March, 2014 Agric Eng Int: CIGR Journal Open access at http://www.cigrjournal.org Vol. 16, No.1 99 Moisture dependent mechanical and thermal properties of Locust bean (Parkia biglobosa) Olajide Ayodele Sadiku1*, Isaac Bamgboye2 (1. Department of Agronomy, Faculty of Agriculture and Forestry, University of Ibadan, Ibadan, Nigeria; 2. Department of Agricultural and Environmental Engineering, Faculty of Technology, University of Ibadan, Ibadan, Nigeria) Abstract: The mechanical and thermal properties of African locust bean (Parkia biglobosa) seeds were investigated as a function of moisture content in the range of 5.9%–28.2% dry basis (d.b.). These properties are required for the engineering design of equipment for handling and processing locust bean. Universal Testing Machine was used to determine the mechanical properties at 5 mm/min load rating transversely. Normal and shear stresses were determined for 200–500 g loads at 100 g interval. Specific heat and thermal conductivity were determined using the method of mixtures and steady-state heat flow method respectively. Linear decreases in rupture force (214.42–129.86 N) and rupture energy (109.17–73.46 N mm) were recorded, while deformation of the seed samples increased (0.98-1.13 mm). Linear increase in normal stress at 200, 300, 400 and 500 g loads were 8.38–8.69, 9.39–9.70, 10.40–10.71 and 11.41–11.72 g/cm2 respectively, while shear stress ranged from 0.589 to 0.845, 0.688 to 0.998, 0.638–1.213 and 0.688–1.359 g/cm2 at 200, 300, 400 and 500 g with increasing seed moisture content. The specific heat and thermal conductivity of locust bean increased from 2.74 to 4.38 kJ kg-1 oC-1 and 0.052 to 0.118 W m-1 oC-1 respectively. Seed moisture content effect was statistically significant (p<0.05) on all properties investigated except rupture force, rupture energy and thermal diffusivity while baseline data were generated for the development of necessary handling and processing equipment. Keywords: bulk density; deformation; rupture force, shear stress, moisture content, thermal conductivity Citation: Sadiku, O. A., and Bamgboye I. 2014. Moisture dependent mechanical and thermal properties of Locust bean (Parkia biglobosa). Agric Eng Int: CIGR Journal, 16(1): 99－106. bean into the food condiment is manual and tedious hence, 1 Introduction not practical for large scale production. The demand for Locust bean seed, among some of its uses, is an this condiment is on the rise because of the increased important raw material for the production of a natural, awareness of the nutritive and medicinal benefits it nutritious and medicinal food condiment largely provides. In processing the seeds into food condiment, consumed in at least, 17 West African countries including the seeds are boiled in water for 8–12 hours. The seed Nigeria (Oni, 1997). The seed has high protein content coat is split to remove the cotyledons (dehulling). (40%), high vitamin, moderate fat content (35%), Parboiling of the cotyledons, after washing them with carbohydrate and macronutrients such as potassium, water, takes 30 minutes to one hour. The parboiled sodium, magnesium, calcium, nitrogen and phosphorus cotyledons are allowed to cool and finally wrapped in (Klanjcar, 2002). In Nigeria, the processing of locust leaves (banana leaves) for fermentation. Therefore, in order to increase supply, it is necessary to modernize Received date: 2013-08-29 Accepted date: 2014-02-24 production techniques and optimize processing conditions * Corresponding author: Olajide Ayodele Sadiku, Department (Audu et al., 2004). To achieve this, adequate of Agronomy, Faculty of Agriculture and Forestry, University of information on the mechanical and thermal properties of Ibadan, Ibadan, Nigeria. Phone: +234 703 298 3180. Email: [email protected]. locust bean required for the design of equipment for its 100 March, 2014 Agric Eng Int: CIGR Journal Open access at http://www.cigrjournal.org Vol. 16, No.1 handling and processing is necessary. levels. The samples were packaged in doubled with low Thermal properties are useful in modeling thermal density polythene bags to preserve the moisture content behavior of seeds during thermal processing operations and was stored afterwards in a refrigerator at 5oC for five such as drying, fermentation, boiling, baking and frying days (Davies, 2010; Akbarpour et al., 2009) to allow for (Alagusundaram et al., 1991; Yang et al., 2002). uniform distribution of moisture within the seed mass in Knowledge of the mechanical properties of grains is each sample lot. Before each experiment was conducted, important in the analysis and prediction of their cracking the required quantity of seeds was taken out from each and or breaking behavior during handling and processing. sample