Intrinsic protein disorder and bacteria-specific proteolytic systems shape the peptidome of fermented camel milk

This study examined the peptidome of camel milk fermented by the lactic acid bacteria Streptococcus thermophilus (St), Lactobacillus delbrueckii ssp. bulgaricus (Lb), and L. helveticus (Lh). Peptide profiles from 3 biological replicates were analyzed using LC-MS/MS-based peptidomics and quantified using MaxQuant software. The main peptide precursors, β- and αS1-caseins and lactophorin, were characterized by high level of intrinsic disorder that enhanced their susceptibility to enzymatic hydrolysis. St-fermented samples showed a greater number of peptides, but lower diversity than that showed by Lb- and Lh-fermented samples. The Lh-fermented samples contained shorter peptides than those of St- and Lb-fermented samples. St- and Lb-derived peptides originated more frequently from the N- and C-terminal regions of precursor proteins, respectively, whereas Lh fermentation showed pronounced hydrolysis within the central regions of proteins. Several peptides correspond to sequences previously reported as angiotensin-converting enzyme (ACE)- and dipeptidyl peptidase-IV (DPP-IV)-inhibitory peptides. Collectively, integrating intrinsic protein disorder with bacterial proteolytic specialization may help improve the understanding and selection of proteolytic processes for different food proteins.