Influence of different microwave seed roasting processes on the changes in quality and fatty acid composition of ...
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AKDENİZ ÜNİVERSİTESİ ZİRAAT FAKÜLTESİ DERGİSİ, 2006, 19(2),207-216
INFLUENCE OF DIFFERENT MICROWAVE SEED ROASTING PROCESSES ON
THE CHANGES IN QUALITY AND FATTY ACID COMPOSITION OF TEHINA
(SESAME BUTTER) OIL
Feramuz ÖZDEMİR
1
Muharrem GÖLÜKCÜ
2
Mustafa ERBAŞ
1
1
Department of Food Engineering, Faculty of Agriculture, Akdeniz University, 07059 Antalya
2
West Mediterranean Agricultural Research Institute, PK: 35, 07100 Antalya
Correspondence addressed E-mail: feramuz@akdeniz.edu.tr
Abstract
The quality characteristics of tehina prepared at different roasting powers (399, 665, 931, 1330 Watt) for
different exposure periods (3-50 min.) and depths of sesame seeds (1-2 cm) using a domestic home microwave oven
(BKMD 1550) were compared with those prepared in a conventional tehina sample. The fatty acid showed erratic
fluctuations for all treatments and there were significant (p<0.05) differences in composition of fatty acids in tehina
oils processed by microwave roasted methods. The acid value decreased with increasing roasting power between 399
and 1330 watts. A longer roasting time in each applied power resulted in more acid value; however the acid value of
oil of tehina roasted in the conventional method was much less than the acid value of oil of tehina roasted through
microwave treatments. The acid value of oil from microwave roasted seeds occurred in relation to increasing the
depth of seeds in a dish from 1 cm to 2 cm. There was no pronounced difference in peroxide value for the oils of
tehina from seeds roasted using different powers of the microwave oven or roasted conventional methods. The
peroxide value was erratically affected by the powers of the microwave oven. The peroxide value increased (p<0.05)
with longer roasting and storage, but increases were more pronounced during the first two weeks of storage.
Keywords:
Sesamum indicum
, microwave, tehina, fatty acid composition, quality
Susam Kavrulmasında Farklı Mikrodalga Uygulamalarının Tahin Yağının Kalitesi ve Yağ Asidi Bileşimi
Üzerine Etkisi
Özet
Ev tipi mikrodalga fırının (BKMD 1550) farklı güçlerinde (399, 665, 931, 1330 Watt) ve her güçte farklı
sürelerde (3-50 dak.) ve farklı yığın yüksekliklerinde (1-2 cm) kavrulan susamlardan elde edilen tahinin kalite
karakteristikleri geleneksel yöntemle üretilen örnekle karşılaştırılmıştır. Örneklerin yağ asitleri bileşimi düzenli
olmamakla birlikte mikrodalga uygulamaları arasında birbirinden önemli derecede (p<0.05) farklılık göstermiştir.
Örneklerin serbest yağ asitliği uygulamada kullanılan mikrodalga fırının güçlerindeki artış ile birlikte azalmıştır. Tüm
mikrodalga güçlerinde örneklerin asitliği artan kavurma süreleri ile birlikte artış göstermiştir. Bununla birlikte
geleneksel yöntemle üretilen tahinin serbest yağ asitliği mikrodalga uygulaması ile üretilen tüm örneklerin serbest
yağ asitliğinden daha düşük olmuştur. Mikrodalga fırında artan yığın yüksekliği uygulaması örneklerin asitliğinde
artışa sebep olmuştur. Geleneksel yöntemle ve mikrodalga fırında kavurarak üretilen tahinlerin peroksit değerleri
birbirinden açık bir farklılık göstermemiştir. Örneklerin peroksit değerleri farklı mikrodalga gücü uygulamaları
arasında da düzenli bir farklılık göstermemiştir. Örneklerin peroksit değerleri artan kavurma süresi ve depolama
periyodu ile birlikte önemli oranda (p<0.05) artış göstermiştir.
Anahtar Kelimeler:
Sesamum indicum
, Mikrodalga, Tahin, Yağ Asidi Bileşimi, Kalite
1. Introduction
Sesame (
Sesamum indicum
L.) is one
of the world’s most important oil seed crops
and it is produced mainly in India, China,
Sudan, Burma and Argentina (Salunkhe et
al., 1992). Sesame seed is used extensively
in baked goods and confectionary products.
