An air-lift biofilm reactor for the production of γ-decalactones by Yarrowia lipolytica

• New simple way to immobilise yeast for an improved production of lactones.
• Y. lipolytica in biofilm presents specific morphological and metabolic characteristics.
• Aeration triggers yeast hydrophobic surface properties and adhesion to plastic.
• Detection of yeast subpopulation of importance to biotransformation.

Decalactones are interesting flavouring compounds that can be produced from ricinoleic acid. In this study, the production of lactones in biofilms using Yarrowia lipolytica is investigated. The hydrophobia of cells increased for increased aeration rates resulting in higher adhesion when the reactor wall was hydrophobic (plastic). To increase adhesion, sheets of methyl-polymethacrylate (PMMA) were added in the reactor and the production of lactones increased with the surface of plastic added, reaching 850 mg/L of 3-hydroxy-γ-decalactone for 60 cm2. In an Airlift bioreactor made of PMMA, biofilms were present at the top of the reactor for increased aeration. In the meantime, a metabolic shift occurred resulting in high amounts of 3-hydroxy-γ-decalactone. At 0.493 vvm and 61 h of culture, the dissolved oxygen ratio was of 28.6% and cells grew to only 1.29 × 106 cells/mL in the liquid medium but 3-hydroxy-γ-decalactone accumulated to 1.7 g/L instead of less than 0.3 mg/L for lower aeration. Adhering cells had a particular elongated shape intermediate between the yeast and the pseudofilamentous forms. It is concluded that adhering Y. lipolytica cells are in a specific physiological state changing their structure but also their metabolic properties and these properties make them good candidate for simple immobilisation process.