Evaluation and comparison of the content of total polyphenols and antioxidant activity in onion, garlic and leek

Abstract

Onion, leek and garlic as onion family are a great source of freely available health-promoting and chemoprotective compounds (polyphenols, flavonoids, fructooligosaccharides, thiosulfinates and other sulfur compounds, vitamins). Chemoprotective compounds belong between natural components. Onion, garlic and leek have high nutritional value. They are an important component of our human diet and we used them as a preventive factor for many diseases of civilization (cancer, coronary heart diseases, and atherosclerosis). In this work we watched and evaluated content of total polyphenols and antioxidant activity in onion, garlic and leek. Samples of plant material (onion, garlic and leek) we collected at the stage of full maturity in the area of Pružina. Pružina is area without negative influences and emission sources. Samples of fresh onion, garlic and leek were homogenized and were prepared an extract: 25 g cut onion, garlic and leek extracted by 50 ml 80% ethanol accourding sixteen hours. These extracts were used for analyses. The content of the total polyphenols was determined by using the Folin-Ciocalteu reagent (FCR). Antioxidant activity was measured by using a compound DPPH˙ (2.2-diphenyl-1-picrylhydrazyl). In the present experiment it was detected, that total polyphenols content in samples ranges from 210.67 mg/kg (leek) - 429.58 mg/kg (onion). Statistically significant highest value of total polyphenols was recorded in onion (389.64 to 429.58 mg/kg). Statistically significant the lowest content of total polyphenols was recorded in leek (210.67-254.80 mg/kg). Another indicator that has been evaluated and compared was the antioxidant activity of onion, garlic and leek. Statistically significant highest value of antioxidant activity was recorded in onion (20.22-25.76%). Statistically significant the lowest value of antioxidant activity was recorded in garlic (4.05-5.07%). Based on the measured values of AOA in onion, garlic and leek samples can be classified as follows: onion (20.22-25.76%) > leek (8.55-12.92%) > garlic (4.05-5.07%).

Full text

Potravinarstvo® Scientific Journal for Food Industry
Volume 8 272 No. 1/2014
INTRODUCTION
Vegetables are important components in the human diet
and protect against many diseases of civilization especially
cardiovascular diseases, high blood pressure, stroke,
neurodegeneration, cancer, obesity and diabetes. Family
belongs Liliaceae among the most important vegetable
observation and demonstrated effects on human organism
Onions, garlic, leeks, shallots and other members of the
onion family are commonly grown in fresh market
gardens. All plants in the Allium are herbaceous, biennial
vegetables that are known as annuals. Plants in the family
Alliaceae are derived their characteristic flavor from the
enzyme alliinase that acts on sulfur compounds. Alliums
with their shallow roots system, grown the best in
well- prepared soil (Delamaunt, 2003).
Onion (Allium cepa var. cepa) is member of the lily
family or Amaryllidaceae and it is classified by the
scientific name Allium cepa. Onions (Allium cepa var.
cepa) are an important source of bioactive compounds
including phenolic compounds, flavonoids,
fructooligosaccharides (FOS), thiosulfinates and other
sulfur compounds, and many of these compounds have
potential beneficial properties for human health Soinen et
al., (2012). Phenolic compounds in onions, garlics and
leeks are an essential part of the human diet and they are of
considerable interest due to their antioxidant properties.
These compounds possess an aromatic ring bearing one or
more hydroxyl groups and their structures may range from
that of a simple phenolic molecule to that of a complex
high-molecular weight polymer Balasundram et al.,
(2005). Polyphenols are reported to in vitro inhibit cancer
cell proliferation, reduce vascularization, protect neurons,
stimulate vasodilation and improve insulin secretion
Rio-Del et al., (2010).
