Extraction of β-Lactoglobulin from Bovine Milk by Affinity Counter-Current Distribution in Aqueous Two-Phase System

The counter-current distribution pattern of milk and whey α-lactalbumin and β-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 5mM EDTA. This hydrophobic binding ability of α-lactalbumin, but not of β-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 β-lactoglobulin, which was apparently free of detectable contamination, as assessed by SDS-PAGE.