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MECHANICAL BEHAVIOR AND PHYSICAL PROPERTIES OF CHICKEN EGG AS AFFECTED BY DIFFERENT EGG WEIGHTS EBUBEKIR ALTUNTAS1,3 and AHMET SEKEROGLU2 1

Department of Agricultural Machinery 2

Department of Animal Science Agricultural Faculty Gaziosmanpasa University 60240 Tokat, Turkey

Accepted for Publication February 19, 2008

ABSTRACT This study was carried out to determine the effect of egg weight on physical properties and mechanical behavior under compression of chicken eggs. Four different weights – including medium, large, extra large and jumbo – were used. Physical properties of chicken egg – such as size, geometric mean diameter, sphericity, volume, surface area, packaging coefficient of eggs, shape index, shell thickness and static coefficient of friction on various surfaces – were determined. The mechanical properties of chicken egg to compression as effected by egg weight were determined in terms of average rupture force, specific deformation and rupture energy along x- and z-axes at different compression speeds. The length, width, geometric mean diameter, unit mass, surface area, egg volume and packaging coefficient increased as the egg weight increased. The average shape index and shell thickness values ranged from 78.37 to 79.56, and 0.400 to 0.387 mm for the eggs tested, respectively. The static coefficients of friction on various surfaces, namely, glass, plywood, galvanized metal, rubber and chipboard, increased linearly with increasing egg weight tested. The rubber surface presented the maximum friction followed by plywood, chipboard, galvanized metal and glass. The force required to initiate egg rupture on the z-axis decreased as egg weight increased from medium to jumbo. The specific deformation and rupture energy values observed for chicken eggs compressed along the z-axis were higher than the values obtained when testing eggs in the x-back and x-front orientations. The results indicated that the rupture force along all three axes is highly dependent on the egg weight over the compression speed ranges investigated. 3

Corresponding author. TEL: +90-356-2521616; FAX: +90-356-2521488; EMAIL: ealtuntas@ gop.edu.tr

Journal of Food Process Engineering 33 (2010) 115–127. All Rights Reserved. © Copyright the Authors Journal Compilation © 2008 Wiley Periodicals, Inc. DOI: 10.1111/j.1745-4530.2008.00263.x

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E. ALTUNTAS and A. SEKEROGLU

PRACTICAL APPLICATIONS The mechanical and physical properties of animal and plant materials are necessary considerations in the design and effective utilization of the equipment used in the transportation, processing, packaging and storage of agricultural products. Several factors – such as age, breed and weight of chicken – influence the size of an egg. Eggs are available in different sizes according to weight, including peewee, small, medium, large, extra large and jumbo. Even a slight shift in egg weight influences size classification which is one of the factors considered when eggs are priced. Egg size and the eggshell thickness are strongly related to each other. A chicken egg is a packaged food and an important quality aspect of the packaged egg material is the mechanical strength of the eggshell. Eggshell quality depends on egg size and weight. Egg properties such as shape index and shell thickness affect the proportion of damaged eggs during handling and transport. Eggshell strength has been described using various variables such as thickness of eggshell, shell stiffness and rupture force. Eggshells must be strong enough to prevent cracking in order to preserve the embryo until hatching. Shell strength is necessary to prevent damage from handling and to preserve eggs during transport from farm to market. As egg weight increases during the production period, eggshell thickness and breaking strength usually decrease. The rupture force of chicken eggs depend on various egg properties such as egg specific gravity, egg mass, egg volume, egg surface area, egg thickness, shell weight and compression speed. For this reason, egg production, processing and packaging systems must be designed while taking these criteria into consideration such as physical properties of eggs and their resistance to damage through mechanical shock.

INTRODUCTION To optimize the equipment design and the effective utilization of the equipment used in the transportation, processing, packaging and storage of agricultural products, the physical and mechanical properties of agricultural (animal and plant) materials must be known. To preserve eggs during transport from farm to market, eggshells must be strong enough to prevent cracking (Altuntas and Sekeroglu 2008). Eggs are available in different sizes according to weight, which include peewee, small, medium, large, extra large and jumbo. The mechanical strength of the eggshell is an important quality aspect of the packaged egg material. Eggshell quality depends on egg size and weight. Eggshell thickness and breaking strength usually decrease while egg weight increases during the production period. Egg shape index and shell thickness

