Food and Nutrition Sciences, 2010, 1, 5-12
doi:10.4236/fns.2010.11002 Published Online July 2010 (http://www.SciRP.org/journal/fns)
5
Characteristics of Antioxidant Isolated from Some
Plant Sources
A. A. El Bedawey, E. H. Mansour, M. S. Zaky, Amal A. Hassan
Department of Food Science and Technology, Faculty of Agriculture, Menufiya University, Shibin El-Kom, Egypt.
Received April 23rd, 2010; revised May 24th, 2010; accepted May 27th, 2010.
ABSTRACT
Antioxidant characteristics of ginger roots, guava leaves, guava seeds, orange peel, sesame coat, rice bran and wheat
germ as affected by ethanol, ethyl acetate, chloroform, hexane and petroleum ether were evaluated. Petroleum ether
extract of ginger roots, ethanol extracts of guava leaves, guava seeds, orange peel and sesame coat and ethyl acetate
extracts of rice bran and wheat germ appeared to possess higher antioxidant activity than those from other solvents.
Ginger roots, orange peel and guava leaves exhibited higher antioxidant activity than that of α-tocopherol, while guava
seeds, sesame coat, rice bran and wheat germ had lower antioxidant activity than that of α-tocopherol. Guava leaves
extract had the highest total phenolics content among the other plant material extracts followed by ginger roots, sesame
coat and orange peel extracts. However, total flavonoids content was the highest in ginger roots extract followed by
guava leaves extract. Ferulic was the highest phenolic compounds in guava leaves and sesame coat extracts. However,
chlorogenic acid was the highest phenolic compounds in ginger roots extract. Antioxidants in ginger roots, guava leaves
and sesame coat extracts as well as α-tocopherol were heat stable with 73.1, 73.8, 66.7 and 71.6% activity, respectively,
after heating at 100°C for 180 min. Induction periods of sunflower oil containing 2% guava leaves and 2% ginger roots
extracts were increased by 230.6% and 226.7%, respectively. However, induction period of sunflower oil containing
sesame coat was increased by 174.1%, at 0.5% concentration. Similar increment was found for the protection factor.
Ginger roots, guava leaves and sesame coat might be promising sources of natural antioxidant to be used in food prod-
ucts.
Keywords: Antioxidative Activity, Ginger Roots, Guava Leaves, Sesame Coat, Rancimat
1. Introduction
The shelf–life of foods is often limited as their stability is
restricted due to reactions such as oxidative degradation
of lipids. Oxidation of lipids not only produces rancid
odours and flavours, but also can decrease the nutritional
quality and safety by the formation of secondary prod-
ucts in food after cooking and processing [1-3]. Antioxi-
dants are used as food additives in order to prevent the
oxidative deterioration of fats and oils in processed food.
Addition of synthetic antioxidants such as butylated hy-
droxyanisole (BHA), butylated hydroxytoluene (BHT)
and tertiary butylhydroquinone (TBHQ) can control lipid
oxidation in foods [4,5]. Since some of synthetic anti-
oxidants had toxigenic, mutagenic, and carcinogenic ef-
fects and some natural antioxidants were effective in
enhancing the shelf life of food but less effective than
synthetic antioxidants, there is a great demand for the use
of new natural antioxidants in food [5,6]. Therefore,
there is a strong need for effective antioxidants from
natural sources to prevent deterioration of foods. Some
components of extracts isolated from oil seeds, spices,
fruits and vegetables have been proven in model systems
to be as effective antioxidants as synthetic antioxidants
[5,7-9].
The present study was conducted to utilize some plant
materials such as ginger roots, guava leaves, guava seeds,
orange peel, rice bran and wheat germ as natural sources
of antioxidants.
2. Materials and Methods
2.1 Materials
Sesame (Sesamum indicum L.) coat was obtained from El
Rashidi El Mizan Company, 6 of October city, second
industrial zone, Egypt. Rice bran (Oryza sativa), guava

Characteristics of Antioxidant Isolated from Some Plant Sources 6
seeds and leaves (Psidium guajava L.), ginger roots
(Zingiber officinale L.), sour (bitter) orange peel (Citrus
aurantium) and wheat germ (Triticum aestium) were ob-
tained from El-Tahanoon El-Masrion, number 16 in the
third industrial zone, 6 of October city, Egypt. Sunflower
oil was obtained from Integrated Oil Industries Company,
Al Adabia, Suez city, Egypt.
