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Extraction of pumpkin peel extract using supercritical CO2 and subcritical water technology: Enhancing oxidative stability of canola oil

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In this study, subcritical water extraction (SWE) and the supercritical fluid extraction (SFE) methods were used for the extraction of pumpkin peel extract. Total phenolic content and carotenoid compounds of extracts were measured. The extracts were added to canola oil at a concentration of 400 ppm and were stored at 30 °C for 60 days. The peroxide, carbonyl and acid values of the oil samples were measured, then compared with 100 ppm of tert-butylhydroquinone (TBHQ) synthetic antioxidants. The results showed that the total phenol content of obtained extract by SFE (353.5 mg GA/100 g extract) was higher than by SWE (213.6 mg GA/100 g extract), while the carotenoid content was higher for obtained extract by SWE (15.22 mg/100 g extract) compared to SFE (11.48 mg/100 g extract). The result of oil oxidation showed that the oxidative stability of the oil containing the mixed extract (SFE–SWE) is higher than the separate extract, consequently showing higher performance in preventing oil oxidation compared to TBHQ.
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ORIGINAL ARTICLE
Extraction of pumpkin peel extract using supercritical CO
2
and subcritical water technology: Enhancing oxidative stability
of canola oil
Azadeh Salami
1
Narmela Asefi
1
Reza Esmaeilzadeh Kenari
2
Mehdi Gharekhani
1
Revised: 15 June 2020 / Accepted: 3 July 2020
ÓThe Author(s) 2020
Abstract In this study, subcritical water extraction (SWE)
and the supercritical fluid extraction (SFE) methods were
used for the extraction of pumpkin peel extract. Total
phenolic content and carotenoid compounds of extracts
were measured. The extracts were added to canola oil at a
concentration of 400 ppm and were stored at 30 °C for
60 days. The peroxide, carbonyl and acid values of the oil
samples were measured, then compared with 100 ppm of
tert-butylhydroquinone (TBHQ) synthetic antioxidants.
The results showed that the total phenol content of obtained
extract by SFE (353.5 mg GA/100 g extract) was higher
than by SWE (213.6 mg GA/100 g extract), while the
carotenoid content was higher for obtained extract by SWE
(15.22 mg/100 g extract) compared to SFE (11.48 mg/
100 g extract). The result of oil oxidation showed that the
oxidative stability of the oil containing the mixed extract
(SFE–SWE) is higher than the separate extract, conse-
quently showing higher performance in preventing oil
oxidation compared to TBHQ.
Keywords Pumpkin peel extract Antioxidant activity
Phenol Carotenoid Canola oil
Introduction
Herbal extracts are a variety of natural antioxidants,
offering a unique range of health benefits. The secondary
metabolites of plants, such as phenolic and carotenoid
compounds, are valuable sources of antioxidants extracted
from different parts of the plant, including leaves, seeds
and, peels (Dabbou et al. 2017).
Pumpkin is a cultivar of a squash plant, most commonly
Cucurbita pepo, cultivated because of the nutritional value
of the pulp and its seeds and used in the production of
syrups, jellies, jam and purees (Provesi et al. 2011). Pepo
peel is usually removed from the fruit before use, and
previous studies showed that C. pepo peel is a rich source
of antioxidant compounds (Tavakoli et al. 2017). Also,
pumpkin peel is a source of pectin, minerals, vitamins and
other compounds beneficial to the human health (de Car-
valho et al. 2012). Pulp and peel of pumpkin contain high
levels of carotenoids, natural molecules containing terpe-
nes with 40 carbon atoms creating yellow–red colors in
flowers, leaves and fruits. They are categorized in carote-
nes and xanthophylls (Oliver and Palou 2000; Kehili et al.
2017).The application of conventional solvent extraction
methods is not recommended due to the dangers of organic
solvent residues in the extract, time-consuming extraction,
damage to the environment, and the active compounds of
the plant. Today, novel extraction techniques, such as,
microwave, ultrasound, SWE and SFE, as green tech-
nologies, have replaced older methods (de Andrade Lima
et al. 2018).