MECHANICAL BEHAVIOR AND PHYSICAL PROPERTIES OF CHICKEN EGGS

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affect the proportion of damaged eggs during handling and transport (Anderson et al. 2004). These physical properties of eggs and their resistance to damage through mechanical shock can be characterized by measures such as rupture force, specific deformation and rupture energy (Voisey and Hunt 1969; Abdallah et al. 1993; Altuntas and Sekeroglu 2008). The various egg physical properties such as egg mass and volume, surface area, shell thickness and weight affect the mechanical properties of chicken eggs. The quasi-static, nondestructive compression of an egg between two parallel steel plates is a common technique for the measurement of the shell strength of a chicken egg (De Ketelaere et al. 2002). The strongest correlation was found between the physical and the mechanical properties of chicken eggs (De Ketelaere et al. 2002; Narushin et al. 2004; Altuntas and Sekeroglu 2008). Several factors influence the size of an egg. The major factor is the age of the hen. As the hen ages, her eggs increase in size. The breed of the hen from which the egg comes is a second factor. Weight of the bird is another. Pullets that are significantly underweight at sexual maturity will produce small eggs. Environmental factors that lower egg weights are heat, stress, overcrowding and poor nutrition. All of these variables are of great importance to the egg producer. Even a slight shift in egg weight influences size classification, which is one of the factors considered when eggs are priced. Careful flock management benefits both the hens and the producer. Sizes are classified according to minimum net weight expressed in oz per dozen. Egg sizes are jumbo (ⱖ70 g), extra large (65–70 g), large (56–65 g), medium (49–56 g), small (42–49 g) and peewee (35–42 g). Medium, large and extra large are the sizes most commonly available (USDA 2000; FAO 2003). Limited research has been conducted on the physical and mechanical properties of chicken and Japanese quail eggs by testing them against various compression loads (Narushin et al. 2004; Polat et al. 2007; Altuntas and Sekeroglu 2008). The eggshell strength is highly dependent on compression speed (Voisey and Hunt 1969; Altuntas and Sekeroglu 2008). Altuntas and Sekeroglu (2008) investigated the effect of egg shape on the mechanical behavior of chicken eggs under a compression load. However, there is a lack of technical information in the scientific area with regard to the physical properties and mechanical behavior of chicken eggs as affected by chicken egg weight. The objective of this study was to investigate egg weight-dependent physical properties, namely, size, geometric mean diameter, sphericity, volume, surface area, packaging coefficient of eggs, shape index, shell thickness and static coefficient of friction on various surfaces were determined. The mechanical properties of chicken egg to compression as effected by egg weight were determined in terms of average rupture force, specific deformation and rupture energy along x-front, x-back and z-axes.

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MATERIALS AND METHODS In this study, the Lohmann-type chicken brown eggs were used. In this experiment, mean egg weight for chicken eggs were 52.23 g, 57.38 g, 64.07 g and 71.58 g for medium, large, extra and jumbo eggs, respectively. The Lohmann-type chicken eggs were obtained from a breeding unit in Tokat, Turkey. The average air temperature and relative humidity were 22C and 55%, respectively, during the egg collection period. The chickens were 33 weeks old and the facility housed four chickens per cage. The composition of the diet used to feed the laying chicken is presented in Table 1. The research was designed as a split-plot in three replications with egg weight as the main factor and compression axis and speed as subfactors. In this study, 10 replications were made for each physical and mechanical property of chicken eggs. Results of the experiment were analyzed using analysis of variance and the means were compared using the least significant difference test (Gomez and Gomez 1984). The length and width (thickness) of the chicken eggs were measured by a dial micrometer with an accuracy of 0.01 mm. To obtain the unit mass of the chicken eggs, they were measured by an electronic balance with an accuracy of 0.001 g. The geometric mean diameter (Dg) of the chicken eggs was calculated by using the following relationships as seen in Eq. (1) (Mohsenin 1970):

Dg = ( LW 2 )

13

(1)

where L is the length and W is the width (thickness) in mm. TABLE 1. COMPOSITION OF CHICKEN FEEDING INGREDIENTS, METABOLIZABLE ENERGY (kcal/kg) AND NUTRIENT VALUES Ingredients

%

Analyzed nutrient contents

%

ATK (28%) ATK (36%) Wheat Maize Full fat soybean SK (44%) Shell of oyster and mussel Di-calcium phosphate Meat and bone flour Vegetable oil Mosaic

5.00 5.00 15.00 41.89 12.50 0.30 3.3 0.30 4.00 0.80 6.00

Premix DL-methionine Vimartox Vimarzyme Crude protein ME (kcal/kg) Calcium Phosphorus available Methionine Methionine + cystine Lysine

0.25 0.10 0.10 0.06 18.08 2,865 3.74 0.42 0.41 0.65 0.89

ATK, sunflower seed cake; SK, soybean seed cake; ME, metabolizable energy.


