Impact of pH on ultrafiltration membrane selectivity during electrodialysis with ultrafiltration membrane (EDUF) purification of soy peptides from a complex matrix

The aim of the present study was to investigate the influence of pH on the separation of a pepsin-pancreatin soy proteins isolate (SPI) hydrolysate, by electrodialysis with ultrafiltration membranes (EDUF) and particularly the influence of pH on ultrafiltration (UF) membrane selectivity. In this context, changes in conductivity, UF and ion-exchange membranes (IEM) electric resistance and peptide migration rates were monitored during a 4 h-EDUF treatment, under three controlled pH conditions (3, 6 and 9). According to these results, the pH value was demonstrated to influence the composition of recovery compartments, but not the migration rate of peptides. However, in contrary to the general accepted idea, even if pH was increased, migration rate in anionic peptides recovery compartment (KCl 1) was stable (no significant effect of pH was reported). As proposed in a tentative model, modification of the UF membrane global charge affected the peptide–membrane interactions which may limit peptide migration to the anionic peptides recovery compartment (KCl 1). Finally, pH modulation appeared to be an efficient way to concentrate the low molecular weight peptides (<400 Da) in the cationic peptides recovery compartment (KCl 2), and to limit the diversity of peptides recovered in the anionic peptides recovery compartment.