2.2 Reagents and Solutions
Ethanol, ethyl acetate, chloroform, hexane and petroleum
ether were obtained from El-Nasr Pharmaceutical
Chemicals, El-Ameriea, Cairo, Egypt. Folin-Ciocalteu
phenol reagent, 2,2-diphenyl-1-picrylhydrazyl (DPPH),
tannic acid (phenolic standard), quercetin (flavonoid
standard), α-tocopherol mixed isomers type v from
vegetable oil were obtained from Sigma Chemical Co.,
St. Louis, MO, USA.
2.3 Preparation of Plant Samples
Rice bran, wheat germ and ginger roots were dried in an
electric air draught oven (Nüve San. Malz, Model FN
500, Akyuri, Ankara, Turkey) at 40ºC for 1hr, however
(orange peel, guava leaves and guava seeds) were dried
at the same temperature for 12hr. The dried samples were
ground using a laboratory electric mill (Braun, Model
2001DL, Germany) then packed in the polyethylene and
stored at –20ºC in the deep freezer (Ultralow, Revco, Inc.,
Sweden) until use.
2.4 Preparation of Antioxidant Extracts
Fifty grams of each ground samples (ginger roots, guava
leaves, guava seeds, rice bran, orange peel, wheat germ,
sesame coat) were extracted three times with 500 ml of
each solvent (ethyl acetate, petroleum ether, ethanol,
hexane, and chloroform) using a Teflon- coated magnetic
stir bar and stir plate (Framo-Geratetechnik, Germany)
for 6 hr at room temperature. Extracts were filtrated
through Whatman No. 1. The combined filtrates from
each material were concentrated in a rotary evaporator
(Laborata 4000; Heidolph Instruments GmbH & Co. KG,
Germany) at 40°C to a final volume of 100 ml of crude
extracts and stored at –20°C until used.
2.5 Determination of Antioxidant Activity
Antioxidant activity was determined using the 2,2-di-
phenyl-1-picrylhydrazyl (DPPH) radical scavenging me-
thod according the procedure described by Brand-Wil-
liams et al. [10]. Fifty µl from each extract (stock solu-
tion was 20.0 g/l) was placed in a cuvette, and 2 ml of 6
× 10-5 M methanolic solution of DPPH was added. Ab-
sorbance was measured immediately at 517 nm (UNICO
2802 C/PCS Series Spectrophotometer, USA). The de-
crease in absorbance was measured every 5 min for 1 h.
Alpha-tocopherol was used for comparative purposes.
The absorbance of the DPPH radical without antioxidant
(control) was measured daily. Special care was taken to
minimize the loss of free radical activity of the DPPH
radical stock solution [11]. The percentage of inhibition
of the DPPH radical by the extracts (antioxidant activity)
was calculated according to the equation of Yen and Duh
[12]:
% inhibition = [(AC(o) 517 – AA(t) 517) ÷ AC(o) 517] × 100
where: AC (o) 517 is the absorbance of the control at t =
0 min.
AA (t) 517 is the absorbance of the antioxidant at t = 1 h.
2.6 Determination of Total Phenolic Compounds
Total phenolic compounds were determined with Fo-
lin–Ciocalteu reagent using tannic acid as standard ac-
cording the method described by Taga et al. [13]. Ab-
sorbance was measured at 750 nm using spectropho-
tometer (UNICO 2802 C/PCS Series Spectrophotometer,
USA) and compared with tannic acid calibration curve.
2.7 Determination of Total Flavonoids
Aluminum chloride colorimetric method was used for the
determination of total flavonoids [14].
2.8 Separation and Identification of Phenolic
Compounds
Separation and identification of phenolic compounds
were carried out as described by Ricardo et al., [15] us-
ing HPLC (Thermo Separation Products Inc.) system
consisting of Consta METRIc 4100 series pump, spectra
series AS-100 auto sampler, spectra system FL 3000
fluorescence detector (Ex: 250 nm – Em: 400 nm) and
interfaced with IBM computer equipped with PC 1000
Chromatography software version 3.5. Methanol: Am-
monium acetate (12: 88; v/v at pH = 5.4) was used as
mobile phase with a flow rate of 1 ml / min. Column
ODC-2 (3 μM; 150 mm × 4.6 mm I.d., Alltech. USA).