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The sphericity (F) is defined as the ratio of the geometric mean diameter of a sample of egg to the length of the egg (Mohsenin 1970). The surface area of the chicken eggs was found by analogy with a sphere of the same geometric mean diameter, using an expression cited by Olajide and Ade-Omowaye (1999) and Altuntas and Sekeroglu (2008):

Sa = π Dg2

(2)

where Sa is the surface area in mm2 and Dg is the geometric mean diameter in mm. Egg shape index is defined as the ratio of the width of a sample of egg to the length of the egg (Anderson et al. 2004). The shell thickness was determined according to Monira et al. (2003). The volume (Ve) of chicken eggs sampled was determined using Eq. (3):

π Ve = ⎛ ⎞ × LW 2 ⎝ 6⎠

(3)

Packaging coefficient (Pc) is defined as the ratio of the volume of a sample of egg to packed total volume (mm3) in a 150 ¥ 100 ¥ 200-mm long rectangular box (Polat et al. 2007; Altuntas and Sekeroglu 2008). To determine the coefficient of static friction, the sample egg was placed on the friction surfaces such as glass, galvanized metal, chipboard, plywood and rubber, and then the surface was gradually tilted from its initial horizontal position by the adjustable screw. When the egg starts sliding over the friction surface, horizontal and vertical height values are measured at this point. The tangent value of the angle gave the coefficient of friction (Baryeh and Mangope 2003; Polat et al. 2007; Altuntas and Sekeroglu 2008). A biological material test device (Instruction Manual for Materials Testing Machines/BDO-FB 0.5 TS; Zwick Roell, Ulm, Germany) was used to determine the mechanical properties of the eggs tested. This device has three main components: a moving platform, a driving unit and a data acquisition (load cell, personal computer card and software) system (Altuntas and Yildiz 2007). The egg sample was placed on the moving platform and loaded at three compression speeds (0.33, 0.66 and 0.99 mm/s) and pressed with a plate fixed on the load cell until the egg ruptured. All these speeds are relevant with studies by several researchers (Voisey et al. 1969; De Ketelaere et al. 2002; Buchar et al. 2003; INSTRON 2007; Altuntas and Sekeroglu 2008). From the compression speed and time, eggshell deformation was recorded. The rupture force and deformation were measured directly from the plotted force– deformation curve (Altuntas and Sekeroglu 2008). The force–deformation curves were obtained at each loading orientation and compression speed level

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for each egg weight (Mamman et al. 2005). The x- and z-compression axes of an egg were used to determine the rupture force, specific deformation and rupture energy. There were three replications for each test and 10 samples were used. The x-axis is the longitudinal axis through the length measured as x-front (xf-axis) and x-back (xb-axis), while the z-axis is the transverse axis containing the minor dimension (width or thickness) at right angles with respect to the x-axis (Altuntas and Sekeroglu 2008). The specific deformation was obtained using Eq. (4):

⎡ L − Ld ⎤ ε = ⎢ un ⎥ × 100 ⎣ Lun ⎦

(4)

where e is the specific deformation (%), Lun (mm) is the undeformed egg length measured in the direction of the compression axis and Ld (mm) is the deformed egg length measured in the direction of the compression axis (Braga et al. 1999). Energy absorbed (E) of the chicken egg at the moment of rupture was determined by calculating the area under the force–deformation curve (Braga et al. 1999).

RESULTS AND DISCUSSION Physical Properties The physical properties of the chicken eggs are presented in Table 2. The mean length and width (or thickness), geometric mean diameter and unit mass of the chicken eggs ranged from 52.90 to 58.63 mm, 41.87 to 46.61 mm, 45.09 to 50.11 mm and 52.23 to 71.58 g for each of the four egg weight categories tested, respectively. The mean sphericity ranged from 0.847 to 0.855%; packaging coefficient 0.603 to 0.817; surface area 6,387.4 to 7,890.7 mm2; and volume of chicken eggs 918.3 to 1,138.0 mm3 for the eggs tested with egg weights in increasing order. The length, width, geometric mean diameter, unit mass, surface area, egg volume and packaging coefficient increased as egg weight increased. In this study, the mean shape index (SI) values were 79.18, 78.63, 78.37 and 79.56 for medium, large, extra large and jumbo eggs, respectively. Shell thickness ranged from 0.400 to 0.387 mm. De Ketelaere et al. (2002) and Altuntas and Sekeroglu (2008) observed that chicken eggs’ shell thickness range from 0.32 mm to 0.36 mm and 0.34 to 0.35 mm, respectively. The static coefficients of friction ranged from 0.021 to 0.042 for glass, 0.040 to 0.061 for galvanized metal, 0.049 to 0.077 for chipboard, 0.062 to


