Content uploaded by Mohamed Ibrahim
Author content
All content in this area was uploaded by Mohamed Ibrahim on Mar 30, 2019
Content may be subject to copyright.
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1125 -
ELASTIC PROPERTIES OF THREE VARIETIES OF
DATE FRUITS DURING THREE DIFFERENT
RIPENING STAGES
M. M. Ibrahim* and A. M. Hassan*
ABSTRACT
The aim of this research work was to determine the physical and elastic
properties of date fruits (Phoenix dactylifera) cv (Talees, Khudari and
Taghit) during three ripening stages (Khalaal, Rutab and Tamr) to
develop a technique that can predict the packing height to protect fruits
from mechanical damage. The physical properties include date mass,
volume, dimensions, moisture content, bulk density, flesh thickness, and
kernel mass. The elastic properties of date fruit include Young's modulus
of elasticity (E), firmness coefficient (FC), bioyield stress (σb), bioyield
strain (εb), rupture stress (σr), rupture strain (εr) and rupture energy
(RE). For different varieties, the results showed that ripening stages have
a significant effect on physical and elasticity properties. The values of E,
FC, σb, σr and RE were decreased from Khalaal to Rutab stage, while
they increased from Rutab to Tamr stage. Accordingly, the maximum
heights of packing box were 141, 106, and 121 mm for Talees, Khudari
and Taghit respectively.
Keywords: Date palm, ripening, elasticity, modulus, bioyield, rupture,
and stress.
INTRODUCTION
ate palm (phoenix dactylifera, L.) is one of the most important
horticultural crops rich in vitamins. Date production in the world
is only confined to a small number of countries, most of them
being the Arab countries. Date palm is the economic crop in Libya,
where production was approximately 150 thousand tons (Arab
Agricultural Statistics Yearbook, 2009).
In Libya date palms are distributed mainly in three areas: coastal, middle
and southern districts. There are about (6) million date palm trees in
Libya grown of about (400) cultivars.
Date fruits pass through several maturity stages, traditionally described
by changes in color, texture and taste.
* Assist. Prof., Ag. Eng. Dept., Fac. of Agric., Cairo University.
D
Misr J. Ag. Eng., 29 (3): 1125 - 1148
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1126 -
Several investigations have shown some of the chemical compositional
changes that take place during maturation, including free sugars and
tannins (Myhara et al., 1999; Sawaya et al., 1983; Sawaya et al., 1982).
Green dates stage (kimri ) are firm in texture with highest moisture
and tannin contents. At the Khalaal ( ) stage, dates begin to lose
moisture and form considerable quantities of sucrose. In the Rutab ()
stage, the loss of moisture is accelerated, and the fruits become softer in
texture, and sucrose is converted into sugars. Dates at Rutab stage are the
most desirable since they are at their softest and sweetest states. In the
final maturity stage (Tamr - ) the fruits contain the least amount of
moisture and maintain a soft texture with a sweet taste. Ismail et al.,
(2001) studied the consumer preference for quality attributes of date
(maturity of Tamr stage). Consumer gave weight on the acceptance as:
high (color, appearance, and sweetness), medium (fruit size, flesh
thickness, chewiness, and solubility).
Knowledge of the physical properties of date fruit is necessary for the
design of post harvesting equipment such as cleaning, sorting, grading,
kernel removing, and packing. The importance of dimensions is in
determining the aperture size of machines, particularly in separation of
materials as discussed by Mohsenin (1986). These dimensions can be
used in designing machine components and parameters.
Grading fruit, based on weight, reduces packing and handling costs and
also provides suitable packing patterns (Khoshnam et al., 2007).
Many studies have been reported on the physical and mechanical
properties of fruits, such as bergamot (Rafiee et al. , 2007), coconut
(Terdwongworakul et al., 2009), date fruit (Jahorni et al., 2008), kiwi
fruit (Lorestani and Tabatabaeefar, 2006), melon (Emadi et al., 2009),
orange (Khojastehnazhand et al., 2009) and citrus fruits (Omid et al.,
2010). Akar and Aydin (2005) evaluated some physical properties of
gumbo fruit varieties as functions of moisture content. Kashaninejad et
al. (2006) and Awady and Sayed (1994) determined some physical and
aerodynamic properties of peanuts pistachio nuts and kernels as functions
of moisture content in order to design processing equipment and
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1127 -
facilities. Ghonimy and Kassem. (2011) reported that there are
significant differences between different production zones of date fruits
for each of fruit mass, flesh mass, fruit volume, fruit moisture content,
fruit dimensions, flesh thickness, fruit projected area and elasticity of
fruits.