2.9 Heat Stability of Antioxidant
2.9.1 Heating
Antioxidant extracts (2 ml) were incubated at different
temperatures in the range of 40-100°C for 30 min. Anti-
oxidant activity was determined as previously mentioned
using DPPH method. The extracts were also boiled in
water bath for 0, 30, 60, 90, 120, 150 and 180 min, and
the residual antioxidant activity was determined [9].
2.9.2 Rancimat
The extracts and α-tocopherol were added to sunflower
oil at the concentrations of 0.5%, 1% and 2%. The mix-
ture was kept at 40ºC for 30 min and then in vacuum
rotary evaporator (Buchi 011, Buchi, Switzerland) below
40ºC for 1 h for complete removal of solvent. A 679
Rancimat (Metrohm, Herisan, Switzerland) was used. A

Characteristics of Antioxidant Isolated from Some Plant Sources 7
5 g portion of each test sample was loaded into the reac-
tion vessel cylinder. Six different samples were con-
ducted in one batch. The air supply was maintained at 20
ml/min and the heating temperature was kept at 110ºC
throughout the experiment as described by Antolovich et
al. [16].
The induction period (IP) (h) was recorded automati-
cally. The protection factor (PF) was calculated accord-
ing to the following equation:
PF = IP extract / IP control
2.9.3. Statistical Analysis
The experimental data were subjected to an analysis of
variance (ANOVA) for a completely randomized design
using a statistical analysis system [17]. Duncan’s multi-
ple range tests were used to determine the differences
among means at the level of 5%.
3. Results and Discussion
3.1 Antioxidant Activity
Data presented in Table 1 showed the effect of solvent
types on the antioxidant activity of different plant mate-
rials. Petroleum ether extract of ginger roots and ethyl
acetate extracts of rice bran and wheat germ had the
highest (p < 0.05) antioxidant activity among other sol-
vent extracts.
Guava leaves, guava seeds, orange peel and sesame
coat exhibited the highest (p < 0.05) antioxidant activity
when extracted with ethanol. Ethyl acetate extract of
guava leaves showed similar (p > 0.05) antioxidant activ-
ity to ethanol extract.
Chang et al. [14] reported that sesame coat extracts
displayed similar antioxidant activity. Qian and Nihorim-
bere [18] reported that the extracts of guava leaves with
50% aqueous ethanol showed higher antioxidant activi-
ties than that with water extract.
Solvent extracts of the plant materials, which showed
the highest antioxidant activity, were selected for further
studies.
Ginger roots, orange peel and guava leaves extracts
exhibited higher (p < 0.05) antioxidant activity than that
of α-tocopherol while, guava seeds, sesame coat, rice
bran and wheat germ extracts had lower (p < 0.05) anti-
oxidant activity compared to α-tocopherol (Table 2).
Ginger roots extract had higher (p < 0.05) antioxidant
activity than those of other plant material extracts. The
antioxidant activity value of ginger roots extract was
similar to that reported by Hussein et al. [5], however, it
was higher than that obtained by Mansour and Khalil [9].
This difference might be due to the interspecies variation.
Chang et al. [14] reported that sesame coat extracts
(methanol, ethanol and acetone) exhibited strong anti-
oxidant activity ranging from 91.8% to 92.6%.
3.2 Total Phenolics and Total Flavoniods
Total phenolics, total flavonoids and the ratio of flavon-
oids/phenolics in plant material extracts are summarized
in Table 3. Guava leaves extract had the highest (p <
0.05) total phenolics content among the other plant mate-
rial extracts followed by ginger roots, sesame coat and
orange peel extracts. On the other hand, guava seeds ex-
tract had the lowest (p < 0.05) total phenolics content.
Total phenolic contents were relatively correlated with
the antioxidant activity previously mentioned in Table 2.
These results are in good agreement with those ob-
tained by Dasgupta and De [19] and Dorman and Hil-
tunen [20] who found highly positive relationship existed
between total phenolics and antioxidant activity in many
plant species. Huang and Zhang [21] found that the ma-
jor components in the ethanol extract of guava leaves
were polyphenols.
Ginger roots extract showed the highest (p ≤ 0.05) to-
tal flavonoids content among all plant material extracts
followed by guava leaves extract. However, guava seeds
extract had the lowest (p ≤ 0.05) total flavonoids content.
