Engineering properties of soybean (variety PDKV-Amba) for design of tractor operated soybean dryer

Introduction

Soybean and Cotton are the major kharif crop grown by farmer in Vidarbha region of Maharashtra state of India. Soybean occupies 49.91% area of kharif crop in Vidarbha. Soybean has good quality of protein but rarely used in human food and mostly used for animal feed. Major use of soybean in India is for oil. It is a leguminous vegetable of the Pea family that grows in tropical, subtropical and temperate climates. Soybean has a high protein content of 40% by weight, 32% carbohydrate, 20% fat, 5% minerals, and 3% fiber and other trace substances. It is used as sources of protein in human food, animal feed and in industries (Adekunle et al., 2006) [1] . Approximately, 85% of the world's soybean crop is processed into soybean meal and vegetable oil (Endres, 2001) [2] . PDKV Amba variety of Soybean is recently released by Dr. Panjabrao Deshmukh Agricultural University, Akola (MS), India particularly for Vidarbha region according to climate and growing pattern of Vidarbha region. Number of researchers have studied and published data on properties of grain and soybean also. But no research has been conducted on PDKV-Amba variety of Soybean. Number of post-harvest equipment including dryer have been developed by researcher for different grains by considering the properties of grains. To develop appropriate equipment for harvesting, handling, conveying cleaning, delivering, separation, packing, storing, drying, mechanical oil extraction and proceeding of agricultural products, their physical properties have to be known (Aviara et al., 1999; Mohsenin, 1980) [3,4] . In recent years, some studies on the physical and mechanical properties which appear to be important in the storage of granular products have been conducted intensively (Karababa, 2006; Baryeh, 2001; Baümler et al., 2006) [6,5,7] . The knowledge of physical properties, during drying, is also relevant for the correct post-harvest management. Information about size, volume, porosity, density and others are basic information for projection and monitoring of drying and storage of several agricultural products (Hauth et.al, 2018) [8] . Major problem of post-harvest operations of Soybean in Vidarbha region is drying of soybean due to climate change. Harvesting period of soybean is August to September when rains are occurred due to climate change. Therefore, moisture content of soybean are very high sometimes upto 30 to 35 %, which deteriorates the quality of soybean. The tractor operated mobile batch type dryer are need of farmer in Vidarbha region of Maharashtra, India. Therefore, work on design and development of dryer for soybean drying has been started at Dr. PDKV, Akola. For the design of this dryer engineering properties of PDKV Amba variety of soybean was evaluated. Therefore, the engineering properties of soybean (variety PDKV Amba) and their relation with moisture content have been studied.

Materials and methods

The soybean cultivar, PDKV Amba, used for this study, was obtained from the Central Research Station, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola (India). Soybean grains were used to determine their engineering properties at various moisture contents. Prior to recording observation, soybean grains were cleaned manually. The initial moisture content of the soybean grains was measured using the oven-drying method at 105 ± 5 °C for duration of 24 hours. Samples were moistened with a calculated quantity of water by using following equation ( 1) and conditioned to raise their moisture content to the desired three different levels. (Nimkar et al., 2005) [9] ………… (1) where: W 1, W 2 = initial and final weight of soybean grain (g) and M 1, M 2 = initial and final moisture content of soybean grain (%) on wet basis. Subsequently, the samples were transferred into individual polyethylene bags, which were then sealed securely. The samples were kept at 5°C in a refrigerator for seven days to allow uniform moisture distribution throughout the grain. Before starting a test, the required quantity of grain was taken out of the refrigerator and allowed to warm up to the room temperature for about 2 h. (Singh et al., 1996) [10] To determine the dimensions, a random sample of one hundred soybean grains was selected. For each soybean grain three principal dimensions, namely length, width and thickness were measured using a vernier caliper having the least count of 0.01 mm. Arithmetic mean diameter, geometric mean diameter, roundness, sphericity, aspect ratio, surface area, projected area, volume, moisture content, thousandgrain weight, bulk density, true density, porosity, angle of repose of soybean grain were measured at different level of moisture content.

Determination of physical properties of soybean grain

The length (L) is the distance from the tip of the seed to the kernel crown. The width (W) is defined as the widest point, taken parallel to the flat surface of the kernel. The thickness (T) is the distance between the two opposite faces of the kernels described by Pordesimo et al. (1990) [11] . After taking the measurements, the shape parameters were calculated.