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TABLE 2. EFFECT OF EGG WEIGHT ON SOME PHYSICAL PROPERTIES OF CHICKEN EGGS Physical properties

Medium

Large

Extra large

Jumbo

Length (mm) Width (mm) Geometric mean diameter (mm) Unit mass (g) Sphericity (%) Shell thickness (mm) Shape index Surface area (cm2) Volume (cm3) Packaging coefficient

52.90 ⫾ 1.04 41.87 ⫾ 0.93 45.09 ⫾ 0.64

54.79 ⫾ 1.25 43.05 ⫾ 0.55 46.47 ⫾ 0.40

57.01 ⫾ 1.27 44.65 ⫾ 0.57 48.25 ⫾ 0.38

58.63 ⫾ 1.31 46.61 ⫾ 0.83 50.11 ⫾ 0.62

52.23 ⫾ 1.64 0.853 ⫾ 0.019 0.400 ⫾ 0.03 0.792 ⫾ 0.26 63.9 ⫾ 1.83 0.92 ⫾ 0.04 0.603 ⫾ 0.054

57.38 ⫾ 1.588 0.849 ⫾ 0.017 0.386 ⫾ 0.02 0.786 ⫾ 0.24 67.9 ⫾ 1.18 0.97 ⫾ 0.02 0.680 ⫾ 0.004

64.07 ⫾ 1.278 0.847 ⫾ 0.017 0.382 ⫾ 0.03 0.784 ⫾ 0.24 73.1 ⫾ 1.17 1.04 ⫾ 0.03 0.729 ⫾ 0.003

71.58 ⫾ 2.849 0.855 ⫾ 0.018 0.387 ⫾ 0.038 0.796 ⫾ 0.25 78.9 ⫾ 1.98 1.14 ⫾ 0.04 0.817 ⫾ 0.025

Measurements were made with 10 replicates, numbers following ⫾ are standard deviations.

TABLE 3. STATIC COEFFICIENT OF FRICTION OF CHICKEN EGGS WI˙TH DIFFERENT WEIGHTS Coefficient of friction

Medium

Large

Extra large

Jumbo

Galvanized metal Plywood Rubber Chipboard Glass

0.040 ⫾ 0.030 0.062 ⫾ 0.038 0.080 ⫾ 0.030 0.049 ⫾ 0.010 0.021 ⫾ 0.004

0.047 ⫾ 0.016 0.067 ⫾ 0.037 0.079 ⫾ 0.031 0.059 ⫾ 0.015 0.033 ⫾ 0.009

0.060 ⫾ 0.030 0.080 ⫾ 0.032 0.090 ⫾ 0.019 0.070 ⫾ 0.040 0.043 ⫾ 0.021

0.061 ⫾ 0.017 0.094 ⫾ 0.051 0.110 ⫾ 0.042 0.077 ⫾ 0.050 0.042 ⫾ 0.027

Measurements were made with 10 replicates, numbers following ⫾ are standard deviations.

0.094 for plywood, 0.080 to 0.110 for rubber for medium to jumbo egg weight tested (Table 3). The static coefficients of friction increased linearly with respect to egg weight for all the five surfaces investigated. The static coefficient of friction was the highest in rubber, followed by plywood, chipboard, galvanized metal and glass. In this study, rubber offered the maximum friction. The glass gave the least amount of friction because of its smooth and polished surface. Similar results have been reported for plant materials such as cactus pears (Kabas et al. 2006), sweet corn seeds (Coskun et al. 2006) and plum cultivars (Ertekin et al. 2006). Mechanical Properties Rupture Force. The rupture forces for eggs measured when loading along the lateral axis (z-axis) were found to be 41.31–40.46 N for medium,

