Nowadays, aroma concentrates are widely used in the food industry to improve the flavor of formulated foods or to compensate for the flavor losses of natural raw products during industrial processing. Consumers are more attracted to food products containing only ‘‘natural’’ or ‘‘nature-identical’’ additives, either for health reasons Žas synthetic compounds are likely to contain traces of harmful organic reactants., or simply because they provide a richer and more subtle sensory profile. Those ‘‘natural’’-labeled aroma compounds are generally found at very low concentration Žin the PPM range.in natural raw materials or in biosynthesis fermentation broths. Therefore, a cost-effective and efficient extraction step constitutes a major challenge for the production of such additives by the flavor industry. In order to recover odor-active organic substances from aqueous streams, the flavor industry relies mainly on the two main specific physico-chemical properties of flavor compounds:
Volatility: The distillation process has been the war-horse of the flavor industry for centuries. This method is efficient mainly for the ‘‘lighter’’ compounds, which generally display a low boiling temperature at atmospheric pressure. However, this method is extremely energy-costing Ždue to the phase Correspondence concerning this article should be addressed to H. E. Smorenburg. Current address of A. Baudot: IFP-Departement Techniques de Separation ŽRG 40., 1 et 4 avenue de Bois-Pr´eau, F-92852 Rueil-Malmaison, France. Current address of J. Floury: GEPEA-ENITIAA, DGPA, Rue de la G´eraudi‘ere, BP 82225, 44322 Nantes Cedex 3, France. change of the feed. and heat-sensitive compounds can easily get spoiled with such a treatment. Moreover, the vapour liquid-phase change is generally not favorable for the recovery of high-boiling flavor compounds. An alternative way to the distillation is the pervaporation technique that associates the evaporation of the aroma compounds with a selective transport by sorption and diffusion of the organic compounds through a dense polymer layer. Although this novel technique generally leads to an enhancement of selectivity if compared to distillation, the solution-diffusion transport step through the membrane induces low transmembrane fluxes ŽBaudot and Marin, 1997.which, until now, has limited the adoption of this technique in the flavor industry.