It is important to note that the total flavonoid contents
in ginger roots extract and guava leaves extract were
Table 1. Antioxidant activity of plant material extracts as affected by different solvents
Antioxidant activity (%)
Solvent
Ginger rootsGuava
leaves Guava seedsOrange peel Sesame coat Rice bran Wheat germ
Ethanol 93.3b ± 0.3786.7a ± 0.39 31.2a ± 0.7790.8a ± 0.74 75.9a ± 2.8 41.0b ± 1.0 41.9b ± 0.49
Ethyl ace-
tate 93.7b ± 0.5485.6a ± 0.91 20.2b ± 0.2169.8b ± 0.63 67.8b ± 0.90 61.6a ± 0.88 59.1a ± 1.7
Chloroform 91.2c ± 0.8955.5c ± 1.0 3.1c ± 0.09 48.7c ± 0.46 51.7c ± 1.7 30.4c ± 0.87 9.7c ± 0.50
Hexane 93.7b ± 0.9950.3d ± 0.20 3.5c ± 0.60 43.4d ± 0.14 15.3e ± 1.1 10.0e ± 0.40 8.5cd ± 0.90
Petroleum
ether 95.2a ± 0.2264.7b ± 0.58 2.0d ± 0.03 24.4e ± 0.20 27.8d ± 0.95 12.2d ± 1.2 6.9d ± 0.40
LSD 1.222 1.309 0.816 0.897 3.006 1.647 1.690
Means in the same column with different letters are significantly different (p < 0.05).

Characteristics of Antioxidant Isolated from Some Plant Sources 8
Table 2. Antioxidant activity of plant material extracts
compared to α-tocopherol
Plant material extracts Antioxidant activity4 (%)
Ginger roots1 95.2a ± 0.22
Guava leaves2 86.7c ± 0.39
Guava seeds2 31.2h ± 0.77
Orange peel2 90.8b ± 0.74
Sesame coat2 75.9e ± 2.8
Rice bran3 61.6f ± 0.88
Wheat germ3 59.1g ± 1.70
α-tocopherol 84.0d ± 0.54
LSD 2.235
1Petroleum ether; 2Ethanol; 3Ethyl acetate; 4Means in the same
column with different letters are significantly different (p < 0.05)
correlated with the antioxidant activity, which indicates
that flavonoids might be the main compound responsible
for its activity (Table 2). The total flavonoids content of
orange peel was much lower than that reported by Wang
et al. [22] for citrus peel.
Total flavonoids and their antioxidant activity as well
as their effects on human nutrition and health have been
reported by Kessler et al. [23]. The mechanisms of action
of flavonoids are through scavenging or chelating proc-
ess.
Ginger roots extract had the highest (p < 0.05) flavon-
oids/phenolics ratio among all other plant material ex-
tracts followed by guava leaves extract (Table 3). No
significant (p > 0.05) difference was found among guava
seeds, orange peel, sesame coat, rice bran and wheat
germ extracts in flavonoids/phenolics ratio.
Marinova et al. [24] attributed the high flavonoids/
phenolics ratio to the rich spectrum of phenolic acids,
while attributed the low ratio to the rich spectrum of fla-
vonoids compounds.
3.3 Separation and Identification of Phenolic
Compounds
Data in Table 4 showed that guava leaves extract con-
tained the highest total phenolic compounds content
among all other plant material extracts followed by ses-
ame coat extract and orange peel extract. Guava seeds
extract contained the lowest total phenolic compounds.
