LAUSR

To study the effect of elevated oxygen concentrations on β-oxidation for the production of lactones by Yarrowia lipolytica W29 in solid state fermentation (SSF), experiments using oxygen-enriched air, with different initial concentrations of oxygen ratio, were carried out. Growth kinetics using an oxygen ratio of 30% reached the stationary phase earlier than other conditions used. In addition, the production of γ-decalactone and 3-hydroxy-γ-decalactone reached the maximal concentrations of 270 mg L−1 and 1190 mg L−1, respectively. Using higher initial oxygen ratios (40% and 50%), an incomplete growth inhibition occurred and resulted in a higher concentration of yeast at the stationary phase and a slightly higher 3-hydroxy-γ-decalactone accumulation. When oxygen-enriched air (oxygen ratio of 30%) was injected twice (at 0 and 20 h), 3-hydroxy-γ-decalactone reached a higher concentration (1620 mg L−1) and it reached a very high concentration of 4600 mg L−1 in the condition of oxygen-enriched air injected many times (at 0, 20, 35, 48 and 60 h). This study suggested that oxygen is required for the production of 3-hydroxy-γ-decalactone in SSF. Oxygen may be consumed preferentially for long-chain fatty acid oxidations rather than at C10-level. Furthermore, the production of γ-decalactone may be improved by optimizing the growth conditions to reach a very high specific growth rate. A low oxygen availability in the system at the stationary growth phase led to an inhibition of γ-decalactone degradation. From the present work, an alternative system is proposed as a novel model to study the effect of elevated oxygen concentration in SSF.