Peptides Released from Foremilk and Hindmilk Proteins by Breast Milk Proteases Are Highly Similar.

Søren D Nielsen,David C Dallas,Robert L Beverly

doi:10.3389/fnut.2017.00054

Abstract

Human milk contains active proteases that initiate hydrolysis of milk proteins within the mammary gland. Milk expressed at the beginning of feeding is known as foremilk and that at the end of feeding is known as hindmilk. As hindmilk contains higher fat, vitamins A and E, and higher calories than foremilk, feeding only hindmilk initially and reserving foremilk for later are practiced in some neonatal intensive care units. This study investigated the difference in peptide profiles, predicted milk protease activities, and bioactive peptides between foremilk and hindmilk. Bioactive peptides are short fragments of proteins that influence biological processes. Four mothers pumped 10 mL of their foremilk and 10 mL of their hindmilk into iced containers prepared with antiproteases and the samples were immediately frozen. The peptide profile of each sample was analyzed by liquid chromatography nano-electrospray ionization Orbitrap Fusion tandem mass spectrometry. Peptide abundance (sum of ion intensities) and count (number of unique peptide sequences) in each milk sample were determined from this analysis. The specific enzymes that participated in peptide release were predicted based on the amino acids positioned at each cleavage site. Peptide bioactivity was predicted based on homology to a known functional peptide database and two bioactivity prediction algorithms. Hindmilk contained a higher count of peptides than foremilk. The higher number of unique peptide sequences in hindmilk was related to hydrolysis of β-casein, osteopontin, αs1-casein and mucin-1 via plasmin and elastase cleavage, and possible aminopeptidase and carboxypeptidase activities. Though hindmilk contained a greater number of peptides than foremilk, the overall peptide abundance did not differ and most of the total peptide abundance derived from peptide sequences that were present in both milk types. The presence of higher numbers of predicted bioactive peptides in the hindmilk could indicate that the practice of providing hindmilk rather than foremilk to premature infants could positively impact health outcomes; however, as there are few differences in overall peptide abundance, the overall effect is likely limited.

Highlights

Human milk has evolved to match the newborn infant’s nutritional needs and is highly important for the growth and development of the neonate
474 ± 14 peptides were identified in the foremilk and 591 ± 14 identified in the hindmilk (Figure 1A)
Though peptides derived from casein proteins were identified, no peptides were identified from α-lactalbumin, immunoglobulin A, lysozyme, or serum albumin and only a single peptide was identified from lactoferrin

Summary

Introduction

Human milk has evolved to match the newborn infant’s nutritional needs and is highly important for the growth and development of the neonate. Besides providing the infant with nutrients, human milk contains many bioactive components that are preformed prior to expression, such as immunoglobulins, hormones, and growth factors, that contribute to the infant’s development. In addition to proteins that are bioactive intact, milk proteins contain encrypted sequences released upon proteolysis that exert an array of functions, often different from that of the parent protein. Milk protein-derived peptides have an array of identified functions that may benefit the infant, including antimicrobial, immunomodulatory, angiotensin-converting enzyme (ACE)- and dipeptidyl peptidase IV inhibitory, and opioid activity [2,3,4]

Methods

Results

Conclusion