INFLUENCE OF HYDRODYNAMIC CONDITIONS IN THE FEED CHANNEL DURING BIOPOLYMER CONCENTRATION Philippe MARÉCHAL, Jeremy JORDA, Luc RIGAL # and Pierre-Yves PONTALIER * Laboratoire de Chimie Agro-Industrielle UMR 1010 INRA / INP-ENSIACET 118 route de Narbonne 31077 Toulouse cedex 4 (France) Tel : 33 5 62 88 57 06 . Fax : 33 5 62 88 57 30 ABSTRACT Ultrafiltration is a very efficient concentration method prior to the atomization of biopolymers extracted from plants. Trials for the concentration of rhamnogalacturonan solutions were realized with PES membrane cassettes with a molecular weight cut-off (MWCO) ranging from 1kDa to 50 kDa. The higher rejection rates were obtained by the two membranes with the highest MWCO. These results can partially be explained by the differences in the membranes’ structure. As a consequence of the biopolymers gel forming properties, the gel layer created in the feed channel may also modify the permeation properties of the membranes. Two parameters seem to act on gel layer properties : the shear-thinning properties of the polymer solution and the screen in the feed channel which both change the flow pattern. KEY WORDS: Ultrafiltration, Polymer, Hydrodynamic, Membrane Cassettes, Mass Transfer INTRODUCTION The technological properties (emulsifying, thickening) of biopolymers offer substantial advantages for many industrial applications [1]. Among these polymers, rhamnogalacturonans are polymers usually extracted from citrus fruit or apple. A new source for their production could come from beet pulp extraction. The objective of the extraction phase is to disrupt cell walls by mechanical and chemical means, in order to release the biopolymers. The extraction leads to the production of complex solutions containing biopolymers along with other vegetable degradation products of (e.g. proteins, sugars and inorganic salts). The purification of this solution is vital as, when the percentage of rhamnogalacturonan is above 75% of the dry matter (DM), the powder can be used as pectin. However, the purification of such solutions is complex and can only be achieved by combining several stages : centrifugation, filtration and alcohol precipitation. Precipitation is an expensive stage because it needs several volumes of alcohol per extract volume. Spray drying can be introduced instead of precipitation. In such a case, it should follow the purification and the pre-concentration of the extract. Ultrafiltration is practical as a method of concentrating sensitive solutions because it functions at room temperature. The purification of the biopolymer is usually achieved with membranes of a MWCO ranging from 10 to 20 kDa [2], some authors having however used 300 kDa [3] or 3 kDa membranes [4]. Optimal conditions for biopolymer filtration are difficult to define because the hydrodynamic volume of the molecule is not directly linked with its molar mass. The flexibility and the branchings of the macromolecules also influence their permeability through the pore and thus, have a bearing on the selection of the membrane’s MWCO [5-6]. Biopolymers also act on the solution’s viscosity and can form a gel above a limit concentration. Hence, hydrodynamic properties, and more particularly membrane configuration, are relevant for filtration efficiency. It is therefore necessary to adapt the processes to each biopolymer.