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, ω3) to
linoleic acid (C 18:3, ω6) 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 (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°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.