Physical Properties of Guna Seeds

J. Agric. Engng Res. (1999) 73, 105}111 Article No. jaer.1998.0374, available online at http://www.idealibrary.com.on

RESEARCH PAPERS

Physical Properties of Guna Seeds N. A. Aviara; M. I. Gwandzang; M. A. Haque Department of Agricultural Engineering, University of Maiduguri, Maiduguri, Nigeria Department of Agricultural Sciences and Technology, Ramat Polytechnic, Maiduguri, Nigeria (Received 29 September 1997; accepted in revised form 6 October 1998)

The study was undertaken to determine the physical properties of guna seeds as a function of moisture content. The seeds tend to be #at and oval in shape. At the moisture content of 4)7% d.b., measurements yielded an average 1000 seed weight of 0)041 kg, major axis of 8)80 mm, intermediate axis of 5)27 mm, and minor axis of 2)04 mm, while the average surface area was 104 mm. In the moisture range from 4)7 to 39)3% d.b., true and bulk densities decreased from 870 to 680 kg/m and from 544 to 400 kg/m, respectively; porosity increased from 0)38 to 0)41; coe$cient of static friction from 0)41 to 0)98 over the surface of di!erent materials, and angle of repose from 28)07 to 43)583. Seed size, volume and 1000 seed weight also increased with the increase in moisture content.  1999 Silsoe Research Institute

Notation a b c f Q M P D <

major axis, mm intermediate axis, mm minor axis, mm static coe$cient of friction moisture content, % porosity seed volume, mm = one thousand seed weight, kg  o bulk density, kg/m @ o true density, kg/m R h angle of repose, deg P

1. Introduction Guna is a drought tolerant crop which belongs to the Cucurbitaceae family of #owering plants. It is mainly grown in the semi-arid region of Northeastern Nigeria. The Hausa name &&Guna'' has been used because its botanical taxonomy is still lacking in conclusive agreement. It is generally considered to be of the Citrullus species and has been referred to as Citrullus lanatus by Dalziel1 and Adamu and Dunham,2 Citrullus colocynthis by Gwandzang 3 and Colocynthis vulgaris by Willis 4 and Olorode.5 0021-8634/99/060105#07 $30.00/0

The crop is important for its seeds (Fig. 1), which have an average protein and oil content of 27 and 50%, respectively (Norton6) and serve as a good source of protein and vegetable oil for human and livestock consumption. Presently, the seeds are extracted either by manual maceration and washing of decayed fruits in a basket or scooping out pulp from fruit, sun drying and beating with a stick to release the seeds. Dehusking of seeds in carried out by pounding in a mortar using a wooden pestle. Prior to this, the seeds are soaked in water. Dehusking of seeds by striking in a jute bag against a wall is also practiced. Clean dehusked seeds (kernels) are obtained by winnowing. The seeds are packaged in jute, hessian or plastic bags and stored in warehouses. These methods of handling, processing and storing the seeds are not only energy sapping, rigorous and time consuming but also wasteful. Therefore, there is the need to develop improved methods of handling, processing and storing the seeds using suitable machines and equipment. To develop such methods and equipment, the physical properties of guna seeds need to be known. The properties may be moisture dependent and this can a!ect the adjustment and performance of the processing equipment. A range of moisture contents usually exist within which optimum performance is achieved and, therefore, the e!ect of moisture content on the physical properties of guna seeds is of important consideration in the design of the handling, processing and storage equipment. However, no work appears to have been

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 1999 Silsoe Research Institute