lot in the refrigerator for two hours to equilibrate Hydration and drying of seeds will cause physical and with room temperature. physiological changes in the seed. Therefore, it will be 2.2 Bulk density safe to determine the mechanical and thermal properties The bulk density is the ratio of the mass of a sample of locust bean as functions of variation in the seed of a seed to total volume (Shafiee et al., 2009). Bulk moisture content. This will also generate baseline data density for all the samples were determined by filling an required for the engineering design of equipment empty 300 mL beaker with locust bean seeds and necessary for handling and processing of seeds. weighing it (Mohsenin, 1986). The weight of the seeds Many researchers have determined the mechanical was obtained by deducting the weight of the empty and thermal properties of various crops as a function of beaker from the weight of the seed-filled beaker. To seed moisture content, such as Ekinci et al. (2010) for achieve uniformity in bulk density, the beaker was tapped carob pod; Ahmadi et al. (2009) for apricot fruits, pits and 10 times for the seeds to consolidate in the beaker kernels; Tavakoli et al. (2009) for barley and soybean (Ahmadi et al, 2009). The beaker was filled with seeds grains; Bamgboye and Adejumo (2010) for roselle seeds; dropped from a 15 cm height and a sharp–edged, flat Aviara and Haque (2001) for sheanut kernel. Therefore metal file was used to remove excess seeds to level the this research investigated the influence of seed moisture surface at the top of the graduated beaker (Nalbandi et al, content on the mechanical and thermal properties of 2010). Bulk density was calculated using the following locust bean. equation: ρb = m/v (2) 2 Materials and methods This was replicated five times and the mean 2.1 Collection and preparation of samples calculated for each sample. Samples were collected from Saki town, in the 2.3 Normal and shear stresses northern part of Oyo State of Nigeria. Locust bean trees A rectangular guide frame of size 11×9×5 cm put naturally exist in abundance in the area, and also known under a cell of size 7×5×5 cm as described by Stepanoff for the processing of the condiment. The seed bulk (1969) and Irtwange (2000) were filled with the sample. collected was cleaned manually to remove all foreign A normal load was placed on top of the cell. The cell matter, broken and immature seeds. The initial moisture was tied with a cord passing over a frictionless pulley and content of the seeds was determined using the ASAE attached to a pan. Weights (w3) were put into the empty (1998) standard; S 352.2 which involved oven-drying at pan to cause the seed-filled cell to just slide. After this, o o 103 C ± 1 C for 72 hours. The samples of other desired new weights (w4) were also put into the empty pan to moisture content levels were prepared by adding cause the cell and the normal load to slide over the guide calculated amount of distilled water using the equation frame. The measurements were carried out for 200, 300, given by Mohsenin (1986), expressed as follows: 400 and 500 g loads and three replications were taken for 2 Q = [Wi (mf – mi)] /(100 – mf) (1) each sample and load. The normal stress (σ) in g/cm The seed bulk was divided into five sample lots at was calculated as: 5.9%, 11.1%, 16.6%, 22.0% and 28.2% (d.b.) moisture σ = (w3 + w4) / A – ρh (3) March, 2014 Moisture dependent mechanical and thermal properties of Locust bean (Parkia biglobosa) Vol. 16, No.1 101 The shear stress (τ) was calculated as: were made using indicating digital ammeter, voltmeter and thermometer. A sample at specified moisture τ = [w5 (1 – w 2 )] / A (4) 2.4 Maximum rupture force and deformation content was put in a 75 mm diameter, circular plastic A preparatory tension/compression-testing machine ware plate and 10 mm thickness. The sample assumed (Instron Universal Testing Machine - U.K. model) was the size of the plate. The probe thermocouple pierced used to determine maximum rupture force and through the cylinder bottom and through the plastic but deformation of locust bean samples. Maximum load slightly penetrating into the sample to avoid touching the employed was 151 kg and test for each sample was hot plate directly. The plastic dish containing the replicated five times. Individual seed was loaded sample was placed at the base of the cylinder. The hot between two parallel plates of the machine and plate was lowered down the cylinder gently until it compressed along its thickness until rupture occurred as touched the sample. The temperature of the hot plate o denoted by a rupture point in the force deformation curve. was pegged around 70 C. The fluctuations in Similar method was adopted by Tavakoli et al.