Partitioning and separation of α-lactalbumin and β-lactoglobulin in PEG/potassium phosphate aqueous two-phase systems

Bovine α-lactalbumin (α-La) and β-lactoglobulin (β-Lg) were partitioned in aqueous two-phase systems composed of polyethylene glycol (PEG) and potassium phosphate. The influences of several system parameters on protein partition coefficients such as PEG molecular weight, phase component concentration, pH, and addition of NaCl were investigated and discussed in terms of possible mechanisms involved. From partition results, α-La and β-Lg in Cheddar cheese whey could be separated by their differential partitionings in an aqueous two-phase system, where partially purified α-La and β-Lg could be recovered in the top and bottom phases, respectively. By using PEG with a low molecular weight (PEG 1000 or PEG 1500) and a high concentration of potassium phosphate (20% w/w), essentially pure β-Lg and 84% pure α-La from SDS-PAGE analysis could be obtained simultaneously from Cheddar cheese whey in a single liquid-liquid extraction step using aqueous two-phase systems.