Relationship between degree of casein hydrolysis and phosphopeptide release

Abstract

In an approach to develop a commercial-scale process for the production of casein phosphopeptides containing the cluster sequence −SerP−SerP−SerP−Glu−Glu–, we have studied the relationship between casein hydrolysis and phosphopeptide release. The degrees of hydrolysis (DH) of casein using Novo trypsin PTN 3.0 S and pancreatin 4NF independently, at enzyme to substrate (E[ratio ]S) ratios of 1[ratio ]50–1[ratio ]1600 (by weight), were determined using the pH-stat method. Casein phosphopeptides (CPP) were selectively precipitated using Ca2+ and ethanol from the acid-clarified hydrolysates. The precipitates were analysed by high performance capillary electrophoresis to calculate individual phosphopeptide yields based on extinction coefficients of the purified peptides. Individual peptides were purified by reversed-phase HPLC and anion-exchange FPLC4 and characterized by MALDI-TOF mass spectrometry and amino acid sequence analysis. For both enzymes, lowering the E[ratio ]S ratio resulted in reductions in the DH and the release of the CPP, and an increase in peptide chain length. The longer chain length offset the reduction in release such that the gravimetric yields of CPP preparations remained relatively constant. For Novo trypsin the highest yields of the major cluster peptides (β-casein(CN)f(1–25), αs1-CNf(59–79), αs2-CNf(1–21), αs2-CNf(46–70) and related peptides) in the selective precipitates were obtained at a casein DH of 17%. At lower DH values (9–15%), there was a decrease in yield of the peptides derived from αs1-CN and αs2-CN while the yield of the β-CN-derived cluster peptides remained relatively constant. The CPP produced using pancreatin were found to be truncated at all E[ratio ]S ratios, relative to the tryptic CPP, owing to higher levels of chymotryptic and carboxypeptidase activities in pancreatin. The highest yields of the truncated forms of the major cluster peptides using pancreatin were obtained at a casein DH of 19–23%.