Table 3. Total phenolics and total flavoniods contents in plant material extracts
Plant material ex-
tracts
Total phenolics
(mg tanic /1 g dried extract)
Total flavonoids
(mg quercetin /1 g dried extract) Flavoniods / phenolics
Ginger roots 39.49b ± 2.9 55.10a ± 1.4 1.40a ± 0.12
Guava leaves 48.83a ± 1.0 35.46b ± 1.9 0.73b ± 0.03
Guava seeds 10.48f ± 0.33 1.10d ± 0.23 0.10c ± 0.02
Orange peel 34.87c ± 0.74 4.24c ± 0.13 0.12c ± 0.01
Sesame coat 37.46bc ± 0.77 2.40d ± 0.12 0.06c ± 0.01
Rice bran 29.03d ± 2.3 4.10c ±0.09 0.14c ± 0.02
Wheat germ 18.5e ± 0.66 1.14d ± 0.23 0.06c ± 0.01
LSD 2.652 1.566 0.083
Means in the same column with different letters are significantly different (p < 0.05)
Table 4. Phenolic compounds of plant material e x tr ac ts as analyzed by HPLC
Plant material extracts
Phenolic compound contents (ppm) Ginger
roots
Guava
leaves
Guava
seeds
Orange
peel
Sesame
coat
Rice
bran
Wheat
germ
Caffeic – – – – 19.6 – 2.7
Caffein – 39.15 11.69 26.65 – 11.3 –
Catechol – – – 92.69 – – –
Chlorogenic 102.49 36.7
– – 29.68 – –
Chrisin 4.09 –
– 11.77 – – –
Cinnamic 29.43 60.26 40.82 36.54 18.3 2.7
–
Coumarin – – – 8.8 32.93 – 9.63
Ferrulic – 4129.74 – – 770.05 160.9 45.17
Protocatchic – – – 1022.3 550.44 – 311.13
Syringic – – – 10.62 43.73 5.73 –
Vanillic – – 21.13 35.45 – – 3.99
Total phenolic compounds 136.01 4265.85 73.64 1244.82 1464.73 180.63 372.62
– Not Detected

Characteristics of Antioxidant Isolated from Some Plant Sources 9
Chlorogenic acid content was the highest phenolic com-
pounds in ginger roots extract. This result was differed
from those reported by Hussein et al. [5] who found that
pyrogallic, hudroqunion; phenol and resorcinol were the
main phenolic compounds in the methanol extract of ginger
roots. This difference may be due to the interspecies
variation. However, ferrulic was the highest phenolic com-
pounds in guava leaves, sesame coat and rice bran extracts.
Also protocatchic represented the highest phenolic com-
pounds in orange peel and wheat germ extracts.
Liang et al. [25] reported that the polyphenolic com-
pounds in guava leaves were gallic acid, quercetin, pro-
catechuic acid, chlorogenic acid, caffeic acid, kaempferol
and ferulic acid. Bocco et al. [26] found that the total
content of phenolic acids (caffeic acid, q-coumaric acid,
ferulic acid and sinapinic acid) in sour orange peel was
twenty times that found in bergamot peel.
3.4 Heat Stability
Antioxidant activity was constant for all plant material
extracts when incubated at 40°C for 30 min. Incubating
all plant material extracts at a temperature higher than
40°C for 30 min, resulted in a significant (p ≤ 0.05) de-
crease in antioxidant activity (Table 5). Mansour and
Khalil [9] and Hussein et al. [5] reported that the anti-
oxidant activity of ginger roots extract was stable when
incubated at a temperature ranging from 40 to 60°C for
30 min.
Increasing the heating temperature from 40°C to
100°C for 30 min resulted in significant (p ≤ 0.05) de-
crease in the antioxidant activity of ginger roots, guava
leaves, guava seed, orange peel, sesame coat, rice bran,
wheat germ extracts and α-tocopherol by 18.1, 15.6, 56.6,
32.9, 16.3, 28.9, 51.1% and 11.8%, respectively. The reduc-
tion in antioxidant activity of α-tocopherol (11.8%) was
lower (p ≤ 0.05) than that of all plant material extracts.
Higher reduction value was reported by Mansour and
Khalil [9] for ginger roots (25%) when heated to 100°C
and comparable reduction value (17.9%) was reported by
Hussein et al. [5].
Ginger roots extract had the highest (p < 0.05) antioxi-
dant activity followed by guava leaves extract and
α-tocopherol. Alpha-tocopherol had a higher (p < 0.05) an-
tioxidant activity than those of guava seeds extract, or-
ange peel extract, sesame coat extract, rice bran extract
and wheat germ extract.
Increasing the boiling time resulted in a significant (p
< 0.05) decrease in the antioxidant activity of all plant
material extracts (Table 6). These results agree well with
those reported by Mansour and Khalil [9] and Hussein et
al. [5] for ginger roots extract.