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Fig. 1. Guna fruit and seeds

carried out on the physical properties of guna seeds and their relationship with moisture content. The object of this study was to investigate some physical properties of guna seeds, namely size, volume, shape, surface area, 1000 seed weight, true density, bulk density, porosity, coe$cient of static friction on the surface of di!erent materials and angle of repose to determine whether the properties are moisture dependent. Methods for the determination of each of the properties were selected on the basis of simplicity, accuracy of results and wide acceptability. Several researchers7+19 described the size of cereal grains and seeds by measuring dimensions of the three principal axes. Makanjuola7 measured the size and shape of the seeds of two melon varieties and correlated the dimensions of the seeds and kernels, while Suthar and Das8, Ramakrishna9 and Joshi et al.10 evaluated and correlated the dimensions and mass of karingda seed and kernel, melon seed and kernel, and pumpkin seed and kernel, respectively. Dutta et al.11 employed the arithmetic mean of the three principal axes, their geometric average and e!ective diameter in calculating the volume of gram with results that approximately predicted the experimentally determined values. In determining the true density of seeds and grains, researchers have used either gas displacement8,13,19,20 or liquid displacement11,12,14,15,18 methods. The liquid displacement method is simpler and involves the immersion of a quantity of grain or seed fully in liquid (water or toluene) and noting the amount of liquid displaced. When water is used, a thin water-resistant coating is applied over the grain to prevent the absorption of

moisture during the experiment. Various investigators8,11,15,17,19,20 determined bulk density using the method which involves "lling a standard container with grain from a certain height, levelling the surface and weighing the content. Mohsenin12 described various methods of determining the porosity of seed grains, and a number of investigators8,11,12,16 employed its dependence on bulk and kernel densities to calculate its values at various moisture contents. The static coe$cient of friction of grains and seeds has been determined by various investigators8+11,14+19,21 using the inclined plane method. These investigations have shown that coe$cient of friction increases with moisture content and varies with the surface on which the grain slides. Various investigations8,11,14,15,19,21 on di!erent grains show that the dynamic angle of repose increases with moisture content. To determine this angle, a specially constructed box with a removable front panel has been used.

2. Materials and methods Guna seeds at the moisture content of 4)7% d.b. were obtained from Nguru in Yobe State, Nigeria. The seeds were cleaned and sampled for experiments using a multislot ri%e box divider. The moisture content of the seeds was determined using the ASAE22 standard method. Samples of seeds were conditioned to moisture contents in the range of 4)7}39)3% d.b. Samples of desired moisture level within the above range were prepared by adding calculated amounts of distilled water and

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Table 1 Axial dimensions of guna seeds (standard deviation in parentheses) Moisture content, % d.b.

Major axis (a), mm

Intermediate axis (b), mm

Minor axis (c), mm

4)7

8)80 (0)43)

5)27 (0)30)

2)04 (0)17)

5)37

4)56

4)46

8)5

8)87 (0)40)

5)30 (0)21)

2)07 (0)11)

5)41

4)60

4)57

15)3

9)01 (0)31)

5)38 (0)30)

2)15 (0)14)

5)51

4)71

4)74

25

9)20 (0)5)

5)41 (0)27)

2)26 (0)18)

5)62

4)82

5)00

39)3

9)45 (0)38)

5)72 (0)27)

2)43 (0)16)

5)87

5)08

5)40

sealing in polythene bags as reported by Dutta et al.11 and Fraser et al.19 Seed size was determined by measuring the dimensions of three principal axes of 100 randomly selected seeds, using a micrometer reading to 0)01 mm. One thousand seed weight was obtained with the help of an electronic balance reading to 0)001 g. The true density was determined using the water displacement method. A thin layer of araldite was used over the seeds to prevent moisture absorption. The average increase in weight due to the adhesive was negligible (less than 2%). Bulk density was determined using the AOAC23 method. Porosity was calculated from true and bulk densities using the relationship given by Mohsenin.12 Static coe$cient of friction of seeds on structural surfaces was determined using the inclined plane method described by Suthar and Das 8 and Dutta et al.11 Five structural surfaces were used: plywood with wood grains perpendicular to the direction of movement, plywood with wood grains parallel to the direction of movement, formica (generically known as papreg), galvanized steel sheet and Hessian bag material. In determining the dynamic angle of repose a box with no lid and a removable front panel8,11 was used. All the experiments were replicated "ve times at each moisture level, and the average values are reported.

