interested in.
This is because extraction is the main step in isolating and using
biocomponents.
The artichoke (Cynara scolymus L.), which grows in South-
ern Europe and the Mediterranean region and has wild forms in
the countries in this basin, is a 50-150 cm tall herbaceous plant
that blooms blue-purple flowers of the daisy-family. Artichoke
contains some phenolic compounds.6The fact that artichoke
is nutritious and beneficial to health is due to certain chemi-
Corresponding Author: Doruk Akdoğan E-mail: doruk.akdogan@nisantasi.edu.tr
Submitted: 27.5.2023 •Revision Requested: 21.07.2023 •Last Revision Received:05.08.2023 •Accepted: 11.08.2023 •Published Online: 04.10.2023
This article is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0)
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European Journal of Biology
cal compositions, including these high levels of polyphenolic
compounds and inulin. Previous studies exhibited that the ex-
tracts from artichoke have antioxidant7, antiseptic8, antibiotic,9
and anticarcinogenic10 effects. The antioxidant-rich artichoke
bracts leaves are a particularly waste of the food industry. Thus,
it would be possible to utilize a cheap and natural material,
which is industrial waste, instead of synthetic antioxidants.
Soxhlet extraction, known as the traditional method, has been
frequently used to obtain plant extracts containing bioactive
compounds. However, situations such as taking a long time and
requiring large amounts of toxic and expensive solvents limit the
usability of this method. Environmentally friendly and effec-
tive extraction techniques are required in order to use bioactive
plant extracts in food technology, pharmaceutical, and cosmetic
formulations. In recent years, sustainable new extraction tech-
niques have reduced extraction time, reduced solvent consump-
tion, and improved the quality of extracts obtained. However,
it has been observed in the literature that studies for extrac-
tion of phenolic compounds from various parts of the artichoke
are carried out by traditional methods (Soxhlet or maceration).6
Ultrasound-assisted extraction (UAE) is an important technique
used in the pharmaceutical and food industry.11 Ultrasonic en-
ergy produces many tiny bubbles in the liquid medium and
causes the particles to break off by causing the solids to me-
chanically. The sound waves usually provide effective contact
between the solid and solvent resulting in good recovery of the
analyte. Ultrasonic application mechanically breaks down cell
walls. With the mechanical destruction of the cell wall, intracel-
lular components easily exit the cell and pass into the solvent.12
Long sonication time may cause degradation of the compounds
for isolation. Therefore, the processing time of UAE necessarily
requires optimization.
The present study aimed to extract from the bract leaves
of globe artichoke by UAE during different extraction times
and to evaluate their antioxidant activities. For these purposes,
different antioxidative properties were studied by optimizing
the extraction time.
MATERIALS AND METHODS
Materials
The bract leaves of the artichoke (Cynara scolymus L.) plant
used as research material in this study were supplied from
the Istanbul local market in April 2018 and were thoroughly
cleaned with distilled water and dried at room temperature for
approximately 7 days in the dark. The leaves were cut into
small pieces before extraction. All material was kept in the
refrigerator at +4 ◦C until used.
Reagents and Solvents
All chemicals used in this study are of high-performance liquid
chromatography purity and have been obtained from Merck,
Sigma Aldrich, Fluka, and Riedel-de Haen companies.
Extraction Procedures: Ultrasound-Assisted Extraction
For UAE, 2.5 g of plant samples were taken into the tared glass
beakers and completed with 25 mL of solvent (96% ethanol).
Extraction was performed in the ultrasonic bath (Bandelin Elec-
tronic 320 w 35 kHz) for different extraction times such as 1,
5, 15, or 30 min, respectively. After this process, the extracts
were centrifuged (10,000 rpm for 15 min) (Sigma 3K30). After
extraction, the solvent was removed using a fume hood and ex-
tracts were obtained. The extracts obtained were kept at +4 ◦C
in the refrigerator.
