To make just 1 kg of nootkatone, 400,000 kg of grapefruits are needed. Since grapefruit production is limited, nootkatone is one of the most expensive flavour ingredients in the world, costing £3000-4000 per kg. Fortunately, nootkatone can also be made from valencene – a similar molecule produced from oranges, which are more easily sourced and therefore vastly cheaper at £300 per kg. The chemical route for the conversion of valencene to nootkatone has traditionally involved heavy-metal catalysts and peroxides and is therefore not classed as natural by the EU.

Oxford Biotrans has used engineering biology to make E. coli that produces Cytochrome P450, an enzyme present in humans, plants and animals. Cytochrome P450, when mixed with valencene, adds an oxygen atom and removes two hydrogen atoms, leaving nootkatone. This natural and environmentally friendly process avoids using the harsh reagents and conditions of many chemical conversions, thus producing less polluting chemical waste and using less energy.