INTRODUCTION
Agricultural products such as bean, wheat, corn, sunflower and chickpea
of physical and mechanical properties gain importance during harvesting
with machines, separation and cleaning processes of this crop and also
during the designation or improvement of this type of machines. Physical
properties consist of dimensional properties such as crop width, length,
thickness and technical properties such as specific gravity, bulk density
and thousand grain weights. However, mechanical properties are the behavior
of the crops against to applied force (Isik and Güler, 2004).
Organic chickpeas are a cultivated plant grown for dry consumption and
raw material of canned food industry. It contains 21.3 g protein, 5.4
g fat, 49.6 g carbohydrates and 1339 kJ energy 100 g-1 (dry)
(Anonymous, 2006).
Turkey had about 606,000 ha of chickpea harvesting area, 620,000 t of
chickpea production per annual with a yield of 4,286 kg ha-1 of
chickpea in 2004 (SIS, 2006). However, detailed statistic of organic chickpeas
has not fount in Turkey.
The physical and mechanical properties have been studied for various
crops such as green gram (Nimkar and Chattopadhyay, 2001), pigeon pea
(Baryeh and Mangope, 2002), cotton (Özarslan, 2002), okra grain (Sahoo
and Srivastava, 2002), vetch (Yalçin and Özarslan, 2004),
Balanites aegyptiaca nuts (Aviara et al., 2005), caper seed
(Dursun and Dursun, 2005), sweet corn seed (Coskun et al., 2006),
black-eyed pea (Ünal et al., 2006), göynük bombay
bean (Tekin et al., 2006) and green laird lentil (Isik, 2006).
Despite some engineering properties have been studied for chick pea grain
(Konak et al., 2002), no published literature was available on
the detailed physical properties of organic chickpea grains of moisture
content in the range of 11.31-25.03% dry basis and their dependency
on operation parameters that would be useful for the design of processing
machineries. Therefore, an investigation was carried out to determine
moisture-dependent physical properties of organic chickpea grains in 11.31,
13.25, 14.96, 17.51, 21.97 and 25.03% dry basis moisture contents.
The purpose of this study was to investigate some moisture-dependent
physical properties, namely, axial dimensions, arithmetic and geometric
mean diameters, sphericity, thousand grain mass, surface and projected
areas, bulk and true densities, porosity, terminal velocity, static coefficient
of friction and shelling resistance of organic chickpea grains.
MATERIALS AND METHODS
The organic chickpea (Cicer arietinum L.) (cv. Kocabaþ)
grains used in the study were produced by TEMA (The Turkish Foundation
for Combating Soil Erosion, for Reforestation and the Protection of Natural
Habitats) in Kemalpaþa, Izmir and certificated by IMOcontrol
IMO-GmbH (certificate number: IMO GmbH: TR7159).
The initial moisture content of the grains was determined by oven drying
at 105±°C for 24 h (Yalçin and Özarslan, 2004)
and then calibrated with digital moisture meter (Pfeuffer HE 50, Germany)
reading to 0.01%.
The samples of the desired moisture contents were prepared by adding
the amount of distilled water as calculated from the following relation
(Saçilik et al., 2003):
The samples were then poured into separate polyethylene bags and the
bags sealed tightly. The samples were kept at 5°C in a refrigerator
for a week to enable the moisture to distribute uniformly throughout the
sample. Before starting a test, the required quantity of the seed was
taken out of the refrigerator and allowed to equilibrate to the room temperature
for about 2 h (Singh and Goswami, 1996).
All the physical properties of the grains were determined at six moisture
contents in the range of 11.31-25.03 d.b. with 10 replications at each
moisture content.
To determine the average size of the seed, 100 grains were randomly picked
and their three linear dimensions namely, length (L), width (W) and thickness
(T) (Fig. 1) were measured using a digital compass (Minolta,
Japan) with a accuracy of 0.01 mm.