Not only is it a source of edible oils, the seed
itself provides a nutritious food source for
human consumption (Yoshida, 1994). In
some Eastern countries, sesame seeds are
used mainly for preparing tehina (a sesame
paste product similar to peanut butter) and
halva (Abou-Gharbia et al., 1997).
The dehulled roasted sesame seeds are
used extensively in The Middle East for
production of tehina. Tehina is generally
served as an appetizer or dressing, after
being hydrated with 1-2 volumes of water in
order to form a thin oil in water emulsion
(Lindler and Kinsella, 1991).
207
Influence of Different Microwave Seed Roasting Processes on the Changes in Quality and Fatty Acid Composition of
Tehina (Sesame Butter) Oil
Sawaya et al. (1985) reported that
halva is prepared by the incorporation of
50% sugar (sucrose alone or glucose) into
tehina. In Turkey, halva is made by adding
sugar, cacao, vanilla, pistachio nut, and
soapwort (
Gypsophia stratium
) root extract
into tehina to produce different halvas.
Sesame oil has a mild, pleasant taste
and is used as a salad oil requiring little or
no winterizing. An important characteristic
of sesame oil is its resistance to oxidative
deterioration. Sesame oil from roasted
sesame seeds has a distinctive flavor and a
long shelf life (Manley et al., 1974;
Kikugawa et al., 1983), and is used as
cooking oil, in shortenings and margarines.
The conventional method for
preparation of tehina involves dehulling,
roasting and grinding. Roasting is the key
step because color, composition, taste and
quality of tehina are influenced by
conditions of roasting. Roasting conditions
also affect the quality of oil. A higher
roasting temperature, used to provide a
strong flavor, results in oil of lower quality
(Yen et al., 1986). The conventional method
for roasting sesame seeds is to roast seeds in
a circular-moving cauldron on a gas flame
for about 4-5 hours.
Microwave ovens are an energy
efficient means of heating and a rapid
method for reheating foods (Mudgett, 1989).
Microwaves have great penetrating power,
and food products heated by them have little
temperature gradient. Foods, which are high
in fat and moisture content are quickly
cooked or baked in microwaves. The
application of microwave processing for
both home and institutional meal preparation
has increased because of its speed and
convenience (Mudgett , 1988).
Few studies concerning the influence
of roasting on composition and quality of
sesame oil have been reported (Fukuda et
al., 1986; Yen and Shyu, 1989; Yen, 1990;
Yoshida and Takagi 1997). Moreover, little
has been reported about how microwave
roasting affects the quality of the sesame oil
(Yoshida and Kajimoto, 1994; Abou-
Gharbia et al., 1997). To our knowledge,
there are no reports on the effect of different
microwave powers and exposure periods on
the stability of tehina oil.
The objective of this study was to
investigate the change in composition and
quality of tehina oil produced from sesame
seeds which were roasted at different powers
and temperatures for different times in a
microwave oven.
2. Material and Methods
The sample of sesame seeds
(
Sesamum indicum
L.) in this study was a
white species which was grown in Antalya,
Turkey. Seeds were purchased from a local
store during harvesting season.
Tehina was prepared by dehulling,
drying, roasting and grinding the sesame
seeds. The seeds were soaked in water for 8
hours, dehulled by mechanical abrasion, and
separated from the hulls flotation on brine
(5% salt concentration on weight base).
After washing with water to remove the salt,
the dehulled wet sesame seeds were spread
to dry on the laboratory bench at a depth of
1 cm and left to dry in an ambient
temperature and breeze. Dried seeds were
spread on the glass plate of a domestic-size
Beko microwave oven (BKMD 1550)
capable of generating 1330 watt powers at
2450 MHz. The microwave oven used
operates at a frequency of 2450 MHz, with
1330, 931, 665 and 399 watts of output with
power levels of high, medium high, medium
and defrost, respectively. Each time the plate
of the microwave oven contained about 180
grams of seeds with a depth of 1 cm, and
about 360 grams of seeds with a depth of 2
cm. After roasting, the seeds were allowed
to cool to ambient temperature before being
processed into tehina. The experimental
design for this study is shown in Table 1.
