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 hydrolys ates were prepared by tryptic (TH) or chymotryptic (CH) hydrolysis of a com mercial 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(M WCO) of 2 500 g.mol(-1). A detailed examination of the peptide separation r evealed that, for both TH and CH, the negatively charged peptides were in l ower proportion in the permeates whereas the opposite trend was observed fo r neutral and positively charged peptides. However, the Fractionation of TH lead to a better separation between charged fragments than that of CH. Thi s can be explained by the broader range of peptide characteristics (mass, c harge) in CH as a result of the broader specificity of chymotrypsin.