Electro-acidification of soybean proteins using bipolar membrane resulted in the migration of K+ across cationic membranes in order to counterbalance H+ generated at bipolar membranes therefore keeping the protein solution electrically neutral. In this study, (1) soya protein concentrate (SPC) was titrated in order to determine the number of H+ necessary to reduce the pH of solutions at different concentrations of protein (15 and 60 g/l SPC), (2) the number of H+ to be generated during bipolar-membrane electro-acidification (BMEA) was deduced, (3) total K+ migrated during BMEA run at different protein concentrations (15, 30 and 60 g/l SPC) in a previous work were measured, and (4) finally, the number of K+ migrated was compared to the number of H+ electro-generated. SPC concentration was found to be correlated with the number of H+ needed to insolubilize protein, and the number of K+ migrated during BMEA. The different mathematical relations obtained from experimental values of H+ added by chemical acidification (in mM/g insoluble protein at pH 4.4 and in mM/g protein insolubilized) allowed the determination of H+ electro-generated during BMEA process in relation to the concentration of protein to be precipitated. Moreover, the electromigration of K+ from the protein solution to the KCl compartment during BMEA has been demonstrated to be strongly correlated with the number of H+ electro-generated. This very good correlation confirms the validity of the H+ calculation.