Evaluating transfers of aroma compounds during the concentration of sucrose solutions by osmotic distillation in a batch-type pilot plant

The transfer of volatiles was studied during the batch concentration of a sucrose solution by osmotic distillation in a semi-industrial pilot plant. The transfer kinetics of four aroma compounds from fruits were measured by gas chromatography. Although significant adsorption phenomena on the membrane were notable; these can easily be limited by saturating the installation before concentration. A simple model, based on the definition of the apparent permeability, was developed to characterize transfer kinetics. Losses in volatiles during concentration are directly linked to the relative value of this permeability, compared with water flux. Decreasing circulation velocity and temperature of the solution to be concentrated slowed the transfer of aroma compounds down considerably. Limiting losses of volatiles by acting on operating conditions is thus possible. Compared with the classic evaporation process, osmotic distillation induces smaller losses in aroma compounds. (C) 2003 Elsevier Science Ltd. All rights reserved.