Boiling the plant material extracts and α-tocopherol for
180 min reduced (p ≤ 0.05) the antioxidant activity of
ginger roots, guava leaves, guava seeds, orange peel,
sesame coat, rice bran and wheat germ extracts and
α-tocopherol by 26.9, 26.2, 80.1, 54.7, 33.3, 54.7 and 72.7
and 28.5%, respectively. These results indicated that anti-
oxidants in ginger roots, guava leaves, sesame coat ex-
tracts and α-tocopherol were relatively heat stable (re-
maining activity ranging from 66.7 to 73.8 %). However,
the remaining antioxidant activity in the other plant ma-
terial extracts ranged from 19.9 to 45.3%.
Good thermal stability of ginger extract has been attrib-
uted to the inhibition of peroxidation of linoleic acid when
the extract was heated to 185°C for 120 min [27]. However,
Hussein et al. [5] found that the remaining antioxidant
activity of ginger roots extract was 29.04% when boiled
for 120 min.
Induction periods of sunflower oil containing different
levels of plant material extracts as well as α-tocopherol
were higher than that of control (Table 7). Induction period
of sunflower oil increased by increasing the concentra-
tion of ginger roots, guava leaves, orange peel and rice
bran extracts. An opposite trend was observed with ses-
ame coat, guava seeds and wheat germ extracts.
Table 5. Effect of temperature on the antioxidant activity of plant material extracts
Antioxidant activity (%)
Temperature
(°C) Ginger
roots
Guava
leaves
Guava
seeds
Orange
peel
Sesame
coat Rice branWheat germ
α-toco-
pherol
Mean1
0 94.9 ± 1.3 85.5 ± 0.2 30.1 ± 1.789.7 ± 0.875.1 ± 0.560.7 ± 1.058.5 ± 0.8 84.7 ± 0.3 72.40a
40 93.9 ± 0.8 84.5 ± 0.1 29.5 ± 0.289.4 ± 0.475.4 ± 0.560.2 ± 0.657.2 ± 0.3 83.7 ± 0.5 71.72a
60 92.9 ± 0.4 83.9 ± 0.7 23.5 ± 0.180.5 ± 0.175.1 ± 0.654.0 ± 0.147.7 ± 0.7 82.0 ± 0.5 67.45 b
80 84.8 ± 0.3 80.0 ± 0.5 17.8 ± 0.667.7 ± 0.171.6 ± 0.547.2 ± 0.436.0 ± 0.9 78.7 ± 0.5 60.48c
100 76.9 ± 0.4 71.3 ± 0.8 12.8 ± 0.560.0 ± 0.363.1 ± 0.342.8 ± 0.528.0 ± 0.5 73.8 ± 0.4 53.59d
Mean2 88.67a 81.03b 22.74g 77.47c 72.07d 52.97e 45.49f 80.57b
1Means in the same column with different letters are significantly different (p < 0.05), LSD = 0.897; 2Means in the same row with differ-
ent letters are significantly different (p < 0.05), LSD = 0.958

Characteristics of Antioxidant Isolated from Some Plant Sources 10
Table 6. Effect of boiling for different time on the antioxidant activity of plant material extracts
Antioxidant activity (%)
Time
(min) Ginger roots Guava
leaves
Guava
Seeds Orange peelSesame coatRice branWheat germ α-tocopherol
Mean1
0 94.9 ± 1.3 85.5 ± 0.2 30.1 ± 1.789.7 ± 0.875.1 ± 0.560.7 ± 1.058.5 ± 0.8 84.7 ± 0.3 72.40a
30 76.9 ± 0.4 71.3 ± 0.8 12.8 ± 0.560.0 ± 0.363.1 ± 0.342.8 ± 0.528.0 ± 0.5 73.8 ± 0.4 53.58b
60 73.1 ± 0.6 68.4 ± 0.9 10.0 ± 0.252.5 ± 0.259.7 ± 0.436.9 ± 0.625.0 ± 0.4 68.0 ± 0.5 49.20c
90 72.0 ± 0.4 67.2 ± 0.8 8.8 ± 0.2 47.9 ± 0.157.5 ± 0.134.0 ± 0.921.6 ± 0.1 64.7 ± 0.4 46.71d
120 71.3 ± 0.2 66.0 ± 0.3 7.8 ± 0.3 44.0 ± 0.755.0 ± 0.530.9 ± 0.818.8 ± 0.2 62.5 ± 0.1 44.53e
150 70.0 ± 0.5 64.3 ± 0.6 6.9 ± 0.8 42.0 ± 0.452.2 ± 0.429.4 ± 0.116.9 ± 0.4 61.5 ± 0.1 42.90f
180 69.4 ± 0.1 63.1 ± 0.5 6.0 ± 0.3 40.6 ± 0.450.1 ± 1.527.5 ± 0.416.0 ± 0.5 60.6 ± 0.6 41.66g
Mean2 75.36a 69.40b 11.77h 53.82e 58.96d 37.45f 26.41g 67.96c
1Means in the same column with different letters are significantly different (p < 0.05), LSD = 0.720; 2Means in the same row with different
letters are significantly different (p < 0.05), LSD = 0.883
The highest induction period of sunflower oil was ob-
tained by the addition of 2% guava leaves extract fol-
lowed by the addition of 2% ginger roots extract. How-
ever, the addition of guava seeds extract at 2% level
showed the lowest induction period. The induction pe-
riod of sunflower oil increased by 230.6 and 226.7% by
the addition of 2% guava leaves extracts and 2% ginger
roots extract respectively.
