Preparative membrane adsorber chromatography for the isolation of cow milk components.

Preparative membrane adsorber (MA) chromatography was used to process milk fractions such as the whey and the permeate commonly obtained during lactose production in modern dairies. In MA systems the fluid-dynamic and mass-transfer properties are superior to conventional HPLC or fast protein liquid chromatography (FPLC) columns. Since the flow resistance caused by the MA stacks is quite low, high throughputs can be realized without loss in resolution. Feed sizes were varied from the laboratory scale (several ml) up to batches of 10 1 during the investigations. MAs based on modified cellulose filtration membranes (average single layer thickness 200 microns, average pore size 5.0 microns) were used for the small-scale experiments. The MAs are functionalized by covalent linkage of strong and weak ion exchanger groups to their surface. Three commercially available types were used [strong ion exchanger: MA Q15 (3 layers of 5 cm2) and MA Q100 (5 layers of 20 cm2); weak ion exchanger: MA D15 (3 layers of 5 cm2); all Sartorious, Germany]. For the large-scale work a dead-end filtration unit containing up to 1300 cm2 of MA-area was used. Here MAs based on a synthetic co-polymer, that 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. The flow-rate could be raised to the limit of the respective chromatographic 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 and a fine-tuned gradient allowed the separation of BSA, alpha-lactalbumin and the genetic variants of beta-lactoglobulin, even though no baseline separation was possible in the latter case. The use of coupled modules rather than a single one is shown to improve the separation considerably.