Shea butter has been a traditional heritage of Africa from time immemorial. The triglyceride which contains a high amount of vitamin A, E, F and some other valuable nutrients is widely used in cosmetics and pharmaceuticals, as well as for domestic use in cooking. Nigeria (as well as many other West African countries) is blessed with abundance of the shea tree (from which the shea butter is obtained). Due to increasing demand for this product, especially in the cosmetic industries across the globe, there is a need for process optimization where
a high yield of shea butter of good grade can be obtained with little energy input.
There are basically three methods of obtaining shea butter from shea nut:
- Solvent Extraction Method
- Use of Mechanical Expeller
- Traditional Method
Solvent extraction makes use chemical solvent such as hexane to absorb the oil from the nut. The oil and the solvent are then separated in another column.
In the mechanical expeller process, an expeller is force driven into the nut contained in a tight container. As the expeller presses against the nut in a screw manner, the oil are forced out and collected at the end.
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The traditional method (in southwest Nigeria for example) typically involves crushing of the nuts (after the outer flesh of the fruit has been removed) with mortar and pestle. The crushed nuts are then roasted in a large pot over an open fire (burning of fire wood). They are then ground and well mixed to form a thick paste. The paste formed is kneaded by hand and leg in a large container and with constant addition of water, the butter oil are separated, melted in another pot and cooled.
Of these three methods, the traditional process gives the best quality shea butter and it is by far the most preferred in the most industry. However, this process requires a lot of rigorous exercises. According to Bonkoungou in 2005 for example, it would take one person 20 to 30 hours to produce 1kg of shea butter. Also the level of personal and professional hygiene observed by the local producers may render the locally made shea butter unfit for use in areas such as pharmaceutical and chocolate industry. For example, in a research by Ademola, Oyesola and Osewa of the Department of Agricultural Extension and Rural Development, Faculty of Agriculture and Forestry, University of Ibadan conducted on 120 local producers of shea butter from different Local Governments Areas in Oyo state Nigeria, 95.8% of them do not actually wash the fruit before use.
Although the mechanical expeller process may be preferred in terms of energy saving, but it yields a denatured shea butter which can never compete in terms of quality with the handmade type.
The solvent extraction process gives the highest yield since it is a large scale industrial operation that may be adopted for commercial production. However, it is too expensive as the cost of equipment and operation may be more than the capacity of an individual. Also, the interaction of the solvent with the oil still makes the shea butter formed be of lower quality than the locally made product.
A good and sustainable process therefore must be one which can give high yield of uncontaminated shea butter, retain the essential vitamin content and at the same time less rigorous but economically feasible. One way of achieving all these is by modeling the traditional method. Model equipment could be fabricated using a stirrer or impeller to substitute the hand; thereby increasing the efficiency, reducing contamination by hand without loss of nutrients. In such modeling, a number of experiments must be carried out to know the optimum condition of operation of the model equipment. Several parameters must be tested for so as to obtain the best result; and according to literature, these include: kneading time and temperature, impeller type, shaft speed, eccentricity, etc.
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1.2 AIMS AND OBJECTIVES
The aim of this research is to investigate the effect of kneading temperature at selected kneading period on the yield of shea butter produced from shea paste in an unbaffled vessel.
1.3 SCOPE OF WORK
This research measures the effect of three parameters on yield – shaft eccentricity, shaft speed and impeller type. While eccentricity tries to determine the best position of the stirrer relative to the center of the vessel, the shaft speeds helps to determine the optimum speed of the stirrer while the impeller type tells something on the nature or type of impeller to use. Other parameters such as kneading time and temperature are not considered here (a complementary work considering these two is being undertaken by another student).
Also, the research measures the effect of these parameters only from the kneading operation, (since this is the most important operation where the actual separation takes place) so that the crushing, roasting and milling operations are done prior to measurement, making work faster. The vessel being considered for kneading is an unbaffled one. This is to avoid deposition of materials inside the vessel which may affect the yield.
In all, this research narrows down to a system where the response can be measured within a short while given different input, thus the use of shea paste in an unbaffled vessel.
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