Recently, the market value of aromas has constantly been rising. Because the supply from natural feedstock is limited, the biotechnological production has received more interest. Thus far, only a few attempts have been made to produce α-ionone, a valued essential aroma of raspberry, biotechnologically. This study reports a production process for enantiopure (R)-α-ionone from lab scale (2–150 L) with typical titer of 285 mg/L broth to industrial scale (up to 10 000 L) with a titer up to 400 mg/L broth, focusing on the development of a downstream process with a maximized yield at minimized effort. The developed recovery consists of solid–liquid extraction from the biomass at φ = 0.4 g of n-hexane/g of biomass for 90 min at ambient temperature and adsorption from the aqueous supernatant at Φ = 0.5 g of Diaion HP-20/mg of α-ionone, followed by desorption at Ψ = 30 g of n-hexane/g of Diaion HP-20. Altogether, natural α-ionone could be gained in substantial quantity and purity of >95%.
BACKGROUND: Nowadays, biotechnological production receives increasing interest as an alternative source of natural aromas. Unfortunately, especially for hydrophobic and semi-volatile aromas, the heterogeneous product partitioning between all phases present in fermentation makes recovery challenging. Additionally, when an aroma displays an inhibitory effect on the production microorganism, product removal during fermentation is recommendable. In-line aroma stripping offers an elegant way to deal with such challenges. This study reports the use of rotating packed bed (RPB) technology for the intensification of stripping of ⊍-ionone, a key aroma of raspberry, from a model fermentation slurry containing Saccharomyces cerevisiae cells in a concentration of 250 g-CWW L −1. RESULTS: Throughout all experimental investigations, yeast cells were robust towards both the chemical stress from aroma exposure at a concentration of up to 400 mg L −1 and the mechanical stress from peripheral equipment and rotation of up to 2750 rpm, as a maximum of 11.3 ± 0.5% disrupted cells were measured during continuous processing in an RPB. An increase in the rotation speed led to an enhanced transfer of ⊍-ionone from the fermentation slurry to the gaseous phase. CONCLUSIONS: RPB technology is found to be promising for the intensification of in-line stripping of biotechnologically produced aromas from crude fermentation broth without cell separation. The use of subsequent RPBs equipped with custom packings and flexibly adjustable rotation speed displays a holistic aroma recovery process supporting the way to commercial competitiveness of biotechnological aromas.
An increasing consumers’ call for natural aromas fuels the development of biotechnological aroma production. Although aroma fermentation is quite advantageous, especially severe product losses of volatile compounds through the bioreactor off‐gas may challenge the downstream processing. The application of novel process intensification methods to overcome the common drawbacks of conventional apparatuses might be helpful on a way to commercial competitiveness of biotechnological aromas. This study explored the suitability of rotating packed bed (RPB), a rotating mass transfer enhancing machine, for the absorption of model aroma compounds in rapeseed oil. Increasing the rotation speed from 500 to 2750 rpm led to two‐ to threefold higher absorption efficiencies at elsewise constant conditions. Aiming for an enriched aromatic intermediate, 2.5 L of rapeseed oil was processed in a recycle for 200 minutes, and a final concentration of benzaldehyde of 0.323 ± 0.026 g/Loil was achieved. Compared to packed columns, the RPB outperforms at equal packing depth or requires less packing area to deliver same efficiency. Especially, the use of custom 3D‐printed spiral packing with elaborated wall film flow combined with rotation supported liquid distribution allows using absorbents with viscosities as high as 100 mPa·s at low pressure drop increase. However, small dimensions severely limit the performance of a laboratory‐scale RPB as the casing contributes disproportionally to mass transfer.
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