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40.39–38.97 N for large, 39.69–38.29 N for extra large and 39.64–38.16 N for jumbo eggs. The rupture force decreased from 45.62 to 42.88 N, 42.55 to 40.90 N, 41.26 to 39.50 N and 40.84 to 38.90 N for the egg weight categories ranging from medium to jumbo eggs, respectively (Fig. 1), as the compression speed increased from 0.33 to 0.99 mm/s. The force required to initiate egg rupture on the z-axis decreased as egg weight increased from medium to jumbo. The results indicated that the rupture force along all three axes is highly dependent on egg weight over the compression speed ranges investigated. The highest rupture forces required when loading along the x-front axis for each egg weight category were found to be 50.77–46.99 N for medium, 44.93–42.59 N for large, 43.23–40.80 N for extra large and 42.16–39.81 N for jumbo. For all the curves, greater force was required to rupture at the lowest compression speed. The effect of egg weight, compression axes and speed on rupture force were significant (P < 0.01). The rupture force values were higher in the medium egg weight than the other egg weight categories and lower in z-axis compared with xf- and xb-axes. This is because of higher values of shell thickness and surface area of the medium egg weight than the other egg weight categories. The strongest correlation was found between rupture force and shell percentage (De Ketelaere et al. 2002; Narushin et al. 2004). The rupture force of chicken eggs depended on various egg properties such as egg weight, egg surface area and egg thickness. Eggshell thickness

rupture force (N)

60

0,33 mm/s 0,66 mm/s 0,99 mm/s

50

40

30 Xf axis

Xb - Z axis axis

Medium (52.23 g)

Xf axis

Xb - Z axis axis Large (57.38 g)

Xf axis

Xb axis

Zaxis

Extra-large (64.07 g)

Xf axis

Xb axis

Zaxis

Jumbo (71.58 g)

egg weight (g) FIG. 1. EFFECTS OF EGG WEIGHT, COMPRESSION AXES AND SPEED ON RUPTURE FORCE OF CHICKEN EGGS


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ranged from 0.400 to 0.387 mm and surface area measured 63.9 to 78.9 cm2 for medium to jumbo egg weight categories. The force required to initiate egg rupture on the z-axis decreased as egg weight increased. This may be because of the contact surface of the z-axis of eggs that provides lower resistance to rupture than those of xf- and xb-axes. The results are similar to those reported by De Ketelaere et al. (2002), Zlatica et al. (2003); Altuntas and Sekeroglu (2008); and Polat et al. (2007). The average rupture force for chicken eggs has been reported to range from 30.9 N to 37.8 N and 33.4 N to 35.3 N (De Ketelaere et al. 2002; Zlatica et al. 2003). Altuntas and Sekeroglu (2008) reported that the rupture force decreased from 25.82 to 31.15 N as the compression speed increased for eggs with shape index values of 76. Polat et al. (2007) also reported that the mean rupture force of Japanese quail eggs ranged from 10.51 N to 6.83 N along the x- and z-axes. Specific Deformation. The effect of egg weight on specific deformation was not significant, whereas the effects of compression axes and speed at specific deformation were significant (P < 0.01). The specific deformation values ranged from 0.50 to 0.61%, 0.44 to 0.60%, 0.40 to 0.65 and 0.46 to 0.58% for medium, large, extra large and jumbo eggs, respectively, as the compression speed increased in the three test speeds. The results show that the specific deformation along any of the xf-, xb- and z-axes is highly dependent on the egg weight over the range of compression speeds investigated. The specific deformation increased along the xf-axis, xb-axis and z-axes as both the egg weight and compression speed increased (Fig. 2). The xb-loading orientation rendered the least specific deformation as z-axes had the highest specific deformation. The specific deformation values for chicken eggs compressed along the z-front axis were higher than those compressed along the xf- and xb-axis. The specific deformation measured while loading along the lateral axis (xb-axis) were found to be 0.43–0.54% (medium); 0.37–0.55% (large); 0.34– 0.48% (extra large) and 0.38–0.52% (jumbo). The highest specific deformation values when loading along the z-front axis were observed to be 0.57– 0.73% in medium egg weight; 0.56–0.73% in large; 0.50–0.75% in extra large; and 0.50–0.75% in jumbo. This may be because of the contact surface of the z-axis of eggs that provides lower resistance to rupture and higher deformation than those of xf- and xb-axes. The specific deformation when loading along the xf-axis were measured as 0.50–0.56%, 0.38–0.51%, 0.35–0.74% and 0.51–0.48% for medium, large, extra large and jumbo egg weight categories, respectively. The deformation values for xf-axis were higher than those for xb- and z-axes. This may be because the front of the chicken egg is more flexible than the other two axes and is more resistant to rupture along the xf-axis.