Fecete (1994) found that the coefficient of elasticity for tomato and apple
can be used to characterize the fruit firmness. Cenkowski et al. (1995)
studied the effect of moisture sorption hysteresis on the mechanical
behaviour of canola and showed that the modulus of elasticity of the
product brought into equilibrium through adsorption was higher than that
of the one obtained through desorption at the same moisture content. The
other products whose mechanical properties have been studied include
kiwi fruit (Abbott and Massie, 1995), apples (Abbott and Lu, 1996) and
sea buckthorn berries (Khazaei and Mann, 2004). Anazodo and
Chikwendu (1983) developed equations for the calculation of the
Poisson’s ratio and elastic modulus of circular bodies subjected to radial
compression and Dinrifo and Faborode (1993) applied the Hertz’s
theory of contact stresses to cocoa pod deformation. Anazodo and Norris
(1981) noted that the modulus of elasticity, crushing strength and
modulus of toughness of corncob all decreased with moisture content.
The aim of this research was to investigate some physical and elastic
properties for three varieties of date fruits (Talees, Khudari and Taghit)
during three stages of ripening (Khalaal, Rutab and Tamr) to develop a
technique that can predict the packing height to protect fruits from
mechanical damage.
MATERIAL AND METHODS
1. Sample preparation
This study was carried out at the Faculty of Agriculture, Omar El-
Mukhtar University, Libya, during season 2010. Physical and mechanical
properties of date fruits (Phoenix dactylifera) were determined at three
ripening stages. Three varieties (Talees, Khudari, and Taghit) were
selected randomly from Sabha ( ) (located in the western south of
Libya). For each variety, 100 date fruits were randomly selected at each
ripening stage. The dates were collected from different farms. Dates were
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1128 -
sorted to discard the damaged fruits, and immediately kept for less than
24 hours in a cold storage at 5 oC.
2. Physical properties of date fruit
2.1. Date fruits dimensions (length and diameter)
All dimensions of date fruit and kernels were measured by Vernier
calliper to an accuracy of 0.1 mm.
2.2. Date fruit moisture content
The moisture content was determined for the flesh of dates using AOAC
procedures (AOAC, 1995) where the samples were dried at 70oC for 48
hours.
2.3. Mass and bulk density
The mass of date fruit was determined using a digital balance with an
accuracy of 0.01 g. The bulk density of date fruits was calculated using
equation (1) by determining the mass of the date and its volume.
V
m
Db
(1)
Where;
Db = The bulk density of date fruit, g/cm3;
m = Mass of date fruit, g;
V = Volume of date fruit, cm3.
3. Mechanical properties of date fruit
3.1. Compression test
The parallel-plate compressive test was carried out to determine the
mechanical properties using a universal testing machine (Instron-1000 N)
Individual date fruits were uniaxilly compressed at a cross-head speed of
0.5 mm/s to a total deformation 10 mm. A plate (diameter 7.5 cm)
compressed a date flesh slab placed on a mounted fixed table. The
contact surfaces were oriented parallel to the compression surfaces
during loading (Fig. 1). A random 10 fruits sample of each cultivar at
each ripening stage were taken for compression tests. All experiments
were carried out at room temperature (23 oC).
The contact area between the parallel-plate disk surface and each tested
fruit surface was determined experimentally. The plunger disk surface
was covered with a white paper, followed by gently pressing the
horizontally oriented upper longitudinal fruit surface in an ink stamp, and
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1129 -
then allowing the plunger to contact the fruit surface. The resulting
contact area traced on the white paper was scanned, and specially
developed software that accurately estimates the scanned surface area
was used to determine the contact area.
Fig. (1): Date fruit loaded between the two parallel plates
3.2. Elastic property of date fruit
A typical force-deformation curve (Mohsenin 1986) is shown in Figure
(2). As it is shown, the force-deformation curve exhibited two peak
points. The first peak corresponds to the yield point at which kernel
damage was initiated. The second peak corresponds to the maximum
compressive force.
For stress-strain tests, the following mechanical properties were
calculated; the modulus of elasticity (E), firmness coefficient (FC),
bioyield stress (σb), bioyield strain (εb), rupture stress (σr), rupture strain
(εr) and rupture energy toughness (RE).
Fig. (2): A typical force-deformation plot for agricultural materials
(Mohsenin 1986).
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1130 -
The Young's modulus of elasticity is a good measure of the elasticity of
ideal materials. The behavior of ideal materials is described by the
Hooke's law and the model of which is a spring without damper.
The Young's modulus of elasticity (E) for compressive stress is expressed
by equation (2).
E
(2)
Where;
E = Young's modulus of elasticity, kPa;
σ = Compressive stress, kPa;
ε = Strain, mm/mm.
The strain was calculated by dividing the deformation of the fruit by the
initial fruit average thickness.
l
l
(3)
Where;
Δl = Variation in the thickness (deformation), mm;
l = Original thickness, mm.
The average stress was calculated by dividing the force on one fruit by
the projected area of the fruit as follows:
p
A
F
1000
(4)
Where;
F = force on one fruit, N,
Ap = Contact area of date fruit, mm2.
