Project Abstract

<p>            <b>  ABSTRACT</b></p><p>&nbsp;Locust bean (Parkia biglobosa) seed is a source of a nutritious and medicinal food condiment consumed in Nigeria. The drudgery associated with locust bean seed processing necessitates its mechanization. However, there is a dearth of information on the engineering properties of locust bean required for machine design. Since water absorption by seeds causes changes in their structure and size, this study was designed to investigate some engineering properties of locust bean at different moisture content levels. Locust bean pods were collected from Araromi, Saki in Oyo State. The moisture content and physical properties were determined using American Society of Agricultural Engineers’ (S 352.2), Mohsenin’s (1986) and Stepanoff’s (1969) methods. Universal testing machine was used to determine the mechanical properties. Force was applied transversely at 5 mm/min loading rate. Normal and shear stresses were determined for 200 – 500 g loads at 100 g interval. Thermal properties were determined using methods of mixture and steady-state heat of vaporization. Data were analysed using ANOVA. Seed length, width and surface area increased from 10.2±1.0 to 11.3±0.9 mm, 8.5±0.8 to 9.1±0.6 mm, and 191.2±24.6 to 208.3±26.3 mm 2 respectively. Static and dynamic angles of repose increased from 48.4±0.9 to 56.0o ±1.4 and 25.2±1.5 to 30o ±1.2 respectively as seed moisture content increased from 5.9 to 28.2 % d.b. Seeds became sticky and clung together at high moisture content, hindering free flow and piling at rest, and increased angle of repose. Static coefficient of friction increased on plywood (0.48±0.02 to 0.60±0.01), glass (0.40±0.05 to 0.54±0.01), mild-steel (0.52±0.04 to 0.54±0.02), galvanized iron (0.51±0.04 to 0.52±0.03), rubber (0.41±0.04 to 0.60±0.05) and decreased on aluminium (0.54±0.02 to 0.52±0.04) and stainless steel (0.55±0.03 to 0.50±0.04). The increase was due to increased adhesion between the seeds and the test surfaces at high moisture levels while surface smoothness reduced adhesion, accounting for the decrease in static friction on aluminium and stainless steel. Seed thickness, sphericity and rupture force decreased from 5.49±0.43 to 5.26±0.62 mm, 0.75±0.04 to 0.71±0.03 and 214.4±82.3 to 129.9±51.9 N respectively while normal stress increased with increase in moisture content and loads; 8.4 to 8.7 gcm-2 for 200 g, 9.4 to 9.7 gcm-2 for 300 g, 10.4 to 10.7 gcm-2 for 400 g and 11.4 to 11.7 gcm-2 for 500 g. Shear stress was&nbsp; highest at 11.11 % moisture d.b. under 500 g load (1.5 gcm-2 ) and lowest at 5.93 % moisture d.b. under 200 g load (0.6 gcm-2 ). Increase in stresses was due to reduced porosity within the grain bulk at high moisture content. Thermal diffusivity, specific heat capacity and thermal conductivity increased from 2.93 x 10-8 to 3.79 x 10-8 m 2 /s, 2.74 to 4.38 kJ/kg oC and 0.052 to 0.118 W/m oC respectively, these showed that seeds were able to transmit and retain heat within the grain bulk at high moisture content. A baseline data of the engineering properties of locust bean seeds useful for design of necessary equipment have been established. The properties are useful in designing flat storage facilities and steamers.&nbsp;</p><p><b>Keywords Locust bean seed, Thermal properties, Mechanical properties, Physical properties, Moisture content. &nbsp;&nbsp;</b><br></p>

Project Overview

<p><b>1.0 INTRODUCTION&nbsp;</b></p><p><b>1.1 The Locust Bean&nbsp;</b></p><p>Locust bean is the matured fruit seed that comes from the Parkia tree. It is the most important part of the tree and a source of a fermented, natural and nutritious condiment that features frequently in the traditional diets of the people of both rural and urban dwellings in at least 17 West African countries including Nigeria. It is harvested, processed and fermented into a product known as ‘Iru’, ‘Ogiri’ and ‘Dawadawa’ in Yoruba, Igbo and Hausa languages respectively (Oni, 1997). Outside Nigeria, among the French-speaking countries of West Africa, the condiment is called Soumbala. In Zitenga, Burkina Faso, soumbala tops the list of edible food products locally sold in the market while in Mali, the seed ranks first among the eighteen edible forest products locally consumed (Diawara, 2000). This accounts for ten percent of the total non-timber forest products locally used as food. In Nigeria, the Locust bean tree is found in the savannah zones with the bulk of it located in the Guinea Savannah i.e. semi arid to sub-humid area. The estimated average consumption for the condiment per head, per day for Nigeria, Togo and Ghana are 10g, 4g and 2g respectively (Oni, 1997). The locust bean after fermentation is eaten alone or cooked along with food e.g. rice, soup, stew as soup condiment. It contains a