The average diameter of seed was calculated by using the arithmetic mean
and geometric mean of the three axial dimensions. The arithmetic mean
diameter Da and geometric mean diameter Dg of the
seed were calculated by using the following relationships (Mohsenin, 1970):
 |
| Fig. 1: |
Three dimensions of organic chickpea grains, length
(L), width (W) and thickness (T) |
The sphericity of grains φ was calculated by using the following
relationship (Mohsenin, 1970):
The one thousand seed mass was determined by means of an electronic balance
reading to 0.001 g.
The surface area As in mm2 of organic chickpea
grains was found by analogy with a sphere of same geometric mean diameter,
using the following relationship (Tunde-Akintunde and Akintunde, 2004):
The projected area Ap was determined from the pictures of
organic chickpea grains which were taken by a digital camera (Creative
DV CAM 316; 6.6 Mpixels), in comparison with the reference area to the
sample area by using the Global Lab Image 2-Streamline (trial version)
computer program (Isik and Güler, 2003).
The average bulk density of the organic chickpea grains was determined
using the standard test weight procedure reported by Gupta and Das (1997)
by filling a container of 500 mL with the seed from a height of 150 mm
at a constant rate and then weighing the content.
The average true density was determined using the toluene displacement
method. The volume of toluene (C7H8) displaced was
found by immersing a weighed quantity of organic chickpea grains in the
toluene (Yalçin and Özarslan, 2004). The porosity was calculated
from the following relationship (Mohsenin, 1970):
where, ε is the porosity in %; ρb is the bulk density
in kg m-3 and ρt is the true density in kg
m-3.
The terminal velocities of seed at different moisture contents were measured
using a cylindrical air column in which the material was suspended in
the air stream (Nimkar and Chattopadhyay, 2001). The air column was 28
mm in diameter. Relative opening of a regulating valve provided at blower
output end was used to control the airflow rate. In the beginning, the
blower output was set at minimum. For each experiment, a sample was dropped
into the air stream from the top of the air column. Then airflow rate
was gradually increased till the seed mass gets suspended in the air stream.
The air velocity which kept the seed suspension was recorded by a digital
anemometer (Thies clima, Germany) having a least count of 0.1 m sec-1
(Özdemir and Akinci, 2004).
The static coefficient of friction of organic chickpea grains against
6 different structural materials, namely rubber, galvanized iron, aluminum,
stainless steel, glass and MDF was determined. A polyvinylchloride cylindrical
pipe of 50 mm diameter and 100 mm height was placed on an adjustable tilting
plate, faced with the test surface and filled with the seed sample. The
cylinder was raised slightly so as not to touch the surface. The structural
surface with the cylinder resting on it was raised gradually with a screw
device until the cylinder just started to slide down and the angle of
tilt was read from a graduated scale (Singh and Goswami, 1996). The coefficient
of friction was calculated from the following relationship:
| μ |
= |
The coefficient of friction. |
| α |
= |
The angle of tilt in degrees. |
Shelling resistance Rs was determined by forces applied to
one axial dimension (length). The shelling resistance of seed was determined
under the point load by using a penetrometer.
Statistical Design
The average size of the grain, 100 grains were randomly chosen and
the other physical and mechanical properties of the grains were determined
at six moisture (from 11.31 to 25.03% d.b.) content with 10 replications
at each moisture content level and the results obtained were subjected
to analysis of variance (ANOVA) and DUNCAN test using SPSS 13.0 software
and analysis of regression using Microsoft Excel.
RESULTS AND DISCUSSION
Seed Dimensions
The mean values and standard errors of the axial dimensions of the
organic chickpea grains at different moisture contents are shown in Fig.
2. The three axial dimensions increased with increase in moisture
content from 11.31-25.03% d.b. The mean dimensions of 100 grains measured
at a moisture content of 11.31% d.b. are: length, 10.304±0.030
mm and width 8.4118±0.062 mm and thickness 8.333±0.051 mm.
The average diameter calculated by the arithmetic mean and geometric
mean are also shown in Fig. 2. The average diameters
increased with the increase in moisture content as axial dimensions. The
arithmetic and geometric mean diameter ranged from 9.01 to 9.85 mm and
8.96 to 9.80 mm as the moisture content increased from 11.31-25.03% d.b.,
respectively.