Firmness coefficient (FC) is calculated as the average slope of force –
deformation curve from zero to point of rupture or failure (Shafiee et al.,
2008). FC was calculated by applying the following equation (5) :
F
FC l
(5)
Toughness (RE) or mechanical energy or work required for rupture was
determined by calculating the area under the force – deformation curve
from the following equation (Braga et al., 1999):
2
rr
FD
RE
(6)
Where;
RE= Toughness, J;
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1131 -
Fr = the rupture force, N;
Dr = the deformation at rupture point, m.
The area was measured by using a computer software program
(AutoCAD), then, to relate the rupture energy to date fruit volume, it was
divided it by date fruit volume.
3.3. Statistical analysis
Statistical analysis was carried out using a randomized complete block
procedure of the MStat-c statistical package. LSD and Duncan multiple
range comparison were used to identify means that were different at
probabilities of 5 % or less (Snedecor and Cochran 1976).
4. Determination of the height of packing box
The force acting on stacks of fruit may be used to estimate the force
acting on a date fruit at the bottom layer of a bulk bin. Figure (3) shows
the force (F) acting on date fruit somewhere in stack. In this study, the
date fruits are represented by cylinders of an average diameter (d) and a
square arrangement which depends on their characteristic diameter and
number of fruits.
Fig. (3): An elevation view through the stack of date fruits in
arrangement.
The following equations (7, 8, and 9) calculated the number of fruit of
fruits above the bottom layer and consequently the height of the packing
box.
max
F n m
(7)
1
th
H d n
(8)
..FS
H
Hth
act
(9)
Where:
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1132 -
Fmax = Maximum allowable force on a date fruit at the bottom layer, N.
Hth = Maximum depth of fruit in box, (without mechanical damage),
mm.
Hact = Actual depth of fruit in box, mm.
n = Number of fruits above the last fruit at bottom layer.
m = Fruit weight, N.
d = Fruit diameter, mm.
S. F. = Safety factor (
1.5) as design factor to avoid any unexpected
risk.
4.1. Determination of the contact stress
Heinrich Hertz (Shigley et al., 2008) proposed a solution for contact
stress in two elastic isotropic bodies, such as the case of two cylinders
(line contact) of the same material touching each other and attempted to
find the magnitude of the maximum pressure. Figure (4) shows two
cylinders of length l (the length of cylinder = fruit length) and diameters
d1 and d2. The area of contact is a narrow rectangle of width 2b and
length l, and the pressure distribution is elliptical.
(1)
(2)
Fig. (4): Line contact of two cylinders: (1) Two circular cylinders held in
contact by forces F uniformly distributed along cylinder length l. (2) Contact
stress has an elliptical distribution across the contact zone width 2b.
d1
d2
2b
y
x
l
y
x
z
z
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1133 -
The half-width b is given by the equation (Shigley et al., 2008):
22
1 1 2 2
12
11
2
1 1
EE
F
bl d d
(10)
Where:
b = half of contact width, mm.
F = Acting force on the two cylinders, N.
l = contact length, mm.
E1, E2 = Modulus of elasticity for cylinders (1) and (2), Pa.
µ1
,
µ2
= Poisson ratio for cylinders (1) and (2), dimensionless.
d1, d2 = Diameter for cylinder (1) and (2), mm.
The maximum pressure (Pmax, Pa) is called the Hertz (compressive) stress
which occurs at the center and is given by following equation:
bl
F
p
2
max
(11)
RESULTS AND DISCUSSIONS
1. Physical properties of date fruit
The averages values of date fruit mass, flesh mass, kernel mass, fruit
volume, bulk density, moisture content, fruit length, fruit diameter and
flesh thickness are shown in table (1).
For Talees variety, moisture contents were measured as 70.87, 60.6 and
21.79 % w.b. for Khalaal, Rutab and Tamr respectively. Results showed
that the moisture content decreased by increasing the ripening. The
average of dimensions were 27.4 mm in length, 17.4 mm in width and
10.11 mm in thickness for Khalaal stage, 36.5 mm in length, 19.1 mm in
width and 11.5 mm in thickness for Rutab stage, and 35.3 mm in length,
19.4 mm in width and 11.57 mm in thickness for Tamr stage. Date
dimensions increased from Khalaal stage to Rutab stage, while decreased
from Rutab to Tamr. Average fruit mass was 7.5, 11.5 and 10.6 g for
Khalaal, Rutab and Tamr respectively. Results showed that the fruit mass
increased from Khalaal stage to Rutab stage, while decreased from Rutab
to Tamr. The same trend was found for Khudari and Taghit varieties.
With Taghit variety the fruit mass was less than Talees and Khudari.
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1134 -
Data proved that the physical properties of date fruit were greatly
influenced by ripening stage with all varieties.
For the three varieties, the statistical analysis (at 5% level) showed
significant differences for most physical properties of date fruits during
three stages of ripening (Khalaal, Rutab and Tamr).
2. Mechanical properties of date fruit
The mechanical properties of date fruit varieties at different ripening
stages included modulus of elasticity (E), firmness coefficient (FC),
bioyield stress (σb), bioyield strain (εb), rupture stress (σr), rupture strain
(εr), and rupture energy (RE) as shown in table (1). Ripening stages for
date fruit showed a significant effect on mechanical properties (P < 0.01).