&Reza Esmaeilzadeh Kenari
reza_kenari@yahoo.com
Azadeh Salami
Azade.salami64@gmail.com
Narmela Asefi
N.asefi@iaut.ac.ir
Mehdi Gharekhani
M.gharekhani@iaut.ac.ir
1
Department of Food Science and Technology, Tabriz Branch,
Islamic Azad University, Tabriz, Iran
2
Department of Food Science and Technology, Sari
Agricultural Sciences and Natural Resources University,
Mazandaran, Iran
123
J Food Sci Technol
https://doi.org/10.1007/s13197-020-04624-x
SFE is a method that basically uses carbon dioxide, as a
solvent, for the extraction and is used as a clean method for
extracting bioactive compounds from plant lesions, such as
fruits and vegetables. In this method, the extraction of
compounds is similar to the conventional extraction
methods; however, the fluids are in the supercritical state of
viscosity and surface tension, like gases, and density, while
they have dissolving power like fluids (Kehili et al. 2017;
de Andrade Lima et al. 2018). Similar properties make
carbon dioxide an ideal fluid for extracting compounds in
shorter time periods with greater efficiency than liquid
solvents (de Andrade Lima et al. 2018).
The oxidation of fats, as a result of the reaction between
oxygen and unsaturated fatty acids, causes a lot of prob-
lems for the oil factories. Not only does oxidation result in
the lower quality of oils and fats due to chemical-corrosive
reactions, but it also leads to the production of peroxyl and
hydroxyl free radicals and reactive oxygen species,
resulting in heart disease, aging and mutagenesis (Islam
et al. 2018). Canola oil is preferable to other vegetable oils
considering its high amounts of unsaturated fatty acids.
However, due to its low thermal stability at high temper-
atures, it is necessary to increase its oxidative stability by
adding antioxidants (Farahmandfar et al. 2015).
Antioxidants are substances used to prevent oxidation in
human bodies and food products. Synthetic antioxidants
are added as additives to foods to prevent spiky reactions,
revealed to their high efficiency, low prices and abundance.
The most important synthetic antioxidants used as preser-
vatives for increasing the stability of vegetable oils in the
food industry include butylated hydroxyl toluene (BHT),
tert-Butyl hydroquinone (TBHQ) and butylated hydroxyl
anisole (BHA). With regard to the identification of the
effects of synthetic antioxidants on the liver and the
development of cancer, consumers’ desire to use natural
antioxidants has increased noticeably (Agrega
´n et al. 2017;
Kehili et al. 2017).
The objective of the present work is to propose a cheap
and environmentally friendly method for extraction of
pumpkin peel extract containing the highest value of car-
otenoid and phenol using subcritical water and supercritical
CO
2
extraction methods and their effect on the stability of
canola oil.
Materials and methods
Materials and chemical reagents
Bleached and odor-neutralized canola oil, without antiox-
idants, was obtained from Beheshahr Agricultural Indus-
trial Complex (Behshahr, Iran). All materials used in the
research were of analytical grade from Sigma- Aldrich
Company (St. Louis, the USA). Pumpkin of Cucurbita
pepo Styarica variety was purchased from a local market in
Sari (Mazandaran Province, Iran) in autumn 2018. All of
the chemicals and solvents used were analytical grade and
provided from Sigma-Aldrich (India).
Pumpkin peel extract preparation
Pumpkins were washed with cold water after entering the
laboratory and their peels were removed manually. The
thickness of the peel was 1.0 ±0.2 cm. The pumpkin peel
was dried in an oven at 40 °C and powdered with a particle
size of 2 mm (Cuco et al. 2019).
Subcritical water extraction(SWE)
First, 12 g pumpkin peel was put inside the extractor with
glass beads. Then, the extractor was installed on the heater.
Water as a solvent was pumped at a flow rate of 1 ml/min
using a HPLC (High Performance Liquid Chromatography)
pump to achieve the desired pressure. The pressure was
adjusted by a heat regulator. Then, the water was heated to
a working temperature using a pre-heating device.
Extractor temperature was measured to ensure that the
desired temperature was reached. The temperature, time
and pressure used were 120 °C, 3 h and 5 MPa, respec-
tively. The extraction was carried out under the optimal
condition of the recovery of carotenoid and total phenolic
compounds. The extracted solution was collected in vial
and stored in a refrigerator (Setyorini et al. 2018).
Supercritical fluid (CO2) extraction (SFE)
First, 12 g pumpkin peel was put inside the extractor with
glass beads. Then, the extractor was installed on the heater.
The carbon dioxide fluid was pumped as a solvent at a flow
rate of 15 ml/min using a HPLC pump to achieve the
desired pressure. Then, ethanol: water (80:20) was pumped
using a HPLC pump at a rate of 0.25 ml/min. A mixture of
carbon dioxide and ethanol: water (80:20) was entered the
extractor. The pressure was adjusted by a heat regulator.