For production of tehina, each sample
of dehulled and microwaved seed was
ground in a blender (Waring). To cool the
seeds when they were being ground, cold
water was placed around the blender in
plastic bags. Seeds were ground for 30 s
followed by a quiescent period of 2 minutes.
This process was repeated 6 times to prepare
the paste known as tehina. Subsequent
analyses were carried out on the paste.
Tehina samples were stored in glass jars in a
dark room.
208
F. ÖZDEMİR, M. GÖLÜKCÜ, M. ERBAŞ
Table 1.The experimental design of microwaving sesame seeds.
Depth of seed 1 cm 2 cm
Power (watt) 1330 931 665 399 1330 931 665 399
Exposure time (min) 3, 4, 5 4, 6, 8 10, 12, 14 30, 40, 50 3, 4, 5 4, 6, 8 10, 12, 14 30, 40, 50
Tehina from each treatment was
homogenized with petroleum ether at 4 °C in
a Waring blender. The ether layer was
separated, and extracts were evaporated
using a vacuum rotary evaporator at 35 °C.
Before microwave and conventional
roasting, saponification number, iodine
number and refractive index value of the
sesame oil were analysed (Nas et al., 1998)
Quantitative changes in peroxide and acid
value of the samples were performed by the
AOAC (1990) method. The fatty acid
methyl esters prepared using methyl alcohol,
benzene, 2,2-dimetoksipropan and n-heptan.
For direct derivatization of lipids,
approximately 10 mg sample was weighed
int 15 x 100 mm test tubes. 3 ml reaction
mixture and two ml n-heptan and was added
next. Sample tubes were screw-capped and
then transferred into water bath maintained
at 85 °C and allowed to heat for 2 hours.
Reaction mixture was prepared using methyl
alcohol, benzene, 2,2-dimetoksipropan and
sulphuric acid (Garces and Mancha, 1993).
After cooling to room temperature, 3 µl of
the upper phase was injected to gas
chromatography instrument. The analysis
was performed on a Fison Inst. HRGC Mega
2 gas chromatography equipped with a 25 m
x 0.25 mm fused silica capillar column. The
flame ionization detector (FID) and injector
parts were maintained at 260°C. Column
heating was performed starting from 150°C
and increasing to 200 °C at 5 °C per minute.
The flow rate of helium carrier gas was 1
ml/min, hydrogen 30 ml/min, air 300
ml/min. Peaks were identified by
comparison of retention times with authentic
compounds (Özdemir et al., 2003).
Tehina preparation was replicated two
times, chemical and instrumental
measurements were duplicated, and mean
values were reported. Analysis of variance
and Duncan’s Multiple Range Test were
performed at a level of p<0.05 to evaluate
the significance of differences between
values, however storage tests were not
replicated.
3. Result and Discussion
Proximate duplicated analyses using
Aoac (1990) procedures showed
composition of the seeds before microwave
and conventional roasting to be as follows:
acid value 0.79%, peroxide value 0.59
meqg/kg, iodine number 109, saponification
number 187 and refractive index n
D
20
1.465.
Furthermore, the fatty acids in the oil of
unroasted seeds were palmitic acid
(10.35%), stearic acid (4.54%), oleic acid
(42.05%) and linoleic acid (43.06%).
3.1. Fatty Acids
The fatty acid composition of oils
extracted from tehinas produced from
sesame seeds roasted in the microwave oven
at four powers (1330, 931, 665 and 399
watts) and different exposure times (3 to 50
min) in each power in depth of 1 cm and 2
cm of seeds, is summarized in Table 2.
Although significant (p<0.05)
differences existed for the fatty acids of
tehina oils from different treatments, no
specific trends were evident for the basic
compositional changes. A linear relationship
did not occur between fatty acid
composition and exposure-time or power
setting. (Figure 1). In addition, the fatty acid
composition and each fatty acid individually
were not affected by the depth of seeds
exposed in the microwaves (Figure 2).
Yoshida and Kajimoto (1994) found
that the fatty acid composition of sesame oil
remained unchanged after 8 min of
microwave heating but exhibited a
significant (p<0.05) reduction in its linoleic
acid content after 12 min of microwaving;
however, similar results were not obtained in
this study. This must be because different
treatments were applied in the present study.
