## 3 Discussion  
In this study, we determined the chemical composition of oils and performed elemental analysis on oil cakes obtained from trees naturally growing in Zambia's Western Province. The oil yield from _S. rautanenii_ seeds was 3 to 12% higher compared to the seed originating from Namibia or Botswana [12]. The chemical composition of oil is partially known, and studies have found that the oil is predominantly composed of \(\alpha\)-eleostearic acid, linoleic acid, oleic acid, palmitic acid, and \(\gamma\)-tocopherol [12; 19], which is generally in agreement with our results. The content of \(\alpha\)-eleostearic and linoleic acid was more dominant compared to the previous studies and was also depended on the extraction method (Table 2). Furthermore, \(\gamma\)-tocopherol content in traditional prepared oil was twice higher [12]. There are only a few studies documenting the chemical composition of _P. curatellifolia_ oil. It was reported that the oil is relatively rich in 18:3 fatty acid isomers and \(\alpha\)- and \(\gamma\)-tocopherol (again, in accordance with our results) [20]. Interestingly, the high content of erucic acid (58%) was reported in the oil from seed of _P. curatellifolia_ collected in Burundi [21]. This toxic fatty acid has been identified in _P. curatellifolia_ in previous studies. This fact can make the use of this oil as food potentially hazardous; further studies are definitely needed to screen the diversity of fatty acid composition of this species within Africa. To the best of our knowledge, this is the first study focusing on the fatty acid, vitamin E, and pigment content of _O. serrulata_ oil. With the exception of _S. rautanenii_[12], this study is also the first to present results on elemental analysis of the cakes. Some differences in chemical composition were observed between traditionally prepared and Soxhlet-extracted oils. The finding that one sample of _S. rautanenii_ contained chiefly \(\alpha\)-eleostearic acid and the other one linoleic acid has also been reported [22], indicating that various factors might affect the final composition of the oil. It is possible that in a specific processing method, enzymes such as conjugate that are responsible for  
Figure 2: The SPME/GC-qTOF chromatogram of _O. serrulata_ oil: 1, propanediol; 2, cyclohexane; 3, ethyl benzene; 4, _m_-xylene; 5, _o_-xylene; 6, \(\alpha\)-phellandrene; 7, camphene; 8, propylisovalerate; 9, myrrene; 10, _p_-cymene; 11, limonene; 12, \(\gamma\)-terpinene. the conversion of linoleic acid to \(\alpha\)-eleostearic acid might be inhibited by excessive heat, resulting in higher concentrations of linoleic acid [18]. Other explanations are related to the observation that trees growing in certain areas, such as Botswana and Zimbabwe, had low levels of \(\alpha\)-eleostearic acid [22]. These trees could be subspecies or variants of _S. rautanenii_ lacking the enzymatic apparatus required for biosynthesis of \(\alpha\)-eleostearic acid. Specific environmental conditions such as water stress and lack of certain macro- and microelements in the soil might also influence the production of this compound. Other inconsistencies were also observed in the case of vitamin E and pigment (chlorophylls \(a\) and \(b\), and carotenoids) content. Again, the processing method together with storage conditions might affect the final composition, since these compounds are prone to degradation when exposed to light and heat [23; 24; 25]. The vitamin E and pigment content might also be influenced by environmental factors such as drought, excessive sunlight, and genetic variability, where mutants lacked enzymes necessary for biosynthesis [26; 27]. The oil, and even the flower and fruit, of O. _serrulata_ has a very distinctive odor, which is described by many Zambian locals as foul or reminiscent of a decayed human body. Despite this, the oil is preferred by the locals over _P. curatellifolia_ and _S. rautanenii_ oil, seemingly due to its superior taste (personal communication, 12 June 2019).