Effect of peptide distribution on the fractionation of whey protein hydrolysates by nanofiltration membranes

The fractionation of tryptic and chymotryptic hydrolysates of whey proteins by nanofiltration (NF) membranes has been investigated. Enzymatic hydrolysates were prepared by tryptic (TH) or chymotryptic (CH) hydrolysis of a commercial whey protein isolate followed by UF-treatment using a 10 000 g.mol(-1) MWCO in order to remove the enzyme and non-hydrolyzed material from the reaction mixture. Both hydrolysates were further fractionated using a SG13 (Osmonics) cellulose acetate NF membrane with a molecular weight cut-off(MWCO) of 2 500 g.mol(-1). A detailed examination of the peptide separation revealed that, for both TH and CH, the negatively charged peptides were in lower proportion in the permeates whereas the opposite trend was observed for neutral and positively charged peptides. However, the Fractionation of TH lead to a better separation between charged fragments than that of CH. This can be explained by the broader range of peptide characteristics (mass, charge) in CH as a result of the broader specificity of chymotrypsin.