Alpha-tocopherol had a higher induction period (11.86 h)
than all plant material extracts at 1% concentration. In-
duction period of sunflower oil containing α-tocopherol
was increased by 232.5%. On the other hand sesame coat
extract had the highest induction period (8.88 h) at 0.5%
concentration. Induction period of sunflower oil contain-
ing sesame coat was increased by 174.1%.
Elleuch et al., [28] found that raw sesame seed oil had
a higher induction period (28.2 h) then followed by de-
hulled sesame seed oil (25.7 h). Thus, the dehulling
processes decrease the stability of the oils.
Data in Table 8 showed the protection factor of sun-
flower oil containing plant material extracts and α-toco-
pherol. All protection factors of plant material extracts
had a positive trend similar to the induction period (Ta-
ble 7). The highest protection factor of sunflower oil was
obtained by the addition of 2% guava leaves extract fol-
lowed by ginger roots and orange peel extracts at the
same level. Protection factor of sunflower oil containing
guava leaves, ginger roots and orange peel extracts was
increased by 231, 227 and 164%, respectively. Similar
increment was found for the induction period (Table 7).
While, guava seeds, rice bran and wheat germ extracts
had lower stabilizing effect than that of α-tocopherol.
Garau et al., [29] reported that the average protection
factor value for orange peel samples was 1.52.
Table 7. Induction period (hr) of sunflower oil containing different levels of plant material extracts and α-tocopherol assessed
by rancimat at 100C
Level of addition (%)
Plant material extracts 0 0.5 1 2
Ginger roots 5.1 6.94 8.54 11.56
Guava leaves 5.1 8.46 9.54 11.76
Guava seeds 5.1 6.36 5.14 5.11
Orange peel 5.1 7.95 8.13 8.36
Sesame coat 5.1 8.88 6.87 6.81
Rice bran 5.1 5.26 5.44 5.98
Wheat germ 5.1 6.30 6.04 5.34
α-tocopherol 5.1 10.00 11.86 11.10

Characteristics of Antioxidant Isolated from Some Plant Sources11
Table 8. Protection factor of sunflower oil containing different levels (%) of plant material extracts and α-tocopherol assessed
by rancimat at 100C
Level of addition (%)
Plant material extracts 0 0.5 1 2
Ginger roots 1 1.36 1.67 2.27
Guava leaves 1 1.66 1.87 2.31
Guava seeds 1 1.25 1.01 1.00
Orange peel 1 1.56 1.59 1.64
Sesame coat 1 1.74 1.35 1.34
Rice bran 1 1.03 1.07 1.17
Wheat germ 1 1.24 1.18 1.05
α-tocopherol 1 1.96 2.33 2.18
Alpha-tocopherol (at 1% concentration) had a higher
protection factor than all plant material extracts. On the
other hand, sesame coat extract (at 0.5% concentration)
had the highest protection factor as compared to the other
plant material extracts.
From the above results, it could be concluded that the
antioxidant activities of ginger roots, guava leaves and
sesame coat were comparable to α-tocopherol. Ginger
roots, guava leaves and sesame coat showed good thermal
stability in comparison with α-tocopherol. Ginger roots,
guava leaves and sesame coat might be promising
sources of natural antioxidant to be used in food prod-
ucts.
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