One Thousand Grains Mass
The one thousand organic chickpea grains mass M1000 increased
logarithmic from 432.22 to 640.00 g as the moisture content increased
from 11.31-25.03% d.b. (Fig. 3).
The logarithmic equation for one thousand seed mass can be formulated
to be:
|
M1000 =
272.03 Ln (Mc)-224.07 (R2 = 0.9516) |
(8) |
A logarithmic increase in the one thousand organic chickpea grains mass
as the seed moisture content increases has been noted by Sahoo and Srivastava
(2002) for okra seed.
 |
| Fig. 2: |
Dimensions of organic chickpea grains, (a-d Values
followed by different letter(s) are significant, p<0.05) |
 |
| Fig. 3: |
Effect of moisture content on thousand grains mass of
organic chickpea grains, (a-fValues followed by different
letter(s) are significant, p<0.05) |
 |
| Fig. 4: |
Effect of moisture content on surface area of organic
chickpea grains, (a,- Values followed by different letter(s)
are significant, p<0.05) |
Surface Area of Seed
The variation of the surface area with the organic chickpea grains
moisture content is plotted in Fig. 4. The figure indicates
that the surface area increases linearly with increase in seed moisture
content. The surface area of organic chickpea grains increased from 252.588
to 302.383 mm2 when the moisture content increased from 11.31-25.03%
d.b.
The variation of moisture content and surface area can be expressed mathematically
as follows:
with a value for the coefficient of determination R2 of 0.9495.
Similar trends have been reported by Deshpande et al. (1993) for
soybean, Dursun and Dursun (2005) for caper seed.
Projected Area of Grains
The projected area of organic chickpea grains increased from 58.30 to
71.50 mm2, when the moisture content of seed increased from
11.31-25.03% d.b. (Fig. 5).
The variation in projected area with moisture content of organic chickpea
grains can be represented by the following equation:
|
Ap = 24.574
Ln (Mc) (R2 = 0.9218) |
(10) |
However, linear increasing trends have been reported by Tang and Sokhansanj
(1993) for lentil, Ögüt (1998) for white lupine, Özarslan
(2002) for cotton and Dursun and Dursun (2005) for caper seed.
Sphericity
The sphericity of organic chickpea grains increased from 0.870 to
0.884 with the increase in moisture content (Fig. 6).
The relationship between sphericity and moisture content Mc
in % d.b. can be represented by the following equation:
| φ = 0.8199+0.0064(Mc)-0.0002(Mc2)
(R2 = 0.8795) |
(11) |
Although this increasing trend is polynomial, linear trends have been
reported by Baryeh and Mangope (2002) for pigeon pea and Saçilik
et al. (2003) for hemp seed.
 |
| Fig. 5: |
Effect of moisture content on projected area of organic
chickpea grains, (a-d Values followed by different letter(s)
are significant, p<0.05) |
 |
| Fig. 6: |
Effect of moisture content on sphericity of organic
chickpea grains, (a-b Values followed by different letter(s)
are significant, p<0.05) |
 |
| Fig. 7: |
Effect of moisture content on bulk density of organic
chickpea grains, (a-f Values followed by different letter(s)
are significant, p<0.05) |
Bulk Density
The values of the bulk density for different moisture levels varied from
700.50 to 550.00 kg m-3 (Fig. 7). The bulk
density of grains was found to bear the following relationship with moisture
content:
| ρb
= 643.12-0.5377(Mc2)+10.333(Mc) |
(12) |
with a value for R2 of 0.8953.
A different decreasing trend in bulk density has been reported by Gupta
and Das (1997) for sunflower seed, Ögüt (1998) for white lupin,
Konak et al. (2002) for chick pea and Coskun et al. (2006)
for sweet corn seed.
True Density
The true density varied from 1000 to 1200 kg m-3 when the
moisture level increased from 11.31-25.03% d.b. (Fig. 7).