The water was heated to a working temperature using a
pre-heating device. Extractor temperature was measured to
ensure that the desired temperature was reached. The
temperature, time and pressure used were 60 °C, 3 h and
25 MPa, respectively. The extraction was carried out under
the optimal condition of the recovery of carotenoid and
total phenolic compounds. The extracted solution was
collected in vial and stored in a refrigerator (Setyorini et al.
2018).
J Food Sci Technol
123
Determination of total phenolic and carotenoid
content
The total phenolic content (TPC) of extract was determined
according to the Folin–Ciocalteu method, as described by
Setyorini et al. (2018). Gallic acid was used as the standard
and results were calculated on the basis of calibration curve
of gallic acid and expressed as gallic acid equivalents (mg
GAE/100 g). b-Carotene content in the extract was mea-
sured using spectrophotometer at a wavelength of 450 nm,
as described by Setyorini et al. (2018).
HPLC-analysis of carotenoid
Carotenoids were analyzed according to the method
(Machmudah et al. 2012) and (Shi et al. 2010) with slight
modifications. Separation was carried out using HPLC
(Shimadzu HPLC-10 AT) with XDB-C18 column (5 lm,
1.4 9150 mm) and UV–vis detector (monitored at
470 nm. The sample was injected in 20 lunits. A mixture
of methanol/ methyl tert-butyl ether/water with different
ration of 81:15:4, v/v/v (A) and 4:92:4, v/v/v (B) was used
as a mobile phase at flow rate of 1.5 ml/min. Gradient
elution program was as follows: 0–60.0 min, solvent B
increasing from 0 to 80%; 60.0–65.0 min, solvent B
increase to 100%; 65.0–70.0 min, solvent B decrease to
0%; 70.0–80.0 min, isocratic with 0% B. The amount of
carotene in the extract was compared based on the retention
time and peak area of the standard sample. In other words,
peaks were determined based on the retention time and UV
absorption patterns of the standards. Because cis-isomer
standards were not available, the quantification of b-car-
otene isomers was carried out by applying the same
response factor as all-trans-b-carotene.
HPLC-analysis of total phenolic compounds
The phenolic compounds of the pumpkin peel extract were
analyzed according to the method of (Uddin et al. 2014)
with slight modifications. Separation was carried out using
HPLC (Shimadzu HPLC-10 AT) with XDB-C18 column
(5 lm, 1.4 9150 mm) and UV–vis detector. The mobile
phase included of acetonitrile (A), acetic acid solution at
pH 3.0 (B), and methanol (C). Gradient chromatography
was run as follows: 0 min, 5%A:95%B; 10 min,
10%A:80%B:10%C; 20 min, 20%A:60%B:20%C and
30 min, 100%A. The flow rate was at 1 ml/min and the
injection volume was 20 ll. For UV detection, the wave-
length was optimized to phenolic compounds at their
maximum absorbance wavelengths (280 nm). The phenol
content of the extract was compared based on the retention
time and peak area of the standard sample. In other words,
peaks were determined based on the retention time and UV
absorption patterns of the standards.
Antioxidant activities of pumpkin peel extract
Free radical scavenging DPPH
First, 2.7 ml of the freshly prepared DPPH solution
(6 910
–5
mol/l) was mixed with 0.3 ml of 4 concentra-
tions of 100, 200, 300 and 400 ppm of extract and 100 ppm
of synthetic anti-oxidant TBHQ, as the positive control.
Then, the resultant mixture was stirred vigorously and kept
in dark for 1 h. Finally, the absorbance was read at 517 nm
and calculated according to the following equation:
DPPH inhibition %ðÞ¼Ablank Asample

=AblankÞ100
where, A
sample
andA
blank
are the absorption of extract and
control without extract, respectively (Esmaeilzadeh Kenari
et al. 2014).
Ferric reducing ability power (FRAP)
In brief, 2.5 ml of the extract solution was combined with
2.5 ml of sodium phosphate buffer (200 mmol/l) and
2.5 ml of 1% ferricyanide and the mixture was incubated
for 20 min at 50 °C. Then, 2.5 ml of 10% v/v tri-
chloroacetic acid was added to the mixture, after which the
resultant mixture was centrifuged at 116 g for 8 min
(HERMEL Z 9 200A). 5 ml of the top solution was com-
bined with 5 ml of the deionized water and 1 ml of iron
chloride (0.1%). Finally, the absorbance of the solution was
read at 700 nm. Synthetic antioxidant TBHQ was used as
the positive control (100 ppm) (Esmaeilzadeh Kenari et al.
2014).