2.1. Stress (σ) – Strain (ε) curve
Figure (5: a, b, c) shows the stress-strain curve of date palm (Talees,
Khudari and Taghit varieties) during different ripening stages. It is clear
that, before the point called proportional limit (Pl). Generally, the elastic
limit is the limit beyond which the date will no longer go back to its
original shape when the load is removed, or it is the maximum stress that
may be developed such that there is no permanent setting when the load
is entirely removed. For the three varieties, the statistical analysis (at 5%
level) showed significant differences for most elasticity properties of date
fruits during three stages of ripening (Khalaal, Rutab and Tamr).
The elastic limits were (110.5, 40 and 50 kPa), (3.3, 3.3, and 4.4 kPa),
and (5.1, 15, and 10.4 kPa) for Talees, Khudari, and Taghit respectively.
The results showed that the elastic limit decreased from Khalaal to Rutab
stage, while increased from Rutab to Tamr. The reason may be due to the
major changes which take place in the structural tissues during the on-
going maturation process and change from Khalaal to Rutab to Tamr
stage of maturity. The most significant changes are in sugar type which
converts from sucrose to fructose and glucose as a result of enzymatic
action during the maturation process. The changes in pectin by pectinase
enzyme lead to softness in the date structure at the Rutab stage compared
to the Khalaal stage despite the reduction in moisture content at the
Rutab stage for Talees is greater than Taghit and Khudria at Khalaal and
Rutab stages, but Tamr stage, the elastic limit with Kudria is greater than
Taghit and Talees.
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1135 -
Table (1). Physical and mechanical properties of the date fruits.
Property
Talees (a)
Khudari (a)
Taghit (a)
Khalaal
Rutab
Tamr
Khalaal
Rutab
Tamr
Khalaal
Rutab
Tamr
Physical properties
Fruit mass, g
7.5 B
11.5 A
10.6 A
7.6 C
10.2 A
9.5 B
4.0 B
7.8 A
7.2 A
Flesh mass, g
3.98 B
5.22 A
6.24 A
3.3 C
4.5 B
5.12 A
4.23 A
5.86 A
5.32 A
Kernel mass, g
0.69 C
1.39 A
1.21 B
1.2 A
1.41A
1.35 A
0.95 B
1.41 A
1.03 B
Fruit volume, cm3
7.0 C
10.8 B
12.0 A
6.2 C
10.8 A
9.1 B
5.15 B
8.0 A
7.1 A
Kernel volume, cm3
1.9 B
2.1 A
2.2 A
1.8 B
2.32 A
2.33 A
1.76 C
2.15 B
2.35 A
Solid density, g/ cm3
0.9 B
1.0 B
1.2 A
1.0 C
1.2 B
1.4 A
0.9 A
1.1 A
1.3 A
Bulk density, g.cm-3
0.61 A
0.64 A
0.67 A
0.66 A
0.65 A
0.69 A
0.59 A
0.62 A
0.65 A
Moisture content,%
70.87 A
30.60 B
21.79 C
66.44 A
29.37 B
20.13 C
62.57 A
31.59 B
21.15 C
Fruit length, mm
27.4 B
36.5 A
35.3 A
30.4 B
36.7 A
35.7 A
27.6 B
33.4 A
32.8 A
Fruit diameter, mm
17.4 B
19.1 A
19.4 A
18.7 B
21.8 A
20.2 A
18.4 B
20.4 A
19.2 A
Fruit thickness, mm
10.11 B
11.5 A
11.57 A
15.3 B
20.3 A
19.5 A
12.15 B
15.2 A
15.3 A
Mechanical properties
Elasticity Modulus (kPa)
1035.7 A
4.59 C
57.24 B
585.42 A
21.50 C
76.47 B
866.41 A
22.01 C
46.18 B
Firmness Coeff. (N/mm)
0.76 A
0.15 C
0.14 B
0.62 A
0.22 B
0.13 C
0.64 A
0.26 B
0.17 B
Bioyield point
stress (kPa)
261.83 A
4.08 C
7.78 B
237.33 A
2.54 C
22.38 B
467.73 A
5.30 C
15.70 B
Strain
0.4 A
0.2 B
0.19 B
0.48 A
0.38 A
0.3 A
0.7 A
0.47 B
0.3 B
Rupture point
stress (kPa)
411.80 A
6.58 B
7.78 B
272.09 A
5.61 C
30.0 B
485.43 A
6.40 C
20.2 B
Strain
0.57 A
0.38 B
0.19 C
0.55 A
0.75 A
0.7 A
0.8 A
0.47 B
0.37 B
Rupture energy (MJ/m3)
0.1071 A
0.0015 C
0.0115 B
0.1073 A
0.0074 C
0.0318 B
0.2603 A
0.0094 C
0.0121 B
(a) Mean values with different letters are significantly different (< 5% level).
