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\begin{document}

\title{Antioxidant Activity of Green Tea Extract on Canola Oil Oxidation
Stability: Comparison of Free and Liposomal extract}



\author[1]{Shima Jahanfar}%
\author[2]{Mehrdad Ghavami}%
\author[2]{Kianoush Khosravi-darani}%
\author[3]{Mahshid Jahadi}%
\affil[1]{Islamic Azad University Science and Research Branch}%
\affil[2]{Affiliation not available}%
\affil[3]{Islamic Azad University Khorasgan Branch}%


\vspace{-1em}



  
  \date{May 04, 2024}


\begingroup
\let\center\flushleft
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\selectlanguage{english}
\begin{abstract}
In the present study, green tea extract was encapsulated in liposomes
prepared by Mozafari method (without any organic solvents) and
characterized for its physicochemical properties e.g. encapsulation
efficiency, particle size and z- potential. The obtained results for
encapsulation efficiency, particles size and z- potential were 51.34,
419 nm and -57 mV, respectively. Total polyphenol content of green tea
was obtained 164.2 mg gallic acid /g extract. Free radical scavenging
activities of free and liposomal extract, with using DPPH method were
measured 90.6\% and 93.37\% respectively. Antioxidant activity of
ethanolic extract of green tea in free and liposomal form were measured
at concentration of 200, 600 and 1000 mg/L on the oxidative stability of
canola oil during 60\selectlanguage{ngerman}°C temperature for 0, 4, 8, 12, 16, 20, 24, 28 and
32 days. The results compared with synthetic antioxidant butylated
hydroxytoluene at 200 mg/L. To evaluate antioxidant activity on canola
oil stability, peroxide value, Thiobarbitoric acid, anisidine value,
TOTOX and rancimat test measured. Results showed that liposomal green
tea extract acted more effective than free extracts. Also, 600 mg/L
concentration of green tea extract showed significant antioxidant
activity in compare to others. The increasing storage time and different
concentrations of ethanolic green tea extracts had significant effects
on canola oil stability (P\selectlanguage{english}[?]0.05). The obtained results showed green tea
extract could act as an effective antioxidant. Green tea extract in free
and liposomal form at 600 mg/L concentration resulted stronger function
than butylated hydroxytoluene synthetic antioxidant.%
\end{abstract}\selectlanguage{ngerman}%



\sloppy


\textbf{Antioxidant Activity of Green Tea Extract on Canola Oil
Oxidation Stability: Comparison of Free and Liposomal extract}

\textbf{Shima Jahanfar\textsuperscript{a}, Mehrdad
Gahavami\textsuperscript{a}, Kianoush
Khosravi-Darani\textsuperscript{*b}, Mahshid Jahadi\textsuperscript{c}}

\textsuperscript{a} Department of Food Science and Technology, Faculty
of Agriculture and Natural Resources, Science and Research Branch,
Islamic Azad University, Tehran, Iran.

\textsuperscript{b} Department of Food Technology Research, National
Nutrition and Food Technology Research Institute, Faculty of Nutrition
Sciences and Food Technology, Shahid Beheshti University of Medical
Sciences, P.O. Box: 19395-4741, Tehran, Iran.

\textsuperscript{c} Department of Food Science and Technology, Isfahan
(Khorasgan) Branch, Islamic Azad University, Isfahan, Iran.

\textbf{Abstract:} In the present study, green tea extract was
encapsulated in liposomes prepared by Mozafari method (without any
organic solvents) and characterized for its physicochemical properties
e.g. encapsulation efficiency, particle size and z- potential. The
obtained results for encapsulation efficiency, particles size and z-
potential were 51.34, 419 nm and -57 mV, respectively. Total polyphenol
content of green tea was obtained 164.2 mg gallic acid /g extract. Free
radical scavenging activities of free and liposomal extract, with using
DPPH method were measured 90.6\% and 93.37\% respectively. Antioxidant
activity of ethanolic extract of green tea in free and liposomal form
were measured at concentration of 200, 600 and 1000 mg/L on the
oxidative stability of canola oil during 60\selectlanguage{ngerman}°C temperature for 0, 4, 8,
12, 16, 20, 24, 28 and 32 days. The results compared with synthetic
antioxidant butylated hydroxytoluene at 200 mg/L. To evaluate
antioxidant activity on canola oil stability, peroxide value,
Thiobarbitoric acid, anisidine value, TOTOX and rancimat test measured.
Results showed that liposomal green tea extract acted more effective
than free extracts. Also, 600 mg/L concentration of green tea extract
showed significant antioxidant activity in compare to others. The
increasing storage time and different concentrations of ethanolic green
tea extracts had significant effects on canola oil stability (P\selectlanguage{english}[?]0.05).
The obtained results showed green tea extract could act as an effective
antioxidant. Green tea extract in free and liposomal form at 600 mg/L
concentration resulted stronger function than butylated hydroxytoluene
synthetic antioxidant.

