Use of nanofiltration membranes for the desalting of peptide fractions from whey protein enzymatic hydrolysates

The performance of nanofiltration membranes for the desalting of a peptide mixture from tryptic hydrolysate of whey proteins containing 0.5 mol.L-1 sodium chloride has been investigated. Membranes are consisting of a strongly negatively charged material (MW15, MGI7, BQ01, B006, B007) or of a polyamide (MX07) layered onto a polysulfone support. A satisfactory desalting of the whey protein tryptic hydrolysate has been obtained with all membranes under study both for dead-end and cross-flow filtration. The most suitable membrane for desalination was MX07, providing the highest permeability for salt and the lowest loss of peptidic material. For all membranes, RP-HPLC analysis of the permeates obtained in dead-end filtration revealed the presence of 6 different peptidic sequences from beta-lactoglobuIin (beta-lg), but in a low amount (<11 %). The peptides found in the permeates are characterized by st net charge of 0 or +1, while other peptides of similar molecular weight but containing negatively charged amino acid residues (Glu, Asp) remain in the retentates. Furthermore, it has been demonstrated that, compared to dead-end filtration, cross-flow filtration results in higher ion-peptide selectivities and less membrane fouling. (C) Inra/Elsevier, Paris.