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1136 -
0
100
200
300
400
500
600
700
0 0.1 0.2 0.3 0.4 0.5 0.6
Strain (mm/mm)
Stress (kPa)
Talees Khudari Taghit
Stress (kPa)
0
100
200
300
400
500
600
700
0 0.1 0.2 0.3 0.4 0.5 0.6
Strain (mm/mm)
Stress (kPa)
Talees Khudari Taghit
0
5
10
15
20
25
30
0 0.1 0.2 0.3 0.4 0.5 0.6
Strain (mm/mm)
Stress (kPa)
Talees Khudari Taghit
0
20
40
60
80
100
120
140
160
180
0 0.1 0.2 0.3 0.4 0.5 0.6
Strain (mm/mm)
Stress (kPa)
Talees Khudari Taghit
Strain (mm/mm)
Fig. (5): Stress- strain curves of date fruit varieties at different ripening
stages.
Rutab
Tamr
Khalaal
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1137 -
2.2. Modulus of elasticity (E)
The average values of Young's modulus of elasticity (E) for date fruits at
different ripening stages and varieties are shown in table (1) and figure
(6-a). It is clear that the modulus of elasticity (E) decreased from Khalaal
to Rutab stage, while increased from Rutab to Tamr which was common
trend for all varieties.
For Talees variety, the values of modulus of elasticity were 1035.7 kPa,
4.59 kPa and 57.27 kPa for Khalaal , Rutab and Tamr stages respectively.
For Khudari variety, the values of modulus of elasticity were 585.42 kPa,
21.50 kPa and 76.47 kPa for Khalaal, Rutab and Tamr stages
respectively. For Taghit variety, the values of E were 866.41 kPa, 22.01
kPa and 46.18 kPa for Khalaal, Rutab and Tamr stages respectively.
In case of Khalaal stage of ripening; E of Talees was greater than Taghit
and Khudari, In case of Rutab stage; E of Taghit was greater than
Khudari and Talees, but in case of Tamr stage; E of Khudari was greater
than Talees and Taghit.
For the three varieties, the statistical analysis (at 5% level) showed
significant differences for E of date fruits during the three stages of
ripening (Khalaal, Rutab and Tamr).
2.3. Firmness Coefficient (FC)
The average values of firmness coefficient (FC) for date fruits at
different ripening stages and varieties are shown in table (1) and figure
(6-b). It is clear that the firmness coefficient (FC) decreased from
Khalaal to Tamr stage, for all different varieties.
For Talees variety, the values of FC were 0.76, 0.15, and 0.14 N/mm for
Khalaal, Rutab and Tamr stages respectively. For Khudari variety, the
values of FC were 0.62, 0.23, and 0.13 N/mm for Khalaal, Rutab and
Tamr stages respectively. For Taghit variety, the values of FC were 0.64,
0.26, and 0.17 N/mm for Khalaal, Rutab and Tamr stages respectively.
The results show that the FC of Talees variety is greater than Taghit and
Khudari with Khalaal stage of ripening, for Taghit variety; the FC is
greater than Khudari and Talees with Rutab stage of ripening, but for
Khudari, the FC was greater than Talees and Taghit with Tamr stage of
ripening.
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1138 -
For the three varieties, the statistical analysis (at 5% level) showed
significant differences for FC of date fruits during the three stages of
ripening (Khalaal, Rutab and Tamr).
Modulus of elasticity (kPa)
0
200
400
600
800
1000
1200
Firmness Coefficient (N/mm)
0.0
0.2
0.4
0.6
0.8
0
5
10
15
20
25
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0
20
40
60
80
100
Talees Khudari Taghit
0.00
0.04
0.08
0.12
0.16
0.20
Talees Khudari Taghit
(a)
(b)
Fig. (6): Modulus of elasticity (E) and firmness coefficient (FC) for
date fruit varieties under study at different ripening stages.
2.4. Bioyield stress (σb)
The average values of bioyield stress (σb) for date fruits at different
ripening stage and varieties are shown in table (1) and figure (7-a). It is
clear that the bioyield stress (σb) decreased from Khalaal to Rutab stage,
while increased from Rutab to Tamr, with all varieties. In case of Talees
variety, the values of (σb) were 261.83, 4.08, and 7.78 kPa for Khalaal,
Rutab and Tamr stages respectively. In case of Khudari variety, the
Khalaal
Khalaal
Rutab
Rutab
Tamr
Tamr
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1139 -
values of (σb) were 237.33, 2.54, and 22.38 kPa for Khalaal, Rutab and
Tamr stage respectively. In the case of Taghit variety, the values of (σb)
were 467.75, 5.30, and 15.70 kPa for Khalaal, Rutab and Tamr stages
respectively.
For the three varieties, the statistical analysis (at 5% level) showed
significant differences for σb of date fruits during the three stages of
ripening (Khalaal, Rutab and Tamr).
