Sub-Saharan Africa is a treasure chest of natural materials remaining to be explored for commercial
applications and as alternative foods to diversify and improve food sustainability. The Marula tree is available
in abundance in South Africa and bears a fruit with a highly nutritious kernel containing high oil and protein
content. The oil from the kernels has various applications from food to cosmetics. The accepted oil processing
practice is required to be a green technology, producing no effluent or using toxic solvents. Therefore, the oil
is extracted using an expeller. However, with average 55 wt. % oil in the kernel the extracted oil yield is far
from optimal, typically ranging from as low as 7 wt. % to 47 wt. %. The latter is obtained only with
proprietary modified expellers. Therefore, an alternative green technology which retains the native
characteristics of the Marula oil is needed. Communication with local producers, South African and
Namibian, confirmed the need for investigation of an alternative means of extraction of Marula oil from the
seed kernels which can improve the yield and potentially the quality of the oilcake. The latter of which is
typically adversely affected by the expelling process.
A review of various processing technologies available for oil extraction was completed and supercritical fluid
extraction utilizing carbon dioxide as the extraction solvent was identified as a potential solution. An
overview on supercritical fluid extraction using carbon dioxide (SFE-CO2) of similar materials to the Marula
kernels, such as hazelnuts, walnuts and pine kernels indicates that yields similar to that of solvent extraction
and of the quality of the oils obtained by cold pressing can be obtained with the technique. The theory,
practical applications, and how one can use the system to improve yield from various natural materials were
reviewed. It was determined that the two main parameters one can manipulate on supercritical extraction
systems to optimize the yield, were pressure and temperature.
Subsequently kernels of the Sclerocarya birrea tree, common name Marula, cultivated in South Africa, were
obtained for extraction with supercritical carbon dioxide. The effects of pressure and temperature on
extraction yield were investigated. The total maximum yield of Marula kernel oil obtained was found to be
54 wt. %, compared to a solvent extracted yield of 52 wt. %, such that a 100 % oil recovery was obtained with
SFE-CO2. The optimal conditions were found to be 450 bar and 60 °C as the yield per kg solvent initially was
41 g kg-1 CO2.
Following the extractions, the oils were characterized for fatty acid composition using gas chromatography.
Quality parameters of a cold pressed sample and a sample obtained at the optimal extraction conditions were
determined and compared; and the results indicate that the two oils are of similar composition and quality. Supercritical fluid extraction using carbon dioxide was successfully verified as a potential processing method
for the extraction of Marula oil from the kernels. The SFE-CO2 provided an improved yield compared to cold
pressing and a quality of oil similar to cold pressed Marula oil. Additionally, after SFE-CO2 processing, the
defatted Marula kernels contain high protein content, 69 wt. %, in the form of a pure white powder. Due to the
favourable nutritional content the residue may be used for human consumption to create new products such as
meat analogues, porridges, and shakes, or can be sold as a high protein powder. / MSc (Engineering Sciences in Chemical Engineering), North-West University, Potchefstroom Campus, 2015
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/15903 |
| Date | January 2015 |
| Creators | Taseski, Natasa |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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