Onion (Allium cepa var. cepa) represents a source of
cysteine derivatives, which makes it a good antioxidant
additive for food Ostrowska et al., (2004). Antioxidants
are important components, which they protect against free
radicals. Free radicals are known to be the major
contributors to degenerative diseases of aging and they are
recognised as major factors causing cancer, cardiovascular
disorders and diabetes Calucci et al., (2003).
Garlic (Allium sativum var. sativum) belongs among the
oldest of all cultivated plants. It has been used
as a medicinal agent for thousands of years. It is a
remarkable plant, which has multiple beneficial effects
Potravinarstvo, vol. 8, 2014, no. 1, p. 272-276
doi:10.5219/394
Received: 31 July 2014. Accepted: 22 October 2014.
Available online: 25 November 2014 at www.potravinarstvo.com
© 2014 Potravinarstvo. All rights reserved.
ISSN 1337-0960 (online)
EVALUATION AND COMPARISON OF THE CONTENT OF TOTAL
POLYPHENOLS AND ANTIOXIDANT ACTIVITY IN ONION, GARLIC AND LEEK
Petra Kavalcová, Judita Bystrická, Ján Tomáš, Jolana Karovičová, Veronika Kuchtová
ABSTRACT
Onion, leek and garlic as onion family are a great source of freely available health-promoting and chemoprotective
compounds (polyphenols, flavonoids, fructooligosaccharides, thiosulfinates and other sulfur compounds, vitamins).
Chemoprotective compounds belong between natural components. Onion, garlic and leek have high nutritional value. They
are an important component of our human diet and we used them as a preventive factor for many diseases of civilization
(cancer, coronary heart diseases, and atherosclerosis). In this work we watched and evaluated content of total polyphenols
and antioxidant activity in onion, garlic and leek. Samples of plant material (onion, garlic and leek) we collected at the stage
of full maturity in the area of Pružina. Pružina is area without negative influences and emission sources. Samples of fresh
onion, garlic and leek were homogenized and were prepared an extract: 25 g cut onion, garlic and leek extracted by 50 ml
80% ethanol accourding sixteen hours. These extracts were used for analyses. The content of the total polyphenols was
determined by using the Folin-Ciocalteu reagent (FCR). Antioxidant activity was measured by using a compound DPPH˙
(2.2-diphenyl-1-picrylhydrazyl). In the present experiment it was detected, that total polyphenols content in samples ranges
from 210.67 mg/kg (leek) - 429.58 mg/kg (onion). Statistically significant highest value of total polyphenols was recorded
in onion (389.64 to 429.58 mg/kg). Statistically significant the lowest content of total polyphenols was recorded in leek
(210.67 - 254.80 mg/kg). Another indicator that has been evaluated and compared was the antioxidant activity of onion,
garlic and leek. Statistically significant highest value of antioxidant activity was recorded in onion (20.22 - 25.76%).
Statistically significant the lowest value of antioxidant activity was recorded in garlic (4.05 - 5.07%). Based on the
measured values of AOA in onion, garlic and leek samples can be classified as follows: onion (20.22 - 25.76%) > leek
(8.55 - 12.92%) > garlic (4.05 - 5.07%).
Keywords: 5 Keywords: onion; garlic; leek; total polyphenols; antioxidant activity

Potravinarstvo® Scientific Journal for Food Industry
Volume 8 273 No. 1/2014
such as antimicrobial, antithrombotic, hypolipidemic,
antiarthritic, hypoglycemic and antitumor activity.
Recently, it has been observed that aged garlic extract
exhibited radical scavenging activity.
The two major compounds in garlic,
S-allylcysteine and S-allylmercapto-L-cysteine, have the
highest radical scavenging activity therefor the
consumption of garlic may provide some kind of
protection from cancer development Thomson et al.,
(2003).
Leeks (Allium ampeloprasum var. porrum) are robust
winter hardy biennials that do not form a hard bulb like
onions or garlic. Leeks are sweeter than onions and have
a creamy texture when cooked (Delamaunt, 2003).