\textbf{Keywords} Green tea extract, Liposome, Canola oil, Oxidative
stability

\textbf{Antioxidant Activity of Green Tea Extract on Canola Oil
Oxidation Stability: Comparison of Free and Liposomal extract}

\textbf{Introduction}

One of the most consumption and nutritious edible oils in the world is
canola oil. The unsaturated acids content in canola oil is higher than
other vegetable oils. The ratio of linolenic acid (C18:3, \selectlanguage{greek}ω\selectlanguage{english}3) to
linoleic acid (C 18:3, \selectlanguage{greek}ω\selectlanguage{english}6) in this oil is about 1:2 that is desirable
from the point of view nutrition (Shahidi., 1990). The high contents of
unsaturated fatty acids in canola oil especially linolenic acid effect
on its stability and quality (Tokarska et al., 1986). Lipids are more
potential to autoxidation than other chemical components of an organic
material. Triglycerides oxidation process rate depends on saturation
degree and double bonds position in molecule (Yanishlieva-Maslarowa.,
2001). One of the most effective ways to prevent oxidation and
development off-flavour is addition antioxidants in foods containing fat
(Jeong et al., 2004). Antioxidants as food additive are used to develop
oils shelf life and fat-based foods during storage and processing (Bitar
et al., 2008). The most extensive synthetic antioxidants useable are
including tert-butyl hydroxy quinoline (TBHQ), butylated hydroxytoluene
(BHT), butylated hydroxyanisole (BHA). However, there are too much worry
about consumption safety these antioxidants such as carcinogenic effects
(Jeong et al., 2004). The demand for using of natural antioxidants
instead of synthetic ones have been increased increasing which cause to
prevent of diseases and having healthy effects (Zhou \& Ly., 2004).
Green tea has known as a potent natural antioxidant. This property
strongly is related with the total phenolic content of green tea
(Langley-Evans, 2000). Green tea leaves are a superior source of
polyphenolic compounds that has shown anticancer properties versus
several types of cancer (Ahmed et el., 2014), such as lung, skin,
esophagus, liver, and stomach (Mandel et al., 2004). A main group of
green tea polyphenols are catechins. Many researches have shown, tea
catechins are included numerous therapeutic effects such as
neuroprotective activity, prevent atherosclerosis, inhibit tumor
angiogenesis and modulate cholesterol metabolism (Tang et al., 2013).
The most importance catechins of green tea are including: epicatechin
(EC), epicatechin-3-gallate (ECG), epigallocatechin (EGC), and
epigallocatechin-3-gallate (EGCG) (Rains et al., 2011). Chander et al.
reported green tea leaves (\emph{Camellia sinensis L} .) contain
polyphenolic components which have been known as strong antioxidants.
One of the most polyphenolic components are catechins. Catechins reduce
fatty acids oxidation ability by chelating iron and copper which cause
to form catalyzed free radicals by metal (Chander et al., 2005). Ou et
al. reported natural antioxidants compounds of green tea such as caffeic
acid, cherogenic acid, quercetin, rutin and catechins have been acted as
stronger antioxidants than vitamins C and E (Ou et al., 2001). Koketsu
and Satoh. studied the antioxidant effect of green tea extract on the
lard and soy bean oil. The green tea extract used in 20 and 40 mg/L
levels. They stated, green tea polyphenols had stronger antioxidant
properties compared with tocopherol in both lard and soy bean oil
(Koketsu and Satoh., 1997). Despite the promising therapeutic effects of
polyphenolic compounds under in vitro conditions and be contain strong
antioxidant activity, their usage is limited due to various reasons
including poor absorption and bioavailability (Zhang et al., 2004). In
addition to, the tea polyphenols are unstable when exposed to light,
heat and oxidants (Shpigelman et al., 2012). An effective method to
overcome this problem is entrapment systems such as liposome,
nanoparticle and microcapsule (Dsai \& Park., 2005). Liposomes possess a
spherical structure along with an aqueous core that have surrounded by
single or several lipid bilayers. The most important advantage of
liposome structures is their ability to encapsulate both hydrophilic and
lipophilic bioactive compounds (Liveny., 2015). Noudoost et al. prepared
liposomes containing green tea polyphenols with thin film layer method
which applied sonication process to reduce of particle size. They
reported green tea polyphenols incorporated in liposome had
significantly more antioxidant activity than free extract (Noudoost et
al. (2015). Rasti et al. studied the oxidative and physical stability of
liposomes and nanoliposomes containing docosahexaenoic and
eicosapentaenoic acid, prepared by the thin film hydration technique and
Mozafari method. They found prepared liposomes by Mozafari method had
the most physicochemical stability (Rasti et al., 2012). Lu et al.
prepared green tea extract liposome by the thin film ultrasonic
dispersion method to increase the bioavailability of tea polyphenol.
They reported that liposomes containing green tea polyphenol were stable
and suitable for more widespread application (Lu et al., 2011).
Considering that harmful effects synthetic antioxidant, the purpose of
this study was the evaluation green tea extract as a natural antioxidant
on the oxidative stability of canola oil in two forms free and
incorporated in liposome during storage at an oven at 60\selectlanguage{ngerman}°C temperature
and compare it with BHT as a synthetic antioxidant. For this purpose,
green tea extract liposomes prepared with using Mozafari method without
using any solvents.