Determination of Antioxidative Properties
Total phenolic compound content was determined using the
method of Slinkard-Singleton.13 Total flavonoid content was
determined by using a colorimetric method according to
Zhishen et al.14 Proline analysis was performed according to the
simple modification of the method developed by Bates.15 An-
thocyanin content in dried leaves, has been determined by the
modification of the method developed by Padmavati et al.16 For
determination of total chlorophyll and total carotenoid content,
used method of Arnon.17 β-Carotene bleaching method analysis
was carried out according to the method developed by Bruni
et al.18 Ferric reducing test was performed according to the
method of Oyaizu.19 Metal chelating activity was determined
according to the method of Decker and Welch.20 2,2-diphenyl-
1-picrylhydrazyl (DPPH) radical scavenging ability of the ex-
tracts was determined using the method of Brand-Williams
et al.21 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)
(ABTS) cation radical scavenging ability of the extracts was de-
termined using the method of the Arnao et al.22 N, N-dimethyl-
p-phenylenediamine (DMPD) cation radical scavenging ability
was determined according to the method of Fogliano et al.23
The method of Osawa and Namiki was studied for the measure-
ment of total antioxidant capacity.24
RESULTS
Amount of Total Phenolic Compounds
The total phenolic content of the extracts prepared by subjecting
the bract leaves of artichokes to different periods in an ultra-
sonic bath was determined. The results are shown in Table 1.
Results are given as μg pyrocatechol equivalent of the phenolic
compounds for each mg extract. The highest total phenolic con-
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Akdogan and Peksel, Antioxidative Properties of Globe Artichoke
tent value was found in UAE-1 extract (193.80 μg pyrocatechol
equivalent/mg extract).
Total Flavonoid Content
The total flavonoid content of the extracts prepared by subject-
ing the bract leaves of artichokes todifferent periods in an ultra-
sonic bath and using ethanol was given in Table 1. The highest
flavonoid amount value was found in UAE-1 extract (254.13
μg catechin equivalent/mg extract). Total phenolic compound
and flavonoid content results also decreased as the extraction
time increased. As a result of the study, the highest antioxidant
activity is observed in the extract which was applied for 1 min
UAE. Therefore, as a result of the study, it can be concluded that
antioxidant activity decreases as long-term ultrasound-assisted
extraction can lead to the loss of these phytocomponents which
have an antioxidant effect.
Proline Content
The proline content of plants is an indicator of stimulation of
the pentose phosphate pathway. The pentose phosphate path-
way is controlled by the synthesis of cytosolic proline. High
proline content in plants is responsible for high phenolic com-
pounds. For these reasons, proline analysis for edible plants is
regarded as an indicator of their antioxidative properties. The
total proline contents of the samples obtained from the arti-
choke leaves are given in Table 1. Among the proline contents
of different extracts, the highest amount was found in UAE-30
extract (0.83 μg proline/mg extract). Research on the proline
content of plants or food is a newly arising area therefore there
is not much data available to compare the results of this study.
Anthocyanin Content
Anthocyanins are dark-coloured pigments extracted from
plants. The results obtained from our study, the anthocyanin
value of the leaves was 0.065 μmol/g.
Total Chlorophyll and Carotenoid Content
The total chlorophyll and carotenoid contents of the extracts
obtained from the artichoke leaves are given in Table 2. The
chlorophyll and carotene contents of artichoke leaf extract
decreased when the extraction time increased. This situation
could be an indication that long-term ultrasound exposure is
damaging to these compounds. It was observed that the UAE-
1 extract of the plant had the highest total carotenoid con-
tent (0.567 μg/mL), and the highest total chlorophyll content
(10.68μg/mL).
β-Carotene Bleaching Test Results
The results obtained in the β-carotene bleaching method are
given in Table 3. According to the results obtained in this
method; two ethanol extracts UAE-15 (1.03), UAE-30 (1.04)
of the artichoke leaves were higher than the positive control
butylated hydroxyanisole (BHA). It was determined that UAE-
1 (0.92) and UAE-5 (0.99) extracts also showed an effect close
to BHA.
Ferric Reducing Test Results
In this section, in order to investigate the reduction capacity of
the extracts of the bract leaves of artichoke in different con-
centrations prepared with ethanol to reduce Fe3+to Fe2+added
to the tubes, the reducing power was tested by comparing it
with standard antioxidants (BHA and α-Tocopherol). Results
are shown in Figure 1. The increase in absorbance values is
directly proportional to the amount of Fe2+in the reaction
medium. In the reducing power assay, the highest reducing
power was exhibited by UAE-15 Ethanol extract (0.692 at 700
nm).