Leeks (Allium ampeloprasum var. porrum) contain
vitamin C, vitamin B, vitamin E, copper, potassium, iron,
carotenoids, chlorophyll (green tops) and flavonoids.
The major flavonoid in leek is kaempferol, with only
a small amount of quercetin like spring onions, leeks
contain carotenoids and chlorophyll mainly in the green
tops.
MATERIAL AND METHODOLOGY
Samples of plant material were collected at full maturity
stages from area of Pružina. The samples of soil and plant
material were analyzed individually by selected
methodologies, and were used fresh material on analysis.
Pružina is located under the Strážovské hills - Strážov.
The attitude of the village is in the middle of 381 m.a.s.l.
Pružina belongs to the mild cold climate zone, average
annual air temperature is 7 °C, annual rainfall is
800 - 1000 mm. Pružina is area without negative
influences, emission sources (carbon), relatively pure from
content of risk permissible forms point of view (Table 1
and Table 2). Samples of fresh onion, garlic and leek were
homogenized and were prepared an extract: 25 g cut onion,
garlic and leek extracted by 50 ml 80% ethanol according
sixteen hours. These extracts were use for analyze.
Determination of total polyphenols
Total polyphenols were determined by the method of
Lachman, et al., (2003) and expressed as mg of gallic
acid equivalent per kg fresh mater. Gallic acid is usually
used as a standard unit for phenolics content determination
because a wide spectrum of phenolic compounds. The total
polyphenol content was estimated using Folin-Ciocalteau
assay. The Folin-Ciocalteau phenol reagent was added to
a volumetric flask containing 100 L of extract. The
content was mixed and 5 mL of a sodium carbonate
solution (20%) was added after 3 min. The volume was
adjusted to 50 mL by adding of distilled water. After
2 hours, the samples were centrifuged for 10 min. and the
absorbance was measured at 765 nm of wavelength against
blank. The concentration of polyphenols was calculated
from a standard curve plotted with known concentration of
gallic acid.
Determination of antioxidant activity
Antioxidant activity was measured by the Brand and
Williams et al., (1995) method-using a compound DPPH˙
(2.2-diphenyl-1-pikrylhydrazyl)). 2.2-diphenyl-1-
pikrylhydrazyl (DPPH˙) was pipetted to cuvette (3.9 m3)
then the value of absorbance, which corresponded to the
initial concentration of DPPH˙ solution in time Ao was
written. Then 0.1 cm3 of the followed solution was added
and then the dependence A = f(t) was immediately started
to measure. The absorbance of 1, 5 and 10 minutes at
515.6 nm in the spectrophotometer Shimadzu
UV/VIS-1240 was mixed and measured. The percentage of
inhibition reflects how antioxidant compound are able to
remove DPPH˙ radical at the given time.
Inhibition (%) = (Ao - At / Ao) x 100
RESULTS AND DISCUSSION
Onion, garlic and leek belong among the most valuable
kinds of vegetables. They are rich on polyphenols,
flavonoids, vitamins and protein. It also contains of
phosphorus, calcium and carbohydrates. Plants in the
onion family have antihelmintic, antioxidant,
antinflammatory and antiseptic effects. The total content of
polyphenolic compounds contained in onion, garlic and
leek are quite variable, may be affected by post-harvest
and climatic conditions. In this work the content of total
polyphenols in onion, garlic and leek was watched and
evaluated.