\textbf{Materials and Methods}

\textbf{Materials}

Green tea plant (\emph{Camellia sinensis} ) belongs to the
family\emph{Theaceae} was obtained from Isfahan province (Iran),
lecithin (99\%, granular phosphatidylcholine) was procured from Across
Company (USA). Ethanol, glycerol, 2-2-diphenyl-1-pycrylhydrazyl (DPPH)
and Folin-ciocalteu reagent were prepared from Merck Company, Germany,
Particle size and Zeta-Sizer analyzer (Horiba scientific Instruments,
SZ-100 Series Germany), ultracentrifuge (Herolab, Hicen, Germany),
spectrophotometer model UV-6600 (Spectro Flex, Germany).

\textbf{Preparation of green tea extract}

Fresh green tea leaves were collected from tea gardens of Mazandaran
province. Then, were sorted, washed, and were dried under sunlight. The
dried tea leaves were crushed in a blender and then sieved using 70/100
mesh sieve-set (Setyopratomo., 2014). The extraction carried out by
mixing 1000 ml of 70\% ethanol in distilled water to 100 g of green tea
powder. The obtained mixture had agitated with a magnetic for 24 hours
at 40 °C temperature. In the next stage, the extract separated by
filtration. Then to obtain to a concentrate extract, the resultant
liquid evaporated by oven at temperature 40 °C. Finally, the extract was
converted to powder by employing a freeze dryer at -50°C and was kept in
air-tight dark bottles in the freezer at -18°C until usage (Vuong et
al., 2011). Nwuha et al. reported the green tea polyphenols solubility
in ethanol solvent was five to seven times higher than in the water
extracts (Nwuha et al., 1999).

\textbf{Liposome preparation}

To prepare liposomes containing green tea extract, in this study, was
applied of mozafari method. The superiority this method than other
methods is the production of liposomes without using any solvent and
detergent (Mozafari \& Khosravi-Darani., 2007). In addition to, in this
method do not use of homogenization or sonication methods for reduction
of particle size which cause to destruction of liposome structure. The
green tea extract (0.7-2 \%) was first mixed with distilled water. Then
phosphatidylcholine (2.5-4.5 \%) and glycerol (3\% v/v) were added to
the green tea extract solution. The mixture was agitated on a hot plate
stirrer at temperatures of (50° - 70°C) for different time intervals
(30-60 min) at a mixing speed of 1,000 rpm. Finally, the mixture was
placed at room temperature for one hour in order to increase the
stability of the liposomes. The formulation was kept in a dark bottle at
4°C under nitrogen. Then, physicochemical properties of green tea
liposomes measured such as encapsulation efficiency (EE), particle size
and z- potential and determined optimal conditions to produce to green
tea extract liposomes. In addition to, total polyphenol content of green
tea and free radical scavenging activities of free and liposomal
extract, with using DPPH method measured (Jahanfar et al., 2020).