2.5. Bioyield strain (εb)
The average values of bioyield strain (εb) for date fruits at different
ripening stages and varieties are shown in table (1). It is clear that the
bioyield strain (εb) decreased from Khalaal to Tamr stage, with all
different varieties.
In the case of Talees variety, the values of εb were 0.4, 0.2, and 0.19
mm/mm for Khalaal, Rutab and Tamr stages respectively. In the case of
Khudari variety, the values of εb were 0.48, 0.38, and 0.3 mm/mm for
Khalaal, Rutab and Tamr stages respectively. In case of Taghit variety
the values of εb were 0.7, 0.47, and 0.3 mm/mm for Khalaal, Rutab and
Tamr stages respectively.
The results show that the εb of Taghit variety was greater than Khudari
and Talees in all ripening stages.
The results show that the (σb) of Taghit variety was greater than Talees
and Khudari with Khalaal and Rutab stages of ripening. However for
Khudari, the (σb) was greater than Talees and Taghit with Tamr stage of
ripening.
For the three varieties, the statistical analysis (at 5% level) showed
significant differences for εb of date fruits during the three stages of
ripening (Khalaal, Rutab and Tamr).
2.6. Rupture stress (σr)
The average values of rupture stress (σr) for date fruits at different
ripening stages for the different varieties are shown in table (1) and
figure (7-b). It is clear that the rupture stress (σr) decreased from Khalaal
to Rutab stage, while increased from Rutab to Tamr, with all different
varieties.
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1140 -
In case of Talees variety, the values of σr were 411.80, 6.58, and 7.78
kPa for Khalaal, Rutab and Tamr stages respectively. In case of Khudari
variety, the values of σr were 272.09, 5.61, and 30 kPa for Khalaal,
Rutab and Tamr stages respectively. In case of Taghit variety, the values
of σr were 485.43, 7.40, and 20.20 kPa for Khalaal, Rutab and Tamr
stages respectively.
The results showed that the σr of Taghit variety was greater than Talees
and Khudari with Khalaal and Rutab stages of ripening, but for Khudari,
the rupture stress was greater than Talees and Taghit with Tamr stage of
ripening.
For the three varieties, the statistical analysis (at 5% level) showed
significant differences for σr of date fruits during the three stages of
ripening (Khalaal, Rutab and Tamr).
Bioyield stress (kPa)
0
100
200
300
400
500
Rupture stress (kPa)
0
100
200
300
400
500
600
0
1
2
3
4
5
6
0
2
4
6
8
0
5
10
15
20
25
Talees Khudari Taghit
0
10
20
30
40
Talees Khudari Taghit
(a)
(b)
Fig. (7): Bioyield stress (σb) and rupture stress (σr) for date fruit
varieties under study at different ripening stages.
Khalaal
Khalaal
Rutab
Rutab
Tamr
Tamr
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1141 -
2.7. Rupture strain (εr)
From the calculated results of rupture strain for date fruits at different
ripening stages with different varieties, as shown in table (1) and figure
(8-a), it can be found that the rupture strain decreased from Khalaal to
Tamr stages, with Talees and Taghit varieties, but in the case of Khudari
variety the rupture strain increased from Khalaal to Rutab stages then
decreased in Tamr stage.
In the case of Talees variety, the values of rupture strain were 0.57, 0.38,
and 0.19 mm/mm for Khalaal, Rutab and Tamr stages respectively. In
case of Khudari variety, the values of rupture strain were 0.55, 0.75, and
0.7 mm/mm for Khalaal, Rutab and Tamr stages respectively. In the case
of Taghit variety, the values of rupture strain were 0.8, 0.47, and 0.37
mm/mm for Khalaal, Rutab and Tamr stages respectively.
The results showed that the rupture strain of Taghit variety was greater
than Talees and Khudari with Khalaal stage of ripening, but for Khudari,
the rupture strain was greater than Talees and Taghit with Rutab and
Tamr stages of ripening.
For the three varieties, the statistical analysis (at 5% level) showed
significant differences for εr of date fruits during the three stages of
ripening (Khalaal, Rutab and Tamr).
2.8. Rupture energy (RE)
The average values of rupture energy (RE) for date fruits at different
ripening stages and varieties are shown in table (1) and figure (8-b). It is
clear that, the rupture energy (RE) decreased from Khalaal to Rutab
stage, while increased from Rutab to Tamr, with all different varieties.
In case of Talees variety, the values of RE were 0.1071, 0.0015, and
0.0115 MJ/m3 for Khalaal, Rutab and Tamr stages respectively. In the
case of Khudari variety, the values of RE were 0.1073, 0.0074, and
0.0318 MJ/m3 for Khalaal, Rutab and Tamr stages respectively, where
for Taghit variety, the values of RE were 0.2603, 0.0094, and 0.0121
MJ/m3 for Khalaal, Rutab and Tamr stages respectively.
