EXTRACTION OF BETA-LACTOGLOBULIN FROM BOVINE-MILK BY AFFINITY COUNTERCURRENT DISTRIBUTION IN AQUEOUS 2-PHASE SYSTEM

The counter-current distribution pattern of milk and whey alpha-lactalbumin and beta-lactoglobulin in a two-phase system containing 7% (wt/wt) Dextran T-500 and 5% (wt/wt) polyethylene glycol 6000 was investigated. Both proteins showed similar distribution profiles and were clearly separated from the main bulk of milk protein. The use of polyethylene glycol bound to a hydrophobic ligand (palmitate polyethylene glycol) enhanced the affinity of both proteins for the upper phase rich in polyethylene glycol when assayed in the presence of 5 mM EDTA. This hydrophobic binding ability of alpha-lactalbumin, but not of beta-lactoglobulin, was strongly sensitive to the presence of Ca2+. Thus, a counter-current distribution of whey in the presence of palmitate-polyethylene glycol and Ca2+ allowed a single extraction of beta-lactoglobulin, which was apparently free of detectable contamination, as assessed by SDS-PAGE.