Preparation of oil
To examine the antioxidant activity of the obtained
extracts, different extracts were added to canola oil at a
concentration of 400 ppm and be compared with 100 ppm
of the synthetic antioxidant TBHQ. The oil samples were
stored at thermal conditions of 30 °C for 60 days. The oil
analysis was performed at different days of 0, 15, 30, 45,
and 60 (Sayyad and Farahmandfar 2017). An antioxidant-
free oil sample was also considered as the control.
Chemical properties of canola oil
Peroxide value
The peroxide value was evaluated based on the AOAC
method, No. 33/965(Chemists 1990). First, 5 g of canola
J Food Sci Technol
123
oil was dissolved in 10 ml of trichloromethane. Then,
15 ml of acetic acid and 1 ml of potassium iodide saturated
solution were added and gently stirred and stored for 5 min
in the dark. After the incubation time was completed,
75 ml of the distilled water was added to it and severely
mixed up. Finally, it was normalized with sodium thio-
sulfate (0.01 N). Finally, the peroxide value was calculated
based on the following equation in terms of mEq of oxy-
gen/kg oil:
PV ¼V2 V1ðÞN1000
m
where, V
2
and V
1
are the sample and control titration
numbers, respectively, N is the sodium thiosulfate nor-
mality and m is the sample weight in gram.
Carbonyl value
First, 1 kg of 2 propanol and 0.5 g sodium borohydride
were refluxed for 1 h, in order to remove additional car-
bonyls in the solvent. Then, 2 and 4 di-nitrofenylhydrazine
(DNPH) of 50 g was dissolved in 100 ml solvent, con-
taining 3.5 ml of chloride acid 37%. Canola oil reached a
volume of 10 ml at the rate of 0.04–1 g through the addi-
tion of a solvent including trinylpyrrole (0.4 mg/ml). After
that, 50 lm solution 2 and 4 decadienal were prepared in
2-propanol. 1 ml of the oil sample was combined with 1 ml
of DNPH and heated to 40 °C for 20 min, and then, after
adding 8 ml of potassium hydroxide (2%), it was cooled in
bath water. Finally, the sample absorption was read after
5 min centrifugation at 2000 g at 420 nm (Endo et al.
2001).
Acid value
Firstly, 10 g of the oil samples were weighed in the
Erlenmeyer and dissolved in 50 ml of chloroform: ethanol
solvent (50:50). Then, a few drops of phenolphthalein were
added as reagent to it and titrated with normal potassium
hydroxide 0.1. Finally, the acid value was obtained
according to the following equation (Firestone 1973).
Acid value ¼VC56:11
m
where, m is the weight of the oil in grams, V is the amount
of potassium hydroxide consumed in milliliters, and C is
the concentration of potassium hydroxide in moles per liter.
Statistical analysis
The statistical analysis of the data, obtained from the
extraction section, was performed using t-test. For chemi-
cal properties of canola oil, a completely randomized
design with one-way ANOVA was used. A significant
statistical difference was found between the means at the
95% probability level using Duncan’s multiple range tests.
The software used was SPSS version 20. In order to reduce
the error, all tests were performed in triplicate.
Results and discussion
The amount of phenolic and carotenoid compounds
of the extracts
The results of measuring the amounts of phenolic and car-
otenoid compounds of the extracts are shown in Table 1.It
was observed that the SFE method used to extract phenolic
compounds was more effective than the SWE. The simul-
taneous application of temperature and pressure in the SFE
played an important role in increasing the strength of carbon
dioxide solubility, effectively increasing the extraction of
phytochemicals and nutrients of pumpkin peel (Prado et al.
2014). High pressure led to the breakdown of the cell walls of
the plant and strong chemical interactions between carbo-
hydrate and lipid compounds with the wall, ultimately pro-
viding the easy exit of carotenoids from the extraction bed
(Khajeh 2011). Carotenoids have high molecular weight and
lower polarity (de Andrade Lima et al. 2018). The total
carotene extracted in the SWE method was higher than that
of the SFE method. Hamdan et al. (2008) showed that the
carotenoid and chlorophyll pigments in the SWE method
were higher than those in the SFE method, which was con-
sistent with the results of the present study.
Effective compounds profiles of the extracts
The profiles of carotene compounds of extracts are shown
in Table 2. As observed, many compounds were identified
by HPLC, and the value of detected carotene compounds in
the extract produced by SWE was more than that produced
by SFE. b-Carotene is also an important compound as an
anti-oxidant and vitamin A precursor (Hamdan et al. 2008).
Lutein is one of the most important carotenoids in the diet.
It is inexpensive and has antioxidant activity (Goto and
Watanabe 2012).
