Abstract: Some physical and mechanical properties of safflower seed were determined as a function of moisture content in the range from 7.4 to 9.2%. The dimensions of the length, width and thickness (major, medium and minor axes) varied from 7.27 to 7.81 mm, 3.5 to 3.79 mm and from 2.8 to 3.5 mm, respectively. The geometric mean diameters, the weight, thousand kernel weight, sphericity and porosity values increased from 4.46 to 4.82 mm, from 0.054 to 0.07 g, from 52.68 to 68.8 g, from 47.14 to 48.83% and from 40.7 to 44.2%, respectively. The static coefficient of friction for four structural surfaces increased from 25.36 to 29.99 for galvanized metal surface, from 22.2 to 26.83 for painted metal surface, from 23.92 to 25.05 for plywood and from 27.56 to 31.88 for textile (with plywood and textile grains parallel to the direction of movement). While fracture force increased from 42.4 to 63.8 N with increasing moisture content, insertion and crushing forces decreased from 48.64 to 30. 65 and from 75.39 to 62.3 N, respectively.
INTRODUCTION
Safflower (Carthamus tinctorius L.) has been cultivating almost all over the world but particularly, it is an important oil plant cultivated as oilseed in arid and semi-arid regions of India, Mexico, the USA, Ethiopia and Australia. During the period of 2000-2003, world safflower production was between 638000-1086514 tons (Anonymous, 2004). Worldwide India is the largest producer of safflower, but almost whole production is consumed internally. While safflower oil finds usage as an important vegetable oil in developing countries, in developed countries it is used in various sectors of the industry such as industrial oil, food coloring and flavoring material, textile dye preparing.
The safflower seed consist of a pericarp, two cotyledons and an embryo. The hull proportion for one seed various from 18 to 59% of the seed total weight related to varieties (Baümler et al., 2004). In the oil industry, the dehulling of the seeds before other production steps must be done. In these all stages, mechanical properties of safflower such as hardness, cracking and crushing forces are important in addition to physical properties to plan the processes and design the equipments for drying, storage, aeration etc.
Although a lot of researches on physical and some engineering properties were carried out for different seed types, such as pumpkin seeds (Joshi et al., 1993), lentil seed (Carman, 1996), guna seed (Aviara et al., 1999), sunflower (Gupta and Das, 2000), sorrel seed (Omobuwajo et al., 2000), arecanut kernels (Kaleemullah and Gunasekar, 2002) and caper seed (Dursun and Dursun, 2005), there are few investigations about physical and mechanical properties of safflower. Baümler et al. (2004) determined effects of 3 thermal pre-treatments on the seed dehulling ability. They reported that cooling the safflower seeds previously at -5°C allowed increasing the dehulling ability respect to the obtained at the reference temperature. Baümler et al. (2006) were studied on some physical properties of safflower and rupture force of the seed for different positions of seed.
The objective of this study was to determine the effects of moisture content (7.4-9.2% in dry base) on some physical and mechanical properties such as fracture, insertion and crushing forces of safflower seeds typically cultivated in Turkey. In addition to these properties static friction coefficients for 4 different surfaces namely galvanized sheet metal, plywood, painted sheet metal and textile were determined to obtain necessary data for designing of post harvest technology equipments that can be used for processes of safflower.
MATERIALS AND METHODS
Dincer variety safflower seeds used to carry out experiments. Safflower seeds were manually cleaned from foreign materials such as broken and immature seeds. The initial moisture content was determined by using air-oven methods (USDA-FGIS, 1986). Initial moisture content of the seeds was found as 7.4% (d.b.). Mean values of measured physical properties of safflower with different moisture contents have been shown in Table 1.
The seeds with desired moisture content were obtained by adding calculated amount distilled water (Baümler et al., 2006). All the tests were carried out with three replications for 4 moisture content namely 8.1, 8.7 and 9.2 in addition to initial content (7.4%).
To determine the length, width, thickness, weight, 30 seeds were selected randomly with 3 replications. Dimension properties was carried out by using a vernier caliper with an accuracy of ±0.01. Weight values of single seeds and one-thousand seed weight were obtained with an electronic balance with accuracy of 0.001 g. Some of determined physical properties were given as seen in Table 1.
