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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.

Flavour and fragrance compounds are extremely important for food, feed, cosmetic and pharmaceutical industries. In the last decades, due to the consumer’s increased trend towards natural products, a great interest in natural aroma compounds has arisen to the detriment of chemically synthesised ones. Recently, solid state fermentation (SSF) has been applied in the production of many metabolites. Aroma compounds can be produced by SSF with a higher yield compared to submerged fermentation (SmF). In SSF processes, aroma compounds can be produced in the solid matrix or in the headspace, but they can be lost or stripped when aeration is required. This review focuses on the production of aroma compounds by SSF processes with a special highlight on in situ systems to recover the volatiles released in the gaseous phase and stripped due to aeration. Following a brief presentation of specificities of SSF processes concerning the choice of microorganisms and the solid matrix used for the production of aroma compounds, bioreactor aspects, factors affecting production of aroma compounds and in situ gas phase aroma recovery systems in aerated SSF bioreactors are discussed.

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[sup.−1] and 1190 mg L[sup.−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[sup.−1] ) and it reached a very high concentration of 4600 mg L[sup.−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.