Chelating Activity on Ferrous Ion
Metal chelating activities based on inhibition of Ferrozin-Fe2+
complex formation in samples and standards are shown in Fig-
ure 2. UAE-1 (46.48%) showed the highest metal chelating ac-
tivity at high concentrations (200 μg/mL). The metal chelating
power increased as the extraction time decreased in the extracts
created by ultrasound-assisted extraction. On the other hand, in-
creasing the concentration increased the metal chelating power.
When comparing extracts with ethylenediaminetetraacetic acid
(EDTA), which is known to be a strong chelating agent, it
has been observed that EDTA gives higher results compared
to all extracts. In addition, according to results the amount of
flavonoids and metal chelating activity decreases when the time
of ultrasound-assisted extraction increases. Flavonoids, which
are from the phenolic family, show strong metal-chelating prop-
erties compared to other phenolic compounds. Therefore, the
decreasing total flavonoid content also support the results of
the metal chelating activity.
DPPH Scavenging Ability
For the determination of DPPH radical scavenging activity in
Cynara scolymus L. extracts, the extracts were prepared us-
ing UAE. The results obtained from samples and standards
are shown in Figure 3. UAE-1 extract prepared by the one-
min ultrasound-assisted method showed the highest results.
According to the results, UAE-1 extract is very close to the stan-
dard antioxidant BHA (91.98%) with high antioxidant activity,
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European Journal of Biology
Table 1. Total flavonoids, phenolics and, proline amount of artichoke bracts for different extraction times.
18
TABLES
Table 1. Total flavonoids, phenolics, and proline amount of artichoke bracts for different
extraction times.
Extract Total Phenolic Content
(µg pyrocatechol
equivalent/mg extract)
Total Flavonoid Content
(µg catechin
equivalent/mg extract)
Proline Content
(µg proline/mg extract)
UAE-1 193.80 254.13 0.43
UAE-5 188.95 223.30 0.60
UAE-15 182.38 214.97 0.82
UAE-30 182.14 211.08 0.83
UAE-1:Ultrasound-assisted extraction-1 min; UAE-5:Ultrasound-assisted extraction-5 min; UAE-15:Ultrasound-assisted
extraction-15 min; UAE-30:Ultrasound-assisted extraction-30 min.
Table 2. Total chlorophyll and carotenoid amounts of bract leaves of artichoke (Cynara
scolymus L.) for different extraction times.
Extract Chlorophyll a
(g/mL)
Chlorophyll b
(g/mL)
Total Chlorophyll
(g/mL)
Total Carotenoid
(g/mL)
UAE-1 4.63 6.08 10.68 0.57
UAE-5 3.48 5.88 9.36 0.45
UAE-15 2.19 4.35 5.62 0.38
UAE-30 2.13 4.18 5.55 0.32
UAE-1:Ultrasound-assisted extraction-1 min; UAE-5:Ultrasound-assisted extraction-5 min; UAE-15:Ultrasound-assisted
extraction-15 min; UAE-30:Ultrasound-assisted extraction-30 min.
Table 3. -Carotene bleaching effects of bract leaves of artichoke (Cynara scolymus L.) for
different extraction times.
Extract RAA (60 min.)* RAA (120 min.)*
UAE-1 0.92 0.84
UAE-5 0.99 0.89
UAE-15 1.03 0.96
UAE-30 1.04 0.97
BHA (Positive Control) 1 1
Negative Control
(Linoleic Acid Emulsion)
0.14 0.13
UAE-1:Ultrasound-assisted extraction-1 min; UAE-5:Ultrasound-assisted extraction-5 min; UAE-15:Ultrasound-assisted
extraction-15 min; UAE-30:Ultrasound-assisted extraction-30 min; RAA*: Relative Antioxidant Activity
Table 2. Total chlorophyll and carotenoid amounts of bract leaves of artichokes (Cynara scolymus L.) for different extraction
times.
18
TABLES
Table 1. Total flavonoids, phenolics, and proline amount of artichoke bracts for different
extraction times.