\textbf{Sample Preparation}

Green tea extracts in three concentration 200, 600 and 1000 mg/L and BHA
in 200 mg/L level added to canola oil without antioxidant and then were
placed in oven at 60°C temperature and oil samples were evaluated to
determine oxidation processes progress. Control samples without any
antioxidant were also placed under the same storage conditions.

\textbf{Oven Test}

Oil samples (250 g) were placed separately in glass dark bottles 300 ml
in oven at 60°C and then samples oxidative stability were evaluated at
intervals 0, 4, 8, 12, 16, 20, 24, 28 and 32 days. The temperature of
60°C used as a rapid method to simulate the storage in real conditions
(Besbes et al., 2004).

\textbf{Rancimat Test}

Rancimat test carried out according to Laubli \& Bruttel by the little
modifications. During the lipid oxidation process are formed volatile
acids that the rancimat test is based on the conductometric measurement
of volatile acids. Oil samples (2.5 g) was oxidized in a reaction vessel
at 140°C and air flow (20 L/h). The end of the induction period (IP) was
determined by the sudden increase of water conductivity, due to the
dissociation of volatile carboxylic acids (Laubli \& Bruttel., 1986).

\textbf{Peroxide Value}

To determine peroxide value used of A.O.A.C (1984) method. From each of
the oil samples, 2g were weighed into different conical flasks. Then,
15ml of the mixture of CH\textsubscript{3}COOH and
CHCl\textsubscript{3}in the ratio of 3:2 was added to the oil samples
respectively. In the next step, 0.5ml of saturated potassium iodide was
added to each conical flask and allowed to stand for 5 minutes left in
room temperature for 5 minutes, thereafter, 15ml of distilled water was
added and titrated with 0.1 N Na 2S2O3 until it appeared yellowish
color. Finally, 0.5 ml of starch indicator was added and the titration
continued to a colorless end-point. The peroxide value was calculated
from the equation:

\begin{equation}
\text{PV}=\ \frac{\left(V2-V1\right)\mathsf{\text{\ x}}\text{\ T}}{M}\ \mathsf{x}\ 1000\nonumber \\
 \end{equation}

where M = mass of oil taken (2g), V2 \selectlanguage{english}= volume of Na2\selectlanguage{english}S2\selectlanguage{english}O3 , \selectlanguage{english}V1 \selectlanguage{english}= volume
of blank and T = normality of Na2\selectlanguage{english}S2 \selectlanguage{english}O3.

\selectlanguage{english}\textbf{Anisidine Value}

The measurement of anisidine value carried out according to AOCS
Official method Cd, 18-90 (1996). For this purpose, 1g oil sample mixed
with iso-Octane into 25ml conical flasks. Then, 5 ml of this solution
mixed to 1ml of 0.25\% p- anisidine solution in glacial acetic acid.
After 10 minutes, solution adsorption read in 350 nm wavelength by
spectrophotometer model UV-6600 (spectroFlex, Germany). The anisidine
value was calculated from the following equation:

\begin{equation}
p-Anisidine\ Value=\frac{25\times(1.2\ As-Ab)}{m}\nonumber \\
 \end{equation}

As, Ab and m is illustrative of solution adsorption before and after
reaction with p-Anisidine solution, respectively.

\textbf{TOTOX Value}

TOTOX value is illustrative the total oxidation amount. This indicator
measures first and secondary oxidation products. This index is expressed
as TOTOX = 2PV+ p-AV (Abbas Ali et al., 2013).

\textbf{Thiobarbituric Acid (T.B.A)}

The TBA value was measured according to AOCS Official method Cd ,19-90
(1998).The TBA value calculated as mg malonaldehyde / kg sample.

\textbf{Statistical Analysis}

Statistical analysis was performed in triplicate. Results were expressed
as the means and standard deviation. Significant differences between
means of same sample were determined by Duncan's multiple range test
using SPSS 26 software package. Differences were considered
statistically significant at P[?]0.05.

