Identification of bioactive peptides derived from caseins, glycosylation-dependent cell adhesion molecule-1 (GlyCAM-1), and peptidoglycan recognition protein-1 (PGRP-1) in fermented camel milk

Camel milk was fermented by Streptococcus thermophilus LMD-9 strain, the proteolytic system of which yielded peptides from the milk proteins. The peptides were isolated by cation-exchange chromatography and ultrafiltration, and then separated into 9 fractions by reversed-phase high-performance liquid chromatography. Two fractions displayed efficient radical-scavenging properties shown by Trolox equivalent antioxidant capacity assay. At least 347 peptides distributed in the different fractions were identified by tandem mass spectrometry. They mainly derived from the four different caseins, glycosylation-dependent cell adhesion molecule-1 (GlyCAM-1), also called lactophorin, and peptidoglycan recognition protein-1. For the first time, cleavage sites were identified for these six proteins and the susceptibility of GlyCAM-1 towards bacterial proteolysis directly in milk was shown. Investigation of peptide sequences homologous to known bioactive peptides highlighted not less than 16 different putative biological activities. Fermentation of camel milk was thus a means of food processing to produce potential bioactive peptides.