Arithmetic mean Geometric mean Equiv. sphere 1/3 diameter ( ?>@>A ), diameter (abc) , e+ective diameter 3 51000 ) 1/3, mm mm mm (1000 MR L

signi"cantly di!erent for the three axes at one and "ve percent levels of signi"cance. Increase in dimension with moisture content may be taken as being uniform along the three axes. This explains the reason why seed shape remained unaltered with change in moisture content. The principal dimensions of the seed are shown schematically in Fig. 2. The dimensions of guna seeds were observed to be lower than those of melon7,9 large and medium sized karingda seed8 and pumpkin,10 and to lie within the same range as those of small size karingda seed.8

3.2. One thousand seed weight At the moisture content of 4)7% d.b., the one thousand seed weight obtained was 0)041 kg with a standard deviation of 6)8;10\ kg. One thousand seed weight = 

3. Results and discussion 3.1. Seed size Results of seed size measured at di!erent moisture contents are given in Table 1. These show that the three axial dimensions increased with moisture content in the moisture range of 4)7}39)3% d.b. The increase was not

Fig. 2. Principal dimensions of guna seed

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Fig. 3. Variation of one thousand seed weight with moisture content

was found to increase with moisture content M as shown in Fig. 3. A linear relationship between = and M was  obtained and this can be expressed using the regression equation as: = "0)388#4)419;10\M 

(1) 3.4. Bulk density

with a correlation coe$cient R of 0)94. Similar trends have been reported for other grains11,14,16 and seeds.15,19

3.3. ¹rue density True density o decreased from 870 to 680 kg/m as the  moisture content increased from 4)7 to 39)3% d.b. The variation was found to be linear and can be represented by the regression equation o "897)26!5)5M R

Fig. 4. Relationship between the true density o and the bulk R density o of guna seeds, with correlation coezcient R 2 @

(2)

with a correlation coe$cient, R of 0)99. The decrease of true density with increase in moisture content may be due to the seed composition. Decrease in water absorption caused by the oil globules and increase in swelling of the protein matrix with moisture content may have combined to cause the decrease in overall true density of the seed. At comparable moisture content, the true density of guna seed is less than that of karingda,8 melon9 and pumpkin10 seeds.

Bulk density o decreased from 544 to 400 kg/m in
the moisture range of 4)7}39)3% d.b. The following linear relationship was found to exist between them: o "564)4!4)2M (3)
with a correlation coe$cient, R of 0)99. This is opposite to the increase in bulk density with moisture content, which has been reported for other Cucurbita seeds.8,10,20 The decrease in bulk density of guna seeds may have resulted from increase in size with moisture content which gives rise to decrease in quantity of seeds occupying the same bulk volume. Also, the resistance of seeds to consolidation may have increased with moisture content as a result of increase in internal pressure. A plot of the experimentally determined data on true and bulk densities corresponding to various moisture contents is presented in Fig. 4 which also shows the equation that expresses the linear relationship existing between them.

P HY SI CA L PR O PE RTI ES O F G U N A SE ED S

3.5. Porosity The porosity calculated for relevant experimental data increased from 0)38 to 0)41 as the moisture content increased from 4)7 to 39)3% d.b. The relationship existing between porosity P and moisture content D appears linear and can be expressed by the regression equation: P "0)37#0)00106M D

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between them are presented in Fig. 5. These show that seed volume increases linearly with moisture content. Values obtained by calculation using the arithmetic mean diameter were signi"cantly greater than those obtained using the geometric mean and e!ective diameters. The geometric mean diameter gave closer values to the experimentally determined volume, and can be conveniently used for the theoretical determination of seed volume.

(4)

with a correlation coe$cient R of 0)96. This is unlike the porosity of karingda seed8 which decreases with increase in moisture content. Increase in moisture content may have caused a decrease in the cohesion of the bulk seed as a result of resistance to consolidation. The porosity of guna seeds is found to be lower than that of karingda8 and pumpkin10 seeds.

