1. Institute of Chemical Engineering, Bulgarian Academy of Sciences, Academician George Bonchev Street, Building 103, 1113 Sofia, Bulgaria, and Equipe Génie Chimique, Laboratoire de Chimie Agro-Industrielle UMR 1010 INRA, Ecole National Superieure des Ingenieurs en Arts Chimques et Technologiques, Institut National Polytechnique de Toulouse, 118, Route de Narbonne 31077 Toulouse, France