Ultrafiltration membrane cut-off impacts structure and functional properties of transmitted proteins: Case study of the metalloprotein α-lactalbumin

•The impact of ultrafiltration on the properties of proteins has to be clarified.•Modifications of a metalloprotein after permeation are dependent on pore size.•Large cut-offs induce a disequilibrium between protein and cofactor permeation.•The use of a small cut-off suggests the role of shear stress inside membrane pores.