A range of microbial oils were cross-metathesized with ethene using Hoveyda−Grubbs second-generation catalyst. The products formed from the microbial oils were compared to alternative firstand second-generation oils. Upon separation, three separate fractions were produced: an alkene hydrocarbon fraction or aviation fuel fraction (AFF), a shorterchain triglyceride fraction that upon transesterification was suitable as a road transport fuel (road transport fraction, RTF), and a volatile short-chain alkene fraction (gas phase fraction, GPF). The fuel fractions were purified through distillation and compared to the relevant fuel standards. Though there was variation for the RTF because of the presence of long-chain saturates, all the RTF produced fell within the ASTM standard for biodiesel. The AFF was found to be highly suitable for aviation, falling entirely within the DEF-STAN fuel standard. In addition, the AFF possessed an energy density higher than that of Jet A-1, whereas 1-decene was found to have an oxidative stability higher than that of jet fuel. Finally, the GPF was found to predominantly contain propene, butene, and pentadiene isomers, all of which have application in the polymer industry. With further development, this process could provide the basis for a microbial oil biorefinery for the production of sustainable biofuels and polymer precursors.

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Global transportation is one of the major contributors to GHG emissions. It is essential therefore, that renewable, carbon neutral fuels are developed to reduce the impact of this sector on the environment. Yeasts, especially Saccharomyces cerevisiae, are key to transforming renewable bioresources to fuels that can be used with little adaption to the current transport infrastructure. Yeasts demonstrate a large diversity that produces a great metabolic plasticity, as such, yeasts are able to produce a range of fuel-like molecules including alcohols, lipids and hydrocarbons. In this article the current and potential fuels produced through fermentation, the latest advances in metabolic engineering and the production of lipids suitable for biodiesel production are all reviewed. Key technical terms Key term Definition Metabolic engineering A method of optimising the regulatory processes within cells, used to produce high amounts of desirable compounds Oleaginous yeast Oil containing yeast, typically the triglyceride oil should be above 20% of the dry weight Advanced biofuels Fuels which are compatible with current fossil fuels, and tend to give higher performance than either bioethanol or biodiesel Pentoses / hexoses C5 and C6 sugars respectively Isoprenoids Diverse range of compounds, derived from isoprene (2-methyl-1,3butadiene) units Future perspective Within 10 years a number of key advances could potentially make advanced fuels derived from yeast a central component of the global energy mix. It seems probable that legislation will be enacted to increase the biofuel content in current transportation fuels, while at the same time ensuring more evidence-based green credentials for biofuels on the market. Strict fuel properties legislation is slowly being relaxed to allow alternatives to ethanol and biodiesel to enter the fuel market, this is likely to continue and within a decade it is probable that a larger range of fuels will certified for general use. From an engineering perspective, advances in the processing, enzyme production and the development of novel strains of yeast will continue to reduce the total costs of converting lignocellulose to fuel molecules. Finally, a range of genetic toolkits are being developed for nonsaccharomyces yeasts, expanding the range of fuels and increasing the sugar to product conversion ratio. It seems likely therefore that alternative, more robust yeast strains to Saccharomyces will become prevalent for industrial biofuel production.

The oleaginous yeast Rhodotorula minuta has been used previously as a biocide agent and for the production of β‐carotene. In addition, R. minuta has been shown to produce up to 40% lipids, while demonstrating a faster growth rate than the similar oleaginous yeasts; Lipomyces starkeyii and R. glutinis. In this study, this promising yeast was evaluated for its potential to produce glyceride lipids under the harsh conditions and complex sugar mixtures produced from depolymerised lignocellulose. The fatty acid profile of R. minuta was not found to change significantly irrespective of the environmental conditions and contained approximately 20% palmitic acid, 5% stearic acid, 60% oleic acid and 15% linolenic acid. R. minuta was found to grow on a range of sugars, and could consume xylose and glucose when both sugars were present; however, R. minuta was found to be highly sensitive to inhibitors, such as furfurals and organic acids, formed under the harsh lignocellulose depolymerisation conditions. Accordingly R. minuta did not grow well on biomass depolymerised with an acid pre‐treatment stage. However, R. minuta was cultured successfully on food waste depolymerised with no additional acids, producing up to 19 g/l cell mass with a lipid content of up to 25% of the dry cell weight. Practical applications: While high oil productivity, fast growth rates and a suitable fatty acid composition are key traits for the economic viability of SCO production, it is essential that the organism can be cultured and produce lipids from low‐cost substrates. This requires the ability to assimilate the nutrients present in the desired hydrolysate, as well as maintain high‐growth rates in the presence of inhibitory compounds produced during the hydrolysis process. In this paper, we demonstrate that the yeast R. minuta has industrial applicability in being able to convert depolymerised waste food to lipids with a profile akin to rapeseed oil. Rhodotorula minuta lipid cultured on depolymerised food waste.