Physical and mechanical properties of two varieties of fresh oil palm fruitIntroductionMaterials and methodsDetermination of physical propertiesDetermination of sizeDetermination of shapeDetermination of fruit massDetermination of true and bulk densityDetermination of density ratio and porosityMeasurement of the mechanical properties of palm fruitResults and discussionConclusionReferencesPhysical and mechanical properties of two varietiesof fresh oil palm fruitO.K. Owolarafe*, M.T. Olabige, M.O. FaborodeDepartment of Agricultural Engineering, Obafemi Awolowo University, Ile-Ife, NigeriaReceived 6 July 2005; accepted 21 December 2005Available online 3 March 2006AbstractAn investigation was carried out on the physical and mechanical properties of two varieties of fresh oil palm fruit (dura and tenera).The physical properties investigated include, size, sphericity index, aspect ratio, true density, bulk density, and porosity. The mechanicalproperties studied were cracking force, pressure, dynamic angle of repose and coefficient of friction.The mean size of the fresh dura fruit i.e. fruit length, width and thickness were found to be 30.25 mm, 19.94 mm and 15.66 mm, respec-tively, while that of the fresh tenera were 35.96 mm, 20.15 mm and 17.11 mm, respectively. The sphericity and aspect ratio of the freshdura variety were found to be 70.67% and 67.78%, respectively, while that of the fresh tenera was 64.23% and 56.77%, respectively.The true densities, bulk densities, densities ratio and porosities of the fresh dura and tenera were 1112.50 kg/m3, 659.40 kg/m3,59.33%, and 40.67% and 995.70 kg/m3, 611.04 kg/m3, 61.45%, and 38.55%, respectively.The coefficient of static friction obtained on four surfaces namely, plywood, aluminium, mild steel sheet and galvanised steel sheetwere 0.58, 0.53, 0.56 and 0.56, respectively, for the fresh dura variety while that of the tenera were found to be 0.5175, 0.52, 0.52 and0.53, respectively, for the aforementioned surfaces.The dynamic angle of repose values obtained on plywood, aluminium, mild steel and galvanised steel were found to be 18.43°, 18.42°,18.59° and 18.32°, respectively, for the fresh tenera while that of the fresh dura were 22.01°, 21.01°, 19.91° and 22.23°, respectively, for thefour aforementioned surfaces.The average cracking force required to break fresh dura and tenera were 2301 N and 1149 N, respectively. The mean pressure appliedon the unsterilised dura and tenera varieties were 5.79 N/mm2and 2.00 N/mm2, respectively.Ó 2006 Published by Elsevier Ltd.1. IntroductionThe oil palm, (Elaeis guineensis) belongs to the familyPalmae and is a major tropical tree crop in Nigeria. It isgrown in the Southern part of the country and the Guineasavannah area of the Middle be lt. It originated from thetropical rain forest region of West Africa with its mainoil palm belt running through the Southern latitudes ofSierra Leone, Liberia, Ivory Coast, Ghana, Togo, Benin,Nigeria, Cameroon and into the equatorial region of Zaireand Angola between latitudes 10°N and 10°S(Opeke, 1982,Chap. 13). The wild oil palm groove in Nigeria is estimatedat 2.1 million hectares whereas plantation estates and smallholdings account for 81,475 and 105,184 ha, respectively.Palm oil, the most important product of the oil pa lm, isthe world’s main edible oil also used for soap making (Bek-Nielson, 1974). It is used for soup and table fats such asmargarine and for the production of cosmetics in manycountries. Palm kernel oil is used in the manufacturing ofsoap, toiletries, surface active ingredients, baking coatings,whipped creams and sugar confectioneries. The mealobtained after oil extraction from the kernel is also usedas animal feed. High quality palm oil is needed for domes-tic and industrial applications.Three types/varieties of palm fruit exist (Opeke, 1982,Chap. 13) viz: the dura, pisfera and tenera. The dura consists0260-8774/$ - see front matter Ó 2006 Published by Elsevier Ltd.doi:10.1016/j.jfoodeng.2005.12.049*Corresponding author.E-mail address: [email protected] (O.K. Owolarafe).www.elsevier.com/locate/jfoodengJournal of Food Engineering 78 (2007) 1228–1232of a thick pericarp or exocarp, 2–8 mm thick, a thin meso-carp (which is responsible for the low palm oil content ofthis variety), thick endocarp (shell) and generally large ker-nels (which make it suitable for kernel oil production). Itsmesocarp content is 35–55%. The pisfera has fruits whichpossesses thick mesocarp (with very little oil content), noendocarp (shell less) and with small kernel. The tenera typepossesses thick mesocarp (much pulp), thin endocarp and areasonably sized kernel. It is the product of the cross of pisf-era and dura . It is useful in the production of mesocarp oilbut less kernel oil when compared with the dura variety. It isnow commonly used as a planting material because of itssuperior yield of palm oil. The oil content of palm fruitdepends on the thickness of the mesocarp (for palm oil)and the size of the kernel (for kernel oil). Fig. 1 shows thestructure of the three types of oil palm fruit.Since the tenera and dura varieties of palm fruit are use-ful in production of palm oil and palm kernel, respectively,it becomes imperative to characterise the fruits with a viewto understanding the properties that may affect the designof machines to handle the processing of the fruits. Suchphysical properties such as size, shape, sphericity, aspectratio, true density, bulk density and por osity, and mechan-ical properties such as coefficient of friction angle of reposeas well as fracture resistance are very important in thedesign of processing machines for major agricultural crops.This study hence investigates these important propertiesfor the two varieties of palm fruit.2. Materials and methods2.1. Determination of physical propertiesThe dura and tenera varieties of palm fruits used for thisstudy were collected from the Teaching Research Farm ofObafemi Awolowo University, Ile-Ife, Nigeria in May 2004.Nomenclaturea length of the fruit, mmApprojected area, mmb width of the fruit, mmc thickness of the fruit, mmDrdensity ratiofrfracture resistance, Nm mass of the fruit, kgRaaspect ratioP porosity, %v volume of the fruit, m3qbbulk density of fruit, kg/m3scsphericity of the fruitqttrue density of the fruit, kg/m3r cracking pressure, N/mm2Fig. 1. Structure of the three types of oil palm fruit.O.K. Owolarafe et al. / Journal of Food Engineering 78 (2007) 1228–1232 1229The
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