Quantitative and qualitative results regarding the num-
ber of phenolic compounds of pumpkin peel extracts are
shown in Table 3. As can be seen, the number of phenolic
compounds extracted by the SFE was higher. Vanillic acid,
p-coumaric acid, and sinapic acid were the most important
phenolic compounds in the pumpkin peel (Dragovic-Uze-
lac et al. 2005) hydroxycinnamic acids (such as caffeic, p-
coumaric, ferulic, and sinapic acids) are compounds in the
cell walls and they are responsible for preventing patho-
gens from entering the plant (Peric
ˇin et al. 2009).
J Food Sci Technol
123
Antioxidant activities of pumpkin peel extract
DPPH free radical scavenging is one of the fastest methods
for determining the capacity of hydrogen donation of
chemicals, and so for evaluating their antioxidant activity.
When the DPPH molecule encountered a radical proton, its
purple color disappeared quickly (Agrega
´n et al. 2017). In
the method of reducing iron, free radicals are neutralized
either by electron transport or the disposal of hydrogen
atoms. These methods are easy and inexpensive, therefore,
frequently used in factories (Hiranvarachat and Devahastin
2014). The results of measuring the antioxidant activity of
the extracts using DPPH radical scavenging and iron-re-
ducing methods are shown in Fig. 1a, b, respectively. As it
can be seen, with increased concentrations of extracts, the
amount of radical scavenging and iron-reducing increased
and a statistically significant difference was seen. Hamdan
et al. (2008) showed that antioxidant activity in the SFE-
Table 1 The amount of
phenolic and carotenoid
compounds of the extracts
Samples Total phenol (mg GA/100 g E) Total carotene (mg carotene/100 g E)
SWE 213.6 ±5.87
b
15.22 ±2.35
a
SFE 353.5 ±8.84
a
11.48 ±0.90
b
Note Pumpkin peel extract obtained bysubcritical water extraction (SWE) and supercritical fluid extraction
(SFE)
Values (Mean ±SD, n = 3) in the same column with different letters are significantly different (P \0.05)
Table 2 The profiles of carotenoid compounds of extracts was
obtained by two different methods
Rt (min) SWE SFE Compound (%)
11.5 4.77 0.22 Neoxanthin
12.0 4.67 0.27 Violaxanthin
15.2 8.78 2.49 Lutheoxanthin
15.4 10.79 3.97 Lutein
17.3 2.25 0.09 Unknown
17.8 3.06 0.06 Zeaxanthin
32.3 1.22 0.14 13-cis-b-carotene
34.8 0.17 0.05 a-Carotene
35.2 0.14 0.09 Unknown
38.7 23.13 25.15 a-Crypthoxanthin
39.6 1.62 1.36 b-Carotene
40.1 2.41 0.05 9-cis-b-carotene
44.2 12.76 24.01 b-Crypthoxanthin
46.0 1.51 0.05 Lycopene
77.28 57.99 Total carotenoid
Note Pumpkin peel extract obtained by supercritical fluid extraction
(SFE) and subcritical water extraction (SWE)
Table 3 The profiles of phenolic compounds of extracts was obtained
by two different methods
Rt (min) SFE SWE Compound (%)
6.5 0.02 6.7 Protocatechuic
9.2 11.9 20.8 p-Hydroxybenzoic
12.3 11.5 1.27 p-Hydroxybenzaldehyde
16.2 4.13 5.61 Vanillic
16.9 21.6 2.32 Caffeic
17.11 0.03 0.06 Syringic
17.3 8.02 1.7 Trans-p-Coumaric
19.2 7.82 3.27 Ferulic
20.4 0.04 3.85 Trans-Sinapic
65.06 45.58 Total phenolic
Note Pumpkin peel extract obtained by supercritical fluid extraction
(SFE) and subcritical water extraction (SWE)
Fig.1 DPPH radical scavenging (a) and iron reducing (b) of different
concentrations of extracts (100–400 ppm) and TBHQ (100 ppm) Note
Pumpkin peel extract obtained by method of supercritical fluid
extraction (SFE) and subcritical water extraction (SWE). MIX(SFE–
SWE) is a mixture of SFE and SWE extracts
J Food Sci Technol
123
derived extract was more than that in SWE extract, in a
good agreement with the results of the present study. The
type of extracted compounds affected the antioxidant
activity of the extracts. Shi et al. (2013) reported that the
antioxidant activity of carotene extracts was related to their
fractional components. The type of extracted compounds
affected the antioxidant activity of the extracts. According
to Shi et al. (2013), the antioxidant activity of carotene
extracts was associated with their fractional components.
