Screening of microorganisms for bioconversion of (+)-valencene to (+)-nootkatone

- We conducted a microorganism screening to convert (+)-valencene to (+)-nootkatone.
- We evaluated different bioconversion systems using orange essential oil.
- Botryodiplodia theobromae and Yarrowia lipolytica showed the highest (+)-nootkatone concentrations in all systems.
- The method presented allowed identification of potential microorganisms for the bioconversion.

The production of (+)-nootkatone, highly appreciated by fragrance and flavour industries, can be performed by whole-cell bioconversion from the sesquiterpene (+)-valencene, a compound readily available in orange essential oil. The aim of this work was to screen for microorganisms that convert (+)-valencene to (+)-nootkatone using different bioconversion systems. The screening was conducted using six different microorganisms, and bioconversion experiments were set up on surface culture using serological flasks containing PDA at 30 °C. It was observed that Botryodiplodia theobromae 1368, Yarrowia lipolytica 2.2ab, and Phanerochaete chrysosporium oxidised (+)-valencene to (+)-nootkatone, reaching (+)-nootkatone concentrations of 231.7 ± 2.1, 216.9 ± 5.8 and 100.8 ± 2.6 mg L−1, respectively. Different bioconversion conditions were also tested-aqueous, organic, and biphasic-all resulting in similar (+)-nootkatone production. Both B. theobromae 1368 and Y. lipolytica 2.2ab showed substrate inhibition above 4.2 × 10−2 and 0.13 g of (+)-valencene (g of biomass)−1, respectively, in aqueous phase experiments. Furthermore, B. theobromae 1368 and Y. lipolytica 2.2ab showed product inhibition when concentrations reached above 17.02 and 34.78 mg of (+)-nootkatone (g of biomass)−1, respectively. The experimental method presented will be useful for ongoing studies on the selection and operation of the proper bioreactor at different bioconversion conditions.