high content of protein (40 %), vitamin and sugar (Klanjcar, 2002). The locust bean seed is flat and spherical in shape and it is blackish – brown in colour. It is covered with hard, smooth testa (seed coat) which makes the raw seed very hard and inedible (Booth and Wickens, 1988). The hard, smooth testa protects the seed even when it passes through the gut of an animal. During processing, dehulling of the seed is made difficult or laborious because of the hardness of the testa (Diawara, 2000). When the seed is removed from the pod, the testa is covered by a yellow, sweet, soft and floury pericarp, referred to as the ‘Pulp’ which is very rich in Vitamin C. The yellowish colour of the pulp is turned to cream colour after drying the seed. The average weight of the seed is approximately 0.25 g (Campbell-Platt, 1980). The seed can be dispersed by man and other vertebrate animals like bats, parrots, baboons, other birds and chimpanzees (Gakou et. al., 1994). <br></p><p> <b>1.2 Economic Importance of the Locust Bean&nbsp;</b></p><p>The socio-economic importance and multi-purpose use of the locust bean cuts across various facets of human life. It is significantly important in human diet as it serves as food and medicine for man. Alabi et. al. (2005) reported that locust bean is rich in lipid, protein, carbohydrate, soluble sugars and ascorbic acid. The cotyledon is very nutritious, has less fibre and ash contents. The oil content is suitable for consumption since it contains very low acid and iodine contents. The oil has very high saponification value and hence would be useful in the soap industry (Diawara et. al., 2000). Locust bean has high protein content (40%) and could adequately serve as a supplement for fish, meat and other animal protein sources. It also contains high vitamin, moderate fat content (35%), carbohydrate and macronutrients such as potassium, sodium, magnesium, calcium, nitrogen and phosphorus. These make the locust bean especially important in the Nigerian diet (Odunfa and Adesomoju, 1985). Campbell-Platt (1980) also reported that locust bean contains 31 – 40 % oil, 11.7 - 15.4% carbohydrate and 39 - 40% protein. It has essential acids and vitamins and serves as a protein supplement in the diet of poor families. Dawadawa is used in soups, sauces and stews to enhance or impart meatiness (Diawara et. al., 2000). Okpala (1990) in his report gave a table of the chemical and nutritive composition of the locust bean seed (Table 1.1). Oni (1997) reported that the locust bean is used to treat ailments like hypertension, veneral diseases, vision and mental alertness, measles, stomach pains, external wounds, fresh cuts, injuries, diabetes, toothache and mouth ulcer, diarrhoea, sore eyes, snake bites, scorpion sting, ear problem, bronchitis, pneumonia, guinea - worm and rickets among many others. These medicinal benefits are derived mostly from the regular consumption of the fermented locust bean product. In his work, he collated and listed in a tabular form (Table 1.2) some medicinal uses of the locust bean. Booth and Wickens (1988) also reported that the liquid extract from the locust bean when pounded and boiled is used as stomach pain reliever in Singapore and Malaysia. <br></p><p> Oni (1997) further stated, in his work that locust bean is also used for the production of beverages, vegetable oil and the manufacturing of margarine and soap. The friable yellow pulp surrounding the seed is sweet and it is eaten or licked raw, especially by children and can be fermented into alcoholic drinks. The pulp is rich in sugars and vitamin C. The seed can also be processed and used as a substitute for coffee (Dalziel, 1937). It is used as cocoa and sugar replacement to produce chocolate – flavoured products, because not only does the bean taste and smell like chocolate, but it is a pure natural ingredient and does not contain caffeine. The effluent from locust bean processing is usually used locally to kill termites when it is used to spray or wet the affected area (Hagos, 1962). Although, the locust bean contains tannin, which is a toxic substance in its cotyledon and testa, the fermentation process enhances the eradication or drastic reduction in tannin level in the seed. This makes it harmless for consumption. The testa is also used for animal feed (Kessler, 1994). Information received from Cadbury Nigeria PLC, manufacturer of the popular ‘Dadawa cube’ stated that the company uses locust bean as raw material for manufacturing the product. It has been reported that ‘Iru’ (fermented locust bean) is exported to countries like the United States of America and Britain by many Nigerian food marketers. Therefore, if the production of ‘Iru’ is increased and well packaged, it can serve as a means of earning foreign exchange. Each stage of ‘Iru’ processing, from harvesting to fermentation, in Nigeria is still largely traditional and cumbersome. It is the vocation of the rural dwellers, who are mostly women. Manual labour is employed for all stages of production hence; the quality and quantity of production remain very low. Processing of locust bean for other various uses in Nigeria is also largely manual and traditional. 