Shea butter is the fat content of the kernel of shea nut (Vitellaria paradoxa) which grows naturally from the wild and uncultivated state in most parts of Africa. The fat is used as edible oil and for raw material in the production of soaps, pomade, drugs and medicinal ointments. Wet extraction process is the method used in shea butter processing industry among women in African rural and urban communities. Apart from the low yield (below 20%), this wet extraction process is associated with environmental polluting effluents as by products. Experiments on dry extraction of shea butter from shea kernel were carried out using an instrumented piston-cylinder rig in conjunction with the TESTOMETRIC Universal Testing Machine (Model M500–50 KN). Shea butter was mechanically expressed when pressures of 1.5, 2.9, 5.8 and 8.8 MPa were applied at the rate of 2.50, 5.00, 7.50 and 10.00 mm/min on crushed shea kernel heated at 50, 70, 90 and 110°C. Measurements were made of oil yield, oil recovery efficiency and process loss during the mechanical expression process. The measured effects of heating temperature, applied pressure and loading speed on oil yield, oil recovery efficiency and process loss were examined using a 43 factorial experiment in randomized complete block design. Model equations were developed by employing multiple regression analysis using SPSS 11.0 package. Further analysis by optimization process revealed optimum heating temperature, applied pressure and loading rate of 82.24°C, 9.69 MPa and 2.50 mm min-1 respectively. These combinations gave 35.39% oil yield, 58.62% oil recovery efficiency and 2.83% process loss. This information provides useful data for developing a process line for dry extraction of shea butter from shea kernel.
Key words: Shea butter, dry extraction, model equations, optimization, oil yield.
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