In the present experiment it was detected, that total
polyphenols content in samples ranges from
210.67 ±16.63 (in variety of leek) to 429.58 ±17.44 (in
variety of onion). Statistically significant highest value of
total polyphenols was recorded in onion (variety of Lusy,
Štutgarská and Všetana). Statistically significant
the lowest content of total polyphenols was recorded in
Table 1 Agrochemical characteristic of soil substrate in mg/kg
pH
(H2O)
pH
(KCl)
Cox
(%)
Humus
(%)
7.70
5.60
1.38
2.39
Table 2 Agrochemical characteristic of soil substrate in mg/kg (heavy metals)
Heavy metals
Zn
Cu
Mn
Fe
Cr
Cd
Pb
Co
aqua regia
85.00
22.4
615.0
2642
34.6
1.28
24.40
14.0
limit value
100.00
60.00
-
-
70.00
0.40
70.00
15.00
HNO3(c=2 mol.dm-3 )
6.50
10.50
454
1500
0.50
0.14
3.10

Potravinarstvo® Scientific Journal for Food Industry
Volume 8 274 No. 1/2014
leek (variety of Arkansas, Nobel, Hannibal). Andrejiová
et al., (2011) said that the content of total polyphenols in
onion was in the interval from 105 to 134 mg/kg. Armand
et al., (2012) reported that the content of polyphenols in
onion was 620 mg/kg. Our values of total polyphenols in
onion were in the range from 389.64 ±20.31 mg/kg to
429.58 ±17.44 mg/kg. Polyphenolic compounds have
antioxidant properties and play an important role in
preventing many of lifestyle diseases. In the work the
content of total polyphenols in leek and garlic was also
watched. Our values of total polyphenols in leek were
210.67 ±16.63 mg/kg to 254.80 ±10.09 mg/kg.
In the case of garlic were measured lower levels of
content of polyphenols (260.62 ±25.56 mg/kg to
279.74 ±16.18 mg/kg) than in onion. Priecina et al.,
(2013) reported that the polyphenols in garlic was in the
amounts from 272.28 to 1818.81 mg/kg.
From the results there is obvious that the highest content
of total polyphenols is characteristic for onion
(389.64 ±20.31 mg/kg to 429.58 ±17.44 mg/kg), followed
by garlic with the measured value of
260.62 ±25.56 mg/kg to 279.74 ±16.18 mg/kg. While the
lowest content of total polyphenols was recorded in leek
(210.67 ±16.63 mg/kg to 254.80 ±10.09 mg/kg.
Polyphenolic compounds contained in onions, garlic and
leeks are one of the largest categories of phytonutrients, it
is essentially the most represented group of secondary
plant metabolites. Another indicator that has been
evaluated and compared was the antioxidant activity of
onion, garlic and leek. The antioxidant activity of
vegetables is often associated with a ß-carotene,
L-ascorbic acid, vitamin E and present polyphenolic
compound such as quercetin, rutin.
Table 3 Average content of total polyphenols (mg/kg) in onion, garlic, leek.
vegetable
variety
TPC (mg/kg)
onion
Lusy
389.64 ±20.3 d
Všetana
396.71 ±18.10 de
Štutgarská
429.58 ±17.44 e
garlic
Makoi
260.62 ±25.56 bc
Mirka
268.09 ±16.61 c
Matin
279.74 ±16.18 c
leek
Arkansas
225.51 ±20.04 ab
Nobel
210.67 ±16.63 a
Hannibal
254.80 ±10.09 bc
HD0,05
26.6589
HD0,01
35.9988
Table 4 Average values of antioxidant activity (% inibition) in onion, garlic, leek.
vegetable
variety
AOA (%)
onion
Lusy
25.76 ±0.53 h
Všetana
23.09 ±0.79 g
Štutgarská
20.22 ±0.53 f
garlic
Makoi
4.45 ±0.28 ab
Mirka
5.07 ±0.47 b
Matin
4.05 ±0.20 a
leek
Arkansas
8.55 ±0.54 c
Nobel
10.82 ±0.53d
Hannibal
12.92 ±0.66 e
HD0,05
0.768657
HD0,01
1.037950

Potravinarstvo® Scientific Journal for Food Industry
Volume 8 275 No. 1/2014
In the present work it was detected, that antioxidant
activity in samples ranges from 4.05% ±0.20% (garlic) to
25.76% ±0.53% (onion). Statistically significant highest
value of antioxidant activity was recorded in onion
(20.22% ±0.53% to 25.76% ±0.53%). Statistically
significant the lowest value of antioxidant activity was
recorded in garlic (4.05% ±0.20% to 5.07% ±0.47%).
