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The production of γ-decalactones as aroma compounds is highly dependent on the access of the biocatalyst to substrate and co-substrate (oxygen). In this work, the potential of solid state fermentation (SSF) is investigated for this production with Y. lipolytica W29. Luffa sponge was used as an inert support and the investigation focused on the impact of aeration on metabolites. In that goal, experiments were carried out in three different SSF reactor types, wide-mouth Erlenmeyer flask (static aeration), forced aeration mini-reactor, and small-headspace bottle (without aeration). Four lactones were detected by GC–MS during the degradation of ricinoleic acid from castor oil by Y. lipolytica W29: 3-hydroxy-γ-decalactone, which reached the high concentration of 5 g/L (in wide-mouth Erlenmeyer flask), γ-decalactone, dec-2-en-4-olide and dec-3-en-4-olide. In this study, some yeast cells changed their morphological properties from the yeast-like shape to pseudo-mycelium and mycelium. These cells may undergo a metabolic shift resulting in the high production of 3-hydroxy-γ-decalactone. The yield of lactone in the small-headspace bottle was very low suggesting insufficient oxygen availability. For their part, forced-aeration conditions in mini-reactors resulted in the stripping of lactone compounds. From the present work, an alternative process is proposed as a novel model for lactone production. [ABSTRACT FROM AUTHOR]

The aim of this study was to optimise airflow rate for glucoamylase and protease production from waste bread via solid state fermentation by Aspergillus awamori in packed bed bioreactors. Airflow rates, between 0.40 and 3.00 vvm, were tested. In all experiments, the fungal growth was almost uniform throughout the solids. Fungi grew both on and within the substrate and fungal cakes were formed. The highest glucoamylase and protease activities were recorded as 130.8 U/g bread (db) and 80.3 U/g bread (db) in the experiments with 1.50 wm airflow rate, respectively. These values are 27.2% and 32.3% higher than the glucoamylase and protease activities obtained in petri dish experiments with static air. At 1.50 vvm airflow rate, the dry weight of the solids had decreased to 46% of the initial value at the end of the fermentation. The temperature of the solids increased up to 37.5 °C with high axial temperature gradients due to high metabolic activity. The average moisture content of the solids first decreased to 150% (db) and then increased to 275% (db) by the end of the fermentation. Both above and below 1.50 wm airflow rate, enzyme production and fungal growth were affected significantly. Also, a Gaussian-based mathematical model was developed to model the effects of airflow rate on enzyme production. The model fitted almost seamlessly to the experimental data. Thus, this study clearly showed the effects of aeration on glucoamylase and protease production from waste bread under solid state fermentations. [ABSTRACT FROM AUTHOR]