Oleaginous species

Although production of yeast lipids as a source of triacylglycerol oils is limited to oleaginous species (Table 9.2), there are several other potentially useful lipid types produced by yeasts. These, however, do not represent alternatives to plant seed oils but are mainly for technical applications within the oleochemical industry. As this area is strictly outside the scope of this book, these alternative yeast lipids are described only briefly. 

Malic enzyme is not believed to be essential for oleaginicity to be achieved as some yeast species appear not to contain it. In these species, NADPH is probably supplied by the oxidation of glucose via the pentose phosphate pathway in which the first two reactions, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, are both producers of NADPH. 

Table 9.2 lists the oleaginous yeasts currently known to produce 20% or more lipid together with their major component fatty acids. It will be seen that this is a relatively short list consisting of less than 30 species including the border-line ones. The total number of yeast species is 590 (Barnett et al., 1990), so it can be instantly appreciated that oleaginicity is not a widespread characteristic amongst yeasts even though many of the species have yet to be fully explored for lipid accumulation. 

In a survey of the literature, the present author could only identify some 64 species from all orders and families of moulds that had been recorded as producing over 25% lipid although there were many more that had between 20 and 25% lipid and thus may be potentially oleaginous (Ratledge, 1989b). A selection of some of these moulds, taken from the main divisions of the moulds, is given in Table 9.7. It should be pointed out that C12 and C14 fatty acids are known to be produced in some abundance by some species of Entomophthora, and that the hydroxy fatty acid, ricinoleic acid, 12-hydroxyoleic acid, is produced by... 

Elaeis guineensis is an edible oleaginous plant, known as African oil pabn or macaw-fat. This tree produces three different edible oils palm oil extracted from the pulp of the palm fruit, coconut oil and palm kernel oil extracted from the kernels of the coconut (copra), and oil palm (Reeves et al., 1979). Palm oil can also be obtained from the American oil palms Elaeis oleifera and Attalea maripa, but only hybrids between these species are planted commercially thus they present higher disease resistance and lower unsaturated fatty acid profiles in the oil. 

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