The results show that the RE of Taghit variety was greater than Talees
and Khudari with Khalaal stage of ripening, but for Khudari, the rupture
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1142 -
energy was greater than Talees and Taghit with Rutab and Tamr stages of
ripening.
For the three varieties, the statistical analysis (at 5% level) showed
significant differences for RE of date fruits during the three stages of
ripening (Khalaal, Rutab and Tamr).
Rupture strain (mm/mm)
0.00
0.20
0.40
0.60
0.80
1.00
Energy (MJ/m3)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.00
0.20
0.40
0.60
0.80
0.000
0.002
0.004
0.006
0.008
0.011
0.00
0.20
0.40
0.60
0.80
Talees Khudari Taghit
0.000
0.010
0.020
0.030
0.040
Talees Khudari Taghit
(a)
(b)
Fig. (8): Rupture strain (εr) and energy (RE) for date fruit varieties
under study at different ripening stages.
In general, the mechanical properties of date fruit are influenced by
varieties and ripening stage. As concluded from the results of the present
study, each of E, FC, σb, σr and RE decreased from Khalaal to Rutab
stage then increased at Tamr stage. The physical and mechanical
properties of the three date fruit varieties namely, Talees, Khudari and
Taghit are important in designing machine used for harvesting and post
harvest handling of dates during ripening stages.
Khalaal
Khalaal
Rutab
Rutab
Tamr
Tamr
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1143 -
3. Predicting the height of packing box
In order to get optimum (prediction) of the height of packing box the
following procedure was applied.
Applying equations (10) and (11) considering the following assumption:
d1 = d2 = fruit thickness.
E1 = E2 = Modulus of elasticity for date fruit.
µ
1 =
µ
2 = Poisson ratio of date fruit (the absolute value of the transverse
strain to the corresponding axial strain resulting from uniformly
distributed axial stress below the proportional limit of the
material, it was measured
0.4 .
l = Fruit length.
Pmax = Bioyield stress of date fruit.
Substitute equation (10) in equation (11) use try and error method to
calculate the maximum allowable force (Fmax) for the three varieties in
Rutab stage (the bioyield stress in Rutab stage is less than other stages),
the values of n, Hth, and Hact can be calculated as shown in table (2).
Table (2): The calculation results of Fmax, Hth, and Hact.
Talees
Khudari
Taghit
Fmax, N
2.00
0.70
0.855
N
17.391
6.8627
10.962
Hth, mm
211.50
159.61
181.82
Hact, mm
141
106.41
121.21
Therefore, the maximum heightsof packing box which does not result in
mechanical damage were141, 106, and 121 mm for Talees, Khudari and
Taghit respectively.
CONCLUSION
The obtained results of physical and mechanical properties of the three
date fruit varieties during three stages of ripening can be summarized as
follows:
1. There were significant differences between ripening stages of date
fruits for most physical properties.
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1144 -
2. There were significant differences between ripening stages of date
fruits for mechanical properties.
3. For different varieties, the values of E, FC, σb, σr and RE decreased
from Khalaal to Rutab stage then increased from Rutab to Tamr
stages.
4. The different measured mechanical properties followed the same
trend which reflected their state behaviour at the three stages same
of ripening for the three tested varieties: decreasing through
Khalaal to Rutab stages then increasing through Rutab to Tamr
stages.
5. The maximum heights of packing box are 141, 106, and 121 mm
for Talees, Khudari and Taghit respectively.
REFERENCES
Abbott, J. A. and D. R. Massie. 1995. Non-destructive dynamic
force/deformation measurement of kiwifruit firmness (Actinidia
Delicious). Trans. ASAE, 38(6): 1809 – 1812.
Abbott, J. A. and R. Lu. 1996. Anistropic mechanical properties of
apples. Trans. ASAE, 39(4): 1451 – 1459.
Akar R. and C. Aydin. 2005. Some physical properties of gumbo fruit
varieties. J. Food Eng., 66: 387-393.
Anazodo, U. G. N. and E. R. Norris. 1981. Effects of genetic and
cultural practices on the mechanical properties of corncobs. J. Agr.
Eng. Res., 26: 97 – 107.
Anazodo, U. G. N. and S. C. Chikwendu. 1983. Poisson’s ratio and
elastic modulus of radially compressive biomaterials – I: small
deformation approximation. Transactions of the ASAE, 26(3): 923 –
929.
AOAC. 1995. Official methods of analysis (16th ed.). Association of
Official Analytical Chemists. Wash., DC.
Arab Agricultural Statistics Yearbook. 2009. Plant production. Part 3.
Vol. 29.
Awady, M. N. and A. S. El Sayed. 1994. Separation of peanut seeds by
air stream. M J A E, 11 (1): 137-147.
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1145 -
Braga, G. C., Couto, S. M., Hara, T., and Neto, J. T. P. A. 1999.
Mechanical behaviour of macadamia nut under compression
loading. J. Ag. Eng. Res., 72: 239–245.
