Ionic balance: a closer look at the K+ migrated and H+ generated during bipolar membrane electro-acidification of soybean proteins

Electro-acidification of soybean proteins using bipolar membrane resulted i n the migration of K+ across cationic membranes in order to counterbalance H+ generated at bipolar membranes therefore keeping the protein solution el ectrically neutral. In this study, (1) soya protein concentrate (SPC) was t itrated in order to determine the number of H+ necessary to reduce the pH o f solutions at different concentrations of protein (15 and 60 g/l SPC), (2) the number of H+ to be generated during bipolar-membrane electro-acidifica tion (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 mea sured, and (4) finally, the number of K+ migrated was compared to the numbe r of H+ electro-generated. SPC concentration was found to be correlated with the number of H+ needed t o 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-gene rated 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 c ompartment during BMEA has been demonstrated to be strongly correlated with the number of H+ electro-generated. This very good correlation confirms th e validity of the H+ calculation. (C) 1999 Elsevier Science B.V. All rights reserved.