Cis isomers in the extract such as 9-cis-b-carotene and
13-cis-b-carotene had higher antioxidant activity than
trans-types (Shi et al. 2013). The combined extracts
exhibited higher antioxidant activity, at the same
concentration.
Agrega
´n et al. (2017) reported that the antioxidant
activity of herbal extracts in the iron reduction test was
related to the concentration of extracts, reporting an
increasing trend in scavenging free radicals by increasing
the concentration of the extract. The type of compounds in
the extract affected their antioxidant activity (Agrega
´n
et al. 2017). As observed, the quality of phenolic com-
pounds in the extracts produced from various methods was
different. The non-phenolic compounds present in the
extract such as molecules of low molecular protein and
carbohydrate weights also affected the amount of free
radical scavenging (Gallardo et al. 2013).The antioxidant
activity of the extracts was related to the value and position
of the hydroxyl groups of phenolic compounds. For
example, caffeic acid with two hydroxyl groups had higher
antioxidant activity than that of p-coumaric acid with one
hydroxyl group (Masek et al. 2016). The amount of both
phenols mentioned in the extract produced with SFE was
higher than those in SWE.
The concentration of 400 ppm of the extract was
showed the highest antioxidant activity with measuring
total phenolic content and antioxidant activity. Then, the
pumpkin peel extract with a concentration of 400 ppm was
chosen to injecting to the canola oil separately and in a
combination form, and compared with 100 ppm of syn-
thetic TBHQ antioxidant.
Chemical properties of canola oil
Peroxide value
Peroxide value is a very good indicator for evaluating
peroxide production at the beginning of the oxidation
process. It is equal to the amount of peroxide and
hydroperoxide formed during the oxidation process (Zhang
et al. 2010; Agrega
´n et al. 2017; Islam et al. 2018). As
shown in Fig. 2, over time, the peroxide value increased in
all treatments, indicating the formation of hydroxides
during the maintenance period (Islam et al. 2018). In the
control sample, in 0 to 45th day of the storage period, the
amount of peroxide increased from 0.88 to 5.17 meq O
2
/kg
oil. In the oil sample containing TBHQ at the end of the
maintenance period, the peroxide value was 4.14 meq O
2
/
kg oil, higher than that of the extract-containing oil sam-
ples. Adding phenolic and carotene extracts of pumpkin
peel to canola oil resulted in the increased oxidative sta-
bility of the oil. Islam et al. (2018) showed that the use of
pomegranate and orange peel extracts in soybean oil and
sunflower oil led to the increased oxidative stability of the
oil. Herbal extracts caused increased human health because
they prevent the oxidation of fats and scavenge-free radi-
cals. Agrega
´n et al. (2017) compared the antioxidant
activity of marine algae extract in canola oil with synthetic
antioxidant BHT. Over time, peroxide value increased and
the control sample had the highest peroxide value.
Peroxide value ranged from 0.68 to 1.52 for the extract
produced by the supercritical fluid, 0.85 to 1.90 for the
extract produced by the following sub-critical water
method and 0.6 to 1.42 for MIX(SFE–SWE). These results
indicated that MIX(SFE–SWE) extract showed a higher
antioxidant effect than separate extract. The higher oxida-
tion stability of the oil sample containing the combined
extract could be attributed to the types of its constituents.
Both the SFE and SWE methods were useful in extracting
plant’s various main components, and each of which
showed different functions in preventing the oil oxidation
process. Therefore, the combined SFE and SWE extract
had been more functional. As shown in Fig. 2, the plant
extracts had higher antioxidant activity than synthetic
antioxidants, which was consistent with the results of Islam
et al. (2018). In addition, the results confirmed that the
extracts had the ability to prevent the oxidation of oil in the
early stages of oxidation by donating electrons and
inhibiting free radicals (Kindleysides et al. 2012; Farvin
and Jacobsen 2013; Agrega
´n et al. 2017).
Fig. 2 The changes of peroxide value of different oil samples during
storage. Note Pumpkin peel extract obtained by method of Super-
critical fluid extraction (SFE) and Subcritical water extraction (SWE).
