A new method for isolation of native α-lactalbumin from sweet whey

A novel approach to α-lactalbumin (α-LA) isolation from sweet whey comprised a membrane filtration and a tryptic treatment of permeate. The ultrafiltration (UF) was performed with a laboratory and a pilot-scale equipment using membranes with 100 and 150 kDa molecular mass cut-off limits, respectively. The transmission of α-La was optimal at 45 °C, 2.0 bar and at pH 6.7. The transmission of proteins was proportional to the volume reduction ratio. Under these conditions, the transmission of α-LA into the permeate was about 25% and the purity was about 36% and 44% (inclusive caseinomacropeptide (CMP)) on the laboratory- and pilot-scale, respectively. For further purification, a tryptic hydrolysis step was applied. At a 10.0% hydrolysis degree, all the β-lactoglobulin was digested and practically no α-LA was degraded, while serum albumin remained in the hydrolysate as the only impurity. If the hydrolysis was prolonged a partial digestion of α-LA was observed. After a second UF and diafiltration of the hydrolysate using a 10 kDa membrane, the calculated overall recoveries were up to 15% of the α-LA present with a purity of 90–95%. The new method was found to be reproducible, selective and robust.