Extract Total Phenolic Content
(µg pyrocatechol
equivalent/mg extract)
Total Flavonoid Content
(µg catechin
equivalent/mg extract)
Proline Content
(µg proline/mg extract)
UAE-1 193.80 254.13 0.43
UAE-5 188.95 223.30 0.60
UAE-15 182.38 214.97 0.82
UAE-30 182.14 211.08 0.83
UAE-1:Ultrasound-assisted extraction-1 min; UAE-5:Ultrasound-assisted extraction-5 min; UAE-15:Ultrasound-assisted
extraction-15 min; UAE-30:Ultrasound-assisted extraction-30 min.
Table 2. Total chlorophyll and carotenoid amounts of bract leaves of artichoke (Cynara
scolymus L.) for different extraction times.
Extract Chlorophyll a
(g/mL)
Chlorophyll b
(g/mL)
Total Chlorophyll
(g/mL)
Total Carotenoid
(g/mL)
UAE-1 4.63 6.08 10.68 0.57
UAE-5 3.48 5.88 9.36 0.45
UAE-15 2.19 4.35 5.62 0.38
UAE-30 2.13 4.18 5.55 0.32
UAE-1:Ultrasound-assisted extraction-1 min; UAE-5:Ultrasound-assisted extraction-5 min; UAE-15:Ultrasound-assisted
extraction-15 min; UAE-30:Ultrasound-assisted extraction-30 min.
Table 3. -Carotene bleaching effects of bract leaves of artichoke (Cynara scolymus L.) for
different extraction times.
Extract RAA (60 min.)* RAA (120 min.)*
UAE-1 0.92 0.84
UAE-5 0.99 0.89
UAE-15 1.03 0.96
UAE-30 1.04 0.97
BHA (Positive Control) 1 1
Negative Control
(Linoleic Acid Emulsion)
0.14 0.13
UAE-1:Ultrasound-assisted extraction-1 min; UAE-5:Ultrasound-assisted extraction-5 min; UAE-15:Ultrasound-assisted
extraction-15 min; UAE-30:Ultrasound-assisted extraction-30 min; RAA*: Relative Antioxidant Activity
Table 3. β–Carotene bleaching effects of bract leaves of artichoke (Cynara scolymus L.) for different extraction times.
18
TABLES
Table 1. Total flavonoids, phenolics, and proline amount of artichoke bracts for different
extraction times.
Extract Total Phenolic Content
(µg pyrocatechol
equivalent/mg extract)
Total Flavonoid Content
(µg catechin
equivalent/mg extract)
Proline Content
(µg proline/mg extract)
UAE-1 193.80 254.13 0.43
UAE-5 188.95 223.30 0.60
UAE-15 182.38 214.97 0.82
UAE-30 182.14 211.08 0.83
UAE-1:Ultrasound-assisted extraction-1 min; UAE-5:Ultrasound-assisted extraction-5 min; UAE-15:Ultrasound-assisted
extraction-15 min; UAE-30:Ultrasound-assisted extraction-30 min.
Table 2. Total chlorophyll and carotenoid amounts of bract leaves of artichoke (Cynara
scolymus L.) for different extraction times.
Extract Chlorophyll a
(g/mL)
Chlorophyll b
(g/mL)
Total Chlorophyll
(g/mL)
Total Carotenoid
(g/mL)
UAE-1 4.63 6.08 10.68 0.57
UAE-5 3.48 5.88 9.36 0.45
UAE-15 2.19 4.35 5.62 0.38
UAE-30 2.13 4.18 5.55 0.32
UAE-1:Ultrasound-assisted extraction-1 min; UAE-5:Ultrasound-assisted extraction-5 min; UAE-15:Ultrasound-assisted
extraction-15 min; UAE-30:Ultrasound-assisted extraction-30 min.
Table 3. -Carotene bleaching effects of bract leaves of artichoke (Cynara scolymus L.) for
different extraction times.
Extract RAA (60 min.)* RAA (120 min.)*
UAE-1 0.92 0.84
UAE-5 0.99 0.89
UAE-15 1.03 0.96
UAE-30 1.04 0.97
BHA (Positive Control) 1 1
Negative Control
(Linoleic Acid Emulsion)
0.14 0.13
UAE-1:Ultrasound-assisted extraction-1 min; UAE-5:Ultrasound-assisted extraction-5 min; UAE-15:Ultrasound-assisted
extraction-15 min; UAE-30:Ultrasound-assisted extraction-30 min; RAA*: Relative Antioxidant Activity
while another high antioxidant activity standard, α-Tocopherol
(85.68%), has an equally strong antioxidant activity.