\textbf{Results and Discussion}

\textbf{The Physicochemical Properties of Liposome}

The obtained amounts for EE, particles size and z- potential was 51.34,
419 nm and -57 mV, respectively (without any data). It should be noted,
in this research, did not use of any method for particle size reduction
(e.g. sonication, homogenization or extrusion). This matter caused to
reduce executive stages, as well as to be economic. Also, these methods
because of using of high stress and pressure, can destroy the membrane
of liposome. The required energy to produce small liposomal particles
supplied by magnet stirrer with agitation speed 1000 rpm along with
thermal treatment. Also, to prepare liposomes by Mozafari method, did
not use any organic solvents or detergent. Because these solvents can
cause production toxicity. In addition to, solvent remove processes are
time-consuming and costly (Jahanfar et al., 2020)

\textbf{Rancimat Test}

The results of rancimat is visible in Figure 1. The lowest and highest
stability belonged to control and green tea extract liposome in 1000
mg/L level. Oil samples containing green tea extract liposome had higher
oxidative stability than free green tea. Green tea extract, in 1000 mg/L
concentration, in the rancimat test, had the best oxidative stability,
with induction period 9.5 h, while in oven test showed the lower
stability. The reason was that in the oven and rancimat test are used of
60 [?]C and 120\selectlanguage{ngerman}ºC, respectively. In the high temperatures such as rancimat
test, lipids oxidation mechanism significantly changes while in oven
test, side reactions including polymerization and cyclization were in
its minimum amount. The rate of oxidation depends to oxygen
concentration and oxygen solubility, in the high temperatures, decreases
(Frankel., 1993). Yin et al. studied the effect of green tea extract
green tea (catechin at 0.25, 0.5 and 1 \selectlanguage{greek}µ\selectlanguage{english}mol/g oil on the sunflower oil
stability by rancimat test. Oil samples induction period had upward
trend by increasing antioxidant concentration. Induction period for
control and oils containing green tea extract in 0.25, 0.5 and 1 \selectlanguage{greek}µ\selectlanguage{english}mol/g
oil concentrations was about 1.9, 4.8, 7.5 and 11.8, respectively (Yin
et al., 2012). Gramza et al. evaluated the effect of antioxidant
properties aqueous and ethanol green tea extracts at 200, 500 and 1000
mg/L on the sunflower stability in the rancimat test. They stated oil
samples containing green tea ethanolic extracts at 1000 mg/L during 6.45
h induction period had the longest oxidative stability (Gramza et al.,
2006).

\textbf{Fig. 1}

\textbf{Peroxide value}

One of the most common tests to evaluate progress rate of lipids
oxidation is peroxide value. This test measures primary products of
oxidation. The antioxidant effects green tea extracts as free and
encapsulated in liposome on canola oil during oven test 60\selectlanguage{ngerman}ºC for 32 days
have been shown in Table 1. The green tea extracts as free and
incorporated in liposome were added at 200, 600 and 1000 mg/L. Among
samples containing green tea extracts, canola oils with green tea
extract liposomes showed higher antioxidant efficiency than free green
tea extracts. It can be explained green tea extracts liposomes are
protect against unfavorable conditions (Lu et al., 2013). The highest
and lowest peroxide value belonged control and 600 mg/L concentration
green tea extract liposome (P \selectlanguage{english}[?] 0.05). With increasing green tea
extracts to 600 mg/L, antioxidant efficiency also increased but further
increasing of extract concentration to 1000 mg/L, may cause to decreased
antioxidant efficiency. Wanasundara and Shahidi applied green tea
extract in 500 and 1000 mg/L on seal blubber oil and menhaden oil. They
found green tea extract, at concentration of 1000 mg/L in both oil
samples, had prooxidant effect and said this effect could be because
existence chlorophyll (Wanasundara and Shahidi.,1997). Also, Endo et al.
reported chlorophyll and their derivatives caused lipids oxidation
progress (Endo et al., 1985). Chen et al. studied on the antioxidant
effects on ethanolic extract of green, yellow and white, black,
dark-green and oolong teas on the heated canola oil at 100degC. The
results indicated that green, white and yellow extracts showed higher
antioxidant activity in compare to BHT to inhibit oxidation canola oil
(Chen et al., 1996). Hassan et al. used of olive leaf ethanolic,
methanolic and water extract as natural antioxidant on the canola oil.
The lowest peroxide value related to ethanolic extracts followed by
methanolic and water extracts (Hassan et al., 2013). Koketsu and Satoh
compared antioxidant effects of green tea polyphenols at 40 and 60 mg/L
and tocopherol in the 200 mg/L concentration on the soybean oil. Green
tea polyphenols showed stronger antioxidant effects as compared
tocopherol. They reported induction time for reaching a peroxide value
100 meq/kg was 27, 24 and 16 for control and oil samples with 40 and 60
mg/L green tea polyphenols (Koketsu and Satoh., 1997).

