A method for preparing a biologically active complex, said method comprising a recombinant protein having the sequence of α-lactalbumin, such as human α-lactalbumin or a fragment thereof but which lacks intra-molecular disulfide bonds, and oleic acid, and process for preparing this are described and claimed. The recombinant protein suitably has cysteines found in the native protein changed to other amino acids, such as alanine. Improvements in recombinant expression, process rationalisation and yields of biologically active complexes, as well as the complexes obtained are also described and claimed.