ABTS Radical Scavenging Activity
The results of ABTS radical scavenging activities are shown
in Figure 4. The ethanol extract UAE-5 (75.04%), which was
extracted for 5 min in the studied extracts at a concentration
of 200 μg/mL, exhibited the highest ABTS radical scavenging
activity. Inhibition values increased in all extracts depending on
the concentration. Trolox, a standard with a known antioxidant
effect, showed an activity of 99.5% at all concentrations studied.
DMPD+Scavenging Ability
DMPD radical scavenging activities of all samples and stan-
dards are shown in Figure 5. At high concentrations (200
μg/mL), in the extracts using UAE 1 minute (UAE-1) has the
highest inhibition values (72.02%). DMPD radical scavenging
activity increased as the extraction time was shortened. When
standard antioxidants were examined, the DMPD radical scav-
enging activity of ascorbic acid was found to be 98% (200
μg/mL). The synthetic standard antioxidant BHA showed an
activity of 65.13% (200 μg/mL). Accordingly, when compared
with standard antioxidants, UAE-1 (72.02%) showed higher
activity than BHA.
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Akdogan and Peksel, Antioxidative Properties of Globe Artichoke
Figure 1. Reducing power of ethanol extracts obtained by UAE methods (1, 5, 15, and 30 min). UAE-1:Ultrasound assisted extraction-1 min; UAE-5:Ultrasound
assisted extraction-5 min; UAE-15:Ultrasound assisted extraction-15 min; UAE-30:Ultrasound assisted extraction-30 min; BHA: Butylated hydroxyanisol.
Figure 2. Chelating activities of ethanol extracts obtained by UAE methods (1, 5, 15, and 30 min). UAE-1:Ultrasound assisted extraction-1 min; UAE-5:Ultrasound
assisted extraction-5 min; UAE-15:Ultrasound assisted extraction-15 min; UAE-30:Ultrasound assisted extraction-30 min; EDTA: Ethylenediaminetetraacetic acid
Figure 3. DPPH radical scavenging activities of ethanol extracts obtained by UAE methods (1, 5, 15, and 30 min). UAE-1:Ultrasound assisted extraction-1 min;
UAE-5:Ultrasound assisted extraction-5 min; UAE-15:Ultrasound assisted extraction-15 min; UAE-30:Ultrasound assisted extraction-30 min; BHA: Butylated
hydroxyanisol.
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European Journal of Biology
Figure 4. ABTS radical scavenging activities of ethanol extracts obtained by UAE methods (1, 5, 15, and 30 min). UAE-1:Ultrasound assisted extraction-1 min;
UAE-5:Ultrasound assisted extraction-5 min; UAE-15:Ultrasound assisted extraction-15 min; UAE-30:Ultrasound assisted extraction-30 min.
Figure 5. DMPD radical scavenging activities of ethanol extracts obtained by UAE methods (1, 5, 15, and 30 min). UAE-1:Ultrasound assisted extraction-1 min;
UAE-5:Ultrasound assisted extraction-5 min; UAE-15:Ultrasound assisted extraction-15 min; UAE-30:Ultrasound assisted extraction-30 min; BHA: Butylated
hydroxyanisol.
Figure 6. Antioxidative effect of ethanolic samples obtained by UAE (1, 5, 15, and 30 min) at the end of the first 24 h. UAE-1:Ultrasound assisted extraction-1 min;
UAE-5:Ultrasound assisted extraction-5 min; UAE-15:Ultrasound assisted extraction-15 min; UAE-30:Ultrasound assisted extraction-30 min; BHA: Butylated
hydroxyanisol.
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Akdogan and Peksel, Antioxidative Properties of Globe Artichoke
Total Antioxidant Capacity
The total antioxidant activity was determined according to the
thiocyanate method with slight modifications. Total antioxidant
activity was determined by taking measurements at 24-hour in-
tervals for 3 days. The effects of extracts and standards on
linoleic acid peroxidation are shown in Figure 6. It was ob-
served that UAE-5 (30.3%) extract had the highest activity
at the end of the first 24 h. The antioxidant activity of this
extract is close to the activity of standard antioxidants BHA
(43.35%) and α-Tocopherol (50.42%). At the end of 48 h, the
total antioxidant activity of the extracts started to decrease due
to deterioration in the structure of the extracts over time. Af-
ter 72 h, ultrasound-assisted extracts and standard antioxidants
were no longer active.