Prakash et al., (2007) published that the value of
antioxidant activity in onion was in interval from 3.6% to
84.1%. Our results of antioxidant activity in onion was
higher than the results Karadeniz et al., (2005), which
found that the value of antioxidant activity was 12.5%.
In the case of garlic was measured the lowest level of
antioxidant activity (in interval from
4.05% ±0.20% to 5.07% ±0.47%) than in onion. Priecina
et al., (2013) reported that value of antioxidant actvity in
garlic was 11.98%. Based on the measured values of AOA
in onion, garlic and leek can be samples classified as
follows: onion > leek > garlic. Antioxidants in onion,
garlic and leek catch reactive form of oxygen, inhibition of
enzymes responsible for superoxide anion production,
chelation of transition metals involved in process forming
radicals and prevention of the peroxidation process by
reducing alcoxyl and peroxyl radicals (Biesaga, 2011).
Figure 1 The content of total polyphenols (mg/kg) in onion, garlic and leek.
Figure 2 Values of antioxidant activity AOA (% inibition) in onion, garlic, leek.
389.64
260.62 225.51
396.71
268.09 210.67
429.58
279.74 254.8
0
50
100
150
200
250
300
350
400
450
500
Onion Garlic Leek
TPC (mg/kg)
25.76
4.45
8.55
23.09
5.07
10.82
20.22
4.05
12.92
0
5
10
15
20
25
30
Onion Garlic Leek
AOA (%)

Potravinarstvo® Scientific Journal for Food Industry
Volume 8 276 No. 1/2014
CONCLUSION
The contribution focuses on the total of polyphenol
content and antioxidant activity in onion, garlic and leek.
The results suggest that the highest value of total
polyphenols and antioxidant activity was in onion. In
generally these vegetables are also characterized by a high
content of chemoprotective compounds (polyphenols,
flavonoids, anthocyanins, quercetin, and many more) and
minerals (zinc, calcium, iron, selenium, and phosphorus),
which positively affecting the human body. The content of
total polyphenols and antioxidant activity may be affected
by many factors for example postharvest (storage) and
climatic conditions (altitude, rainfall, mean annual
temperature) and the agrochemical composition of the soil
(humus of content, nutrients) and type varieties.
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Acknowledgments:
This work was supported by grant VEGA 1/0290/14,
VEGA 1/0456/12.
Contact address:
Petra Kavalcová, Slovak University of Agriculture in
Nitra, Faculty of Biotechnology and Food Sciences,
Department of Chemistry, Tr. A. Hlinku 2, 949 76 Nitra,
Slovakia, E-mail: kavalcova.petra@gmail.com.
Judita Bystrická, Slovak University of Agriculture in
Nitra, Faculty of Biotechnology and Food Sciences,
Department of Chemistry, Tr. A. Hlinku 2, 949 76 Nitra,
Slovakia, E-mail: Judita.bystricka@centrum.sk.
Ján Tomáš, Slovak University of Agriculture in Nitra,
Faculty of Biotechnology and Food Sciences, Department
of Chemistry, Tr. A. Hlinku 2, 949 76 Nitra, Slovakia,
E-mail: jan.tomas@uniag.sk.
Jolana Karovičová, Slovak University of Technology in
Bratislava, Faculty of Chemical and Food Technology,
Department of Food Science and Technology,
Radlinského 9, 812 37 Bratislava, Slovakia,
E-mail: jolana.karovicova@stuba.sk.
Veronika Kuchtová, Slovak University of Technology in
Bratislava, Faculty of Chemical and Food Technology,
Department of Food Science and Technology,
Radlinského 9, 812 37 Bratislava, Slovakia,
E-mail:veronika.kuchtova@stuba.sk.