Current projections for the crop mix in the Bio-Plex and the future Lunar bioregenerative life support system indicate that without supplemental oil production, the crew's diet will be extremely low in fat, with little refined oil available for food processing or preparation. Although soybeans, peanuts and dwarf brassica (similar to canola) have been suggested as oil crops, each one poses significant problems either in horticulture, harvesting, productivity or byproduct utilization. An alternative to plant oils is “single-cell oil” or SCO. Lipid-accumulating “oleaginous” micro-organisms may accumulate up to 60% of their dry weight as triglycerides. Their high growth rates enable them to synthesize lipids with far greater productivity than higher plant systems. The current top candidate species for use in a bioregenerative system is a yeast, Cryptococcus curvatus.
Oleaginous micro-organisms can be cultivated heterotrophically or autotrophically, depending on the species and bioreactor type. Initial estimates have suggested that the needed quantity of oil can be produced heterotrophically from the inedible biomass expected to be generated in a bioregenerative system. Heterotrophic production would be expected to reduce the system equivalent mass.
Any oil produced on station will need to satisfy various requirements for functionality, safety and stability. Anticipated uses include baked goods, stir-frying, sauces, and bread spreads. Standards for the oil's physicochemical properties - melting curve, color, odor, flavor, heat stability and storage stability - must be established based on anticipated uses, to focus development work and allow fair comparison of SCO, locally produced higher plant oils, and “imported” oils.
This paper identifies the state of the art in production of microbial oils, presents preliminary experimental results, describes initial criteria for the chemical and culinary properties of these oils, and evaluates the economics of single-cell oil production in a bioregenerative life support system.