Extractive fermentation of aroma with supercritical CO2

This work deals with the feasibility of achieving an extractive fermentation of 2-phenylethyl alcohol, the rose aroma, coupling fermentation with Kluyveromyces marxianus and supercritical carbon dioxide (SCCO2) extraction. The extractive process is, in this case, of special interest due to the strong yeast inhibition by 2-phenylethyl alcohol. First results confirmed that direct SCCO2 extraction is not possible, due to a drastic CO2 effect on cell viability. It is therefore necessary to perform cell separation prior to the extraction. Aroma extraction conditions from a synthetic mixture were then optimized, a pressure of 200 bar and a temperature in the range 35-45 degrees C being chosen. Under these conditions, the distribution coefficient Kd is 2 times higher than during the extraction using a conventional organic solvent, n-hexane. Using a simple model of aroma partition between aqueous and SCCO2 phases, the parameters of a continuous extraction from a synthetic broth were defined. The two substrates, glucose and phenylalanine, are not extracted whatever the conditions. As predicted by the model, more than 90% of 2-phenylethyl alcohol can be extracted, while the extraction of ethanol, the second main product, can be easily tuned with respect to operating conditions, as a function of its influence on the fermentation. Finally, the feasibility of the aroma recovery using two depressurization steps at the outflow of the extraction vessel was demonstrated; 97% of the extracted aroma was recovered, and a mass purity of 91% was achieved. Copyright 1999 John Wiley & Sons, Inc.