MIX(SFE–SWE) is a mixture of SFE and SWE extracts
J Food Sci Technol
123
Carbonyl value
The results obtained for the value changes of carbonyl of
different oil samples are shown in Table 5. As can be seen,
carbonyl content increased in all treatments over time, and
a significant statistical difference was seen. The lowest
increase in the carbonyl content was observed in the oil
samples containing combined extracts; besides, the oil
containing TBHQ had a higher carbon value than the
extract-based oils. Elbadrawy and Sello (2016) examined
the antioxidant properties of tomato peel extract in
increasing the stability of flaxseed oil during 28 days of
storage. Carbonyl value changes were incremental in all
samples and the control sample and BHT-containing oil
had the highest carbon number, respectively. The olive oil
containing petroleum extract of tomato wort had the lowest
carbon number. The extract of tomato peel had high
antioxidant properties due to phenolic and lycopene com-
pounds. Other research results showed that the amount of
phenolic and flavonoid compounds in the peel was higher
than seeds and pulp (Stewart et al. 2000). As shown in
Table 4, the carbonyl value of SWE extract was slightly
higher than that of SFE extract, although the lowest content
of carbonyl value was related to the oil sample contain-
ingMIX (SFE–SWE) extract.
Acid value
The acid value is an indicator of fatty acid hydrolysis. Free
fatty acids, formed as a result of the hydrolysis of
triglycerides, are an indicator of the rate of oil shrinkage
(Islam et al. 2018). Table 5shows the results of the acid
value of different oil samples during the maintenance
period. The control sample had the highest acid value. The
acid value in TBHQ-containing oil samples was higher
than that of the extract containing oil samples. The acid
value in the oil samples containing the MIX (SFE–SWE)
extract was lower than that in the oil samples containing
extracts individually. The extract produced by the SFE,
compared to the extract obtained by SWE, showed higher
antioxidant properties in reducing the acid value of oil.
These results were consistent with those of El-aal and
Halaweish (2010), showing that in soybean oil containing
ethanolic extracts of orange peel, hydrolysis of fatty acids
occurred less than synthetic antioxidants. Also, Lutfullah
et al. (2015) showed that formed free fatty acids in soybean
oil containing pomegranate peel extract, were less than
those in the oil containing synthetic BHT antioxidants.
Arawande and Borokini (2015) examined the antioxidant
properties of orange peel extract in peanut oil during
14 months of storage at 27 to 30 °C. According to their
results, over time, the acid value increased and the sample
showed the highest acid value. Furthermore, the antioxi-
dant activity of the extracts was better than that of synthetic
antioxidants in reducing the acid value, consistent with the
Table 4 The value changes of
carbonyl of different oil samples
during storage (lmol/g)
Sample Day
015304560
CON 10.51
Da
11.36
Da
18.79
Ca
33.80
Ba
35.64
Aa
TBHQ 9.46
Db
10.22
Db
16.91
Cb
30.42
Bb
33.72
Ab
SFE 8.62
Da
9.07
Db
12.35
Cc
17.23
Bc
21.05
Ac
SWE 9.57
Db
9.20
Db
12.52
Ccd
17.90
Bc
22.73
Ac
MIX(SFE–SWE) 7.18
Dc
7.25
Dc
9.88
Ce
15.34
Be
18.04
Ad
Note Pumpkin peel extract obtained by supercritical fluid extraction (SFE) and subcritical water extraction
(SWE). MIX(SFE–SWE) is a mixture of SFE and SWE extracts, and CON is control oil (Without any
antioxidant)
Different little letters within the same column indicate significant differences (P \0.05)
Different big letters within the same row indicate significant differences (P \0.05)
Table 5 The acid value of different oil samples during storage (mg
KOH/g oil)
Sample Day
0 15 304560
CON 0.24
Ea
0.36
Da
0.53
Ca
1.08
Ba
1.63
Aa
TBHQ 0.20
Db
0.23
Db
0.39
Cb
0.70
Bb
1.17
Ab
SFE 0.18
Db
0.20
Db
0.25
Cc
0.34
Bc
0.432
Ac
SWE 0.19
Db
0.20
Db
0.27
Cd
0.39
Bd
0.50
Ad
MIX(SFE–SWE) 0.17
Db
0.17
Dc
0.22
Ce
0.30
Be
0.36
Ag
Note Pumpkin peel extract obtained by supercritical fluid extraction
(SFE) and subcritical water extraction (SWE). MIX(SFE–SWE) is a
mixture of SFE and SWE extracts, and CON is control oil (Without
any antioxidant)
Different little letters within the same column indicate significant
differences (P \0.05)
Different big letters within the same row indicate significant differ-
ences (P \0.05)
J Food Sci Technol
123
results of this study (Arawande and Borokini 2015). Pur-
waningsih et al. (2019) showed that the use of banana peel
extract led to a reduction in the acid value of vegetable oil
samples, due to the presence of phenolic compounds.