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0,8 0,7 0,6 0,5 0,4 0,3 0,2

Medium (52.23 g)

Large (57.38 g)


Z - axis

Xb - axis

Xf - axis

Z - axis

Xb - axis

Xf - axis

Z - axis

Xb - axis

Xb - axis

Xf - axis

0

Xf - axis

0,33 mm/s 0,66 mm/s 0,99 mm/s

0,1

Z - axis

specific deformation (%)

0,9

Jumbo (71.58 g)

egg weight (g) FIG. 2. EFFECTS OF EGG WEIGHT, COMPRESSION AXES AND SPEED ON SPECIFIC DEFORMATION e (%) OF CHICKEN EGGS

The specific deformation values ranged from 0.36 to 0.53%, 0.41 to 0.50% and 0.36 to 0.54% for sharp, normal and round eggs, respectively, as the compression speed increased in the three compression speeds. The specific deformation also increased along the compression axes as both the SI value and compression speed increased (Altuntas and Sekeroglu 2008). The mean deformation values of Japanese quail eggs ranged from 0.9 to 1.5 mm for the compression axes. The deformation varied from 1.5 to 1.8 mm (xf-axis); 0.9 to 1.0 mm (xb-axis); and 1.0 to 1.2 mm (z-axis) (Polat et al. 2007). Rupture Energy. The results showed that the rupture energy along any of the test axes is represented in Fig. 3. The effect of compression speed on rupture energy was significant (P < 0.01), whereas the effect of egg weight and compression axes on rupture energy were not significant. The rupture energy is highly dependent on the compression speed and egg weight value of the sample tested. The energy of rupture decreased along the x- and z-axes as the egg weight increased through the four test categories. The least energy to rupture was obtained for chicken egg loaded along the xf-axis while those loaded along the z-axis required the highest rupture energy. The rupture energy values were 5.10–5.96 mJ (medium), 4.34–6.35 mJ (large), 4.04–5.32 mJ (extra large) and 4.57–5.83 mJ (jumbo) when loading along the xb-axis of the eggs tested. Absorbed energy to rupture the shell along the xb-axis is lower than the other two orientations. The rupture energy values


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9

rupture energy (mJ)

8 7 6 5 4 0,33 mm/s 0,66 mm/s 0,99 mm/s

3 2 Xf axis

Xb axis

Zaxis

Medium (52.23 g)

Xf axis

Xb axis

Zaxis

Large (57.38 g)

Xf axis

Xb axis

Zaxis


Xf axis

Xb axis

Zaxis

Jumbo (71.58 g)

egg weight (g) FIG. 3. EFFECTS OF EGG WEIGHT, COMPRESSION AXES AND SPEED ON RUPTURE ENERGY (mJ) OF CHICKEN EGGS

were determined to be 4.90–6.29 mJ, 4.89–6.32 mJ, 4.47–6.43 mJ and 4.66– 6.68 mJ for each of the four egg weight categories (in increasing order), respectively, when loading along the z-front axis. These results are similar to those reported by Altuntas and Sekeroglu (2008) and Polat et al. (2007). The rupture energy values were 2.92–3.14 mJ (sharp), 3.64–3.58 mJ (normal) and 3.01–3.30 mJ (round) when loading along the xb-axis of the eggs tested (Altuntas and Sekeroglu 2008). The mean rupture energy values of Japanese quail eggs were 7.88 mJ, 3.41 mJ and 4.35 mJ along the xf -, xb and z-axis, respectively (Polat et al. 2007).

CONCLUSIONS The physical properties of chicken eggs such as length, width, geometric mean diameter, unit mass, surface area, egg volume and packaging coefficient increased as egg weight increased. The static coefficients of friction on various surfaces, namely, glass, plywood, galvanized metal, rubber and chipboard, increased linearly with increasing egg weight tested. The rubber surface offered the maximum friction followed by plywood, chipboard, galvanized metal and glass. The results indicated that the mechanical properties are highly dependent on egg weight value in all the three compression speeds. The effect of egg weight on rupture force was statistically significant in the same way as

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the effects of compression axes and speed on rupture force and specific deformation were statistically significant. The specific deformation and rupture energy values observed for chicken eggs compressed along the z-front axis were higher than the values obtained when testing eggs in the x-back and x-front orientations.

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