3.7. Shape and surface area Guna seeds tend to have the shape of a #at disc with a major axis which is signi"cantly greater than the intermediate axis. The seeds may therefore be described as being oval in shape. At the moisture content of 4)7% d.b., average surface area was determined by the projection method12 and found to be 104 mm with a standard deviation of 4)82 mm.

3.6. Seed volume Seed volume was found to be a function of moisture content in the moisture range of 4)7}39)3% d.b. A plot of experimentally obtained values against moisture content and the regression equation expressing the relationship

Fig. 5. Variation of guna seed volume V with moisture content M; correlation coezcient R 2

Fig. 6. Variation of guna seed static coezcient of friction f with Q structural surface and moisture content M: correlation coezcient R2 plywood with grains perpendicular; plywood with grains parallel; Hessian bag material; galvanized steel; formica (papreg)

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3.8. Static coe.cient of friction

3.9. Angle of repose

The plots of static coe$cient of friction obtained experimentally on "ve structural surfaces against moisture content in the range of 4)7}39)3% d.b., are presented in Fig. 6. These show that the coe$cient of friction of guna seeds increases linearly with moisture content and varies according to the surface. The regression equations expressing these relationships are also presented. Similar variations have been reported for karingda8 and pumpkin10 seeds. It was observed that for plywood with grains parallel to the direction of movement and Hessian bag material, variation of static coe$cient of friction with moisture content maintained a constant trend within the above range while, for plywood with grains perpendicular to the direction of movement, formica and galvanized steel sheet, a moisture level existed at which the trend changed. The static coe$cient of friction was found to be a maximum on plywood with grains perpendicular to the direction of movement at all moisture levels in the above range. This may be due to the development of higher shear stress at the plywood*seed asperite contacts, when the wood grains are perpendicular to the direction of movement. Minimum values were obtained on formica and the galvanized steel sheet at the moisture contents of 4)7 and 39)3% d.b., respectively. Within the same moisture range and for the same structural surface, the static coe$cient of friction of guna seeds is higher than that of karingda seed,8 gram11 and cowpea.15

Values of experimentally determined angle of repose are plotted against moisture content as shown in Fig. 7. From this, it is observed that the angle of repose increased from 28)07 to 43)583 as the moisture content increased from 4)7 to 39)3% d.b. An equation of the power-law type was "tted to the values with high correlation coe$cient using STAGRAPHICS 6)1. This shows that the dynamic angle of repose of guna seeds has a multiplicative relationship with moisture content. It is lower than the angle of repose of pumpkin,10 higher than those of gram,11 pigeon pea14 and fababean,19 and within the same range as that of karingda seed 8 and cowpea.15

4. Conclusions The investigation of various physical properties of guna seeds revealed the following. (1) As the moisture content increases, the dimensions of the seed increases uniformly in the three axes. (2) The 1000 seed weight increases linearly with moisture content. (3) The true and bulk densities decrease linearly with increase in moisture content and have a linear relationship with each other. (4) Seed volume and porosity also increase linearly with moisture content. (5) The seed resembles a #at disc with major axis signi"cantly greater than the intermediate axis. It is therefore described as being oval in shape. (6) The static coe$cient of friction increases linearly with moisture content and varies according to the surface. Maximum values were obtained on plywood with the grain of the timber perpendicular to the direction of movement, while minimum values were obtained on formica and the galvanized steel sheet. (7) The dynamic angle of repose increases with moisture content and has a multiplicative relationship with it.

Acknowledgement

Fig. 7. Change of angle of repose h of guna seeds with moisture P content M; correlation coezcient R 2

The authors are grateful to Mr. Ali A. Bwala of the National Agency for Food and Drug Administration and Control, Maiduguri, and Mr. Audu Garba Kwagyang of the Department of Agricultural Engineering, University of Maiduguri, for their assistance during this work.

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