DISCUSSION
The antioxidative properties of bract leaves of the artichoke
plant (Cynara scolymus L.) were investigated using UAE in
different antioxidant parameters. According to our results ob-
tained from the study, extracts obtained from the leaves of the
artichoke (Cynara scolymus L.) bract showed a high antiox-
idative effect. From these effects, the ethanol extract exhibited
high reducing power, noteworthy phenolic content, and DPPH
scavenging capability at the same conditions.
The total amount of phenolic compounds was found to be
193.80 μg pyrocatechol equivalent per mg of ethanol extract
after one minute of extraction time. There are no studies con-
ducted with bract leaves of artichoke. However, there are studies
on the leaves of the artichoke plant. For example, Ben Salem
et al.25 extracted the leaves by maceration method using dif-
ferent increasing solvent polarities (such as hexane, butanol,
ethyl acetate, 75% EtOH/H2O, and aqueous. They found the
maximum content of the total phenolic compound by using
ethanol extracts. Their result corresponded to 54.54 mg gal-
lic acid equivalent per g dry weight of extract. Our results are
higher than the work of Ben Salem et al.25 Kollia et al.26 found
the phenolic content of artichoke leaves as 1.45 mg GAE/g DW
by UAE. All these results comply with our studies in terms
of proving the presence of phenolic content in bract leaves of
artichoke.
Stumpf et al.27 prepared extracts from artichoke leaves by us-
ing three different extraction methods. The extracts were com-
pared with their total phenolic compounds and total antioxi-
dant capacities. Extraction according to the European Pharma-
copoeia or UAE gave similar results when compared. How-
ever, the results obtained with hot water extraction are quite
inadequate. This study shows us the importance of the UAE-
method. Stumpf et al.27 prepared artichoke leaf extract with
80% methanol by using UAE. All extracts were directly used
for the determination of total phenolic concentration and an-
tioxidant capacity. This study was showed that total phenolic
content and total antioxidant capacity are closely related to the
extraction method.
Reche et al.28 performed mathematical modeling of UAE
and they studied the kinetics of bioactive compounds obtained
from artichoke by-products. In this study, an evaluation of an
artichoke by-product rich in bioactive compounds by UAE and
ethanol solvent was proposed. The effective diffusion coeffi-
cient exhibited temperature dependence, whereas the external
mass transfer coefficient and the equilibrium extraction yield
depended on both temperature and ultrasound power density.
This study also supports our study.
Lavecchia et al.29 extracted the artichoke residues they pre-
pared using ethanol as a solvent in a thermostated bath at 60°C
and determined the phenolic compounds in the stems and bracts
by obtaining 51.10±0.74 and 24.58±0.57 mg gallic acid equiv-
alent per g extracts, respectively. These values are very low
when compared to our study. Ultrasound-assisted technology
is known to act on plant tissues by the cavitational phenomenon
induced at the solid/liquid interface. This effect facilitates the
release of extractable compounds and enhances mass trans-
port by disrupting the plant cell walls. Pasqualone et al.30 ana-
lyzed the extracts obtained from three artichoke varieties (Opal,
Capriccio, and Catanese) in terms of antioxidant parameters; in
the UAE of samples, the extract showed a total phenolic content
higher than non-ultrasound extraction method. The results were
expressed as mg gallic acid equivalent per kg. Zuorro et al.31
reported total polyphenol content in bracts (24.14 mg GAE/g)
using a 50:50 ethanol-water mixture as an efficient extraction
method, and solvent-extraction procedure. In our study, UAE-1
extract also exhibited the highest flavonoid amount value with
254.13 µg catechin equivalent per mg of extract. This result
was very high when compared the other similar studies. Ben
Salem et al.25 found that ethanol extract had the highest value
in terms of total flavonoid content (12±0.83 CE/g DW) by
using the maceration method. These studies also determined
the flavonoid content of the artichoke leaves, like our study.