Cenkowski, S., Q. Zhang and W.J. Crerar. 1995. Effect of sorption
hysteresis on the mechanical behaviour of canola. Transactions of
the ASAE, 38(5): 1455 – 1460.
Dinrifo, R. R. and M. A. Faborode. 1993. Application of Hertz’s theory
of contact stresses to cocoa pod deformation. J. Ag. Eng. and Tec.,
1: 63 – 73.
Emadi B., M. H. Abbaspour-Fard, and P. Yarlagadda. 2009.
Mechanical properties of melon measured by compression, shear,
and cutting modes. I. J. Food Properties; 12(4): 780-790.
Fecete, A. 1994. Elasticity characteristics of fruits. International
Agrophysics, 8(3): 411- 414.
Ghonimy, M. I., and M. A. Kassem. 2011. The elasticity
characteristics of palm date. Misr, J. Ag. Eng., 28 (2): 386 – 400.
Ismail, B., Haffar, I., Baalbaki, R., and J. Henry. 2001. Development
of a total quality scoring system based on consumer preference
weightings and sensory profiles: application to fruit dates (Tamr).
Food Quality Preference, 12: 499–506.
Jahorni, M., S. Rafiee, A. Jafari, BMR. Ghasemi, R. Mirasheh, and
S. S. Mohtasebi. 2008. Some physical properties of date fruit (cv.
Dairi). I. Agrophys., 22:221-224.
Kashaninejad M., A. Mortazavi, A. Safekordi, and L. G. Tabil. 2006.
Some physical properties of pistachio ( Pistacia veraL.) nut and its
kernel. J. Food. Eng., 72, 30-38. Agrophysics. 22: 221-224.
Khazaei, J. and D. D. Mann. 2004. Effects of temperature and loading
characteristics on mechanical and stress relaxation properties of sea
buckthorn berries, Part 1: Compression tests. Ag. Eng. I. Ejournal,
Manuscript FP 03 011, http//cigr-ejournal.tamu.edu/html/Volume
6, April.
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1146 -
Khojastehnazhand M., M. Omid, and A. Tabatabaeefar. 2009.
Determination of orange volume and surface area using image
processing technique. I. Agrophys.; 23: 237-24.
Khoshnam, F., A. Tabatabaeefar, M. Ghasemi Varnamkhasti and A.
Borghei. 2007. Mass modeling of pomegranate (Punica granatum
L.) fruit with some physical characteristics. Scientia Horticulturae
114: 1, 21-26.
Lorestani, A. N., and A. Tabatabaeefar. 2006. Modeling the mass of
kiwi fruit by geometrical attributes. I. Agrophys. 20: 135-139.
Mohsenin, N. N. 1986. Physical properties of plant and animal materials,
2nd ed. Gordon and Breach Sc. Publishers
Myhara, R. M., Karkalas, J., and M. S. Taylor. 1999. The
composition of maturing Omani dates. Journal of the Science and
Food Agriculture, 79, 1–6.
Omid M., M. Khojastehnazhand, and A. Tabatabaeefar. 2010.
Estimating volume and mass of citrus fruits by image processing
technique. J. Food Eng.; 100(2): 315-321.
Rafiee, S., M. Keramat, A. Jafari, A. R. Keyhani and R. Mirasheh.
2007. Determination of dimension and mass of date (ghasb). Proc.
I. Conf. on Innovations in Food and Bioprocess Tech. , Thailand.
Sawaya, W. N., Khalil, J. K., Safi, W. N., and A. Al-Shalhat. 1983.
Physical and chemical characterization of three Saudi date cultivars
at various stages of development. Canadian Inst. Food Sc. and Tec.,
16, 87–91.
Sawaya, W. N., Khatchadourian, H. A., Khalil, J. K., Safi, W. M.,
and A. Al-Shalhat. 1982. Growth and compositional changes
during various developmental stages of some Saudi Arabian date
cultivars. J. Food Sc., 47: 489–492.
Shafiee, S. , A. M. Motlagh, A. R. Didar and S. Minaee. 2008.
Investigation the effect of skin on mechanical behaviour of apple. J.
Food Tec., 6(2): 86 -91.
Shigley, J. E., C. R. Mischke, C. R. and R. G. Budynas. 2008.
Mechanical engineering design. MC Graw-Hill, Singapore.
Snedecor, G. A. and W. G. Cochran. 1976. Statistical Method. Iowa
State Univ. Press, Ames.
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1147 -
Terdwongworakul A., S. Chaiyapong, B. Jari mopas, and W.
Meeklangsaen. 2009. Physical properties of fresh young Thai
coconut for maturity sorting. Biosys. Eng. 103: 208–216.
585.421035.7
4.5922.01
46.1876.50
0.620.76
0.150.26
0.130.17
PROCESS ENGINEERING
Misr J. Ag. Eng., July, 2012
- 1148 -
237.33
467.782.545.30
7.7822.38
272.09485.45
5.616.58
7.7830.0
0.1071
0.2603
3
0.00150.0094
3
0.01150.0318
3
141106121
