Abstract
Bulk density, kernel density, particle porosity and shrinkage of sheanut krnel slices were determined as a function of moisture content and slice thickness in order to establish preliminary design parameters for drying in an indirect solar dryer. Solid density increased linearly while bulk density decreased non-linearly during drying as the moisture content decreased from 150 to 5 %d.b. The porosities of the kernels ranged from 60.12 -67.91, 57.05-64.87 and 56.88-62.49%, respectively, for the 5, 10 and 15 mm slices. The volumetric shrinkage of the shea slices reduced with decrease in moisture content for all the particle sizes evaluated in this study. Among the shrinkage models tested, the empirical quadratic model gave the best fit of the experimental data. It is proposed that the mechanism of shrinkage in sheanut kernel slices is linked to the removal of water that leads to structural collapse. Key words: Density, porosity, volumetric shrinkage, sheanut kernel, slices.
Highlights
The shea tree has long been reported as important livelihood tree (Maranz et al, 2003)
The solid density for all the slices at all moisture contents was greater than unity, implying that the slices are heavier than water
No clear relation was established between solid density and particle size as the solid density was higher for the 10 mm thick slices at higher moisture content (150-100% d.b.) as compared to the 5 and 15 mm thick slices
Summary
The shea tree has long been reported as important livelihood tree (Maranz et al, 2003). In the processing of shea fruits to obtain butter, drying of the kernels after depulping and dehusking has been described as one of the key steps indispensable in the production process (Womeni et al, 2004) This is because sheanut kernels at harvest contain about 45-60% moisture content on a wet mass bases and are prone to deterioration if not properly preserved. Drying for more than 12 days may lead to the development of moulds which contain lipases that catalyse hydrolyses thereby leading to rancidity in the resultant oil (Kapseu et al, 2007) To reduce this drying time it is advisable to dry these kernel as thin slices in solar dryers which can be cheap and affordable to local African women, the main processors of shea fruits to butter. The understanding and modelling of the drying behaviour of sheanut kernel slices and the development of a solar
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