Abstract
Bovine milk contains a variety of endogenous peptides, partially formed by milk proteases that may exert diverse bioactive functions. Milk storage allows further protease activities altering the milk peptidome, while processing, e.g., heat treatment can trigger diverse chemical reactions, such as Maillard reactions and oxidations, leading to different posttranslational modifications (PTMs). The influence of processing on the native and modified peptidome was studied by analyzing peptides extracted from raw milk (RM), ultra-high temperature (UHT) milk, and powdered infant formula (IF) by nano reversed-phase liquid chromatography coupled online to electrospray ionization (ESI) tandem mass spectrometry. Only unmodified peptides proposed by two independent software tools were considered as identified. Thus, 801 identified peptides mainly originated from αS- and β-caseins, but also from milk fat globular membrane proteins, such as glycosylation-dependent cell adhesion molecule 1. RM and UHT milk showed comparable unmodified peptide profiles, whereas IF differed mainly due to a higher number of β-casein peptides. When 26 non-enzymatic posttranslational modifications (PTMs) were targeted in the milk peptidomes, 175 modified peptides were identified, i.e., mostly lactosylated and a few hexosylated or oxidized peptides. Most modified peptides originated from αS-caseins. The numbers of lactosylated peptides increased with harsher processing.
Highlights
The bovine raw milk contains a variety of endogenous peptides
The data sets acquired for peptides in raw milk (RM), ultra-high temperature (UHT) milk, and infant formula (IF) were processed by two different
The data sets acquired for peptides in RM, UHT milk, and IF were processed by two different software packages relying on different strategies (Proteome Discoverer 2.2 and PEAKS Studio 10.5) to software packages relying on different strategies (Proteome Discoverer 2.2 and PEAKS Studio 10.5)
Summary
The bovine raw milk contains a variety of endogenous peptides. Many of them exert bioactive functions, such as immunomodulatory effects and antimicrobial or mineral binding activities [1,2].Native peptides are cleaved from the proteins by proteases naturally present in milk [1]. The bovine raw milk contains a variety of endogenous peptides. Many of them exert bioactive functions, such as immunomodulatory effects and antimicrobial or mineral binding activities [1,2]. Native peptides are cleaved from the proteins by proteases naturally present in milk [1]. The dominant protease in bovine milk, shows a high specificity for β-, αS1 -, and αS2 -casein with only low or no activity towards κ-casein, β-lactoglobulin, and α-lactalbumin [3,4,5]. Cathepsin D digests mostly β-casein and α-lactalbumin at two specific sites, whereas native β-lactoglobulin is resistant to cleavage [4]. Other important proteases in bovine milk are elastase and cathepsin B [6]
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