Conclusion
According to the results of the present study, the use of
pumpkin peel extracts, obtained using SFE, showed a
strong protective effect against canola oil oxidation during
storage, in contrast to those obtained by SWE. In addition,
the mixture extract (SFE–SWE) with higher free-radical
scavenging and iron-reducing effect, compared to the
extracts obtained by SFE and SWE did separately, pro-
longed the stability of canola oil during storage. The fact
that the SFE ?SWE extract was more effective could be
attributed to the synergistic effects of the extracts as well as
the different types of materials extracted by two methods.
The findings of this study indicated that the natural
antioxidant extract of pumpkin peel, thanks to phenolic and
carotene compounds under these conditions, can be used as
an alternative to synthetic antioxidants in edible oil
refineries.
Funding No funding information provided.
Compliance with ethical standards
Conflict of interest None declared.
Ethical approval This study does not involve any human or animal
testing.
Open Access This article is licensed under a Creative Commons
Attribution 4.0 International License, which permits use, sharing,
adaptation, distribution and reproduction in any medium or format, as
long as you give appropriate credit to the original author(s) and the
source, provide a link to the Creative Commons licence, and indicate
if changes were made. The images or other third party material in this
article are included in the article’s Creative Commons licence, unless
indicated otherwise in a credit line to the material. If material is not
included in the article’s Creative Commons licence and your intended
use is not permitted by statutory regulation or exceeds the permitted
use, you will need to obtain permission directly from the copyright
holder. To view a copy of this licence, visit http://creativecommons.
org/licenses/by/4.0/.
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... Similarly, Song et al. [34] reported a maximum yield of total carotenoids (trans-and cis-isomers) content to be 358 µg/g after extracted with UAE from peel of Cucurbita moschata. In addition, Salami et al. [35] compared the other innovative extractions and reported that the carotenoids content of Cucurbita pepo extract was found higher with subcritical water extraction (15.22 mg/100 g) when compared to supercritical fluid extraction (11.48 mg/100 g). ...
... Previously, Salami et al. [35] analysed the effect of subcritical water extraction (SWE) and supercritical fluid extraction (SFE) techniques on TPC of pumpkin (Cucurbita pepo) peels and reported that the TPC in SFE (353 mg GA/100 g) was higher as compared to SWE (213 mg GA/100 g). Similarly, TPC has been reported by Mala and Kurian [39] from pumpkin peels (5.21 mg GAE/g) and pulp (5.19 mg GAE/g). ...
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The susceptibility of Teucrium polium essential oil (EO) as an antioxidant for canola oil was studied. Major compounds of the EO were 11-acetoxyeudesman-4-α-ol (26.3%) and α-bisabolol (24.6%). Different concentrations (200, 600 and 1200 ppm) of EO and synthetic antioxidant BHA (200 ppm) were added to canola oil and incubated for 60 days at room temperature. Acid value (AV), peroxide value (PV), carbonyl value (CV), iodine value (IV), total phenolics (TP), total polar compounds (TPC) and oxidative stability index (OSI) of canola oil were determined. Antioxidant capacity of the EO was measured by DPPH and β-carotene–linoleic acid assays. Results exhibited that DPPH and β-carotene–linoleic acid experiment detections on the EO were analogous in high concentrations to those detected on BHA. Moreover, incorporated EO samples had better AV, PV, CV, IV, TP and TPC than control. EO at concentration of 600 ppm indicated higher antioxidant activity in canola oil compared with BHA.
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Abstract: Background: A new vegetable cultivated in North Iran (Guilan and Mazandaran) is Cucurbita pepo. C. pepo peel is often removed from the fruit before use. Thus, Antioxidant activity of C. pepo peel could be an interesting topic for research. Methods: In this research, antioxidative activity of peels from C. pepo cultivated in Behshar and Amol areas (in Mazandaran province, Iran) was investigated. For this purpose, water-ethanol extracts of C. pepo were prepared by common and ultrasound-assisted methods. Antioxidative activities of the extracts were investigated by three methods including β-carotene bleaching assay, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay and rancimat test. Moreover, total phenolics and tocopherols of the extracts were measured. Results: C. pepo extract was better than tert-Butylhydroquinone (TBHQ) in β-carotene bleaching assay and DPPH radical-scavenging assay; while the opposite was the case for rancimat test. Moreover, antioxidative power of peel from C. pepo cultivated Behshahr region was better than that of Amol region. Ultrasound waves promoted extraction of phenolic compounds, too. Conclusion: The results obtained in this research indicated that C. pepo peel is rich source of antioxidative compounds. Keywords: Cucurbita pepo, peel, antioxidative activity, phenolic compounds, water-ethanol extracts, Ultrasound waves