Figure 1. Characteristic dimensions of a soybean grain

Using these measurements, the following shape parameters were computed:

Arithmetic mean diameter (D a )

The arithmetic mean diameter was determined as the average of the grain's three principal dimensions, using the formula from Baryeh (2002) [12] :

Roundness (R)

Roundness was calculated using the formula described by Baryeh (2002) [12] . R= ….…... ( 4)

Sphericity (ϕ)

Sphericity describes how closely the grain resembles a sphere and was calculated as per Mohsenin (1986) [13] and Baryeh (2002) [12] = …... ( 5) Where: ϕ = Sphericity (%)

Aspect ratio (R a )

Aspect ratio, indicating the shape elongation, was computed using the formula by Omobuwajo et al. (1999) [14] = …... ( 6) Where: R a = aspect ratio of grain

Surface area (S a )

Surface area was calculated using the geometric mean diameter, as provided by Baryeh (2002) [12] = …... ( 7) Where: S a = surface area of grain (mm 2 )

Projected area (A p )

The projected area was calculated using the empirical formula suggested by Mirzabe et al. (2013) [15] = ….... ( 8)

Volume (V)

Volume was determined using a standard formula involving the geometric mean diameter, as per Mohsenin (1986) [13] V= ….... ( 9) Where: V = Volume of grain (mm 3 ) Moisture Content Determination Initially, the samples were cleaned by removing dust, debris, and broken grains. The moisture content of both the original and moistened samples was measured in triplicate using the hot air oven methodat105 °C for 72 hours, following Bako et al. (2019) [16] .

Moisture content % (wb) ....( 10)

A set of 1,000 grains was counted from the cleaned sample and weighed using a Mettler electronic balance with 0.01 g precision. The measurement was repeated three times.

Bulk density (ρ b )

Bulk density was assessed by filling a 20 ml test tube with soybean grains and weighing the contents using an electronic balance. The bulk density was determined by dividing the mass of the kernels by the volume of the container, as described by Garnayak et al. (2008) [17] ."Bulk density was then calculated as: ….... ( 11) Where:

) True Density (ρ t ) True density was determined by water displacement method. A known quantity of soybean grains was added into a 100 ml measuring cylinder containing 50 ml of distilled water. The rise in water level indicated the displaced volume. This test was repeated three times and the true density was calculated using (Pradhan et al., 2013) [18] .

….... ( 12) Where: ρ t = True density of soybean grain (kg/m 3 ), M = Mass of soybean grain (kg) V = Volume of displacement of water (m 3 ). Porosity ( ) Porosity represents the percentage of air space between grains in a bulk sample and was calculated using equation (Mohsenin, 1986) [13] = …… (13) Where: ρ o = porosity of soybean grain (%), ρ b = bulk density of soybean grain (kg/m 3 ), ρ t = true density of soybean g(kg/m 3 ). Angle of Repose (θ) The angle of repose was determined by filling an open-ended cylinder (15 cm diameter, 30 cm height) placed at the center of a 70 cm diameter plate. After filling, the cylinder was lifted vertically to allow the grains to form a cone. The height (H) of the cone was measured, and the angle was computed using equation (Umogbai, 2009; Davies, 2009) [20,19] = ..... ( 14) Where: θ = Angle of repose (degrees) H = Height of the grain cone (mm) D = Diameter of the base (mm)

Results and discussion

The results of experiments for engineering properties of soybean grain are presented as follows.

Length, width and thickness

The average dimensions of soybean grain, namely length, width, thickness measured at different moisture content of 5.94, 15.02, 25.75 and 35.28 % (wb) are presented in Table 1. It was observed that the average length (L) of the soybean grain ranged from 7.26 to 7.62 mm, the width (W) ranged from 6.18 to 6.52 mm and the thickness (T) ranged from 5.16 to 5.52 mm, as the level of moisture content increased from 5.94 to 35.28 % (wb). As per the result we can say that the values of length, width and thickness increases as the level of moisture content increases. Similar results are reported for soybean by Kibar et al. (2008) [21] and Shirkole et al. (2011) [22] , for maize by Sangamithra et al. (2016) [23] , and for lentil by Amin et al. ( 2004) [24] . The relationships in Length (L), Width (W), Thickness (T) of soybean grain with respect to their moisture content (M) given using the following regression equation: 𝐿 = 7.144 + 0.013𝑀 𝑅 2 = 0.919

Sphericity

The sphericity of soybean grains increased from 0.83 to 0.84 as the moisture content increased from 5.94% to 35.28% (wb). Similar results have been reported for soybean (Unde et al., 1996) [25] , vetch seed (Yalcin et al., 2004) [26] and moth gram (Nimkaret al., 2005) [9] . The regression equation between the sphericity and the moisture content was obtained as: = 0.831+ 0.0003M R 2 = 0.579 ...... (18) where: S = sphericity, (% ) and M = moisture content, (%) wb

