Globular milk proteins have lots of potential applications in the form of highly purified fractions due to their numerous biological, nutritional and functional properties. Membrane filtration is now envisaged as a promising purification technology as it can be more environmental-friendly than chromatography and quite as efficient as this current technique. However, the impact of membrane filtration on the final properties of proteins still needs to be clarified and especially in case of metalloproteins as they have the specificity to bind one cofactor entity which is highly decisive for the preservation of their structure and functionality. In this study, the impact of dead-end ultrafiltration on the properties of the metalloprotein alpha-lactalbumin (alpha-LA) was described depending on the membrane cut-off. For membranes with a cut-off larger than alpha-LA molecular weight (30 or 100 kg mol(-1)), structural and functional modifications evidenced after permeation of a mixture between the apo- (without cofactor) and holo-form (native form) were consistent with an increase in the holo-alpha-LA content but did not point out any physical impact on alpha-LA structure. The modification of alpha-LA properties was rather attributed to the displacement of the equilibrium between the apo- and halo-forms during filtration. With a membrane cut-off close to alpha-LA molecular weight (10 kg mol(-1)), structural and functional properties of the protein observed after permeation could not be reasonably associated with the increase in the holo-alpha-LA content. Results suggested that shear stress inside membrane pores slightly impacted alpha-LA structure and thus dictated final properties of the permeated fraction especially in terms of solubility and thermal stability. The impact of dead-end UF through the 10 kg mol(-1) membrane was supposed to be moderate and to affect less than 30-40% of permeated proteins. (C) 2013 Elsevier B.V. All rights reserved.