Peptidomic study of casein proteolysis in bovine milk by Lactobacillus casei PRA205 and Lactobacillus rhamnosus PRA331

Lactobacilli contain different cell envelope proteinases (CEPs) responsible for the hydrolysis of caseins and the release of various bioactive peptides. In this work, we explored the CEP activity of Lactobacillus casei PRA205 and Lactobacillus rhamnosus PRA331 whole cells towards beta-, alpha(S1)-, kappa- and alpha(S2)-caseins in bovine milk. Mass spectrometry analysis of fermented milk hydrolysates identified a total of 331 peptides, which were mainly derived from beta-caseins (59.0 and 60.1% for PRA205 and PRA331, respectively). Analysis of alpha(S1)-casein (f1-23) cleavage site specificity congruently supports that Lb. casei PRA205 and Lb. rhamnosus PRA331 exhibited a mixed-type CEPI/III activity. PRA205 and PRA331 CEPs also showed cleavage site specificity toward beta-casein. These CEPs cleaved the peptide bond preferentially when hydrophobic or negatively charged amino acids were present. 13.5% and 13.7% of peptides released by Lb. casei PRA205 and Lb. rhamnosus PRA331 CEPs were found to have 100% homology with previously identified bioactive peptides. (C) 2018 Elsevier Ltd. All rights reserved.