Surface area

The surface area of the soybean grains increased from 114.12 mm 2 to 127.79 mm 2 as the moisture content increased from 5.94% to 35.28% (wb). Similar trend has been reported for guna seed (Aviara et al., 1999) [3] , for hemp seed (Sacilik et al., 2003) [27] , for soybean (Davies et al., 2009) [28] . The relationship between the surface area and the moisture content was represented by the following equation: ) and M = moisture content, (%)wb

Projected area

The projected area of soybean grain (Table 1) was increased from 35.22 to 39.06 mm 2 , while the moisture content increased from 5.94 to 35.28 % (wb). Similar trends reported by Carman (1996) [29] for lentil, Ogut (1998) [30] for white lupin and Tang et al. (1993) [31] for lentil. The relationship between the projected area and the moisture content was obtained as:

Volume

The grain volume varied from 121.16 to 143.85 mm 3 as the moisture content increased from 5.94 to 35.28 % (wb). The volumetric expansion observed may be adduced to moisture absorption which increases the axial dimension of the grain. (Davies et al., 2011) [32] . Similar trend has been reported for pigeon pea (Obi et al., 2014) [33] , for gram (Dutta et al., 1988) [34] , for soybean (Deshpande et al., 1993), for moth gram (Nimkar et al., 2005) [9] . The relationship between the volume and the moisture content was obtained as: 𝑉 = 115.8 + 0.807𝑀 𝑅 2 = 0.986 (21) where: V= volume, (mm 3 ), M = moisture content, (%) wb

Thousand grain weight

The values of thousand grain weight varied from 144.20 to 167.07 g as the moisture content increased from 5.94 to 35.28 % (wb). This increase could be attributed to the moisture absorbed by the grain. Similar results of the effect of grain moisture on thousand grain weight reported by Nimkar et al., (2005) [9] for moth gram, Kulkarni et al. (1993) [35] , Deshpande et al., (1993) and Shirkole et al., (2011) [22] for soybean, Khan et al., (2017) [36] for pigeon pea and Munde, (1999) [37] for black gram. The relationship between the thousand grain weight and the moisture content was obtained as below: 𝑊 = 0.835𝑀 + 137.3 𝑅 2 = 0.956 (22) where: W = weight (g), M = moisture content, (%) wb

Bulk density

The results of bulk density with increasing moisture content are shown in Table 1. The grain bulk density at different moisture levels varied from 781.19 to 648.99 kg/m 3 with the moisture range of 5.94 to 35.28 % (wb) and indicated a decrease in bulk density with an increase in moisture content. The bulk volume of the grain sample expanded more significantly than the increase in its mass due to moisture absorption. Similar trend was found for green gram (Nimkar et al., 2001) [38] , soybean (Shirkole et al., 2011) [22] , moth gram (Nimkar et al., 2005) [9] , pigeon pea (Shepherd et al., 1986) [39] , Chickpea (Dutta et al., 1988, Gupta and Prakash, 1990) [34] . The bulk density of soybean grain was found to bear the following relationship with moisture content: 𝜌 𝑏 = 805.5 -4.150𝑀 𝑅 2 = 0.936 (23) where: ρ b = bulk density (kg/m 3 ), M = moisture content, (%)wb

True density

The true density decreased from 1000.66 to 994.73 kg/m 3 when the moisture level increased from 5.94 to 35.28 % (wb) (Table 1). The results were similar to those reported for vetch seed (Yalcin et al., 2004) [26] , soybean (Kibar et al., 2008) [21] , soybean (Davis and El-okene, 2009) [28] , green gram (Nimkar et al., 2001) [38] , moth gram (Nimkar et al., 2005) [9] . A regression equation is

Conclusions

This study analyzed the engineering properties of soybean grain (Amba variety) across a significant range of moisture content (5.94% to 35.28% wb). The findings demonstrate a clear and consistent relationship between moisture level and grain characteristics. Specifically, linear dimensions, roundness, sphericity, aspect ratio, surface and projected areas, volume, thousand grain weight, porosity, and angle of repose were found to increase with increasing moisture content. However, as moisture content increased, both bulk density and true density were found to decrease. The established relationships and the specific range of values determined in this research are critical for engineers and manufacturers involved in the design and optimization of machinery and systems for the effective handling, processing, and storage of soybean seeds. 100-107.

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