Petropoulos et al.3found very low flavonoid content in the edi-
ble head of artichoke. They studied eight different genotypes of
artichoke heads and determined the highest value as 7.2 mg/g
extract. The chlorophyll and carotenoid contents of our stud-
ied samples were also high. In order to make a comparison of
chlorophyll and carotenoid contents, no studies were found in
the literature with artichoke bracte leaves. Ben Salem et al.25
measured that the β-carotene bleaching effect of ethanol extract
(70.74%) is the highest inhibition rate and higher than butylated
hydroxytoluene (BHT) (47.94%).
Flavonoids are a main class of polyphenols in plants. They are
known as antioxidants and free radical scavengers. The antioxi-
dant activity of plants has been correlated to the total flavonoid
content. For this reason, in our study, especially free or cation
radical scavenging capacity was found to be very high. DPPH
radical scavenging activity of UAE-1 extract showed similar
7

European Journal of Biology
activities to the standard antioxidants such as BHA and α-
tocopherol, at all concentrations tested. DMPD cation radical
scavenging ability of the extract was determined higher than
BHA in all the concentrations studied. These results are very
pleasing. In addition, in extraction time optimization studies, it
is seen that an effective extraction takes place in a very short
time such as one minute. Ergezer et al.32 prepared artichoke
bracte leaf extract with 80% ethanol by using the maceration
method. They obtained the DPPH radical scavenging activity
as 79.91 % after the 7th day of storage. The result we found in
our study is that the DPPH radical scavenging activity is 89.09
% for the extract concentration of 200 μg/mL. This result is
higher than α-tocopherol (85.68%). Mena García et al.33 re-
ported lower results of DPPH (26.59 ±0.62 mg TE/g) using a
mixture of ethanol/water (50:50 v/v) and a microwave-assisted
extraction method from the artichoke. Shallan et al.34 showed
that the antioxidant activity (DPPH) of Globe artichoke bracts
extract in ethanolic solution was 6.42 mg/L. Quispe et al.,35
determined the total phenolic compounds of artichoke bracts
between 10.86 mg and 24.82 mg GAE/g in artichoke extracts
prepared using ultrasound-assisted extraction and ethanol as
solvent. The radical scavenging activity of DPPH was found
between 15.49 mM and 38.65 mM trolox, and the trolox equiv-
alent antioxidant capacity from 12.56 to 32.52 mM trolox, re-
spectively.
To investigate the reducing capacity of Fe3+to Fe2+, the re-
ducing power was tested by comparing the extracts with the
standards. The increase in absorbance values is directly pro-
portional to the amount of Fe2+in the environment. The best
activity among the prepared extracts was UAE-15 (0.692 at 700
nm). The good results obtained from ethanol extracts may sug-
gest that the preparation of artichoke extracts in a moderately
apolar solvent such as ethanol will have a more active effect
in terms of reducing power than solvents with high polarity
or high apolarity. In terms of ultrasound-assisted extraction, it
can be argued that the 1-minute and 5-minute extraction times
are not fully sufficient to reduce Fe3+, while the 15-minute
extraction period provides the necessary optimization for this
reduction event. It can be said that in longer extractions such
as 30 min, the extract may be damaged by sound waves and
cause it to lose its reducing power feature. Ben Salem et al.25
examined the reducing power parameter in artichoke leaf ex-
tracts in their study. For the reducing power test of Cynara
scolymus L., they measured the absorbance at 515 nm in a UV-
VIS spectrophotometer of the ferric reducing antioxidant power
mixture prepared with extracts. expressed the antioxidant ca-
pacity of artichokes as trolox Equivalent. Among all extracts
of artichoke in their work, the ethanol extract demonstrated a
favorable iron-reducing capacity (527.79 µmol Fe2+/mg dry ex-
tract). Thang et al.36 studied and compared different extraction
techniques to extract cynarine and chlorogenic acid (classical
extraction, ultrasound-assisted extraction, enzyme-assisted ex-
traction) from leaves of Cynara scolymus L. In addition, the
extracts were also studied for antioxidant activities. The antiox-
idant activity of the artichoke extract was tested by the ferric-
reducing antioxidant power method. They found the highest re-
ducing power of ferric iron in pectinase enzyme extracts from
artichoke leaves. The measurement of reducing power of ascor-
bic acid and artichoke extract from dried artichokes treated with
pectinase enzymes was exhibited as 48.0 and 77.8 mg/L, re-
spectively. Artichoke extract hydrolyzed by pectinase enzymes
also had a higher radical scavenging capacity (IC50=30 mg/L)
compared to ascorbic acid (IC50=11 mg/L). Wioletta Biel et
al.37 reported that the antioxidant capacity of artichoke extract
was measured at 1060.8 μmol trolox/1 g dry matter.
