The aim of this work is to accurately measure fundamental surface properties, i.e., zeta potential, isoelectric point and protein size that determine the optimal separation conditions of Bovine serum albumin and lactoferrin, two high added value food proteins whose similarity in weight makes their separation a scientific and technical challenge. The systematic study of these proteins' surface properties was performed under different conditions: (i) 3.0 < pH < 10.0, (ii) electrolyte type: KCl, NaCl and CaCl2 and concentration (0.01-0.1 M KCl) and (iii) protein concentration in the range of 0.04-4.0 g L-1 for BSA and 0.01-1.0 g L-1 for LF with the objective of establishing the optimal separation conditions. Finally, the comparison of the experimental and theoretically calculated values revealed significant deviations under specific conditions, highlighting the simplicity of the theoretical assumptions and leading to the conclusion that the use of experimental surface properties is still needed for the correct design of food protein separation processes. (C) 2014 Elsevier B.V. All rights reserved.