The true density and the moisture content of seed can be correlated
as follows:
| ρb
= 709.54-0.5152 Mc2)+32.143(Mc) |
(13) |
with a value for R2 of 0.9807.
However, linear increasing trends were reported by Singh and Goswami
(1996) for cumin seed, Özarslan (2002) for cotton, Yalçin
and Özarslan (2004) for vetch seed, Aviara et al. (2005) for
Balanites aegypticiaca nuts and Coskun et al. (2006) for sweet
corn seed.
Porosity
The porosity of organic chickpea grains increased from 29.95 to 54.17%
with the increase in moisture content from 11.31-25.03% d.b. (Fig.
9).
 |
| Fig. 8: |
Effect of moisture content on true density of organic
chickpea grains, ns: not significant |
 |
| Fig. 9: |
Effect of moisture content on porosity of organic chickpea
grains, (a-f Values followed by different letter(s) are
significant, p<0.05) |
The relationship between porosity and moisture content can be represented
by the following equation:
| ε = 14.4416+1.5225
Mc |
(14) |
with a value for R2 of 0.9273.
Gupta and Das (1997), Ögüt (1998), Nimkar and Chattopadhyay
(2001), Nimkar et al. (2005), Aviara et al. (2005) and Coskun
et al. (2006) reported similar trends in the case of sunflower
seed, white lupine, green gram, moth gram, Balanites aegyptiaca nuts and
sweet corn seed, respectively; however, logarithmic increasing trend was
reported by Konak et al. (2002) for chick pea.
Terminal Velocity
The experimental results for the terminal velocity of organic chickpea
grains at various moisture levels are shown in Fig. 10.
The relationship between terminal velocity and moisture content can be
represented by the following equation:
| V = 4.1408-0.0067(Mc2)+0.3493
(Mc) (R2 = 0.9948) |
(15) |
The terminal velocity was found to increase polynomial from 7.20 to 8.70
m s-1 as the moisture content increased from 11.31-25.03% d.b.
However, linear increase of terminal velocity with increase of moisture
content was reported by Joshi et al. (1993), Suthar and Das (1996),
Gupta and Das (1997) in the case of pumpkin grains, sunflower and karingda,
respectively.
Static Coefficient of Friction
The static coefficient of friction of organic chickpea grains on six
surfaces (rubber, stainless steel, aluminum, glass, MDF(medium density
fiberboard) and galvanized iron) against moisture content in the range
11.31-25.03% d.b. are presented in Fig. 11.
It was observed that the static coefficient of friction increased with
increase in moisture content for all the surfaces. This is due to the
increased adhesion between the seed and the material surfaces at higher
moisture values. Increases of from 0.4452 to 0.4986, 0.3541 to 0.3899,
0.3939 to 0.4411, 0.3057 to 0.3541, 0.2867 to 0.3249 and 0.4040 to 0.4557
were recorded in the case of rubber, stainless steel, aluminum, glass,
MDF and galvanized iron, respectively, as the moisture content increased
from 11.31-25.03% d.b.
 |
| Fig. 10: |
Effect of moisture content on terminal velocity of organic
chickpea grains, (a-f Values followed by different letter(s)
are significant, p<0.05) |
 |
| Fig. 11: |
Effect of moisture content on static coefficient of
friction of organic chickpea grains against various surface |
At all moisture contents, the least static coefficient of friction were
on MDF. This may be owing to smoother and more polished surface of the
MDF sheet than the other materials used. The relationships between static
coefficients of friction and moisture content on rubber (μrub),
aluminum (μal), galvanized iron (μgi),
stainless steel (μss), MDF (μmdf) and
glass (μgl) can be represented by the following equations:
| μru
= 0.4071+0.0037(Mc) (R2 = 0.9725) |
(16) |
|
μla
= 0.3611+0.0033(Mc) (R2 = 0.9648) |
(17) |
|
μgi
= 0.3671+0.0036(Mc) (R2 = 0.9723) |
(18) |
|
μ22
= 0.3313+0.0024(Mc) (R2 = 0.9612) |
(19) |
|
μmdf
= 0.2596+0.0026(Mc) (R2 = 0.9269) |
(20) |
|
μgi
= 0.2709+0.0033(Mc) (R2 = 0.9798) |
(21) |
Similar results were found by Singh and Goswami (1996) for cumin seed,
Özarslan (2002) for cotton, Yalçin and Özarslan (2004)
for vetch seed, Aviara et al. (2005) for Balanites aegypticiaca
nuts and Coskun et al. (2006) for sweet corn seed.