UAE-1 (46.48%) showed the highest metal chelating activ-
ity at high concentrations (200 μg/mL). It was observed that
the percentages of metal chelating activity increased as the ex-
traction time was shortened in the extracts applied ultrasound-
assisted extraction. Flavonoids from the phenolic family show
strong metal chelating properties compared to other phenolic
compounds. Therefore, the decrease in the total flavonoid con-
tent due to the increase in the extraction time also supports
the results of the metal chelating activity. Among the analyzed
extracts, the ethanol extract UAE-5 (75.04%), which was ex-
tracted for 5 min at a concentration of 200 μg/mL, exhibited
the highest ABTS radical scavenging activity. It can be said
that the ultrasonic extraction time, which gives the optimum
value and can be considered ideal is 5 min in terms of the high
value of ABTS radical scavenging activity of artichoke extracts
prepared with ethanol. Kollia et al.26 found ABTS radical scav-
enging activity in artichoke leaves as 1.25 mg TE/g DW by
UAE in their study with artichoke leaves. Ben Salem et al.25
also analyzed the scavenging activity of the artichoke extract
and found that ethanol extract had a high activity. Sihem et
al.1also demonstrated that the extracts of the head leaves ob-
tained by using the maceration method had the highest activity.
It was observed that UAE-5 (30.3%) extract had the highest
total antioxidant activity at the end of the first 24 h. The antiox-
idant activity of this extract is close to the activity of standard
antioxidants BHA (43.35%) and α-tocopherol (50.42%).
It is a very important detail that a waste material can be used
instead of synthetic antioxidants in the food, pharmaceutical,
or cosmetic industry. It is known that the bract leaves of the ar-
tichoke are a waste in local markets and the food industry. The
high flavonoid content and high antioxidant activity of these
leaves can be evaluated. Thus, the natural antioxidant needs
of the food, pharmaceutical, or cosmetic industry can be met.
For example, it may be possible for an inexpensive material
to replace antioxidants with artificial and toxic properties in
the industry by using it for purposes such as preserving prop-
erties, extending shelf life, adding nutritional value, flavoring,
and coloring in foods. It was determined that extracts (UAE-1)
prepared in 1 min in the ultrasound-assisted extraction method
had the highest antioxidative properties in most of the param-
eters studied. Extracts prepared in 30 min (UAE-30) showed
8

Akdogan and Peksel, Antioxidative Properties of Globe Artichoke
the lowest inhibition values in most of the parameters studied.
Therefore, it can be argued that the increase in the extraction
time may cause the extract to lose its properties and lead to a
decrease in its antioxidative properties.
CONCLUSION
UAE could be preferred instead of the traditional method as a
shorter, eco-friendly, and low energy cost. For further stud-
ies, it may be recommended to isolate specific compounds
from the extracts and optimize extraction methods, especially
ultrasound-assisted extraction, through experimental design.
Optimization can be achieved by examining the antioxidant
activity in conditions where solvent, pH and temperature pa-
rameters change.
Peer Review: Externally peer-reviewed.
Author Contributions: Conception/Design of Study- D.A.,
A.P.; Data Acquisition- D.A.; Data Analysis/Interpretation-
D.A., A.P.; Drafting Manuscript- D.A.; Critical Revision of
Manuscript- D.A., A.P.; Final Approval and Accountability-
D.A., A.P.
Conflict of Interest: Authors declared no conflict of interest.
Financial Disclosure: Authors declared no financial support.
ORCID IDs of the authors
Doruk Akdogan 0000-0002-3113-9756
Aysegul Peksel 0000-0003-3881-8513
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How cite this article
Akdogan D, Peksel A. The Effectiveness of Ultrasound-
Assisted Extraction on Antioxidative Properties of
Bract Leaves of Globe Artichoke. Eur J Biol 2023.
DOI:10.26650/EurJBiol.2023.1304325
10