The geometric mean diameter values (Gmd) were calculated according to Eq. (1) (Song and Litchfield, 1991):
| (1) |
Where a is length, b is width and c thickness of safflower seeds in mm.
| Table 1: | Some mean physical properties of safflowers |
According to Mohsenin (1980) sphericity of safflower seeds was calculated with Eq. (2) by values of length (L), width (W) and thickness (T):
| (2) |
One thousand kernels weight was obtained by using electronic balance with 0.001 accuracy. For this aim 200 seeds were selected at random from each of the five lots to obtain the 1000 seeds required (Omobuwajo et al., 2000). Subsequently the true density values (ρt) were determined as the ratio of the mass of the sample of the seed to the solid volume occupied by the sample by using electronic balance and pycnometer (liquid displacement method).
| Fig. 1: | Porosity measurement apparatus (Kocabiyik et al., 2004) |
Porosity values were measured by using an apparatus (Fig. 1) that works according to Ideal Gas Law (Kocabiyik et al., 2004). For this aim seed material was divided 3 lots for every moisture content separately, namely 12 lots were obtained.
Fracture force, insertion force and crushing force values were determined by using Algol handy type force gauge by using its different apparatus (heads) with different shapes (Fig. 2).
| Fig. 2: | Measurements of mechanical properties (1: Force gauge, 2, 3, 4: Compression heads, 5: Safflower seed) |
Coefficients of friction between safflower seeds and 4 different surfaces namely galvanized sheet metal, plywood, painted sheet metal and textile surfaces were measured with a experimental setup. In this system a platform was inclined gradually with a screw device until the safflower seed just started to slide down and the angle of tilt a was read from a graduated scale. The angle of the inclined surfaces and of repose for that sample was measured. The coefficient of friction, μ, is equal to the tangent of the repose angle, α, for the safflower seed. It was calculated from the following relationship (Mohsenin, 1980):
Where (μ) is the coefficient of friction and α is the angle of tilt in degree.
RESULTS AND DISCUSSION
Mean values of measured physical properties for individual kernels have been shown in Table 1. As shown in Table 1 dimensions and length and Geometric Mean Diameter of safflower kernels increase linearly while moisture content increases. Width values increase exponentially with increasing of moisture content. In addition to this, thickness, weight, 1000 kernel weight, sphericity, porosity values increase polynomial by increasing of moisture content.
| Table 2: | Relationship between physical properties and moisture contents (M) |
| Table 3: | Mean values of mechanical properties of safflower related to moisture content |
| Table 4: | Mean values of friction coefficients of safflower related to 4 different moisture contents and 4 different surfaces |
| Table 5: | Variance analysis of static friction coefficients |
| Table 6: | Multiple comparisons and different groups for friction coefficient according to Scheffe test |
| * The mean difference is significant at the 0.05 level | |
Model equations for relationships and R-squared values were shown in Table 2. True density values of safflower also slightly increased by increasing of moisture content.
As shown in Table 3 while fracture force increases, insertion and crushing forces decrease with increasing of moisture contents. These can be explained that husk becomes softer and week due to absorption of water on the other hand inside part of seed in husk swells up and fill the clearance between this part and husk. This causes structurally turgid and resulted in an increase in fracture force, decrease insertion force and crushing force.
The static coefficient of friction for safflower seed, determined with respect to four different structural surfaces for four different moisture content. Mean static friction coefficients were shown in Table 4. The static coefficient of friction values increase by increasing of moisture content values (Table 4). While mean friction coefficients obtained with galvanized sheet metal, painted sheet metal, plywood and textile surfaces were determined as 25.36, 22.2, 23.92, 27.56 for the 7.4% moisture content, they were determined as 29.99, 26.83, 25.05 and 31.88 for the 9.2% moisture content, respectively. The smallest friction coefficient was determined for painted metal sheet at 7.4% and the biggest friction coefficient was determined for textile surface at 9.2 %.
Difference between groups was found important as statistically at 0.05 significance level (Table 5). Different groups were shown in Table 6. As seen in this table difference between 2, 3 and 4 groups were found significant at 0.05 importance level.
CONCLUSIONS
The investigation of the some physical and mechanical properties of safflower seed as a function of moisture content revealed the following:
According to results, all measured and calculated dimensional properties (length, width, thickness, geometric mean diameter), one kernel weight and thousand kernel weight, true density, sphericity and porosity of safflower increased as the moisture content increased from 7.4 to 9.2% (d.b.).
The static coefficient of friction increased with increasing moisture content for all surfaces. Maximum static coefficient values were found for textile surface. Difference between friction coefficients was found important as statistically at 0.05 significance level. As the fracture force increased, insertion and crushing forces decreased with increasing of moisture contents.