Shelling Resistance
The shelling resistance of organic chickpea grains was found to decrease
with the increase in moisture content (Fig. 12).
The small shelling resistance at higher moisture content might have resulted
from the fact that the grain became more sensitive to cracking at high
moisture. The variation in shelling resistance of organic chickpea grains
Rs in N with moisture content can be represented by the following
equation:
with value for R2 of 0.9824.
 |
| Fig. 12: |
Effect of moisture content on shelling resistance of
organic chickpea grains, (□) length, ns: not significant |
Özarslan (2002) and Konak et al. (2002) reported as different
decrease in shelling resistance when the moisture content was increased
for cotton and chick pea grains, respectively.
CONCLUSIONS
The average length, width and thickness of grains ranged from 10.30 to
11.11 (7.86%), 8.41 to 9.42 (12%) and 8.33 to 9.02 (8.23%) mm as the moisture
content increased from 11.31-25.03% d.b., respectively. The arithmetic
and geometric mean diameters were found to increase from 9.01 to 9.85
mm (9.32%) and 8.96 to 9.80 mm (9.37%), respectively. The thousand seed
mass increased from 432.22 to 640.00 g (48.07%) and the sphericity increased
from 0.870 to 0.884 (1.6%) with the increase in moisture content from
11.31-25.03% d.b. The bulk density decreased from 700.50 to 550.00 kg
m-3 (28.5%), whereas the true density increased from 1000 to
1200 (20%) kg m-3. The terminal velocity increased logarithmic
from 7.20 to 8.70 m sec-1 as the moisture content increased
from 11.31-25.03% d.b. The static coefficient of friction of organic chickpea
grains increased the linear against surfaces of six structural materials,
namely, rubber (11.99%), aluminum (11.98%), galvanized iron (12.79%),
stainless steel (10.11%), MDF (13.32%) and glass (15.83%) as the moisture
content increased from 11.31-25.03% d.b. The shelling resistance decreased
as the moisture content increased from 101 to 70 N (30.69%).
NOMENCLATURE
| Ap |
: |
Projected area (mm2) |
:W |
: |
Width of seed (mm) |
| As |
: |
:Surface area (mm2) |
Wi |
: |
Initial mass of sample (kg) |
| Da |
: |
Arithmetic mean diameter of seed (mm) |
ε |
: |
Porosity (%) |
| Dg |
: |
Geometric mean diameter of seed (mm) |
α |
: |
Angle of tilt (degree) |
| L |
: |
:Length of seed (mm) |
μ |
: |
Static coefficient of friction |
| M1000 |
: |
:Thousand seed mass (g) |
ρb |
: |
Bulk density (kg m-3) |
| Mi |
: |
Initial moisture content of sample (% d.b.) |
ρt |
: |
True density (kg m-3) |
| Mf |
: |
Final moisture content of sample (% d.b.)φ :Sphericity of seed
(decimal) |
φ |
: |
Sphericity of seed (decimal) |
| Mc |
: |
Moisture content (% d.b.) |
Subscripts |
: |
|
| Rs |
: |
Shelling resistance (N) |
al |
: |
Aluminum |
| R2 |
: |
:Coefficient of determination |
gi |
: |
Galvanized iron |
| Q |
: |
Mass of water to added (kg) |
gl |
: |
Glass |
| T |
: |
Thickness of seed (mm) |
mdf |
: |
Medium density fiberboard |
| Vt |
: |
Terminal velocity (m sec-1) |
ru |
: |
Rubber |
| |
: |
|
ss |
: |
Stainless steel |
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