Yoshida and Takagi (1997) reported that
there was almost no change in fatty acid
composition of the sesame oil when
prepared by roasting below 200 °C.
However, the higher the roasting
209
Influence of Different Microwave Seed Roasting Processes on the Changes in Quality and Fatty Acid Composition of
Tehina (Sesame Butter) Oil
Table 2.
The percentage of mean fatty acid values of tehina oils obtained from seeds roasted at
different power levels and exposure times with different depth using a microwave oven
and the conventional method
a
.
Power
(Watt)
Exposure time (Min.)
16:0
16:1
18:0
18:1
3
10.66
4.22
42.47
42.61
1330
4
10.37
3.77
41.04
43.77
5
9.98
4.32
42.38
43.32
4
10.63
4.07
42.18
43.05
Depth
of
Seeds
(1 cm)
931
6
10.72
4.38
42.81
43.10
8
10.61
3.84
42.01
43.49
10
9.86
4.60
42.49
43.04
665
12
10.17
4.68
42.15
43.00
14
11.42
4.43
42.17
41.92
30
10.72
4.71
42.41
42.13
399
40
10.69
3.82
42.51
42.96
50
10.70
4.32
42.19
42.78
3
10.66
3.97
43.07
42.32
1330
4
10.14
4.33
42.56
43.04
5
10.57
4.46
42.81
42.17
4
11.44
4.18
42.32
42.12
Depth
of
Seeds
(2 cm)
931
6
10.24
4.42
42.38
43.02
8
10.01
4.46
42.36
43.19
10
10.77
4.25
41.93
43.04
665
12
9.85
4.51
42.22
43.43
14
10.88
4.29
42.09
42.76
30
10.09
4.08
42.40
43.43
399
40
10.34
3.83
42.33
43.50
50
10.50
4.13
42.07
43.30
Conventional Method
10.06
4.13
42.23
43.51
a
Values are the averages of two replications and analyzed in parallel.
temperature and the longer the roasting time,
the greater was the percentage of palmitic
acid and oleic acid, and the lesser was that
of linolic acid. In particular, the total fatty
acid contents of sesame oils obtained
through roasting at over 220°C,
demonstrated a more pronounced trend. In
this present study the temperature of sesame
seeds was not over 170 °C. A small but
significant difference (p<0.05) occurred
infatty acid composition between treatments
because roasting temperatures were less than
200°C. Moreover there were no significant
differences between the fatty acid
composition of tehina oils obtained from
microwaved seeds and tehina oil from the
conventional roasting method. Results
showed that the microwave method of
heating sesame seeds to process tehina is
possible and a new method to utilize (Figure
2).
3.2. Acid Value
The acid values of tehina oils
obtained from microwaved seeds at different
210
F. ÖZDEMİR, M. GÖLÜKCÜ, M. ERBAŞ
11,5
A
4,9
B
11,0
4,7
4,5
10,5
4,3
4,1
10,0
3,9
3,7
9,5
3,5
1
2
3
1
2
3
D
43,0
44,0
C
42,8
43,5
42,6
43,0
42,4
42,5
42,2
42,0
42,0
1
2
3
1
2
3
Figure 1. Changes in the fatty acids of tehina oils prepared from sesame seeds roasted in a
microwave oven
[ at a frequency of 2450 MHz with the power of 1330 W (
—
♦
—)
, 931 W (
—■—
),
665 W (
—∆—
) and 399 W (
—□—
), for different exposure time (see Table 1 about experimental design:
1, 2 and 3 on the x-axis of the graphs represent the 1
st
, 2
nd
and
3
rd
exposure times of each power), n = 4)].
12
5
10
4
8
3
6
2
4
2
1
0
0
1330 931 665 399 Conv
1330
931
665
399 Conv
45
45
30
30
15
15
0
0
1330 931 665 399 Conv
1330
931
665
399 Conv
Figure 2. Relationships between the depth of seeds ( 1 cm,
▩
2 cm) and fatty acids of tehina
oils prepared from sesame seeds roasted in a microwave oven
[ at a frequency of 2450 MHz
with the powers of 1330, 931, 665 and 399 watt for different exposure time (3-50 min)) and conventional
methods (Conv), n=6 ].
211
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