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

Peptide separation by selective membrane filtration has numerous poten tial applications such as production of peptides with biological activ ities or specific enrichment in compounds acting as flavoring agents o r as growth factors required by the fermentation industry. The retenti on of peptides arising from tryptic hydrolysis of beta-casein using an M5 Carbosep membrane (molecular weight cutoff = 10,000 D) has been st udied. The peptides with known sequences were characterized by their m olecular weight, isoelectric point, and hydrophobicity. Our experiment s highlighted that their transmission involves mechanisms other than s ize exclusion as developed elsewhere. The effect of ionic interactions between peptides and membrane has been investigated by varying pH, io nic strength of bulk, and electric potential of filtering material. Th e 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 t ransmission than expected from the size exclusion model, whereas pepti des with opposite sign have higher transmission than expected, and eve n higher than 1 with some of them. (C) 1995 John Wiley & Sons, Inc.