1.3 Moisture content and engineering properties of agricultural materials: the importance. Engineering properties of agricultural materials are important in solving problems that are related to the engineering development of agricultural machines and equipment. They are also important in the analysis of the behaviour of agricultural materials during handling which is very important in agricultural production and food sustainability. <br></p><p> The knowledge of engineering properties of an agricultural material is highly imperative in the design of agricultural processes. Kutte, reported by Akaiimo and Raji (2006) stated that: in the design of agricultural machines, properties of the crop must be taken into account such as grain length, width, mass, hardness, angle of repose, grain – straw ratio and bulk density. Pneumatic separation and conveyance during handling and processing of agricultural materials are often done using air as the medium for transporting and separating unwanted materials from the desirable product. Therefore aerodynamic properties of agricultural materials are needed. Frictional properties of agricultural materials are also of necessity in predicting the lateral pressure on the wall of storage structures and hoppers for gravity flow. The angle of friction is applied to problems of flow of bulk granular materials in the design of gravity and forced flow equipment. Dynamic and static effect of friction of grains on engineering material surfaces (e.g wood, galvanized metal, glass and rubber) are required for the prediction of motion of the material in the design of harvesting and handling equipment. The physical properties of materials such as size, shape, surface area and drag coefficient are needed in the determination of the terminal velocity of an object in a fluid. Hence, to allow a gentle fall of a particle the air velocity is adjusted to a level below its terminal velocity. Mechanical properties of agricultural materials also help in predicting the behavior of a material under loading such as its yielding point, maximum rupture force that can be applied and the extent of its deformation when load is applied. <br></p><p> <b>1.3 Problem statement&nbsp;</b></p><p>Beaumont (2002) identified several constraints to the processing of locust bean into a condiment. These include among others, low production due to the use of rudimentary equipment, high wood fuel consumption and poor manufacturing practices. He further stated that it is time consuming, laborious and inefficient hence, production has not increased substantially. The declining popularity of Iru (fermented locust bean) especially among the growing urban population has led to rapid increase in importation of foreign soup flavours. In order to increase supply, it is necessary to modernize production techniques or optimize processing conditions (Audu et al., 2004). To increase production, mechanization of processing stages and conditions is imperative. Therefore the determination of the engineering properties of locust bean required for the design of equipment for its handling and processing is necessary. Efforts have been made to determine some engineering properties of Parkia biglobosa relative to pod shelling at a single moisture content level (Oje, 1993). Work has also been done to determine some physical properties of Parkia filicoidea, another variety of Parkia at a single moisture content level (Ogunjimi et. al., 2002). Mohsenin (1986) stated that the compression behaviour of agricultural products is affected by the physical nature of such products, moisture content and maturity, rate of loading, temperature and other processing parameters. Therefore, there is a need to determine the relationship between the engineering properties of Parkia biglobosa and seed moisture content variation which will be useful in generating a baseline data required for the engineering design and development of equipment needed for handling and processing of locust bean.&nbsp;</p><p><b>&nbsp;1.5 Objectives&nbsp;</b></p><p>This work was therefore carried out to:&nbsp;</p><p>1. Determine the physical, mechanical and thermal properties of locust bean at five different moisture levels.&nbsp;</p><p>2. Determine the relationship between moisture content and the properties of locust bean stated above.&nbsp;</p><p>3. Generate equations for predicting the properties of locust bean at any moisture level. <br></p>