SELECTIVE SEPARATION OF TRYPTIC BETA-CASEIN PEPTIDES THROUGH ULTRAFILTRATION MEMBRANES - INFLUENCE OF IONIC INTERACTIONS

Peptide separation by selective membrane filtration has numerous potential applications such as production of peptides with biological activities or specific enrichment in compounds acting as flavoring agents or as growth factors required by the fermentation industry. The retention of peptides arising from tryptic hydrolysis of beta-casein using an M5 Carbosep membrane (molecular weight cutoff = 10,000 D) has been studied. The peptides with known sequences were characterized by their molecular weight, isoelectric point, and hydrophobicity. Our experiments highlighted that their transmission involves mechanisms other than size exclusion as developed elsewhere. The effect of ionic interactions between peptides and membrane has been investigated by varying pH, ionic strength of bulk, and electric potential of filtering material. The charge of both peptides and membrane plays an important role in the transmission, particularly with small size and high or low isoelectric point. Then, peptides with the same sign as the membrane have lower transmission than expected from the size exclusion model, whereas peptides with opposite sign have higher transmission than expected, and even higher than 1 with some of them. (C) 1995 John Wiley & Sons, Inc.