Table 1

\textbf{Anisidine Value}

To determine oxidation progression, peroxide value alone is not enough.
Because it shows only primary oxidation productions. p-Anisidine value
is an indicator to measure lipid oxidation secondary products. This
method determines the aldehydes amount principally 2-alkenals and 2,
4-alkadienals vegetable oils (Shahidi, 1997). The anisidine value of
canola oils is shown in Table 2. The results showed green tea extract
has acted as an effective natural antioxidant. In addition to, it was
found that green tea extract liposomes had the better function than free
extracts. The most important reason of this phenomenon is the controlled
release of green tea extracts from liposome and protection of extract's
polyphenols against unfavorable conditions that cause to increase
antioxidant properties (Lu et al., 2011). The findings displayed, the
extract concentration and the increasing storage time in oven had the
significant effect on anisidine test of canola oil (P\selectlanguage{english}[?]0.05). The best
antioxidant function was observed at 600 mg/L of green tea extract
liposome. While the control samples had the highest anisidine value that
determined a higher rate of secondary products formation of lipids
oxidation.

Table 2

\textbf{TOTOX Value}

TOTOX values of canola oil samples are shown in Table 3. The obtained
results determined green tea extracts whether free or encapsulated in
liposome was acted in the form of an effective antioxidant and was while
green tea extract liposomes were stronger in the retarding oxidation
rate than free extracts. The lowest TOTOX value related to green tea
extract liposome at 600 mg/L. Shahidi and Wanasundara reported TOTOX
values, in the treated canola oils with canola extract, were lower than
control (Shahidi and Wanasundara., 1997).

\textbf{Table 3.}

\textbf{Thiobarbituric Acid Reactive Substances (TBARS)}

TBA test is an index of secondary oxidation products which can use for
monitoring vegetable oils oxidation (Shahidi \& Wanasundara., 1997). In
this research, the addition green tea extracts as free and encapsulated
in liposome had a significantly affect (P\selectlanguage{english}[?]0.05) in reducing TBARS
formation as compared control canola oils that have shown in Table 4.
Among green tea extracts, liposomes containing extracts had better
efficiency to decrease canola oil oxidation. The lowest TBA value was
observed at 600 mg/L concentration of liposomal extract of green tea.
Zokti et al. reported, encapsulated green tea extracts had the higher
antioxidant activity than free green tea extract in mango drink (Zokti
et al., 2016). Free green tea extract at concentration of 600 mg/L and
liposomal extract at 200, 600 and 1000 mg/L showed higher efficiency in
compare to BHT. The obtained results are in agreement with other reports
(Semwal \& Arya., 2001; Hassan et al., 2013). They found TBA values,
respectively, on the sunflower and canola oils, increased during storage
time.

\textbf{Table 4}

\textbf{Conclusion}

The obtained extracts of green tea were very effective to prevent of the
primary and secondary oxidation products in the studied canola oil.
Green tea extract both free and incorporated in liposome showed a good
antioxidant activity. The 600 mg/L concentration of green tea extract
had stronger antioxidant properties than BHT and other green tea
concentrations that its reason can be extract polyphenols. In addition
to, the results determined green tea extract liposomes possessed
powerful antioxidant activity that showed liposome structure caused to
improve the stability of tea polyphenol. The increasing storage time
caused to upward trend of canola oil oxidation. While the increasing
green tea extract concentration from 200 to 600 mg/L had a significant
impact in preventing of oxidation process (P\selectlanguage{english}[?]0.05) but green tea extract
in concentration of 1000 mg/L did not show any strong antioxidant
activity and causing delay in canola oil oxidation. This study
determined natural antioxidants such as green tea extract can be a good
alternative instead of synthetic antioxidants.

\textbf{Conflict of Interest}

The authors declare that there are no conflicts of interest.

\textbf{Acknowledgement}

Authors are grateful to the Shahid Beheshti University of Medical
Sciences for finical support.

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\textbf{Figure Legend:}

\textbf{Figure. 1} . Green tea extracts influence on canola oil
stability, expressed as induction period value (Ip{[}h{]}), under
Rancimat test conditions. a, b, c, d, e, f, g, h. mean values with
different letters differ statistically between lines.

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