PREPARATIVE MEMBRANE ADSORBER CHROMATOGRAPHY FOR THE ISOLATION OF COWMILK COMPONENTS

Preparative membrane adsorber (MA) chromatography was used to process milk fractions such as the whey and the permeate commonly obtained dur ing lactose production in modern dairies. in MA systems the fluid-dyna mic and mass-transfer properties are superior to conventional HPLC or fast protein liquid chromatography (FPLC) columns. Since the flow resi stance caused by the MA stacks is quite low, high throughputs can be r ealized without loss in resolution. Feed sizes were varied from the la boratory scale (several mi) up to batches of 10 1 during the investiga tions. MAs based on modified cellulose filtration membranes (average s ingle layer thickness 200 mu m, average pore size 5.0 mu m) were used for the small-scale experiments. The MAs are functionalized by covalen t linkage of strong and weak ion exchanger groups to their surface. Th ree commercially available types were used [strong ion exchanger: MA Q 15 (3 layers of 5 cm(2)) and MA Q100 (5 layers of 20 cm(2)); weak ion exchanger: MA D15 (3 layers of 5 cm(2)); all Sartorius, Germany]. For the large-scale work a dead-end filtration unit containing up to 1300 cm(2) of MA-area was used. Here MAs based on a synthetic co-polymer, t hat were prepared from cut-out sheets, were inserted. Chromatographic conditions were transferable from the cellulose- to the polymer-based MA carrying the same functional groups. The influence of the flow-rate and the pH of the mobile phase on the separation was investigated. Th e flow-rate could be raised to the limit of the respective chromatogra phic systems and/or MA modules without loss in resolution. The use of the strong anion exchanger MA together with a mobile phase pH of 6.0 a nd a fine-tuned gradient allowed the separation of BSA, alpha-lactalbu min and the genetic variants of beta-lactoglobulin, even though no bas eline separation was possible in the latter case. The use of coupled m odules rather than a single one is shown to improve the separation con siderably.